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* [<EFBFBD><EFBFBD>һ<EFBFBD><EFBFBD> <20><><EFBFBD><EFBFBD>](#<23><>һ<EFBFBD><D2BB>-<2D><><EFBFBD><EFBFBD>)
* [<EFBFBD><EFBFBD><EFBFBD><EFBFBD>ϵͳ<EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD>](#<23><><EFBFBD><EFBFBD>ϵͳ<CFB5><CDB3><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD>)
* [1. <EFBFBD><EFBFBD><EFBFBD><EFBFBD>](#1-<EFBFBD><EFBFBD><EFBFBD><EFBFBD>)
* [2. <EFBFBD><EFBFBD><EFBFBD><EFBFBD>](#2-<EFBFBD><EFBFBD><EFBFBD><EFBFBD>)
* [3. <EFBFBD><EFBFBD><EFBFBD><EFBFBD>](#3-<EFBFBD><EFBFBD><EFBFBD><EFBFBD>)
* [4. <EFBFBD>첽](#4-<EFBFBD>첽)
* [ϵͳ<EFBFBD><EFBFBD><EFBFBD><EFBFBD>](#ϵͳ<CFB5><CDB3><EFBFBD><EFBFBD>)
* [<EFBFBD>жϷ<EFBFBD><EFBFBD><EFBFBD>](#<23>жϷ<D0B6><CFB7><EFBFBD>)
* [1. <EFBFBD><EFBFBD><EFBFBD>ж<EFBFBD>](#1-<EFBFBD><EFBFBD><EFBFBD>ж<EFBFBD>)
* [2. <EFBFBD>쳣](#2-<EFBFBD>쳣)
* [3. <EFBFBD><EFBFBD><EFBFBD><EFBFBD>](#3-<EFBFBD><EFBFBD><EFBFBD><EFBFBD>)
* [<EFBFBD><EFBFBD><EFBFBD>ں˺<EFBFBD>΢<EFBFBD>ں<EFBFBD>](#<23><><EFBFBD>ں˺<DABA>΢<EFBFBD>ں<EFBFBD>)
* [1. <EFBFBD><EFBFBD><EFBFBD>ں<EFBFBD>](#1-<EFBFBD><EFBFBD><EFBFBD>ں<EFBFBD>)
* [2. ΢<EFBFBD>ں<EFBFBD>](#2-΢<EFBFBD>ں<EFBFBD>)
* [<EFBFBD>ڶ<EFBFBD><EFBFBD><EFBFBD> <20><><EFBFBD>̹<EFBFBD><CCB9><EFBFBD>](#<23>ڶ<EFBFBD><DAB6><EFBFBD>-<2D><><EFBFBD>̹<EFBFBD><CCB9><EFBFBD>)
* [<EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD>߳<EFBFBD>](#<23><><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD>߳<EFBFBD>)
* [1. <EFBFBD><EFBFBD><EFBFBD><EFBFBD>](#1-<EFBFBD><EFBFBD><EFBFBD><EFBFBD>)
* [2. <EFBFBD>߳<EFBFBD>](#2-<EFBFBD>߳<EFBFBD>)
* [3. <EFBFBD><EFBFBD><EFBFBD><EFBFBD>](#3-<EFBFBD><EFBFBD><EFBFBD><EFBFBD>)
* [<EFBFBD><EFBFBD><EFBFBD><EFBFBD>״̬<EFBFBD><EFBFBD><EFBFBD>л<EFBFBD>](#<23><><EFBFBD><EFBFBD>״̬<D7B4><CCAC><EFBFBD>л<EFBFBD>)
* [<EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD>㷨](#<23><><EFBFBD><EFBFBD><EFBFBD>㷨)
* [1. <EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD>ϵͳ<EFBFBD>еĵ<EFBFBD><EFBFBD><EFBFBD>](#1-<2D><><EFBFBD><EFBFBD><EFBFBD><EFBFBD>ϵͳ<CFB5>еĵ<D0B5><C4B5><EFBFBD>)
* [1.1 <EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD>ȷ<EFBFBD><EFBFBD><EFBFBD>](#11-<2D><><EFBFBD><EFBFBD><EFBFBD>ȷ<EFBFBD><C8B7><EFBFBD>)
* [1.2 <EFBFBD><EFBFBD><EFBFBD><EFBFBD>ҵ<EFBFBD><EFBFBD><EFBFBD><EFBFBD>](#12-<2D><><EFBFBD><EFBFBD>ҵ<EFBFBD><D2B5><EFBFBD><EFBFBD>)
* [1.3 <EFBFBD><EFBFBD><EFBFBD><EFBFBD>ʣ<EFBFBD><EFBFBD>ʱ<EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD>](#13-<2D><><EFBFBD><EFBFBD>ʣ<EFBFBD><CAA3>ʱ<EFBFBD><CAB1><EFBFBD><EFBFBD><EFBFBD><EFBFBD>)
* [2. <EFBFBD><EFBFBD><EFBFBD><EFBFBD>ʽϵͳ<EFBFBD>еĵ<EFBFBD><EFBFBD><EFBFBD>](#2-<2D><><EFBFBD><EFBFBD>ʽϵͳ<CFB5>еĵ<D0B5><C4B5><EFBFBD>)
* [2.1 <EFBFBD><EFBFBD><EFBFBD><EFBFBD>Ȩ<EFBFBD><EFBFBD><EFBFBD><EFBFBD>](#21-<2D><><EFBFBD><EFBFBD>Ȩ<EFBFBD><C8A8><EFBFBD><EFBFBD>)
* [2.2 ʱ<EFBFBD><EFBFBD>Ƭ<EFBFBD><EFBFBD>ת](#22-ʱ<EFBFBD><EFBFBD>Ƭ<EFBFBD><EFBFBD>ת)
* [2.3 <EFBFBD>༶<EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD>](#23-<2D>༶<EFBFBD><E0BCB6><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD>)
* [2.4 <EFBFBD>̽<EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD>](#24-<2D>̽<EFBFBD><CCBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD>)
* [3. ʵʱϵͳ<EFBFBD>еĵ<EFBFBD><EFBFBD><EFBFBD>](#3-ʵʱϵͳ<CFB5>еĵ<D0B5><C4B5><EFBFBD>)
* [<EFBFBD><EFBFBD><EFBFBD><EFBFBD>ͬ<EFBFBD><EFBFBD>](#<23><><EFBFBD><EFBFBD>ͬ<EFBFBD><CDAC>)
* [1. <EFBFBD>ٽ<EFBFBD><EFBFBD><EFBFBD>](#1-<EFBFBD>ٽ<EFBFBD><EFBFBD><EFBFBD>)
* [2. ͬ<EFBFBD><EFBFBD><EFBFBD>뻥<EFBFBD><EFBFBD>](#2-ͬ<><CDAC><EFBFBD>뻥<EFBFBD><EBBBA5>)
* [3. <EFBFBD>ź<EFBFBD><EFBFBD><EFBFBD>](#3-<EFBFBD>ź<EFBFBD><EFBFBD><EFBFBD>)
* [4. <EFBFBD>ܳ<EFBFBD>](#4-<EFBFBD>ܳ<EFBFBD>)
* [<EFBFBD><EFBFBD><EFBFBD><EFBFBD>ͨ<EFBFBD><EFBFBD>](#<23><><EFBFBD><EFBFBD>ͨ<EFBFBD><CDA8>)
* [1. <EFBFBD>ܵ<EFBFBD>](#1-<EFBFBD>ܵ<EFBFBD>)
* [2. <EFBFBD>ź<EFBFBD><EFBFBD><EFBFBD>](#2-<EFBFBD>ź<EFBFBD><EFBFBD><EFBFBD>)
* [3. <EFBFBD><EFBFBD>Ϣ<EFBFBD><EFBFBD><EFBFBD><EFBFBD>](#3-<2D><>Ϣ<EFBFBD><CFA2><EFBFBD><EFBFBD>)
* [4. <EFBFBD>ź<EFBFBD>](#4-<EFBFBD>ź<EFBFBD>)
* [5. <EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD>ڴ<EFBFBD>](#5-<2D><><EFBFBD><EFBFBD><EFBFBD>ڴ<EFBFBD>)
* [6. <EFBFBD>׽<EFBFBD><EFBFBD><EFBFBD>](#6-<EFBFBD>׽<EFBFBD><EFBFBD><EFBFBD>)
* [<EFBFBD><EFBFBD><EFBFBD><EFBFBD>ͬ<EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD>](#<23><><EFBFBD><EFBFBD>ͬ<EFBFBD><CDAC><EFBFBD><EFBFBD><EFBFBD><EFBFBD>)
* [1. <EFBFBD><EFBFBD><EFBFBD><EFBFBD>-д<><D0B4><EFBFBD><EFBFBD><EFBFBD><EFBFBD>](#1-<2D><><EFBFBD><EFBFBD>-д<><D0B4><EFBFBD><EFBFBD><EFBFBD><EFBFBD>)
* [2. <EFBFBD><EFBFBD>ѧ<EFBFBD>ҽ<EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD>](#2-<2D><>ѧ<EFBFBD>ҽ<EFBFBD><D2BD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD>)
* [<EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD> <20><><EFBFBD><EFBFBD>](#<23><><EFBFBD><EFBFBD><EFBFBD><EFBFBD>-<2D><><EFBFBD><EFBFBD>)
* [<EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD>](#<23><><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD>)
* [<EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD>Ĵ<EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD>](#<23><><EFBFBD><EFBFBD><EFBFBD>Ĵ<EFBFBD><C4B4><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD>)
* [1. <EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD>](#1-<2D><><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD>)
* [2. <EFBFBD><EFBFBD><EFBFBD><EFBFBD>Ԥ<EFBFBD><EFBFBD>](#2-<2D><><EFBFBD><EFBFBD>Ԥ<EFBFBD><D4A4>)
* [2.1 <EFBFBD>ƻ<EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD>](#21-<2D>ƻ<EFBFBD><C6BB><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD>)
* [2.2 <EFBFBD>ƻ<EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD>뱣<EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD>](#22-<2D>ƻ<EFBFBD><C6BB><EFBFBD><EFBFBD><EFBFBD><EFBFBD>뱣<EFBFBD><EBB1A3><EFBFBD><EFBFBD><EFBFBD><EFBFBD>)
* [2.3 <EFBFBD>ƻ<EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD>ռ<EFBFBD><EFBFBD><EFBFBD><EFBFBD>](#23-<2D>ƻ<EFBFBD><C6BB><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD>ռ<EFBFBD><D5BC><EFBFBD><EFBFBD>)
* [2.4 <EFBFBD>ƻ<EFBFBD><EFBFBD><EFBFBD>·<EFBFBD>ȴ<EFBFBD>](#24-<2D>ƻ<EFBFBD><C6BB><EFBFBD>·<EFBFBD>ȴ<EFBFBD>)
* [3. <EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD>](#3-<2D><><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD>)
* [3.1 <EFBFBD><EFBFBD>ȫ״̬](#31-<EFBFBD><EFBFBD>ȫ״̬)
* [3.2 <EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD>Դ<EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD>м<EFBFBD><EFBFBD>㷨](#32-<2D><><EFBFBD><EFBFBD><EFBFBD><EFBFBD>Դ<EFBFBD><D4B4><EFBFBD><EFBFBD><EFBFBD>м<EFBFBD><D0BC>㷨)
* [3.3 <EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD>Դ<EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD>м<EFBFBD><EFBFBD>㷨](#33-<2D><><EFBFBD><EFBFBD><EFBFBD><EFBFBD>Դ<EFBFBD><D4B4><EFBFBD><EFBFBD><EFBFBD>м<EFBFBD><D0BC>㷨)
* [4. <EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD>ָ<EFBFBD>](#4-<2D><><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD>ָ<EFBFBD>)
* [4.1 <EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD>㷨](#41-<2D><><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD>㷨)
* [4.2 <EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD>ָ<EFBFBD>](#42-<EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD>ָ<EFBFBD>)
* [<EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD> <20>洢<EFBFBD><E6B4A2><EFBFBD><EFBFBD><EFBFBD><EFBFBD>](#<23><><EFBFBD><EFBFBD><EFBFBD><EFBFBD>-<2D>洢<EFBFBD><E6B4A2><EFBFBD><EFBFBD><EFBFBD><EFBFBD>)
* [<EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD>ڴ<EFBFBD>](#<23><><EFBFBD><EFBFBD><EFBFBD>ڴ<EFBFBD>)
* [<EFBFBD><EFBFBD>ҳ<EFBFBD><EFBFBD><EFBFBD>ֶ<EFBFBD>](#<23><>ҳ<EFBFBD><D2B3><EFBFBD>ֶ<EFBFBD>)
* [1. <EFBFBD><EFBFBD>ҳ](#1-<EFBFBD><EFBFBD>ҳ)
* [2. <EFBFBD>ֶ<EFBFBD>](#2-<EFBFBD>ֶ<EFBFBD>)
* [3. <EFBFBD><EFBFBD>ҳʽ](#3-<EFBFBD><EFBFBD>ҳʽ)
* [4. <EFBFBD><EFBFBD>ҳ<EFBFBD><EFBFBD><EFBFBD>ֶ<EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD>](#4-<2D><>ҳ<EFBFBD><D2B3><EFBFBD>ֶ<EFBFBD><D6B6><EFBFBD><EFBFBD><EFBFBD>)
* [ҳ<EFBFBD><EFBFBD><EFBFBD>û<EFBFBD><EFBFBD>㷨](#ҳ<><D2B3><EFBFBD>û<EFBFBD><C3BB>㷨)
* [1. <EFBFBD><EFBFBD><EFBFBD>ѣ<EFBFBD>Optimal<EFBFBD><EFBFBD>](#1-<EFBFBD><EFBFBD><EFBFBD><EFBFBD>optimal)
* [2. <EFBFBD>Ƚ<EFBFBD><EFBFBD>ȳ<EFBFBD><EFBFBD><EFBFBD>FIFO<EFBFBD><EFBFBD>](#2-<EFBFBD>Ƚ<EFBFBD><EFBFBD>ȳ<EFBFBD>fifo)
* [3. <EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD>δʹ<EFBFBD>ã<EFBFBD>LRU, Least Recently Used<EFBFBD><EFBFBD>](#3-<EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD>δʹ<EFBFBD><EFBFBD>lru,-least-recently-used)
* [4. ʱ<EFBFBD>ӣ<EFBFBD>Clock<EFBFBD><EFBFBD>](#4-ʱ<EFBFBD><EFBFBD>clock)
* [<EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD> <20>豸<EFBFBD><E8B1B8><EFBFBD><EFBFBD>](#<23><><EFBFBD><EFBFBD><EFBFBD><EFBFBD>-<2D>豸<EFBFBD><E8B1B8><EFBFBD><EFBFBD>)
* [<EFBFBD><EFBFBD><EFBFBD>̵<EFBFBD><EFBFBD><EFBFBD><EFBFBD>㷨](#<23><><EFBFBD>̵<EFBFBD><CCB5><EFBFBD><EFBFBD>㷨)
* [1. <EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD>ȷ<EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD>FCFS, First Come First Serverd<EFBFBD><EFBFBD>](#1-<EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD>ȷ<EFBFBD><EFBFBD><EFBFBD>fcfs,-first-come-first-serverd)
* [2. <EFBFBD><EFBFBD><EFBFBD><EFBFBD>Ѱ<EFBFBD><EFBFBD>ʱ<EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD>ȣ<EFBFBD>SSTF, Shortest Seek Time First<EFBFBD><EFBFBD>](#2-<EFBFBD><EFBFBD><EFBFBD><EFBFBD>Ѱ<EFBFBD><EFBFBD>ʱ<EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD>sstf,-shortest-seek-time-first)
* [3. ɨ<EFBFBD><EFBFBD><EFBFBD>㷨<EFBFBD><EFBFBD>SCAN<EFBFBD><EFBFBD>](#3-ɨ<EFBFBD><EFBFBD><EFBFBD>㷨scan)
* [4. ѭ<EFBFBD><EFBFBD>ɨ<EFBFBD><EFBFBD><EFBFBD>㷨<EFBFBD><EFBFBD>CSCAN<EFBFBD><EFBFBD>](#4-ѭ<EFBFBD><EFBFBD>ɨ<EFBFBD><EFBFBD><EFBFBD>㷨cscan)
* [<EFBFBD>ο<EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD>](#<23>ο<EFBFBD><CEBF><EFBFBD><EFBFBD><EFBFBD>)
* [第一章 概述](#第一章-概述)
* [操作系统基本特征](#操作系统基本特征)
* [1. 并发](#1-并发)
* [2. 共享](#2-共享)
* [3. 虚拟](#3-虚拟)
* [4. 异步](#4-异步)
* [系统调用](#系统调用)
* [中断分类](#中断分类)
* [1. 外中断](#1-外中断)
* [2. 异常](#2-异常)
* [3. 陷入](#3-陷入)
* [大内核和微内核](#大内核和微内核)
* [1. 大内核](#1-大内核)
* [2. 微内核](#2-微内核)
* [第二章 进程管理](#第二章-进程管理)
* [进程与线程](#进程与线程)
* [1. 进程](#1-进程)
* [2. 线程](#2-线程)
* [3. 区别](#3-区别)
* [进程状态的切换](#进程状态的切换)
* [调度算法](#调度算法)
* [1. 批处理系统中的调度](#1-批处理系统中的调度)
* [1.1 先来先服务](#11-先来先服务)
* [1.2 短作业优先](#12-短作业优先)
* [1.3 最短剩余时间优先](#13-最短剩余时间优先)
* [2. 交互式系统中的调度](#2-交互式系统中的调度)
* [2.1 优先权优先](#21-优先权优先)
* [2.2 时间片轮转](#22-时间片轮转)
* [2.3 多级反馈队列](#23-多级反馈队列)
* [2.4 短进程优先](#24-短进程优先)
* [3. 实时系统中的调度](#3-实时系统中的调度)
* [进程同步](#进程同步)
* [1. 临界区](#1-临界区)
* [2. 同步与互斥](#2-同步与互斥)
* [3. 信号量](#3-信号量)
* [4. 管程](#4-管程)
* [进程通信](#进程通信)
* [1. 管道](#1-管道)
* [2. 信号量](#2-信号量)
* [3. 消息队列](#3-消息队列)
* [4. 信号](#4-信号)
* [5. 共享内存](#5-共享内存)
* [6. 套接字](#6-套接字)
* [经典同步问题](#经典同步问题)
* [1. 读者-写者问题](#1-读者-写者问题)
* [2. 哲学家进餐问题](#2-哲学家进餐问题)
* [第三章 死锁](#第三章-死锁)
* [死锁的条件](#死锁的条件)
* [死锁的处理方法](#死锁的处理方法)
* [1. 鸵鸟策略](#1-鸵鸟策略)
* [2. 死锁预防](#2-死锁预防)
* [2.1 破坏互斥条件](#21-破坏互斥条件)
* [2.2 破坏请求与保持条件](#22-破坏请求与保持条件)
* [2.3 破坏不可抢占条件](#23-破坏不可抢占条件)
* [2.4 破坏环路等待](#24-破坏环路等待)
* [3. 死锁避免](#3-死锁避免)
* [3.1 安全状态](#31-安全状态)
* [3.2 单个资源的银行家算法](#32-单个资源的银行家算法)
* [3.3 多个资源的银行家算法](#33-多个资源的银行家算法)
* [4. 死锁检测与死锁恢复](#4-死锁检测与死锁恢复)
* [4.1 死锁检测算法](#41-死锁检测算法)
* [4.2 死锁恢复](#42-死锁恢复)
* [第四章 存储器管理](#第四章-存储器管理)
* [虚拟内存](#虚拟内存)
* [分页与分段](#分页与分段)
* [1. 分页](#1-分页)
* [2. 分段](#2-分段)
* [3. 段页式](#3-段页式)
* [4. 分页与分段区别](#4-分页与分段区别)
* [页面置换算法](#页面置换算法)
* [1. 最佳（Optimal）](#1-最佳optimal)
* [2. 先进先出（FIFO）](#2-先进先出fifo)
* [3. 最近最久未使用（LRU, Least Recently Used）](#3-最近最久未使用lru,-least-recently-used)
* [4. 时钟（Clock）](#4-时钟clock)
* [第五章 设备管理](#第五章-设备管理)
* [磁盘调度算法](#磁盘调度算法)
* [1. 先来先服务（FCFS, First Come First Serverd）](#1-先来先服务fcfs,-first-come-first-serverd)
* [2. 最短寻道时间优先（SSTF, Shortest Seek Time First）](#2-最短寻道时间优先sstf,-shortest-seek-time-first)
* [3. 扫描算法（SCAN）](#3-扫描算法scan)
* [4. 循环扫描算法（CSCAN）](#4-循环扫描算法cscan)
* [参考资料](#参考资料)
<!-- GFM-TOC -->
# <20><>һ<EFBFBD><D2BB> <20><><EFBFBD><EFBFBD>
## <20><><EFBFBD><EFBFBD>ϵͳ<CFB5><CDB3><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD>
# 第一章 概述
### 1. <20><><EFBFBD><EFBFBD>
## 操作系统基本特征
<EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD>ָ<EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD>һ<EFBFBD><EFBFBD>ʱ<EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD>ͬʱ<EFBFBD><EFBFBD><EFBFBD>ж<EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD>򣬶<EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD>ָͬһʱ<EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD>ж<EFBFBD><EFBFBD><EFBFBD>ָ<EFBFBD>
### 1. 并发
<EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD>ҪӲ<EFBFBD><EFBFBD>֧<EFBFBD>֣<EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD>ˮ<EFBFBD>߻<EFBFBD><EFBFBD>߶ദ<EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD>
并发性是指宏观上在一段时间内能同时运行多个程序，而并行性则指同一时刻能运行多个指令。
<EFBFBD><EFBFBD><EFBFBD><EFBFBD>ϵͳͨ<EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD>̺<EFBFBD><EFBFBD>̣߳<EFBFBD>ʹ<EFBFBD>ó<EFBFBD><EFBFBD><EFBFBD><EFBFBD>ܹ<EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD>С<EFBFBD>
并行需要硬件支持，如多流水线或者多处理器。
### 2. <20><><EFBFBD><EFBFBD>
操作系统通过引入进程和线程，使得程序能够并发运行。
<EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD>ָϵͳ<EFBFBD>е<EFBFBD><EFBFBD><EFBFBD>Դ<EFBFBD><EFBFBD><EFBFBD>Թ<EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD>̹<EFBFBD>ͬʹ<EFBFBD>á<EFBFBD>
### 2. 共享
<EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD>ֹ<EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD>ʽ<EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD>⹲<EFBFBD><EFBFBD><EFBFBD><EFBFBD>ͬʱ<EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD>
共享是指系统中的资源可以供多个并发进程共同使用。
<EFBFBD><EFBFBD><EFBFBD>⹲<EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD>Դ<EFBFBD><EFBFBD>Ϊ<EFBFBD>ٽ<EFBFBD><EFBFBD><EFBFBD>Դ<EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD>ӡ<EFBFBD><EFBFBD><EFBFBD>ȣ<EFBFBD><EFBFBD><EFBFBD>ͬһʱ<EFBFBD><EFBFBD>ֻ<EFBFBD><EFBFBD><EFBFBD><EFBFBD>һ<EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD>̷<EFBFBD><EFBFBD>ʣ<EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD>ִ<EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD>Ҫ<EFBFBD><EFBFBD>ͬ<EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD>ʵ<EFBFBD>ֶ<EFBFBD><EFBFBD>ٽ<EFBFBD><EFBFBD><EFBFBD>Դ<EFBFBD>ķ<EFBFBD><EFBFBD>ʡ<EFBFBD>
有两种共享方式：互斥共享和同时共享。
### 3. <20><><EFBFBD><EFBFBD>
互斥共享的资源称为临界资源，例如打印机等，在同一时间只允许一个进程访问，否则会出现错误，需要用同步机制来实现对临界资源的访问。
<EFBFBD><EFBFBD><EFBFBD>⼼<EFBFBD><EFBFBD><EFBFBD><EFBFBD>һ<EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD>ʵ<EFBFBD><EFBFBD>ת<EFBFBD><EFBFBD>Ϊ<EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD>߼<EFBFBD>ʵ<EFBFBD>塣<EFBFBD><EFBFBD>Ҫ<EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD>⼼<EFBFBD><EFBFBD><EFBFBD><EFBFBD>ʱ<EFBFBD>ָ<EFBFBD><EFBFBD>ü<EFBFBD><EFBFBD><EFBFBD><EFBFBD>Ϳշָ<EFBFBD><EFBFBD>ü<EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD>ͬһ<EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD>ϲ<EFBFBD><EFBFBD><EFBFBD>ִ<EFBFBD><EFBFBD>ʹ<EFBFBD><EFBFBD><EFBFBD><EFBFBD>ʱ<EFBFBD>ָ<EFBFBD><EFBFBD>ü<EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD>ÿ<EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD>ռ<EFBFBD>д<EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD>ÿ<EFBFBD><EFBFBD>ִֻ<EFBFBD><EFBFBD>һС<EFBFBD><EFBFBD>ʱ<EFBFBD><EFBFBD>Ƭ<EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD>л<EFBFBD><EFBFBD><EFBFBD>
### 3. 虚拟
### 4. <20>첽
虚拟技术把一个物理实体转换为多个逻辑实体。主要有两种虚拟技术：时分复用技术和空分复用技术，例如多个进程能在同一个处理器上并发执行使用了时分复用技术，让每个进程轮流占有处理器，每次只执行一小个时间片并快速切换。
<EFBFBD>첽<EFBFBD><EFBFBD>ָ<EFBFBD><EFBFBD><EFBFBD>̲<EFBFBD><EFBFBD><EFBFBD>һ<EFBFBD><EFBFBD><EFBFBD><EFBFBD>ִ<EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD>ϣ<EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD>ͣͣ<EFBFBD><EFBFBD><EFBFBD>Բ<EFBFBD><EFBFBD><EFBFBD>֪<EFBFBD><EFBFBD><EFBFBD>ٶ<EFBFBD><EFBFBD><EFBFBD>ǰ<EFBFBD>ƽ<EFBFBD><EFBFBD><EFBFBD>
### 4. 异步
## ϵͳ<CFB5><CDB3><EFBFBD><EFBFBD>
异步是指进程不是一次性执行完毕，而是走走停停，以不可知的速度向前推进。
<EFBFBD><EFBFBD><EFBFBD><EFBFBD>һ<EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD>û<EFBFBD>̬<EFBFBD><EFBFBD>Ҫ<EFBFBD>õ<EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD>ϵͳ<EFBFBD><EFBFBD>һЩ<EFBFBD><EFBFBD><EFBFBD>ܣ<EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD>Ҫʹ<EFBFBD><EFBFBD>ϵͳ<EFBFBD><EFBFBD><EFBFBD>ôӶ<EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD>ںˣ<EFBFBD><EFBFBD>ɲ<EFBFBD><EFBFBD><EFBFBD>ϵͳ<EFBFBD><EFBFBD>Ϊ<EFBFBD><EFBFBD><EFBFBD>ɡ<EFBFBD>
## 系统调用
<EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD>ϵͳ<EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD>Ĺ<EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD>豸<EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD>ļ<EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD>̹<EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD>ͨ<EFBFBD>š<EFBFBD><EFBFBD>洢<EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD>ȡ<EFBFBD>
如果一个进程在用户态需要用到操作系统的一些功能，就需要使用系统调用从而陷入内核，由操作系统代为完成。
## <20>жϷ<D0B6><CFB7><EFBFBD>
可以由系统调用请求的功能有设备管理、文件管理、进程管理、进程通信、存储器管理等。
### 1. <20><><EFBFBD>ж<EFBFBD>
## 中断分类
<EFBFBD><EFBFBD> CPU ִ<><D6B4>ָ<EFBFBD><D6B8><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD>¼<EFBFBD><C2BC><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD> I/O <20><><EFBFBD><EFBFBD><EFBFBD>жϣ<D0B6><CFA3><EFBFBD>ʾ<EFBFBD>豸<EFBFBD><E8B1B8><EFBFBD><EFBFBD>/<2F><><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD>Ѿ<EFBFBD><D1BE><EFBFBD><EFBFBD>ɣ<EFBFBD><C9A3><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD>ܹ<EFBFBD><DCB9><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD>һ<EFBFBD><D2BB><EFBFBD><EFBFBD><EFBFBD><EFBFBD>/<2F><><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD>󡣴<EFBFBD><F3A1A3B4>⻹<EFBFBD><E2BBB9>ʱ<EFBFBD><CAB1><EFBFBD>жϡ<D0B6><CFA1><EFBFBD><EFBFBD><EFBFBD>̨<EFBFBD>жϵȡ<CFB5>
### 1. 外中断
### 2. <20>쳣
由 CPU 执行指令以外的事件引起，如 I/O 结束中断，表示设备输入/输出处理已经完成，处理器能够发送下一个输入/输出请求。此外还有时钟中断、控制台中断等。
<EFBFBD><EFBFBD> CPU ִ<><D6B4>ָ<EFBFBD><D6B8><EFBFBD><EFBFBD><EFBFBD>ڲ<EFBFBD><DAB2>¼<EFBFBD><C2BC><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD>Ƿ<EFBFBD><C7B7><EFBFBD><EFBFBD><EFBFBD><EFBFBD>롢<EFBFBD><EBA1A2>ַԽ<D6B7>硢<EFBFBD><E7A1A2><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD>ȡ<EFBFBD>
### 2. 异常
### 3. <20><><EFBFBD><EFBFBD>
由 CPU 执行指令的内部事件引起，如非法操作码、地址越界、算术溢出等。
<EFBFBD><EFBFBD><EFBFBD>û<EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD>ʹ<EFBFBD><EFBFBD>ϵͳ<EFBFBD><EFBFBD><EFBFBD>á<EFBFBD>
### 3. 陷入
## <20><><EFBFBD>ں˺<DABA>΢<EFBFBD>ں<EFBFBD>
在用户程序中使用系统调用。
### 1. <20><><EFBFBD>ں<EFBFBD>
## 大内核和微内核
<EFBFBD><EFBFBD><EFBFBD>ں<EFBFBD><EFBFBD>ǽ<EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD>ϵͳ<EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD>Ϊһ<EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD>ܽ<EFBFBD><EFBFBD>ϵ<EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD>ŵ<EFBFBD><EFBFBD>ںˣ<EFBFBD><EFBFBD><EFBFBD><EFBFBD>ڸ<EFBFBD>ģ<EFBFBD>鹲<EFBFBD><EFBFBD><EFBFBD><EFBFBD>Ϣ<EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD>кܸߵ<EFBFBD><EFBFBD><EFBFBD><EFBFBD>ܡ<EFBFBD>
### 1. 大内核
### 2. ΢<>ں<EFBFBD>
大内核是将操作系统功能作为一个紧密结合的整体放到内核，由于各模块共享信息，因此有很高的性能。
<EFBFBD><EFBFBD><EFBFBD>ڲ<EFBFBD><EFBFBD><EFBFBD>ϵͳ<EFBFBD><EFBFBD><EFBFBD>ϸ<EFBFBD><EFBFBD>ӣ<EFBFBD><EFBFBD><EFBFBD><EFBFBD>˽<EFBFBD>һ<EFBFBD><EFBFBD><EFBFBD>ֲ<EFBFBD><EFBFBD><EFBFBD>ϵͳ<EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD>Ƴ<EFBFBD><EFBFBD>ںˣ<EFBFBD><EFBFBD>Ӷ<EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD>ں˵ĸ<EFBFBD><EFBFBD><EFBFBD><EFBFBD>ԡ<EFBFBD><EFBFBD>Ƴ<EFBFBD><EFBFBD>IJ<EFBFBD><EFBFBD>ָ<EFBFBD><EFBFBD>ݷֲ<EFBFBD><EFBFBD><EFBFBD>ԭ<EFBFBD>򻮷ֳ<EFBFBD><EFBFBD><EFBFBD><EFBFBD>ɷ<EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD>໥<EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD>ҪƵ<EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD>û<EFBFBD>̬<EFBFBD>ͺ<EFBFBD><EFBFBD><EFBFBD>̬֮<EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD>л<EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD>һ<EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD>ʧ<EFBFBD><EFBFBD>
### 2. 微内核
# <20>ڶ<EFBFBD><DAB6><EFBFBD> <20><><EFBFBD>̹<EFBFBD><CCB9><EFBFBD>
由于操作系统不断复杂，因此将一部分操作系统功能移出内核，从而降低内核的复杂性。移出的部分根据分层的原则划分成若干服务，相互独立。但是需要频繁地在用户态和核心态之间进行切换，会有一定的性能损失。
## <20><><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD>߳<EFBFBD>
# 第二章 进程管理
### 1. <20><><EFBFBD><EFBFBD>
## 进程与线程
<EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD>Dz<EFBFBD><EFBFBD><EFBFBD>ϵͳ<EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD>Դ<EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD>Ļ<EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD>λ<EFBFBD><EFBFBD>
### 1. 进程
<EFBFBD><EFBFBD><EFBFBD>̿<EFBFBD><EFBFBD>ƿ<EFBFBD> (Process Control Block, PCB) <20><><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD>̵Ļ<CCB5><C4BB><EFBFBD><EFBFBD><EFBFBD>Ϣ<EFBFBD><CFA2><EFBFBD><EFBFBD><EFBFBD><EFBFBD>״̬<D7B4><CCAC><EFBFBD><EFBFBD>ν<EFBFBD>Ĵ<EFBFBD><C4B4><EFBFBD><EFBFBD><EFBFBD><EFBFBD>̺ͳ<CCBA><CDB3><EFBFBD><EFBFBD><EFBFBD><EFBFBD>̣<EFBFBD><CCA3><EFBFBD><EFBFBD><EFBFBD>ָ<EFBFBD><D6B8> PCB <20>IJ<EFBFBD><C4B2><EFBFBD><EFBFBD><EFBFBD>
进程是操作系统进行资源分配的基本单位。
### 2. <20>߳<EFBFBD>
进程控制块 (Process Control Block, PCB) 描述进程的基本信息和运行状态，所谓的创建进程和撤销进程，都是指对 PCB 的操作。
һ<EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD>п<EFBFBD><EFBFBD><EFBFBD><EFBFBD>ж<EFBFBD><EFBFBD><EFBFBD><EFBFBD>̣߳<EFBFBD><EFBFBD>߳<EFBFBD><EFBFBD>Ƕ<EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD>ȵĻ<EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD>λ<EFBFBD><EFBFBD>ͬһ<EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD>еĶ<EFBFBD><EFBFBD><EFBFBD><EFBFBD>߳<EFBFBD>֮<EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD>Բ<EFBFBD><EFBFBD><EFBFBD>ִ<EFBFBD>У<EFBFBD><EFBFBD><EFBFBD><EFBFBD>ǹ<EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD>Դ<EFBFBD><EFBFBD>
### 2. 线程
### 3. <20><><EFBFBD><EFBFBD>
一个进程中可以有多个线程，线程是独立调度的基本单位。同一个进程中的多个线程之间可以并发执行，它们共享进程资源。
- ӵ<><D3B5><EFBFBD><EFBFBD>Դ<EFBFBD><D4B4><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD>Դ<EFBFBD><D4B4><EFBFBD><EFBFBD><EFBFBD>Ļ<EFBFBD><C4BB><EFBFBD><EFBFBD><EFBFBD>λ<EFBFBD><CEBB><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD>̲߳<DFB3>ӵ<EFBFBD><D3B5><EFBFBD><EFBFBD>Դ<EFBFBD><D4B4><EFBFBD>߳̿<DFB3><CCBF>Է<EFBFBD><D4B7><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD>̵<EFBFBD><CCB5><EFBFBD>Դ<EFBFBD><D4B4>
### 3. 区别
- <EFBFBD><EFBFBD><EFBFBD>ȣ<EFBFBD><EFBFBD>߳<EFBFBD><EFBFBD>Ƕ<EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD>ȵĻ<EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD>λ<EFBFBD><EFBFBD><EFBFBD><EFBFBD>ͬһ<EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD>У<EFBFBD><EFBFBD>̵߳<EFBFBD><EFBFBD>л<EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD>л<EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD>һ<EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD>ڵ<EFBFBD><EFBFBD>߳<EFBFBD><EFBFBD>л<EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD>һ<EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD>е<EFBFBD><EFBFBD>߳<EFBFBD>ʱ<EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD>л<EFBFBD><EFBFBD><EFBFBD>
- 拥有资源：进程是资源分配的基本单位，但是线程不拥有资源，线程可以访问率属进程的资源。
- ϵͳ<EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD>ڴ<EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD>ʱ<EFBFBD><EFBFBD>ϵͳ<EFBFBD><EFBFBD>ҪΪ֮<EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD>Դ<EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD>ڴ<EFBFBD><EFBFBD>ռ䡢I/O <20>豸<EFBFBD>ȣ<EFBFBD><C8A3><EFBFBD><EFBFBD>˲<EFBFBD><CBB2><EFBFBD>ϵͳ<CFB5><CDB3><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD>Ŀ<EFBFBD><C4BF><EFBFBD>Զ<EFBFBD><D4B6><EFBFBD>ڴ<EFBFBD><DAB4><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD>߳<EFBFBD>ʱ<EFBFBD>Ŀ<EFBFBD><C4BF><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD>Ƶأ<C6B5><D8A3>ڽ<EFBFBD><DABD>н<EFBFBD><D0BD><EFBFBD><EFBFBD>л<EFBFBD>ʱ<EFBFBD><CAB1><EFBFBD>漰<EFBFBD><E6BCB0>ǰִ<C7B0>н<EFBFBD><D0BD><EFBFBD> CPU <20><><EFBFBD><EFBFBD><EFBFBD>ı<EFBFBD><C4B1>漰<EFBFBD>µ<EFBFBD><C2B5>Ƚ<EFBFBD><C8BD><EFBFBD> CPU <20><><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD>á<EFBFBD><C3A1><EFBFBD><EFBFBD>߳<EFBFBD><DFB3>л<EFBFBD>ʱֻ<CAB1>豣<EFBFBD><E8B1A3><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD>Ĵ<EFBFBD><C4B4><EFBFBD><EFBFBD><EFBFBD><EFBFBD>ݣ<EFBFBD><DDA3><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD>С<EFBFBD><D0A1>
- 调度：线程是独立调度的基本单位，在同一进程中，线程的切换不会引起进程切换，从一个进程内的线程切换到另一个进程中的线程时，会引起进程切换。
- ͨ<EFBFBD>ŷ<EFBFBD><EFBFBD>棺<EFBFBD><EFBFBD><EFBFBD>̼<EFBFBD>ͨ<EFBFBD><EFBFBD> (IPC) <20><>Ҫ<EFBFBD><D2AA><EFBFBD><EFBFBD>ͬ<EFBFBD><CDAC><EFBFBD>ͻ<EFBFBD><CDBB><EFBFBD><EFBFBD>ֶεĸ<CEB5><C4B8><EFBFBD><EFBFBD><EFBFBD><EFBFBD>Ա<EFBFBD>֤<EFBFBD><D6A4><EFBFBD>ݵ<EFBFBD>һ<EFBFBD><D2BB><EFBFBD>ԣ<EFBFBD><D4A3><EFBFBD><EFBFBD>̼߳<DFB3><CCBC><EFBFBD><EFBFBD><EFBFBD>ͨ<EFBFBD><CDA8>ֱ<EFBFBD>Ӷ<EFBFBD>/дͬһ<CDAC><D2BB><EFBFBD><EFBFBD><EFBFBD>е<EFBFBD><D0B5><EFBFBD><EFBFBD>ݶΣ<DDB6><CEA3><EFBFBD>ȫ<EFBFBD>ֱ<EFBFBD><D6B1><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD>ͨ<EFBFBD>š<EFBFBD>
- 系统开销：由于创建或撤销进程时，系统都要为之分配或回收资源，如内存空间、I/O 设备等，因此操作系统所付出的开销远大于创建或撤销线程时的开销。类似地，在进行进程切换时，涉及当前执行进程 CPU 环境的保存及新调度进程 CPU 环境的设置。而线程切换时只需保存和设置少量寄存器内容，开销很小。
<EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD>QQ <20><><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD>̣<EFBFBD><CCA3><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD>кܶ<D0BA><DCB6>̣߳<DFB3><CCA3><EFBFBD><EFBFBD><EFBFBD> HTTP <20><><EFBFBD><EFBFBD><EFBFBD>̡߳<DFB3><CCA1>¼<EFBFBD><C2BC><EFBFBD>Ӧ<EFBFBD>̡߳<DFB3><CCA1><EFBFBD>Ⱦ<EFBFBD>̵߳ȵȣ<C8B5><C8A3>̵߳IJ<CCB5><C4B2><EFBFBD>ִ<EFBFBD><D6B4>ʹ<EFBFBD><CAB9><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD>е<EFBFBD><D0B5><EFBFBD>һ<EFBFBD><D2BB><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD>ӴӶ<D3B4><D3B6><EFBFBD><EFBFBD><EFBFBD> HTTP <20><><EFBFBD><EFBFBD>ʱ<EFBFBD><CAB1><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD>Ӧ<EFBFBD>û<EFBFBD><C3BB><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD>¼<EFBFBD><C2BC><EFBFBD>
- 通信方面：进程间通信 (IPC) 需要进程同步和互斥手段的辅助，以保证数据的一致性，而线程间可以通过直接读/写同一进程中的数据段（如全局变量）来进行通信。
## <20><><EFBFBD><EFBFBD>״̬<D7B4><CCAC><EFBFBD>л<EFBFBD>
举例：QQ 和浏览器是两个进程，浏览器进程里面有很多线程，例如 HTTP 请求线程、事件响应线程、渲染线程等等，线程的并发执行使得在浏览器中点击一个新链接从而发起 HTTP 请求时，浏览器还可以响应用户的其它事件。
![](https://github.com/CyC2018/InterviewNotes/blob/master/pics/1706ce58-a081-4fed-9b36-c3c0d7e22b3a.jpg)
## 进程状态的切换
<EFBFBD><EFBFBD><EFBFBD><EFBFBD>״̬<EFBFBD><EFBFBD>ȱ<EFBFBD><EFBFBD><EFBFBD><EFBFBD>Ҫ<EFBFBD><EFBFBD><EFBFBD><EFBFBD>Դ<EFBFBD>Ӷ<EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD>״̬ת<EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD>Ǹ<EFBFBD><EFBFBD><EFBFBD>Դ<EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD> CPU<50><55>ȱ<EFBFBD><C8B1> CPU <20><><EFBFBD>ý<EFBFBD><C3BD>̴<EFBFBD><CCB4><EFBFBD><EFBFBD><EFBFBD>̬ת<CCAC><D7AA>Ϊ<EFBFBD><CEAA><EFBFBD><EFBFBD>̬<EFBFBD><CCAC>
![](https://github.com/CyC2018/InterviewNotes/blob/master/pics//1706ce58-a081-4fed-9b36-c3c0d7e22b3a.jpg)
ֻ<EFBFBD>о<EFBFBD><EFBFBD><EFBFBD>̬<EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD>̬<EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD>໥ת<EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD>Ķ<EFBFBD><EFBFBD>ǵ<EFBFBD><EFBFBD><EFBFBD>ת<EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD>״̬<EFBFBD>Ľ<EFBFBD><EFBFBD><EFBFBD>ͨ<EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD>㷨<EFBFBD>Ӷ<EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD> CPU ʱ<>䣬תΪ<D7AA><CEAA><EFBFBD><EFBFBD>״̬<D7B4><CCAC><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD>״̬<D7B4>Ľ<EFBFBD><C4BD>̣<EFBFBD><CCA3>ڷ<EFBFBD><DAB7><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD> CPU ʱ<><CAB1>Ƭ<EFBFBD><C6AC><EFBFBD><EFBFBD>֮<EFBFBD><D6AE><EFBFBD>ͻ<EFBFBD>תΪ<D7AA><CEAA><EFBFBD><EFBFBD>״̬<D7B4><CCAC><EFBFBD>ȴ<EFBFBD><C8B4><EFBFBD>һ<EFBFBD>ε<EFBFBD><CEB5>ȡ<EFBFBD>
阻塞状态是缺少需要的资源从而由运行状态转换而来，但是该资源不包括 CPU，缺少 CPU 会让进程从运行态转换为就绪态。
## <20><><EFBFBD><EFBFBD><EFBFBD>㷨
只有就绪态和运行态可以相互转换，其它的都是单向转换。就绪状态的进程通过调度算法从而获得 CPU 时间，转为运行状态；而运行状态的进程，在分配给它的 CPU 时间片用完之后就会转为就绪状态，等待下一次调度。
<EFBFBD><EFBFBD>Ҫ<EFBFBD><EFBFBD><EFBFBD>Բ<EFBFBD>ͬ<EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD>۵<EFBFBD><EFBFBD><EFBFBD><EFBFBD>㷨<EFBFBD><EFBFBD>
## 调度算法
### 1. <20><><EFBFBD><EFBFBD><EFBFBD><EFBFBD>ϵͳ<CFB5>еĵ<D0B5><C4B5><EFBFBD>
需要针对不同环境来讨论调度算法。
#### 1.1 <20><><EFBFBD><EFBFBD><EFBFBD>ȷ<EFBFBD><C8B7><EFBFBD>
### 1. 批处理系统中的调度
first-come first-serverd<72><64>FCFS<46><53><EFBFBD><EFBFBD>
#### 1.1 先来先服务
<EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD>Ƚ<EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD>е<EFBFBD><EFBFBD><EFBFBD>ҵ<EFBFBD><EFBFBD>
first-come first-serverd（FCFS）。
<EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD>ڳ<EFBFBD><EFBFBD><EFBFBD>ҵ<EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD>ڶ<EFBFBD><EFBFBD><EFBFBD>ҵ<EFBFBD><EFBFBD><EFBFBD><EFBFBD>Ϊ<EFBFBD><EFBFBD><EFBFBD><EFBFBD>ҵ<EFBFBD><EFBFBD><EFBFBD><EFBFBD>һֱ<EFBFBD>ȴ<EFBFBD>ǰ<EFBFBD><EFBFBD><EFBFBD>ij<EFBFBD><EFBFBD><EFBFBD>ҵִ<EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD>ϲ<EFBFBD><EFBFBD><EFBFBD>ִ<EFBFBD>У<EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD>ҵ<EFBFBD><EFBFBD><EFBFBD><EFBFBD>Ҫִ<EFBFBD>кܳ<EFBFBD>ʱ<EFBFBD>䣬<EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD>˶<EFBFBD><EFBFBD><EFBFBD>ҵ<EFBFBD>ȴ<EFBFBD>ʱ<EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD>
调度最先进入就绪队列的作业。
#### 1.2 <20><><EFBFBD><EFBFBD>ҵ<EFBFBD><D2B5><EFBFBD><EFBFBD>
有利于长作业，但不利于短作业，因为短作业必须一直等待前面的长作业执行完毕才能执行，而长作业又需要执行很长时间，造成了短作业等待时间过长。
shortest job first<73><74>SJF<4A><46><EFBFBD><EFBFBD>
#### 1.2 短作业优先
<EFBFBD><EFBFBD><EFBFBD>ȹ<EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD>ʱ<EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD>̵<EFBFBD><EFBFBD><EFBFBD>ҵ<EFBFBD><EFBFBD>
shortest job first（SJF）。
<EFBFBD><EFBFBD><EFBFBD><EFBFBD>ҵ<EFBFBD>п<EFBFBD><EFBFBD>ܻ<EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD>һֱ<EFBFBD>ȴ<EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD>ҵִ<EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD>ϵ<EFBFBD>״̬<EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD>һֱ<EFBFBD>ж<EFBFBD><EFBFBD><EFBFBD>ҵ<EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD>ô<EFBFBD><EFBFBD><EFBFBD><EFBFBD>ҵ<EFBFBD><EFBFBD>Զ<EFBFBD>ò<EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD>ȡ<EFBFBD>
调度估计运行时间最短的作业。
#### 1.3 <20><><EFBFBD><EFBFBD>ʣ<EFBFBD><CAA3>ʱ<EFBFBD><CAB1><EFBFBD><EFBFBD><EFBFBD><EFBFBD>
长作业有可能会饿死，处于一直等待短作业执行完毕的状态。如果一直有短作业到来，那么长作业永远得不到调度。
shortest remaining time next<78><74>SRTN<54><4E><EFBFBD><EFBFBD>
#### 1.3 最短剩余时间优先
### 2. <20><><EFBFBD><EFBFBD>ʽϵͳ<CFB5>еĵ<D0B5><C4B5><EFBFBD>
shortest remaining time next（SRTN）。
#### 2.1 <20><><EFBFBD><EFBFBD>Ȩ<EFBFBD><C8A8><EFBFBD><EFBFBD>
### 2. 交互式系统中的调度
<EFBFBD><EFBFBD><EFBFBD>˿<EFBFBD><EFBFBD><EFBFBD><EFBFBD>ֶ<EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD>Ȩ֮<EFBFBD>⣬<EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD>԰<EFBFBD><EFBFBD><EFBFBD>Ӧ<EFBFBD><EFBFBD><EFBFBD><EFBFBD>Ϊ<EFBFBD><EFBFBD><EFBFBD><EFBFBD>Ȩ<EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD>ֵ<EFBFBD><EFBFBD>ȷ<EFBFBD>ʽ<EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD>Ӧ<EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD>ȵ<EFBFBD><EFBFBD><EFBFBD><EFBFBD>㷨<EFBFBD><EFBFBD>
#### 2.1 优先权优先
<EFBFBD><EFBFBD>Ӧ<EFBFBD><EFBFBD> = (<28>ȴ<EFBFBD>ʱ<EFBFBD><CAB1> + Ҫ<><D2AA><EFBFBD><EFBFBD><EFBFBD><EFBFBD>ʱ<EFBFBD><CAB1>) / Ҫ<><D2AA><EFBFBD><EFBFBD><EFBFBD><EFBFBD>ʱ<EFBFBD><CAB1> = <20><>Ӧʱ<D3A6><CAB1> / Ҫ<><D2AA><EFBFBD><EFBFBD><EFBFBD><EFBFBD>ʱ<EFBFBD><CAB1>
除了可以手动赋予优先权之外，还可以把响应比作为优先权，这种调度方式叫做高响应比优先调度算法。
<EFBFBD><EFBFBD><EFBFBD>ֵ<EFBFBD><EFBFBD><EFBFBD><EFBFBD>㷨<EFBFBD><EFBFBD>Ҫ<EFBFBD><EFBFBD>Ϊ<EFBFBD>˽<EFBFBD><EFBFBD><EFBFBD> SJF <20>г<EFBFBD><D0B3><EFBFBD>ҵ<EFBFBD><D2B5><EFBFBD>ܻ<EFBFBD><DCBB><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD>⣬<EFBFBD><E2A3AC>Ϊ<EFBFBD><CEAA><EFBFBD>ŵȴ<C5B5>ʱ<EFBFBD><CAB1><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD>Ӧ<EFBFBD><D3A6>Ҳ<EFBFBD><D2B2>Խ<EFBFBD><D4BD>Խ<EFBFBD>ߡ<EFBFBD>
响应比 = (等待时间 + 要求服务时间) / 要求服务时间 = 响应时间 / 要求服务时间
#### 2.2 ʱ<><CAB1>Ƭ<EFBFBD><C6AC>ת
这种调度算法主要是为了解决 SJF 中长作业可能会饿死的问题，因为随着等待时间的增长，响应比也会越来越高。
<EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD>о<EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD>̰<EFBFBD> FCFS <20><>ԭ<EFBFBD><D4AD><EFBFBD>ų<EFBFBD>һ<EFBFBD><D2BB><EFBFBD><EFBFBD><EFBFBD>У<EFBFBD>ÿ<EFBFBD>ε<EFBFBD><CEB5><EFBFBD>ʱ<EFBFBD><CAB1><EFBFBD><EFBFBD> CPU <20><><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD>׽<EFBFBD><D7BD>̣<EFBFBD><CCA3>ý<EFBFBD><C3BD>̿<EFBFBD><CCBF><EFBFBD>ִ<EFBFBD><D6B4>һ<EFBFBD><D2BB>ʱ<EFBFBD><CAB1>Ƭ<EFBFBD><C6AC><EFBFBD><EFBFBD>ʱ<EFBFBD><CAB1>Ƭ<EFBFBD><C6AC><EFBFBD><EFBFBD>ʱ<EFBFBD><CAB1><EFBFBD>ɼ<EFBFBD>ʱ<EFBFBD><CAB1><EFBFBD><EFBFBD><EFBFBD><EFBFBD>ʱ<EFBFBD><CAB1><EFBFBD>жϣ<D0B6><CFA3><EFBFBD><EFBFBD>ȳ<EFBFBD><C8B3><EFBFBD><EFBFBD><EFBFBD>ֹͣ<CDA3>ý<EFBFBD><C3BD>̵<EFBFBD>ִ<EFBFBD>У<EFBFBD><D0A3><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD>е<EFBFBD>ĩβ<C4A9><CEB2>ͬʱ<CDAC><CAB1><EFBFBD><EFBFBD><EFBFBD><EFBFBD> CPU <20><><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD>׵Ľ<D7B5><C4BD>̡<EFBFBD>
#### 2.2 时间片轮转
ʱ<EFBFBD><EFBFBD>Ƭ<EFBFBD><EFBFBD>ת<EFBFBD>㷨<EFBFBD><EFBFBD>Ч<EFBFBD>ʺ<EFBFBD>ʱ<EFBFBD><EFBFBD>Ƭ<EFBFBD>Ĵ<EFBFBD>С<EFBFBD>кܴ<EFBFBD><EFBFBD><EFBFBD>ϵ<EFBFBD><EFBFBD><EFBFBD><EFBFBD>Ϊÿ<EFBFBD>ν<EFBFBD><EFBFBD><EFBFBD><EFBFBD>л<EFBFBD><EFBFBD><EFBFBD>Ҫ<EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD>̵<EFBFBD><EFBFBD><EFBFBD>Ϣ<EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD>½<EFBFBD><EFBFBD>̵<EFBFBD><EFBFBD><EFBFBD>Ϣ<EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD>ʱ<EFBFBD><EFBFBD>Ƭ̫С<EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD>л<EFBFBD>̫Ƶ<EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD>ڽ<EFBFBD><EFBFBD><EFBFBD><EFBFBD>л<EFBFBD><EFBFBD>ϾͻỨ<EFBFBD><EFBFBD><EFBFBD><EFBFBD>ʱ<EFBFBD>䡣
将所有就绪进程按 FCFS 的原则排成一个队列，每次调度时，把 CPU 分配给队首进程，该进程可以执行一个时间片。当时间片用完时，由计时器发出时钟中断，调度程序便停止该进程的执行，并将它送往就绪队列的末尾，同时继续把 CPU 分配给队首的进程。
#### 2.3 <20>༶<EFBFBD><E0BCB6><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD>
时间片轮转算法的效率和时间片的大小有很大关系。因为每次进程切换都要保存进程的信息并且载入新进程的信息，如果时间片太小，进程切换太频繁，在进程切换上就会花过多时间。
![](https://github.com/CyC2018/InterviewNotes/blob/master/pics/042cf928-3c8e-4815-ae9c-f2780202c68f.png)
#### 2.3 多级反馈队列
1. <20><><EFBFBD>ö<EFBFBD><C3B6><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD>У<EFBFBD><D0A3><EFBFBD>Ϊ<EFBFBD><CEAA><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD>и<EFBFBD><D0B8>費ͬ<E8B2BB><CDAC><EFBFBD><EFBFBD><EFBFBD>ȼ<EFBFBD><C8BC><EFBFBD><EFBFBD><EFBFBD>һ<EFBFBD><D2BB><EFBFBD><EFBFBD><EFBFBD>е<EFBFBD><D0B5><EFBFBD><EFBFBD>ȼ<EFBFBD><C8BC><EFBFBD><EFBFBD>ߣ<EFBFBD><DFA3>ڶ<EFBFBD><DAB6><EFBFBD><EFBFBD><EFBFBD><EFBFBD>д<EFBFBD>֮<EFBFBD><D6AE><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD>е<EFBFBD><D0B5><EFBFBD><EFBFBD><EFBFBD>Ȩ<EFBFBD><C8A8><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD>͡<EFBFBD><CDA1><EFBFBD><EFBFBD>㷨<EFBFBD><E3B7A8><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD>н<EFBFBD><D0BD><EFBFBD>ִ<EFBFBD><D6B4>ʱ<EFBFBD><CAB1>Ƭ<EFBFBD>Ĵ<EFBFBD>СҲ<D0A1><D2B2><EFBFBD><EFBFBD><EFBFBD><EFBFBD>ͬ<EFBFBD><CDAC><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD>ȨԽ<C8A8>ߵĶ<DFB5><C4B6><EFBFBD><EFBFBD>У<EFBFBD>Ϊÿ<CEAA><C3BF><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD>涨<EFBFBD><E6B6A8>ִ<EFBFBD><D6B4>ʱ<EFBFBD><CAB1>Ƭ<EFBFBD><C6AC>ԽС<D4BD><D0A1>
![](https://github.com/CyC2018/InterviewNotes/blob/master/pics//042cf928-3c8e-4815-ae9c-f2780202c68f.png)
2. <EFBFBD><EFBFBD>һ<EFBFBD><EFBFBD><EFBFBD>½<EFBFBD><EFBFBD>̽<EFBFBD><EFBFBD><EFBFBD><EFBFBD>ڴ<EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD>Ƚ<EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD>һ<EFBFBD><EFBFBD><EFBFBD>е<EFBFBD>ĩβ<EFBFBD><EFBFBD><EFBFBD><EFBFBD> FCFS ԭ<><D4AD><EFBFBD>Ŷӵȴ<D3B5><C8B4><EFBFBD><EFBFBD>ȡ<EFBFBD><C8A1><EFBFBD><EFBFBD>ֵ<EFBFBD><D6B5>ý<EFBFBD><C3BD><EFBFBD>ִ<EFBFBD><D6B4>ʱ<EFBFBD><CAB1><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD>ڸ<EFBFBD>ʱ<EFBFBD><CAB1>Ƭ<EFBFBD><C6AC><EFBFBD><EFBFBD><EFBFBD>ɣ<EFBFBD><C9A3><EFBFBD><EFBFBD><EFBFBD>׼<EFBFBD><D7BC><EFBFBD><EFBFBD><EFBFBD><EFBFBD>ϵͳ<CFB5><CDB3><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD>һ<EFBFBD><D2BB>ʱ<EFBFBD><CAB1>Ƭ<EFBFBD><C6AC><EFBFBD><EFBFBD>ʱ<EFBFBD><CAB1>δ<EFBFBD><CEB4><EFBFBD>ɣ<EFBFBD><C9A3><EFBFBD><EFBFBD>ȳ<EFBFBD><C8B3><EFBFBD><EFBFBD>㽫<EFBFBD>ý<EFBFBD><C3BD><EFBFBD>ת<EFBFBD><D7AA><EFBFBD><EFBFBD>һ<EFBFBD><D2BB><EFBFBD><EFBFBD><EFBFBD>еĶ<D0B5>β<EFBFBD><CEB2>
1. 设置多个就绪队列，并为各个队列赋予不同的优先级。第一个队列的优先级最高，第二个队列次之，其余各队列的优先权逐个降低。该算法赋予各个队列中进程执行时间片的大小也各不相同，在优先权越高的队列中，为每个进程所规定的执行时间片就越小。
3. <EFBFBD><EFBFBD><EFBFBD><EFBFBD>ǰ i -1 <20><><EFBFBD><EFBFBD><EFBFBD>о<EFBFBD><D0BE><EFBFBD>ʱ<EFBFBD><CAB1><EFBFBD>Ż<EFBFBD><C5BB><EFBFBD><EFBFBD>ȵ<EFBFBD> i <20><><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD>еĽ<D0B5><C4BD>̡<EFBFBD>
2. 当一个新进程进入内存后，首先将它放入第一队列的末尾，按 FCFS 原则排队等待调度。当轮到该进程执行时，如它能在该时间片内完成，便可准备撤离系统；如果它在一个时间片结束时尚未完成，调度程序便将该进程转入下一个队列的队尾。
<EFBFBD>ŵ㣺ʵʱ<EFBFBD>Ժã<EFBFBD>ͬʱ<EFBFBD>ʺ<EFBFBD><EFBFBD><EFBFBD><EFBFBD>ж<EFBFBD><EFBFBD><EFBFBD>ҵ<EFBFBD>ͳ<EFBFBD><EFBFBD><EFBFBD>ҵ<EFBFBD><EFBFBD>
3. 仅当前 i -1 个队列均空时，才会调度第 i 个队列中的进程。
#### 2.4 <20>̽<EFBFBD><CCBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD>
优点：实时性好，同时适合运行短作业和长作业。
### 3. ʵʱϵͳ<CFB5>еĵ<D0B5><C4B5><EFBFBD>
#### 2.4 短进程优先
ʵʱϵͳҪһ<EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD>һ<EFBFBD><EFBFBD>ȷ<EFBFBD><EFBFBD>ʱ<EFBFBD><EFBFBD><EFBFBD>ڵõ<EFBFBD><EFBFBD><EFBFBD>Ӧ<EFBFBD><EFBFBD>
### 3. 实时系统中的调度
<EFBFBD><EFBFBD>ΪӲʵʱ<EFBFBD><EFBFBD><EFBFBD><EFBFBD>ʵʱ<EFBFBD><EFBFBD>ǰ<EFBFBD>߱<EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD>ԵĽ<EFBFBD>ֹʱ<EFBFBD>䣬<EFBFBD><EFBFBD><EFBFBD>߿<EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD>һ<EFBFBD><EFBFBD><EFBFBD>ij<EFBFBD>ʱ<EFBFBD><EFBFBD>
实时系统要一个服务请求在一个确定时间内得到响应。
## <20><><EFBFBD><EFBFBD>ͬ<EFBFBD><CDAC>
分为硬实时和软实时，前者必须满足绝对的截止时间，后者可以容忍一定的超时。
### 1. <20>ٽ<EFBFBD><D9BD><EFBFBD>
## 进程同步
<EFBFBD><EFBFBD><EFBFBD>ٽ<EFBFBD><EFBFBD><EFBFBD>Դ<EFBFBD><EFBFBD><EFBFBD>з<EFBFBD><EFBFBD>ʵ<EFBFBD><EFBFBD>Ƕδ<EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD>Ϊ<EFBFBD>ٽ<EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD>
### 1. 临界区
Ϊ<EFBFBD>˻<EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD>ٽ<EFBFBD><EFBFBD><EFBFBD>Դ<EFBFBD><EFBFBD>ÿ<EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD>ڽ<EFBFBD><EFBFBD><EFBFBD><EFBFBD>ٽ<EFBFBD><EFBFBD><EFBFBD>֮ǰ<EFBFBD><EFBFBD><EFBFBD><EFBFBD>Ҫ<EFBFBD>Ƚ<EFBFBD><EFBFBD>м<EFBFBD><EFBFBD>顣
对临界资源进行访问的那段代码称为临界区。
为了互斥访问临界资源，每个进程在进入临界区之前，需要先进行检查。
```html
// entry section
@ -250,44 +251,44 @@ shortest remaining time next
// exit section
```
### 2. ͬ<EFBFBD><EFBFBD><EFBFBD>뻥<EFBFBD><EFBFBD>
### 2. 同步与互斥
ͬ<EFBFBD><EFBFBD>ָ<EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD>̰<EFBFBD>һ<EFBFBD><EFBFBD>˳<EFBFBD><EFBFBD>ִ<EFBFBD>У<EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD>ָ<EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD>ͬһʱ<EFBFBD><EFBFBD>ֻ<EFBFBD><EFBFBD>һ<EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD>ܽ<EFBFBD><EFBFBD><EFBFBD><EFBFBD>ٽ<EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD>
同步指多个进程按一定顺序执行；互斥指多个进程在同一时刻只有一个进程能进入临界区。
ͬ<EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD>ڶ<EFBFBD><EFBFBD>ٽ<EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD>ʵĻ<EFBFBD><EFBFBD><EFBFBD><EFBFBD>ϣ<EFBFBD>ͨ<EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD>ʵ<EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD>ʵġ<EFBFBD>
同步是在对临界区互斥访问的基础上，通过其它机制来实现有序访问的。
### 3. <EFBFBD>ź<EFBFBD><EFBFBD><EFBFBD>
### 3. 信号量
**<EFBFBD>ź<EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD>Samaphore<EFBFBD><EFBFBD>** <20><>һ<EFBFBD><D2BB><EFBFBD><EFBFBD><EFBFBD>ͱ<EFBFBD><CDB1><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD>Զ<EFBFBD><D4B6><EFBFBD>ִ<EFBFBD><D6B4> down <EFBFBD><EFBFBD> up <EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD>Ҳ<EFBFBD><EFBFBD><EFBFBD>dz<EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD> P <EFBFBD><EFBFBD> V <EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD>
**信号量（Samaphore）** 是一个整型变量，可以对其执行 down 和 up 操作，也就是常见的 P 和 V 操作。
- **down** : <EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD>ź<EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD> 0 <20><>ִ<EFBFBD><D6B4> -1 <20><><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD>ź<EFBFBD><C5BA><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD> 0<><30><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD>˯<EFBFBD>ߣ<EFBFBD><DFA3>ȴ<EFBFBD><C8B4>ź<EFBFBD><C5BA><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD> 0<><30>
- **up**<EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD>ź<EFBFBD><EFBFBD><EFBFBD>ִ<EFBFBD><EFBFBD> +1 <20><><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD>һ<EFBFBD><D2BB><EFBFBD>˯<EFBFBD>ߵĽ<DFB5><C4BD>̣<EFBFBD><CCA3>ý<EFBFBD><C3BD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD> down <20><><EFBFBD><EFBFBD><EFBFBD><EFBFBD>
- **down** : 如果信号量大于 0 ，执行 -1 操作；如果信号量等于 0，将进程睡眠，等待信号量大于 0；
- **up**：对信号量执行 +1 操作，并且唤醒睡眠的进程，让进程完成 down 操作。
down <EFBFBD><EFBFBD> up <EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD>Ҫ<EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD>Ƴ<EFBFBD>ԭ<EFBFBD><EFBFBD><EFBFBD><EFBFBD>ɷָͨ<EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD>ִ<EFBFBD><EFBFBD><EFBFBD><EFBFBD>Щ<EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD>ʱ<EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD>жϡ<EFBFBD>
down 和 up 操作需要被设计成原语，不可分割，通常的做法是在执行这些操作的时候屏蔽中断。
<EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD>ź<EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD>ȡֵֻ<EFBFBD><EFBFBD>Ϊ 0 <20><><EFBFBD><EFBFBD> 1<><31><EFBFBD><EFBFBD>ô<EFBFBD>ͳ<EFBFBD>Ϊ<EFBFBD><CEAA>**<2A><><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD>Mutex<65><78>**<2A><>0 <20><>ʾ<EFBFBD>ٽ<EFBFBD><D9BD><EFBFBD><EFBFBD>Ѿ<EFBFBD><D1BE><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD>1 <20><>ʾ<EFBFBD>ٽ<EFBFBD><D9BD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD>
如果信号量的取值只能为 0 或者 1，那么就成为了**互斥量（Mutex）**，0 表示临界区已经加锁，1 表示临界区解锁。
```c
typedef int samaphore;
samaphore mutex = 1;
void P1() {
down(mutex);
// <EFBFBD>ٽ<EFBFBD><EFBFBD><EFBFBD>
// 临界区
up(mutex);
}
void P2() {
down(mutex);
// <EFBFBD>ٽ<EFBFBD><EFBFBD><EFBFBD>
// 临界区
up(mutex);
}
```
**ʹ<EFBFBD><EFBFBD><EFBFBD>ź<EFBFBD><EFBFBD><EFBFBD>ʵ<EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD>-<2D><><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD>**
**使用信号量实现生产者-消费者问题**
ʹ<EFBFBD><EFBFBD>һ<EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD> mutex <20><><EFBFBD><EFBFBD><EFBFBD>ٽ<EFBFBD><D9BD><EFBFBD>Դ<EFBFBD><D4B4><EFBFBD>з<EFBFBD><D0B7>ʣ<EFBFBD>empty <20><>¼<EFBFBD>ջ<EFBFBD><D5BB><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD>full <20><>¼<EFBFBD><C2BC><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD>
使用一个互斥量 mutex 来对临界资源进行访问；empty 记录空缓冲区的数量，full 记录满缓冲区的数量。
ע<EFBFBD>⣬<EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD>ִ<EFBFBD><EFBFBD> down <20><><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD>û<EFBFBD><C3BB><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD>ٽ<EFBFBD><D9BD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD>Ϊ<EFBFBD><CEAA><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD>ȶ<EFBFBD><C8B6>ٽ<EFBFBD><D9BD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD>Ȼ<EFBFBD><C8BB><EFBFBD><EFBFBD>ִ<EFBFBD><D6B4> down <20><><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD>ô<EFBFBD><C3B4><EFBFBD>ܻ<EFBFBD><DCBB><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD>߶<EFBFBD><DFB6>ٽ<EFBFBD><D9BD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD>ִ<EFBFBD><D6B4> down(empty) <20><><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD> empty = 0<><30><EFBFBD><EFBFBD>ʱ<EFBFBD><CAB1><EFBFBD><EFBFBD><EFBFBD><EFBFBD>˯<EFBFBD>ߡ<EFBFBD><DFA1><EFBFBD><EFBFBD><EFBFBD><EFBFBD>ߴ<EFBFBD>ʱ<EFBFBD><CAB1><EFBFBD>ܽ<EFBFBD><DCBD><EFBFBD><EFBFBD>ٽ<EFBFBD><D9BD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD>Ϊ<EFBFBD><CEAA><EFBFBD><EFBFBD><EFBFBD>߶<EFBFBD><DFB6>ٽ<EFBFBD><D9BD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD>ˣ<EFBFBD>Ҳ<EFBFBD><D2B2><EFBFBD>޷<EFBFBD>ִ<EFBFBD><D6B4> up(empty) <20><><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD>ô<EFBFBD><C3B4><EFBFBD><EFBFBD><EFBFBD>ߺ<EFBFBD><DFBA><EFBFBD><EFBFBD><EFBFBD><EFBFBD>߾ͻ<DFBE>һֱ<D2BB>ȴ<EFBFBD><C8B4><EFBFBD>ȥ<EFBFBD><C8A5>
注意，必须先执行 down 操作再用互斥量对临界区加锁，否则会出现死锁。因为如果都先对临界区加锁，然后再执行 down 操作，那么可能会出现这种情况：生产者对临界区加锁后，执行 down(empty) 操作，发现 empty = 0，此时生成者睡眠。消费者此时不能进入临界区，因为生产者对临界区加锁了，也就无法执行 up(empty) 操作，那么生产者和消费者就会一直等待下去。
```c
#define N 100
@ -319,11 +320,11 @@ void consumer() {
}
```
### 4. <EFBFBD>ܳ<EFBFBD>
### 4. 管程
ʹ<EFBFBD><EFBFBD><EFBFBD>ź<EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD>ʵ<EFBFBD>ֵ<EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD>Ҫ<EFBFBD>ͻ<EFBFBD><EFBFBD>˴<EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD>ܶ<EFBFBD><EFBFBD><EFBFBD><EFBFBD>ƣ<EFBFBD><EFBFBD><EFBFBD><EFBFBD>̰ܳѿ<EFBFBD><EFBFBD>ƵĴ<EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD>׳<EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD>Ҳʹ<EFBFBD>ÿͻ<EFBFBD><EFBFBD>˴<EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD>ø<EFBFBD><EFBFBD><EFBFBD><EFBFBD>ס<EFBFBD>
使用信号量机制实现的生产者消费者问题需要客户端代码做很多控制，而管程把控制的代码独立出来，不仅不容易出错，也使得客户端代码调用更容易。
c <EFBFBD><EFBFBD><EFBFBD>Բ<EFBFBD>֧<EFBFBD>ֹ̣ܳ<EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD>ʾ<EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD>ʹ<EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD> Pascal <20><><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD>̡ܳ<DCB3>ʾ<EFBFBD><CABE><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD>еĹܳ<C4B9><DCB3>ṩ<EFBFBD><E1B9A9> insert() <EFBFBD><EFBFBD> remove() <EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD>ͻ<EFBFBD><EFBFBD>˴<EFBFBD><EFBFBD><EFBFBD>ͨ<EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD>-<2D><><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD>⡣
c 语言不支持管程，下面的示例代码使用了类 Pascal 语言来描述管程。示例代码中的管程提供了 insert() 和 remove() 方法，客户端代码通过调用这两个方法来解决生产者-消费者问题。
```pascal
monitor ProducerConsumer
@ -342,11 +343,11 @@ monitor ProducerConsumer
end monitor;
```
<EFBFBD>ܳ<EFBFBD><EFBFBD><EFBFBD>һ<EFBFBD><EFBFBD><EFBFBD><EFBFBD>Ҫ<EFBFBD><EFBFBD><EFBFBD>ԣ<EFBFBD><EFBFBD><EFBFBD>һ<EFBFBD><EFBFBD>ʱ<EFBFBD><EFBFBD>ֻ<EFBFBD><EFBFBD><EFBFBD><EFBFBD>һ<EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD>ʹ<EFBFBD>ù̡ܳ<EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD>޷<EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD>ִ<EFBFBD>е<EFBFBD>ʱ<EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD>һֱռ<EFBFBD>ụ̀ܳ<EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD>Զ<EFBFBD><EFBFBD><EFBFBD><EFBFBD>ʹ<EFBFBD>ù̡ܳ<EFBFBD>
管程有一个重要特性：在一个时刻只能有一个进程使用管程。进程在无法继续执行的时候不能一直占用管程，否者其它进程永远不能使用管程。
<EFBFBD>ܳ<EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD> **<EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD>** <20>Լ<EFBFBD><D4BC><EFBFBD><EFBFBD>صIJ<D8B5><C4B2><EFBFBD><EFBFBD><EFBFBD>**wait()** <EFBFBD><EFBFBD> **signal()** <EFBFBD><EFBFBD>ʵ<EFBFBD><EFBFBD>ͬ<EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD>ִ<EFBFBD><EFBFBD> wait() <20><><EFBFBD><EFBFBD><EFBFBD>ᵼ<EFBFBD>µ<EFBFBD><C2B5>ý<EFBFBD><C3BD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD>ѹܳ<D1B9><DCB3>ó<EFBFBD><C3B3><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD>һ<EFBFBD><D2BB><EFBFBD><EFBFBD><EFBFBD>̳<EFBFBD><CCB3>С<EFBFBD>signal() <20><><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD>ڻ<EFBFBD><DABB>ѱ<EFBFBD><D1B1><EFBFBD><EFBFBD><EFBFBD><EFBFBD>Ľ<EFBFBD><C4BD>̡<EFBFBD>
管程引入了 **条件变量** 以及相关的操作：**wait()** 和 **signal()** 来实现同步操作。对条件变量执行 wait() 操作会导致调用进程阻塞，把管程让出来让另一个进程持有。signal() 操作用于唤醒被阻塞的进程。
**ʹ<EFBFBD>ùܳ<EFBFBD>ʵ<EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD>-<2D><><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD>**
**使用管程实现生成者-消费者问题**
```pascal
monitor ProducerConsumer
@ -390,53 +391,53 @@ begin
end;
```
## <EFBFBD><EFBFBD><EFBFBD><EFBFBD>ͨ<EFBFBD><EFBFBD>
## 进程通信
<EFBFBD><EFBFBD><EFBFBD><EFBFBD>ͨ<EFBFBD>ſ<EFBFBD><EFBFBD>Կ<EFBFBD><EFBFBD><EFBFBD><EFBFBD>Dz<EFBFBD>ͬ<EFBFBD><EFBFBD><EFBFBD>̼<EFBFBD><EFBFBD><EFBFBD><EFBFBD>߳<EFBFBD>ͨ<EFBFBD>ţ<EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD>ͬһ<EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD>̵߳<EFBFBD>ͨ<EFBFBD>ŷ<EFBFBD>ʽ<EFBFBD><EFBFBD><EFBFBD><EFBFBD>Ҫʹ<EFBFBD><EFBFBD><EFBFBD>ź<EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD>ͬ<EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD>ơ<EFBFBD>
进程通信可以看成是不同进程间的线程通信，对于同一个进程内线程的通信方式，主要使用信号量、条件变量等同步机制。
### 1. <EFBFBD>ܵ<EFBFBD>
### 1. 管道
<EFBFBD>ܵ<EFBFBD><EFBFBD>ǵ<EFBFBD><EFBFBD><EFBFBD><EFBFBD>ġ<EFBFBD><EFBFBD>Ƚ<EFBFBD><EFBFBD>ȳ<EFBFBD><EFBFBD>ġ<EFBFBD><EFBFBD>޽ṹ<EFBFBD>ġ<EFBFBD><EFBFBD>̶<EFBFBD><EFBFBD><EFBFBD>С<EFBFBD><EFBFBD><EFBFBD>ֽ<EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD>һ<EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD>̵ı<EFBFBD>׼<EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD>һ<EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD>̵ı<EFBFBD>׼<EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD>һ<EFBFBD><EFBFBD><EFBFBD><EFBFBD>д<EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD>ڹܵ<EFBFBD><EFBFBD><EFBFBD>β<EFBFBD><EFBFBD>д<EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD>ݣ<EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD>ڹܵ<EFBFBD><EFBFBD><EFBFBD><EFBFBD>׶˶<EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD>ݡ<EFBFBD><EFBFBD><EFBFBD><EFBFBD>ݶ<EFBFBD><EFBFBD><EFBFBD><EFBFBD>󽫴ӹܵ<EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD>ߣ<EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD>̶<EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD>ٶ<EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD>Щ<EFBFBD><EFBFBD><EFBFBD>ݡ<EFBFBD>
管道是单向的、先进先出的、无结构的、固定大小的字节流，它把一个进程的标准输出和另一个进程的标准输入连接在一起。写进程在管道的尾端写入数据，读进程在管道的首端读出数据。数据读出后将从管道中移走，其它读进程都不能再读到这些数据。
<EFBFBD>ܵ<EFBFBD><EFBFBD>ṩ<EFBFBD>˼򵥵<EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD>ƻ<EFBFBD><EFBFBD>ƣ<EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD>ͼ<EFBFBD><EFBFBD><EFBFBD>չܵ<EFBFBD>ʱ<EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD>д<EFBFBD><EFBFBD><EFBFBD>ܵ<EFBFBD>ǰ<EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD>̽<EFBFBD>һֱ<EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD>ͬ<EFBFBD><EFBFBD><EFBFBD>أ<EFBFBD><EFBFBD>ܵ<EFBFBD><EFBFBD>Ѿ<EFBFBD><EFBFBD><EFBFBD>ʱ<EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD>ͼд<EFBFBD>ܵ<EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD>̴ӹܵ<EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD>֮ǰ<EFBFBD><EFBFBD>д<EFBFBD><EFBFBD><EFBFBD>̽<EFBFBD>һֱ<EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD>
管道提供了简单的流控制机制，进程试图读空管道时，在有数据写入管道前，进程将一直阻塞。同样地，管道已经满时，进程再试图写管道，在其它进程从管道中移走数据之前，写进程将一直阻塞。
Linux <EFBFBD>йܵ<EFBFBD><EFBFBD><EFBFBD>ͨ<EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD>ļ<EFBFBD><EFBFBD><EFBFBD>ʵ<EFBFBD>֡<EFBFBD>
Linux 中管道是通过空文件来实现。
<EFBFBD>ܵ<EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD>֣<EFBFBD>
管道有三种：
1. <EFBFBD><EFBFBD>ͨ<EFBFBD>ܵ<EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD>ƣ<EFBFBD>һ<EFBFBD><EFBFBD>ֻ֧<EFBFBD>ְ<EFBFBD>˫<EFBFBD><EFBFBD>ͨ<EFBFBD>ŷ<EFBFBD>ʽ<EFBFBD><EFBFBD><EFBFBD><EFBFBD>ֻ<EFBFBD>ܵ<EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD>䣻<EFBFBD><EFBFBD><EFBFBD><EFBFBD>ֻ<EFBFBD><EFBFBD><EFBFBD>ڸ<EFBFBD><EFBFBD>ӽ<EFBFBD><EFBFBD><EFBFBD>֮<EFBFBD><EFBFBD>ʹ<EFBFBD>ã<EFBFBD>
2. <EFBFBD><EFBFBD><EFBFBD>ܵ<EFBFBD><EFBFBD><EFBFBD>ȥ<EFBFBD><EFBFBD><EFBFBD><EFBFBD>һ<EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD>ƣ<EFBFBD>֧<EFBFBD><EFBFBD>˫<EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD>䣻
3. <EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD>ܵ<EFBFBD><EFBFBD><EFBFBD>ȥ<EFBFBD><EFBFBD><EFBFBD>ڶ<EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD>ƣ<EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD>ڲ<EFBFBD><EFBFBD><EFBFBD><EFBFBD>ؽ<EFBFBD><EFBFBD><EFBFBD>֮<EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD>ͨ<EFBFBD>š<EFBFBD>
1. 普通管道：有两个限制：一是只支持半双工通信方式，即只能单向传输；二是只能在父子进程之间使用；
2. 流管道：去除第一个限制，支持双向传输；
3. 命名管道：去除第二个限制，可以在不相关进程之间进行通信。
### 2. <EFBFBD>ź<EFBFBD><EFBFBD><EFBFBD>
### 2. 信号量
<EFBFBD>ź<EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD>һ<EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD>ƶ<EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD>̶Թ<EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD>Դ<EFBFBD>ķ<EFBFBD><EFBFBD>ʡ<EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD>Ϊһ<EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD>ƣ<EFBFBD><EFBFBD><EFBFBD>ֹij<EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD>ڷ<EFBFBD><EFBFBD>ʹ<EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD>Դʱ<EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD>Ҳ<EFBFBD><EFBFBD><EFBFBD>ʸ<EFBFBD><EFBFBD><EFBFBD>Դ<EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD>ˣ<EFBFBD><EFBFBD><EFBFBD>Ҫ<EFBFBD><EFBFBD>Ϊ<EFBFBD><EFBFBD><EFBFBD>̼<EFBFBD><EFBFBD>Լ<EFBFBD>ͬһ<EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD>ڲ<EFBFBD>ͬ<EFBFBD>߳<EFBFBD>֮<EFBFBD><EFBFBD><EFBFBD><EFBFBD>ͬ<EFBFBD><EFBFBD><EFBFBD>ֶΡ<EFBFBD>
信号量是一个计数器，可以用来控制多个进程对共享资源的访问。它常作为一种锁机制，防止某进程正在访问共享资源时，其它进程也访问该资源。因此，主要作为进程间以及同一进程内不同线程之间的同步手段。
### 3. <EFBFBD><EFBFBD>Ϣ<EFBFBD><EFBFBD><EFBFBD><EFBFBD>
### 3. 消息队列
<EFBFBD><EFBFBD>Ϣ<EFBFBD><EFBFBD><EFBFBD>п˷<EFBFBD><EFBFBD><EFBFBD><EFBFBD>źŴ<EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD>Ϣ<EFBFBD>١<EFBFBD><EFBFBD>ܵ<EFBFBD>ֻ<EFBFBD>ܳ<EFBFBD><EFBFBD><EFBFBD><EFBFBD>޸<EFBFBD>ʽ<EFBFBD>ֽ<EFBFBD><EFBFBD><EFBFBD><EFBFBD>Լ<EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD>С<EFBFBD><EFBFBD><EFBFBD>޵<EFBFBD>ȱ<EFBFBD>㡣
消息队列克服了信号传递信息少、管道只能承载无格式字节流以及缓冲区大小受限等缺点。
### 4. <EFBFBD>ź<EFBFBD>
### 4. 信号
<EFBFBD>ź<EFBFBD><EFBFBD><EFBFBD>һ<EFBFBD>ֱȽϸ<EFBFBD><EFBFBD>ӵ<EFBFBD>ͨ<EFBFBD>ŷ<EFBFBD>ʽ<EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD>֪ͨ<EFBFBD><EFBFBD><EFBFBD>ս<EFBFBD><EFBFBD><EFBFBD>ij<EFBFBD><EFBFBD><EFBFBD>¼<EFBFBD><EFBFBD>Ѿ<EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD>
信号是一种比较复杂的通信方式，用于通知接收进程某个事件已经发生。
### 5. <EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD>ڴ<EFBFBD>
### 5. 共享内存
<EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD>ڴ<EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD>ӳ<EFBFBD><EFBFBD>һ<EFBFBD><EFBFBD><EFBFBD>ܱ<EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD>ʵ<EFBFBD><EFBFBD>ڴ棬<EFBFBD><EFBFBD><EFBFBD>ι<EFBFBD><EFBFBD><EFBFBD><EFBFBD>ڴ<EFBFBD><EFBFBD><EFBFBD>һ<EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD>̴<EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD>̶<EFBFBD><EFBFBD><EFBFBD><EFBFBD>Է<EFBFBD><EFBFBD>ʡ<EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD>ڴ<EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD> IPC <20><>ʽ<EFBFBD><CABD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD> IPC <20><><EFBFBD><EFBFBD>Ч<EFBFBD>ʵͶ<CAB5>ר<EFBFBD><D7A8><EFBFBD><EFBFBD><EFBFBD>Ƶġ<C6B5><C4A1><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD>ͨ<EFBFBD>Ż<EFBFBD><C5BB>ƣ<EFBFBD><C6A3><EFBFBD><EFBFBD>ź<EFBFBD><C5BA><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD>ʹ<EFBFBD>ã<EFBFBD><C3A3><EFBFBD>ʵ<EFBFBD>ֽ<EFBFBD><D6BD>̼<EFBFBD><CCBC><EFBFBD>ͬ<EFBFBD><CDAC><EFBFBD><EFBFBD>ͨ<EFBFBD>š<EFBFBD>
共享内存就是映射一段能被其它进程所访问的内存，这段共享内存由一个进程创建，但多个进程都可以访问。共享内存是最快的 IPC 方式，它是针对其它 IPC 运行效率低而专门设计的。它往往与其它通信机制（如信号量）配合使用，来实现进程间的同步和通信。
### 6. <EFBFBD>׽<EFBFBD><EFBFBD><EFBFBD>
### 6. 套接字
<EFBFBD>׽<EFBFBD><EFBFBD><EFBFBD>Ҳ<EFBFBD><EFBFBD>һ<EFBFBD>ֽ<EFBFBD><EFBFBD>̼<EFBFBD>ͨ<EFBFBD>Ż<EFBFBD><EFBFBD>ƣ<EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD>ͨ<EFBFBD>Ż<EFBFBD><EFBFBD>Ʋ<EFBFBD>ͬ<EFBFBD><EFBFBD><EFBFBD>ǣ<EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD>ڲ<EFBFBD>ͬ<EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD>Ľ<EFBFBD><EFBFBD><EFBFBD>ͨ<EFBFBD>š<EFBFBD>
套接字也是一种进程间通信机制，与其它通信机制不同的是，它可用于不同机器间的进程通信。
## <EFBFBD><EFBFBD><EFBFBD><EFBFBD>ͬ<EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD>
## 经典同步问题
<EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD>ߺ<EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD>ǰ<EFBFBD><EFBFBD><EFBFBD>Ѿ<EFBFBD><EFBFBD><EFBFBD><EFBFBD>۹<EFBFBD><EFBFBD><EFBFBD>
生产者和消费者问题前面已经讨论过。
### 1. <EFBFBD><EFBFBD><EFBFBD><EFBFBD>-д<><D0B4><EFBFBD><EFBFBD><EFBFBD><EFBFBD>
### 1. 读者-写者问题
<EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD>ͬʱ<EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD>ݽ<EFBFBD><EFBFBD>ж<EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD>Dz<EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD>д<EFBFBD>Լ<EFBFBD>д<EFBFBD><EFBFBD>д<EFBFBD><EFBFBD><EFBFBD><EFBFBD>ͬʱ<EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD>
允许多个进程同时对数据进行读操作，但是不允许读和写以及写和写操作同时发生。
һ<EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD>ͱ<EFBFBD><EFBFBD><EFBFBD> count <20><>¼<EFBFBD>ڶ<EFBFBD><DAB6><EFBFBD><EFBFBD>ݽ<EFBFBD><DDBD>ж<EFBFBD><D0B6><EFBFBD><EFBFBD><EFBFBD><EFBFBD>Ľ<EFBFBD><C4BD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD>һ<EFBFBD><D2BB><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD> count_mutex <EFBFBD><EFBFBD><EFBFBD>ڶ<EFBFBD> count <EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD>һ<EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD> data_mutex <20><><EFBFBD>ڶԶ<DAB6>д<EFBFBD><D0B4><EFBFBD><EFBFBD><EFBFBD>ݼ<EFBFBD><DDBC><EFBFBD><EFBFBD><EFBFBD>
一个整型变量 count 记录在对数据进行读操作的进程数量，一个互斥量 count_mutex 用于对 count 加锁，一个互斥量 data_mutex 用于对读写的数据加锁。
```c
typedef int semaphore;
@ -448,7 +449,7 @@ void reader() {
while(TRUE) {
down(count_mutex);
count++;
if(count == 1) down(data_mutex); // <EFBFBD><EFBFBD>һ<EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD>Ҫ<EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD>ݽ<EFBFBD><EFBFBD>м<EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD>ֹд<EFBFBD><EFBFBD><EFBFBD>̷<EFBFBD><EFBFBD><EFBFBD>
if(count == 1) down(data_mutex); // 第一个读者需要对数据进行加锁，防止写进程访问
up(count_mutex);
read();
down(count_mutex);
@ -467,13 +468,13 @@ void writer() {
}
```
### 2. <EFBFBD><EFBFBD>ѧ<EFBFBD>ҽ<EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD>
### 2. 哲学家进餐问题
![](https://github.com/CyC2018/InterviewNotes/blob/master/pics/a9077f06-7584-4f2b-8c20-3a8e46928820.jpg)
![](https://github.com/CyC2018/InterviewNotes/blob/master/pics//a9077f06-7584-4f2b-8c20-3a8e46928820.jpg)
<EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD>ѧ<EFBFBD><EFBFBD>Χ<EFBFBD><EFBFBD>һ<EFBFBD><EFBFBD>Բ<EFBFBD>ܣ<EFBFBD>ÿ<EFBFBD><EFBFBD><EFBFBD><EFBFBD>ѧ<EFBFBD><EFBFBD><EFBFBD><EFBFBD>ǰ<EFBFBD><EFBFBD><EFBFBD>ŷ<EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD>ѧ<EFBFBD>ҵ<EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD>ֽ<EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD>Է<EFBFBD><EFBFBD>Լ<EFBFBD>˼<EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD>һ<EFBFBD><EFBFBD><EFBFBD><EFBFBD>ѧ<EFBFBD>ҳԷ<EFBFBD>ʱ<EFBFBD><EFBFBD><EFBFBD><EFBFBD>Ҫ<EFBFBD><EFBFBD>һ<EFBFBD><EFBFBD>һ<EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD>ߵĿ<EFBFBD><EFBFBD>ӡ<EFBFBD>
五个哲学家围着一张圆周，每个哲学家面前放着饭。哲学家的生活有两种交替活动：吃饭以及思考。当一个哲学家吃饭时，需要先一根一根拿起左右两边的筷子。
<EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD>һ<EFBFBD>ִ<EFBFBD><EFBFBD><EFBFBD><EFBFBD>Ľⷨ<EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD>ǵ<EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD>ÿ<EFBFBD><EFBFBD><EFBFBD><EFBFBD>ѧ<EFBFBD><EFBFBD>ͬʱ<EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD>ֱߵĿ<EFBFBD><EFBFBD>ӣ<EFBFBD><EFBFBD><EFBFBD>ô<EFBFBD><EFBFBD><EFBFBD>޷<EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD>ֱߵĿ<EFBFBD><EFBFBD>ӣ<EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD>
下面是一种错误的解法，考虑到如果每个哲学家同时拿起左手边的筷子，那么就无法拿起右手边的筷子，造成死锁。
```c
#define N 5
@ -494,7 +495,7 @@ void philosopher(int i) {
}
```
Ϊ<EFBFBD>˷<EFBFBD>ֹ<EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD>ķ<EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD>Լ<EFBFBD>һ<EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD>ƣ<EFBFBD>ֻ<EFBFBD><EFBFBD><EFBFBD><EFBFBD>ͬʱ<EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD>ߵĿ<EFBFBD><EFBFBD>ӣ<EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD>һ<EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD>ӵ<EFBFBD><EFBFBD>Ƕδ<EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD>
为了防止死锁的发生，可以加一点限制，只允许同时拿起左右两边的筷子，方法是引入一个互斥量，对拿起两个筷子的那段代码加锁。
```c
semaphore mutex = 1;
@ -515,220 +516,220 @@ void philosopher(int i) {
}
```
# <EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD> <20><><EFBFBD><EFBFBD>
# 第三章 死锁
## <EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD>
## 死锁的条件
![](https://github.com/CyC2018/InterviewNotes/blob/master/pics/c037c901-7eae-4e31-a1e4-9d41329e5c3e.png)
![](https://github.com/CyC2018/InterviewNotes/blob/master/pics//c037c901-7eae-4e31-a1e4-9d41329e5c3e.png)
1. <EFBFBD><EFBFBD><EFBFBD><EFBFBD>
2. <EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD>뱣<EFBFBD><EFBFBD>
3. <EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD>ռ
4. <EFBFBD><EFBFBD>·<EFBFBD>ȴ<EFBFBD>
1. 互斥
2. 请求与保持
3. 不可抢占
4. 环路等待
<EFBFBD><EFBFBD><EFBFBD>У<EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD>뱣<EFBFBD><EFBFBD><EFBFBD><EFBFBD>ָһ<EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD>Դ<EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD>ʱ<EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD>ѻ<EFBFBD><EFBFBD>õ<EFBFBD><EFBFBD><EFBFBD>Դ<EFBFBD><EFBFBD><EFBFBD>ֲ<EFBFBD><EFBFBD>š<EFBFBD>
其中，请求与保持是指一个进程因请求资源而阻塞时，对已获得的资源保持不放。
## <EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD>Ĵ<EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD>
## 死锁的处理方法
### 1. <EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD>
### 1. 鸵鸟策略
<EFBFBD><EFBFBD>ͷ<EFBFBD><EFBFBD><EFBFBD><EFBFBD>ɳ<EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD>װ<EFBFBD><EFBFBD><EFBFBD><EFBFBD>û<EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD>⡣
把头埋在沙子里，假装根本没发生问题。
<EFBFBD><EFBFBD><EFBFBD>ֲ<EFBFBD><EFBFBD>Բ<EFBFBD><EFBFBD><EFBFBD>ȡ<EFBFBD><EFBFBD>
这种策略不可取。
### 2. <EFBFBD><EFBFBD><EFBFBD><EFBFBD>Ԥ<EFBFBD><EFBFBD>
### 2. 死锁预防
<EFBFBD>ڳ<EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD>֮ǰԤ<EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD>
在程序运行之前预防发生死锁。
#### 2.1 <EFBFBD>ƻ<EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD>
#### 2.1 破坏互斥条件
<EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD>ѻ<EFBFBD><EFBFBD><EFBFBD>ӡ<EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD>ɸ<EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD>ͬʱ<EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD>Ψһ<EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD>ӡ<EFBFBD><EFBFBD><EFBFBD>Ľ<EFBFBD><EFBFBD><EFBFBD><EFBFBD>Ǵ<EFBFBD>ӡ<EFBFBD><EFBFBD><EFBFBD>ػ<EFBFBD><EFBFBD><EFBFBD><EFBFBD>̡<EFBFBD>
例如假脱机打印机技术允许若干个进程同时输出，唯一真正请求物理打印机的进程是打印机守护进程。
#### 2.2 <EFBFBD>ƻ<EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD>뱣<EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD>
#### 2.2 破坏请求与保持条件
һ<EFBFBD><EFBFBD>ʵ<EFBFBD>ַ<EFBFBD>ʽ<EFBFBD>ǹ涨<EFBFBD><EFBFBD><EFBFBD>н<EFBFBD><EFBFBD><EFBFBD><EFBFBD>ڿ<EFBFBD>ʼִ<EFBFBD><EFBFBD>ǰ<EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD>Ҫ<EFBFBD><EFBFBD>ȫ<EFBFBD><EFBFBD><EFBFBD><EFBFBD>Դ<EFBFBD><EFBFBD>
一种实现方式是规定所有进程在开始执行前请求所需要的全部资源。
#### 2.3 <EFBFBD>ƻ<EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD>ռ<EFBFBD><EFBFBD><EFBFBD><EFBFBD>
#### 2.3 破坏不可抢占条件
#### 2.4 <EFBFBD>ƻ<EFBFBD><EFBFBD><EFBFBD>·<EFBFBD>ȴ<EFBFBD>
#### 2.4 破坏环路等待
<EFBFBD><EFBFBD><EFBFBD><EFBFBD>Դͳһ<EFBFBD><EFBFBD><EFBFBD>ţ<EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD>ֻ<EFBFBD>ܰ<EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD>˳<EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD>Դ<EFBFBD><EFBFBD>
给资源统一编号，进程只能按编号顺序来请求资源。
### 3. <EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD>
### 3. 死锁避免
<EFBFBD>ڳ<EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD>ʱ<EFBFBD><EFBFBD><EFBFBD>ⷢ<EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD>
在程序运行时避免发生死锁。
#### 3.1 <EFBFBD><EFBFBD>ȫ״̬
#### 3.1 安全状态
![](https://github.com/CyC2018/InterviewNotes/blob/master/pics/ed523051-608f-4c3f-b343-383e2d194470.png)
![](https://github.com/CyC2018/InterviewNotes/blob/master/pics//ed523051-608f-4c3f-b343-383e2d194470.png)
ͼ a <EFBFBD>ĵڶ<EFBFBD><EFBFBD><EFBFBD> has <20><>ʾ<EFBFBD><CABE>ӵ<EFBFBD>е<EFBFBD><D0B5><EFBFBD>Դ<EFBFBD><D4B4><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD> max <20><>ʾ<EFBFBD>ܹ<EFBFBD><DCB9><EFBFBD>Ҫ<EFBFBD><D2AA><EFBFBD><EFBFBD>Դ<EFBFBD><D4B4><EFBFBD><EFBFBD>free <20><>ʾ<EFBFBD><CABE><EFBFBD>п<EFBFBD><D0BF><EFBFBD>ʹ<EFBFBD>õ<EFBFBD><C3B5><EFBFBD>Դ<EFBFBD><D4B4><EFBFBD><EFBFBD><EFBFBD><EFBFBD>ͼ a <20><>ʼ<EFBFBD><CABC><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD> B ӵ<><D3B5><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD>Դ<EFBFBD><D4B4><EFBFBD><EFBFBD><EFBFBD>н<EFBFBD><D0BD><EFBFBD><EFBFBD><EFBFBD><EFBFBD>ͷ<EFBFBD> B<><42><EFBFBD><EFBFBD>ʱ free <20><>Ϊ 4<><34><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD>ͬ<EFBFBD><CDAC><EFBFBD>ķ<EFBFBD>ʽ<EFBFBD><CABD><EFBFBD><EFBFBD> C <20><> A<><41>ʹ<EFBFBD><CAB9><EFBFBD><EFBFBD><EFBFBD>н<EFBFBD><D0BD>̶<EFBFBD><CCB6>ܳɹ<DCB3><C9B9><EFBFBD><EFBFBD>У<EFBFBD><D0A3><EFBFBD><EFBFBD>˿<EFBFBD><CBBF>Գ<EFBFBD>ͼ a <20><>ʾ<EFBFBD><CABE>״̬ʱ<CCAC><CAB1>ȫ<EFBFBD>ġ<EFBFBD>
图 a 的第二列 has 表示已拥有的资源数，第三列 max 表示总共需要的资源数，free 表示还有可以使用的资源数。从图 a 开始出发，先让 B 拥有所需的所有资源，运行结束后释放 B，此时 free 变为 4；接着以同样的方式运行 C 和 A，使得所有进程都能成功运行，因此可以称图 a 所示的状态时安全的。
<EFBFBD><EFBFBD><EFBFBD>壺<EFBFBD><EFBFBD><EFBFBD><EFBFBD>û<EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD>Ҽ<EFBFBD>ʹ<EFBFBD><EFBFBD><EFBFBD>н<EFBFBD><EFBFBD><EFBFBD>ͻȻ<EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD>Դ<EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD>Ҳ<EFBFBD><EFBFBD>Ȼ<EFBFBD><EFBFBD><EFBFBD><EFBFBD>ij<EFBFBD>ֵ<EFBFBD><EFBFBD>ȴ<EFBFBD><EFBFBD><EFBFBD><EFBFBD>ܹ<EFBFBD>ʹ<EFBFBD><EFBFBD>ÿһ<EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD>ϣ<EFBFBD><EFBFBD><EFBFBD><EFBFBD>Ƹ<EFBFBD>״̬<EFBFBD>ǰ<EFBFBD>ȫ<EFBFBD>ġ<EFBFBD>
定义：如果没有死锁发生，并且即使所有进程突然请求对资源的最大需求，也仍然存在某种调度次序能够使得每一个进程运行完毕，则称该状态是安全的。
#### 3.2 <EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD>Դ<EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD>м<EFBFBD><EFBFBD>㷨
#### 3.2 单个资源的银行家算法
һ<EFBFBD><EFBFBD>С<EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD>мң<EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD>һȺ<EFBFBD>ͻ<EFBFBD><EFBFBD>ֱ<EFBFBD><EFBFBD><EFBFBD>ŵ<EFBFBD><EFBFBD>һ<EFBFBD><EFBFBD><EFBFBD>Ĵ<EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD>ȣ<EFBFBD><EFBFBD>㷨Ҫ<EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD>ж϶<EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD>Ƿ<EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD>벻<EFBFBD><EFBFBD>ȫ״̬<EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD>ǣ<EFBFBD><EFBFBD>;ܾ<EFBFBD><EFBFBD><EFBFBD><EFBFBD>󣻷<EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD>Է<EFBFBD><EFBFBD>䡣
一个小城镇的银行家，他向一群客户分别承诺了一定的贷款额度，算法要做的是判断对请求的满足是否会进入不安全状态，如果是，就拒绝请求；否则予以分配。
![](https://github.com/CyC2018/InterviewNotes/blob/master/pics/d160ec2e-cfe2-4640-bda7-62f53e58b8c0.png)
![](https://github.com/CyC2018/InterviewNotes/blob/master/pics//d160ec2e-cfe2-4640-bda7-62f53e58b8c0.png)
<EFBFBD><EFBFBD>ͼ c Ϊ<><CEAA><EFBFBD><EFBFBD>ȫ״̬<D7B4><CCAC><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD>㷨<EFBFBD><E3B7A8><EFBFBD>ܾ<EFBFBD>֮ǰ<D6AE><C7B0><EFBFBD><EFBFBD><EFBFBD>󣬴Ӷ<F3A3ACB4><D3B6><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD>ͼ c <20>е<EFBFBD>״̬<D7B4><CCAC>
上图 c 为不安全状态，因此算法会拒绝之前的请求，从而避免进入图 c 中的状态。
#### 3.3 <EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD>Դ<EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD>м<EFBFBD><EFBFBD>㷨
#### 3.3 多个资源的银行家算法
![](https://github.com/CyC2018/InterviewNotes/blob/master/pics/62e0dd4f-44c3-43ee-bb6e-fedb9e068519.png)
![](https://github.com/CyC2018/InterviewNotes/blob/master/pics//62e0dd4f-44c3-43ee-bb6e-fedb9e068519.png)
<EFBFBD><EFBFBD>ͼ<EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD>̣<EFBFBD><EFBFBD>ĸ<EFBFBD><EFBFBD><EFBFBD>Դ<EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD>ߵ<EFBFBD>ͼ<EFBFBD><EFBFBD>ʾ<EFBFBD>Ѿ<EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD>Դ<EFBFBD><EFBFBD><EFBFBD>ұߵ<EFBFBD>ͼ<EFBFBD><EFBFBD>ʾ<EFBFBD><EFBFBD><EFBFBD><EFBFBD>Ҫ<EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD>Դ<EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD>ұߵ<EFBFBD> E<><45>P <20>Լ<EFBFBD> A <20>ֱ<EFBFBD><D6B1><EFBFBD>ʾ<EFBFBD><CABE><EFBFBD><EFBFBD><EFBFBD><EFBFBD>Դ<EFBFBD><D4B4><EFBFBD>ѷ<EFBFBD><D1B7><EFBFBD><EFBFBD><EFBFBD>Դ<EFBFBD>Լ<EFBFBD><D4BC><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD>Դ<EFBFBD><D4B4>ע<EFBFBD><D7A2><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD>Ϊ<EFBFBD><CEAA><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD>Ǿ<EFBFBD><C7BE><EFBFBD><EFBFBD><EFBFBD>ֵ<EFBFBD><D6B5><EFBFBD><EFBFBD><EFBFBD><EFBFBD> A=(1020)<29><><EFBFBD><EFBFBD>ʾ 4 <20><><EFBFBD><EFBFBD>Դ<EFBFBD>ֱ<EFBFBD><D6B1><EFBFBD>ʣ<EFBFBD><CAA3> 1/0/2/0<EFBFBD><EFBFBD>
上图中有五个进程，四个资源。左边的图表示已经分配的资源，右边的图表示还需要分配的资源。最右边的 E、P 以及 A 分别表示：总资源、已分配资源以及可用资源，注意这三个为向量，而不是具体数值，例如 A=(1020)，表示 4 个资源分别还剩下 1/0/2/0。
<EFBFBD><EFBFBD><EFBFBD><EFBFBD>һ<EFBFBD><EFBFBD>״̬<EFBFBD>Ƿ<EFBFBD><EFBFBD><EFBFBD>ȫ<EFBFBD><EFBFBD><EFBFBD>㷨<EFBFBD><EFBFBD><EFBFBD>£<EFBFBD>
检查一个状态是否安全的算法如下：
- <EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD>ұߵľ<EFBFBD><EFBFBD><EFBFBD><EFBFBD>Ƿ<EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD>һ<EFBFBD><EFBFBD>С<EFBFBD>ڵ<EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD> A<><41><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD>У<EFBFBD><D0A3><EFBFBD>ôϵͳ<CFB5><CDB3><EFBFBD>ᷢ<EFBFBD><E1B7A2><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD>״̬<D7B4>Dz<EFBFBD><C7B2><EFBFBD>ȫ<EFBFBD>ġ<EFBFBD>
- <EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD>ҵ<EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD>һ<EFBFBD>У<EFBFBD><EFBFBD><EFBFBD><EFBFBD>ý<EFBFBD><EFBFBD>̱<EFBFBD><EFBFBD><EFBFBD>Ϊ<EFBFBD><EFBFBD>ֹ<EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD>ѷ<EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD>Դ<EFBFBD>ӵ<EFBFBD> A <20>С<EFBFBD>
- <EFBFBD>ظ<EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD>ֱ<EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD>н<EFBFBD><EFBFBD>̶<EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD>Ϊ<EFBFBD><EFBFBD>ֹ<EFBFBD><EFBFBD><EFBFBD><EFBFBD>״̬ʱ<EFBFBD><EFBFBD>ȫ<EFBFBD>ġ<EFBFBD>
- 查找右边的矩阵是否存在一行小于等于向量 A。如果不存在这样的行，那么系统将会发生死锁，状态是不安全的。
- 假若找到这样一行，将该进程标记为终止，并将其已分配资源加到 A 中。
- 重复以上两步，直到所有进程都标记为终止，则状态时安全的。
### 4. <EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD>ָ<EFBFBD>
### 4. 死锁检测与死锁恢复
<EFBFBD><EFBFBD><EFBFBD><EFBFBD>ͼ<EFBFBD><EFBFBD>ֹ<EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD>ǵ<EFBFBD><EFBFBD><EFBFBD><EFBFBD>⵽<EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD>ʱ<EFBFBD><EFBFBD><EFBFBD><EFBFBD>ȡ<EFBFBD><EFBFBD>ʩ<EFBFBD><EFBFBD><EFBFBD>лָ<EFBFBD><EFBFBD><EFBFBD>
不试图阻止死锁，而是当检测到死锁发生时，采取措施进行恢复。
#### 4.1 <EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD>㷨
#### 4.1 死锁检测算法
<EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD>Ļ<EFBFBD><EFBFBD><EFBFBD>˼<EFBFBD><EFBFBD><EFBFBD>ǣ<EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD>һ<EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD>Դ<EFBFBD>ܹ<EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD>㣬<EFBFBD><EFBFBD>ô<EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD>ִ<EFBFBD>У<EFBFBD><EFBFBD>ͷ<EFBFBD><EFBFBD><EFBFBD>ӵ<EFBFBD>е<EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD>Դ<EFBFBD><EFBFBD>Ȼ<EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD>Ľ<EFBFBD><EFBFBD><EFBFBD>ִ<EFBFBD>С<EFBFBD>
死锁检测的基本思想是，如果一个进程所请求的资源能够被满足，那么就让它执行，释放它拥有的所有资源，然后让其它能满足条件的进程执行。
![](https://github.com/CyC2018/InterviewNotes/blob/master/pics/e1eda3d5-5ec8-4708-8e25-1a04c5e11f48.png)
![](https://github.com/CyC2018/InterviewNotes/blob/master/pics//e1eda3d5-5ec8-4708-8e25-1a04c5e11f48.png)
<EFBFBD><EFBFBD>ͼ<EFBFBD>У<EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD>ĸ<EFBFBD><EFBFBD><EFBFBD>Դ<EFBFBD><EFBFBD>ÿ<EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD>ݴ<EFBFBD><EFBFBD><EFBFBD><EFBFBD>ĺ<EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD>£<EFBFBD>
上图中，有三个进程四个资源，每个数据代表的含义如下：
- E <EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD>Դ<EFBFBD><EFBFBD><EFBFBD><EFBFBD>
- A <EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD>Դʣ<EFBFBD><EFBFBD><EFBFBD><EFBFBD>
- C <EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD>ÿ<EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD>ӵ<EFBFBD>е<EFBFBD><EFBFBD><EFBFBD>Դ<EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD>ÿһ<EFBFBD>ж<EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD>һ<EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD>ӵ<EFBFBD><EFBFBD><EFBFBD><EFBFBD>Դ<EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD>
- R <EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD>ÿ<EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD>Դ<EFBFBD><EFBFBD><EFBFBD><EFBFBD>
- E 向量：资源总量
- A 向量：资源剩余量
- C 矩阵：每个进程所拥有的资源数量，每一行都代表一个进程拥有资源的数量
- R 矩阵：每个进程请求的资源数量
<EFBFBD><EFBFBD><EFBFBD><EFBFBD> P<sub>1</sub> <EFBFBD><EFBFBD> P<sub>2</sub> <EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD>Դ<EFBFBD><EFBFBD><EFBFBD>ò<EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD>㣬ֻ<EFBFBD>н<EFBFBD><EFBFBD><EFBFBD> P<sub>3</sub> <EFBFBD><EFBFBD><EFBFBD>ԣ<EFBFBD><EFBFBD><EFBFBD> P<sub>3</sub> ִ<EFBFBD>У<EFBFBD>֮<EFBFBD><EFBFBD><EFBFBD>ͷ<EFBFBD> P<sub>3</sub> ӵ<EFBFBD>е<EFBFBD><EFBFBD><EFBFBD>Դ<EFBFBD><EFBFBD><EFBFBD><EFBFBD>ʱ A = (2 2 2 0)<EFBFBD><EFBFBD>P<sub>1</sub> <EFBFBD><EFBFBD><EFBFBD><EFBFBD>ִ<EFBFBD>У<EFBFBD>ִ<EFBFBD>к<EFBFBD><EFBFBD>ͷ<EFBFBD> P<sub>1</sub> ӵ<EFBFBD>е<EFBFBD><EFBFBD><EFBFBD>Դ<EFBFBD><EFBFBD>A = (4 2 2 2) <EFBFBD><EFBFBD>P<sub>2</sub> Ҳ<EFBFBD><EFBFBD><EFBFBD><EFBFBD>ִ<EFBFBD>С<EFBFBD><EFBFBD><EFBFBD><EFBFBD>н<EFBFBD><EFBFBD>̶<EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD>˳<EFBFBD><EFBFBD>ִ<EFBFBD>У<EFBFBD>û<EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD>
进程 P<sub>1</sub> 和 P<sub>2</sub> 所请求的资源都得不到满足，只有进程 P<sub>3</sub> 可以，让 P<sub>3</sub> 执行，之后释放 P<sub>3</sub> 拥有的资源，此时 A = (2 2 2 0)。P<sub>1</sub> 可以执行，执行后释放 P<sub>1</sub> 拥有的资源，A = (4 2 2 2) ，P<sub>2</sub> 也可以执行。所有进程都可以顺利执行，没有死锁。
<EFBFBD>㷨<EFBFBD>ܽ<EFBFBD><EFBFBD><EFBFBD><EFBFBD>£<EFBFBD>
算法总结如下：
ÿ<EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD>ʼʱ<EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD>ǣ<EFBFBD>ִ<EFBFBD>й<EFBFBD><EFBFBD><EFBFBD><EFBFBD>п<EFBFBD><EFBFBD>ܱ<EFBFBD><EFBFBD><EFBFBD><EFBFBD>ǡ<EFBFBD><EFBFBD><EFBFBD><EFBFBD>㷨<EFBFBD><EFBFBD><EFBFBD><EFBFBD>ʱ<EFBFBD><EFBFBD><EFBFBD>κ<EFBFBD>û<EFBFBD>б<EFBFBD><EFBFBD><EFBFBD><EFBFBD>ǵĽ<EFBFBD><EFBFBD>̶<EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD>̡<EFBFBD>
每个进程最开始时都不被标记，执行过程有可能被标记。当算法结束时，任何没有被标记的进程都是死锁进程。
1. Ѱ<EFBFBD><EFBFBD>һ<EFBFBD><EFBFBD>û<EFBFBD>б<EFBFBD><EFBFBD>ǵĽ<EFBFBD><EFBFBD><EFBFBD> P<sub>i</sub><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD>ԴС<EFBFBD>ڵ<EFBFBD><EFBFBD><EFBFBD> A<><41>
2. <EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD>ҵ<EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD>һ<EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD>̣<EFBFBD><EFBFBD><EFBFBD>ô<EFBFBD><EFBFBD> C <20><><EFBFBD><EFBFBD><EFBFBD>ĵ<EFBFBD> i <20><><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD>ӵ<EFBFBD> A <20>У<EFBFBD><D0A3><EFBFBD><EFBFBD>Ǹý<C7B8><C3BD>̣<EFBFBD><CCA3><EFBFBD>ת<EFBFBD><D7AA> 1<><31>
3. <EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD>û<EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD>һ<EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD>̣<EFBFBD><EFBFBD>㷨<EFBFBD><EFBFBD>ֹ<EFBFBD><EFBFBD>
1. 寻找一个没有标记的进程 P<sub>i</sub>，它所请求的资源小于等于 A。
2. 如果找到了这样一个进程，那么将 C 矩阵的第 i 行向量加到 A 中，标记该进程，并转回 1。
3. 如果有没有这样一个进程，算法终止。
#### 4.2 <EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD>ָ<EFBFBD>
#### 4.2 死锁恢复
- <EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD>ռ<EFBFBD>ָ<EFBFBD>
- ɱ<EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD>
- 利用抢占恢复
- 杀死进程
# <EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD> <20>洢<EFBFBD><E6B4A2><EFBFBD><EFBFBD><EFBFBD><EFBFBD>
# 第四章 存储器管理
## <EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD>ڴ<EFBFBD>
## 虚拟内存
ÿ<EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD>ӵ<EFBFBD><EFBFBD><EFBFBD>Լ<EFBFBD><EFBFBD>ĵ<EFBFBD>ַ<EFBFBD>ռ䣬<EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD>ַ<EFBFBD>ռ䱻<EFBFBD>ָ<EFBFBD><EFBFBD>ɶ<EFBFBD><EFBFBD><EFBFBD><EFBFBD>飬ÿһ<EFBFBD><EFBFBD><EFBFBD><EFBFBD>Ϊһҳ<EFBFBD><EFBFBD><EFBFBD><EFBFBD>Щҳ<EFBFBD><EFBFBD>ӳ<EFBFBD>䵽<EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD>ڴ棬<EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD>Ҫӳ<EFBFBD>䵽<EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD>ڴ棬Ҳ<EFBFBD><EFBFBD><EFBFBD><EFBFBD>Ҫ<EFBFBD><EFBFBD><EFBFBD><EFBFBD>ҳ<EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD>ڴ<EFBFBD><EFBFBD>С<EFBFBD>
每个程序拥有自己的地址空间，这个地址空间被分割成多个块，每一块称为一页。这些页被映射到物理内存，但不需要映射到连续的物理内存，也不需要所有页都必须在物理内存中。
<EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD>õ<EFBFBD>һ<EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD>ڴ<EFBFBD><EFBFBD>еĵ<EFBFBD>ַ<EFBFBD>ռ<EFBFBD>ʱ<EFBFBD><EFBFBD><EFBFBD><EFBFBD>Ӳ<EFBFBD><EFBFBD>ִ<EFBFBD>б<EFBFBD>Ҫ<EFBFBD><EFBFBD>ӳ<EFBFBD>䣬<EFBFBD><EFBFBD>ȱʧ<EFBFBD>IJ<EFBFBD><EFBFBD><EFBFBD>װ<EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD>ڴ沢<EFBFBD><EFBFBD><EFBFBD><EFBFBD>ִ<EFBFBD><EFBFBD>ʧ<EFBFBD>ܵ<EFBFBD>ָ<EFBFBD>
当程序引用到一部分在物理内存中的地址空间时，由硬件执行必要的映射，将缺失的部分装入物理内存并重新执行失败的指令。
## <EFBFBD><EFBFBD>ҳ<EFBFBD><EFBFBD><EFBFBD>ֶ<EFBFBD>
## 分页与分段
### 1. <EFBFBD><EFBFBD>ҳ
### 1. 分页
<EFBFBD>û<EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD>ĵ<EFBFBD>ַ<EFBFBD>ռ䱻<EFBFBD><EFBFBD><EFBFBD><EFBFBD>Ϊ<EFBFBD><EFBFBD><EFBFBD>ɹ̶<EFBFBD><EFBFBD><EFBFBD>С<EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD>򣬳<EFBFBD>Ϊ<EFBFBD><EFBFBD>ҳ<EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD>Ӧ<EFBFBD>أ<EFBFBD><EFBFBD>ڴ<EFBFBD><EFBFBD>ռ<EFBFBD><EFBFBD>ֳ<EFBFBD><EFBFBD><EFBFBD><EFBFBD>ɸ<EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD>飬ҳ<EFBFBD>Ϳ<EFBFBD><EFBFBD>Ĵ<EFBFBD>С<EFBFBD><EFBFBD><EFBFBD>ȡ<EFBFBD><EFBFBD>ɽ<EFBFBD><EFBFBD>û<EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD>һҳ<EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD>ڴ<EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD>һ<EFBFBD><EFBFBD><EFBFBD>У<EFBFBD>ʵ<EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD>ɢ<EFBFBD><EFBFBD><EFBFBD>䣬<EFBFBD><EFBFBD>һ<EFBFBD><EFBFBD>ҳ<EFBFBD><EFBFBD><EFBFBD><EFBFBD>ά<EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD>֮<EFBFBD><EFBFBD><EFBFBD><EFBFBD>ӳ<EFBFBD><EFBFBD><EFBFBD><EFBFBD>ϵ<EFBFBD><EFBFBD>
用户程序的地址空间被划分为若干固定大小的区域，称为“页”。相应地，内存空间分成若干个物理块，页和块的大小相等。可将用户程序的任一页放在内存的任一块中，实现了离散分配，由一个页表来维护它们之间的映射关系。
### 2. <EFBFBD>ֶ<EFBFBD>
### 2. 分段
![](https://github.com/CyC2018/InterviewNotes/blob/master/pics/22de0538-7c6e-4365-bd3b-8ce3c5900216.png)
![](https://github.com/CyC2018/InterviewNotes/blob/master/pics//22de0538-7c6e-4365-bd3b-8ce3c5900216.png)
<EFBFBD><EFBFBD>ͼΪһ<EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD>ڱ<EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD>н<EFBFBD><EFBFBD><EFBFBD><EFBFBD>Ķ<EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD> 4 <20><><EFBFBD><EFBFBD><EFBFBD>Ƕ<EFBFBD>̬<EFBFBD><CCAC><EFBFBD><EFBFBD><EFBFBD>ģ<EFBFBD><C4A3><EFBFBD><EFBFBD><EFBFBD>ʹ<EFBFBD>÷<EFBFBD>ҳϵͳ<CFB5><CDB3>һά<D2BB><CEAC>ַ<EFBFBD>ռ䣬<D5BC><E4A3AC>̬<EFBFBD><CCAC><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD>ص<EFBFBD><D8B5>ᵼ<EFBFBD>¸<EFBFBD><C2B8><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD>ij<EFBFBD><C4B3>֡<EFBFBD>
上图为一个编译器在编译过程中建立的多个表，有 4 个表是动态增长的，如果使用分页系统的一维地址空间，动态递增的特点会导致覆盖问题的出现。
![](https://github.com/CyC2018/InterviewNotes/blob/master/pics/e0900bb2-220a-43b7-9aa9-1d5cd55ff56e.png)
![](https://github.com/CyC2018/InterviewNotes/blob/master/pics//e0900bb2-220a-43b7-9aa9-1d5cd55ff56e.png)
<EFBFBD>ֶε<EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD>ǰ<EFBFBD>ÿ<EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD>ֳɶΣ<EFBFBD>һ<EFBFBD><EFBFBD><EFBFBD>ι<EFBFBD><EFBFBD><EFBFBD>һ<EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD>ĵ<EFBFBD>ַ<EFBFBD>ռ䡣ÿ<EFBFBD><EFBFBD><EFBFBD>εij<EFBFBD><EFBFBD>ȿ<EFBFBD><EFBFBD>Բ<EFBFBD>ͬ<EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD>ҿ<EFBFBD><EFBFBD>Զ<EFBFBD>̬<EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD>
分段的做法是把每个表分成段，一个段构成一个独立的地址空间。每个段的长度可以不同，并且可以动态增长。
ÿ<EFBFBD><EFBFBD><EFBFBD>ζ<EFBFBD><EFBFBD><EFBFBD>Ҫ<EFBFBD><EFBFBD><EFBFBD><EFBFBD>Ա<EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD>֡<EFBFBD>
每个段都需要程序员来划分。
### 3. <EFBFBD><EFBFBD>ҳʽ
### 3. 段页式
<EFBFBD>÷ֶη<EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD>͹<EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD>洢<EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD>ĵ<EFBFBD>ַ<EFBFBD>ռ䰴<EFBFBD>߼<EFBFBD><EFBFBD><EFBFBD>λ<EFBFBD>ֳɻ<EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD>ĶΣ<EFBFBD><EFBFBD><EFBFBD>ÿһ<EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD>Լ<EFBFBD><EFBFBD>Ķ<EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD>ٰ<EFBFBD>ÿ<EFBFBD>ηֳɹ̶<EFBFBD><EFBFBD><EFBFBD>С<EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD>ҳ<EFBFBD><EFBFBD>
用分段方法来分配和管理虚拟存储器。程序的地址空间按逻辑单位分成基本独立的段，而每一段有自己的段名，再把每段分成固定大小的若干页。
<EFBFBD>÷<EFBFBD>ҳ<EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD>͹<EFBFBD><EFBFBD><EFBFBD>ʵ<EFBFBD>档<EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD>ֳ<EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD>ҳ<EFBFBD><EFBFBD>С<EFBFBD><EFBFBD><EFBFBD>ȵĴ洢<EFBFBD>飬<EFBFBD><EFBFBD>װ<EFBFBD><EFBFBD><EFBFBD><EFBFBD>ҵ<EFBFBD><EFBFBD><EFBFBD>κ<EFBFBD>һҳ<EFBFBD><EFBFBD>
用分页方法来分配和管理实存。即把整个主存分成与上述页大小相等的存储块，可装入作业的任何一页。
<EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD>ڴ<EFBFBD><EFBFBD>ĵ<EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD>ǰ<EFBFBD>ҳ<EFBFBD><EFBFBD><EFBFBD>еģ<EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD>ֿɰ<EFBFBD><EFBFBD><EFBFBD>ʵ<EFBFBD>ֹ<EFBFBD><EFBFBD><EFBFBD><EFBFBD>ͱ<EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD>
程序对内存的调入或调出是按页进行的，但它又可按段实现共享和保护。
### 4. <EFBFBD><EFBFBD>ҳ<EFBFBD><EFBFBD><EFBFBD>ֶ<EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD>
### 4. 分页与分段区别
- <EFBFBD>Գ<EFBFBD><EFBFBD><EFBFBD>Ա<EFBFBD><EFBFBD>͸<EFBFBD><EFBFBD><EFBFBD>ԣ<EFBFBD><EFBFBD><EFBFBD>ҳ͸<EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD>Ƿֶ<EFBFBD><EFBFBD><EFBFBD>Ҫ<EFBFBD><EFBFBD><EFBFBD><EFBFBD>Ա<EFBFBD><EFBFBD>ʾ<EFBFBD><EFBFBD><EFBFBD><EFBFBD>ÿ<EFBFBD><EFBFBD><EFBFBD>Ρ<EFBFBD>
- 对程序员的透明性：分页透明，但是分段需要程序员显示划分每个段。
- <EFBFBD><EFBFBD>ַ<EFBFBD>ռ<EFBFBD><EFBFBD><EFBFBD>ά<EFBFBD>ȣ<EFBFBD><EFBFBD><EFBFBD>ҳ<EFBFBD><EFBFBD>һά<EFBFBD><EFBFBD>ַ<EFBFBD>ռ䣬<EFBFBD>ֶ<EFBFBD><EFBFBD>Ƕ<EFBFBD>ά<EFBFBD>ġ<EFBFBD>
- 地址空间的维度：分页是一维地址空间，分段是二维的。
- <EFBFBD><EFBFBD>С<EFBFBD>Ƿ<EFBFBD><EFBFBD><EFBFBD><EFBFBD>Ըı䣺ҳ<EFBFBD>Ĵ<EFBFBD>С<EFBFBD><EFBFBD><EFBFBD>ɱ䣬<EFBFBD>εĴ<EFBFBD>С<EFBFBD><EFBFBD><EFBFBD>Զ<EFBFBD>̬<EFBFBD>ı䡣
- 大小是否可以改变：页的大小不可变，段的大小可以动态改变。
- <EFBFBD><EFBFBD><EFBFBD>ֵ<EFBFBD>ԭ<EFBFBD>򣺷<EFBFBD>ҳ<EFBFBD><EFBFBD>Ҫ<EFBFBD><EFBFBD><EFBFBD><EFBFBD>ʵ<EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD>ڴ棬<EFBFBD>Ӷ<EFBFBD><EFBFBD><EFBFBD><EFBFBD>ø<EFBFBD><EFBFBD><EFBFBD><EFBFBD>ĵ<EFBFBD>ַ<EFBFBD>ռ䣻<EFBFBD>ֶ<EFBFBD><EFBFBD><EFBFBD>Ҫ<EFBFBD><EFBFBD>Ϊ<EFBFBD><EFBFBD>ʹ<EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD>ݿ<EFBFBD><EFBFBD>Ա<EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD>Ϊ<EFBFBD>߼<EFBFBD><EFBFBD>϶<EFBFBD><EFBFBD><EFBFBD><EFBFBD>ĵ<EFBFBD>ַ<EFBFBD>ռ䲢<EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD>ڹ<EFBFBD><EFBFBD><EFBFBD><EFBFBD>ͱ<EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD>
- 出现的原因：分页主要用于实现虚拟内存，从而获得更大的地址空间；分段主要是为了使程序和数据可以被划分为逻辑上独立的地址空间并且有助于共享和保护。
## ҳ<EFBFBD><EFBFBD><EFBFBD>û<EFBFBD><EFBFBD>㷨
## 页面置换算法
<EFBFBD>ڳ<EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD>й<EFBFBD><EFBFBD><EFBFBD><EFBFBD>У<EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD>Ҫ<EFBFBD><EFBFBD><EFBFBD>ʵ<EFBFBD>ҳ<EFBFBD>治<EFBFBD><EFBFBD><EFBFBD>ڴ<EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD>Ҫ<EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD>ǵ<EFBFBD><EFBFBD><EFBFBD><EFBFBD>ڴ棬<EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD>ڴ<EFBFBD><EFBFBD><EFBFBD><EFBFBD>޿<EFBFBD><EFBFBD>пռ<EFBFBD>ʱ<EFBFBD><EFBFBD>ϵͳ<EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD>ڴ<EFBFBD><EFBFBD>е<EFBFBD><EFBFBD><EFBFBD>һ<EFBFBD><EFBFBD>ҳ<EFBFBD>浽<EFBFBD><EFBFBD><EFBFBD>̶Ի<EFBFBD><EFBFBD><EFBFBD><EFBFBD>У<EFBFBD><EFBFBD><EFBFBD><EFBFBD>ҽ<EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD>Ҫ<EFBFBD><EFBFBD>ҳ<EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD>ڴ<EFBFBD><EFBFBD>С<EFBFBD>ҳ<EFBFBD><EFBFBD><EFBFBD>û<EFBFBD><EFBFBD>㷨<EFBFBD><EFBFBD><EFBFBD><EFBFBD>ҪĿ<EFBFBD><EFBFBD><EFBFBD><EFBFBD>ʹҳ<EFBFBD><EFBFBD><EFBFBD>û<EFBFBD>Ƶ<EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD>ͣ<EFBFBD>Ҳ<EFBFBD><EFBFBD><EFBFBD><EFBFBD>˵ȱҳ<EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD>ͣ<EFBFBD><EFBFBD><EFBFBD>
在程序运行过程中，若其所要访问的页面不在内存而需要把它们调入内存，但是内存已无空闲空间时，系统必须从内存中调出一个页面到磁盘对换区中，并且将程序所需要的页面调入内存中。页面置换算法的主要目标是使页面置换频率最低（也可以说缺页率最低）。
### 1. <EFBFBD><EFBFBD><EFBFBD>ѣ<EFBFBD>Optimal<EFBFBD><EFBFBD>
### 1. 最佳（Optimal）
<EFBFBD><EFBFBD>ѡ<EFBFBD><EFBFBD><EFBFBD>ı<EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD>ҳ<EFBFBD>潫<EFBFBD><EFBFBD><EFBFBD>ʱ<EFBFBD><EFBFBD><EFBFBD>ڲ<EFBFBD><EFBFBD>ٱ<EFBFBD><EFBFBD><EFBFBD><EFBFBD>ʣ<EFBFBD>ͨ<EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD>Ա<EFBFBD>֤<EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD>͵<EFBFBD>ȱҳ<EFBFBD>ʡ<EFBFBD>
所选择的被换出的页面将是最长时间内不再被访问，通常可以保证获得最低的缺页率。
<EFBFBD><EFBFBD>һ<EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD>ϵ<EFBFBD><EFBFBD>㷨<EFBFBD><EFBFBD><EFBFBD><EFBFBD>Ϊ<EFBFBD>޷<EFBFBD>֪<EFBFBD><EFBFBD>һ<EFBFBD><EFBFBD>ҳ<EFBFBD><EFBFBD><EFBFBD>೤ʱ<EFBFBD><EFBFBD><EFBFBD>ᱻ<EFBFBD>ٷ<EFBFBD><EFBFBD>ʵ<EFBFBD><EFBFBD><EFBFBD>
是一种理论上的算法，因为无法知道一个页面多长时间会被再访问到。
<EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD>һ<EFBFBD><EFBFBD>ϵͳΪij<EFBFBD><EFBFBD><EFBFBD>̷<EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD>飬<EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD>ҳ<EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD>У<EFBFBD>
举例：一个系统为某进程分配了三个物理块，并有如下页面引用序列：
7<EFBFBD><EFBFBD>0<EFBFBD><EFBFBD>1<EFBFBD><EFBFBD>2<EFBFBD><EFBFBD>0<EFBFBD><EFBFBD>3<EFBFBD><EFBFBD>0<EFBFBD><EFBFBD>4<EFBFBD><EFBFBD>2<EFBFBD><EFBFBD>3<EFBFBD><EFBFBD>0<EFBFBD><EFBFBD>3<EFBFBD><EFBFBD>2<EFBFBD><EFBFBD>1<EFBFBD><EFBFBD>2<EFBFBD><EFBFBD>0<EFBFBD><EFBFBD>1<EFBFBD><EFBFBD>7<EFBFBD><EFBFBD>0<EFBFBD><EFBFBD>1
7，0，1，2，0，3，0，4，2，3，0，3，2，1，2，0，1，7，0，1
<EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD>ʱ<EFBFBD><EFBFBD><EFBFBD>Ƚ<EFBFBD> 7,0,1 <20><><EFBFBD><EFBFBD>ҳ<EFBFBD><D2B3>װ<EFBFBD><D7B0><EFBFBD>ڴ档<DAB4><E6A1A3><EFBFBD><EFBFBD><EFBFBD><EFBFBD>Ҫ<EFBFBD><D2AA><EFBFBD><EFBFBD>ҳ<EFBFBD><D2B3> 2 ʱ<><CAB1><EFBFBD><EFBFBD><EFBFBD><EFBFBD>ȱҳ<C8B1>жϣ<D0B6><CFA3>Ὣҳ<E1BDAB><D2B3> 7 <20><><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD>Ϊҳ<CEAA><D2B3> 7 <20>ٴα<D9B4><CEB1><EFBFBD><EFBFBD>ʵ<EFBFBD>ʱ<EFBFBD><CAB1><EFBFBD><EFBFBD><EEB3A4>
进程运行时，先将 7,0,1 三个页面装入内存。当进程要访问页面 2 时，产生缺页中断，会将页面 7 换出，因为页面 7 再次被访问的时间最长。
### 2. <EFBFBD>Ƚ<EFBFBD><EFBFBD>ȳ<EFBFBD><EFBFBD><EFBFBD>FIFO<EFBFBD><EFBFBD>
### 2. 先进先出（FIFO）
<EFBFBD><EFBFBD>ѡ<EFBFBD>񻻳<EFBFBD><EFBFBD><EFBFBD>ҳ<EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD>Ƚ<EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD>ҳ<EFBFBD>档
所选择换出的页面是最先进入的页面。
<EFBFBD><EFBFBD><EFBFBD>㷨<EFBFBD>Ὣ<EFBFBD><EFBFBD>Щ<EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD>ʵ<EFBFBD>ҳ<EFBFBD><EFBFBD>Ҳ<EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD>Ӷ<EFBFBD>ʹȱҳ<EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD>ߡ<EFBFBD>
该算法会将那些经常被访问的页面也被换出，从而使缺页率升高。
### 3. <EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD>δʹ<EFBFBD>ã<EFBFBD>LRU, Least Recently Used<EFBFBD><EFBFBD>
### 3. 最近最久未使用（LRU, Least Recently Used）
<EFBFBD><EFBFBD>Ȼ<EFBFBD>޷<EFBFBD>֪<EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD>Ҫʹ<EFBFBD>õ<EFBFBD>ҳ<EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD>ǿ<EFBFBD><EFBFBD><EFBFBD>֪<EFBFBD><EFBFBD><EFBFBD><EFBFBD>ȥʹ<EFBFBD><EFBFBD>ҳ<EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD>LRU <20><><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD>δʹ<CEB4>õ<EFBFBD>ҳ<EFBFBD>滻<EFBFBD><E6BBBB><EFBFBD><EFBFBD>
虽然无法知道将来要使用的页面情况，但是可以知道过去使用页面的情况。LRU 将最近最久未使用的页面换出。
<EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD>ջ<EFBFBD><EFBFBD>ʵ<EFBFBD>ָ<EFBFBD><EFBFBD>㷨<EFBFBD><EFBFBD>ջ<EFBFBD>д洢ҳ<EFBFBD><EFBFBD><EFBFBD><EFBFBD>ҳ<EFBFBD><EFBFBD><EFBFBD>š<EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD>̷<EFBFBD><EFBFBD><EFBFBD>һ<EFBFBD><EFBFBD>ҳ<EFBFBD><EFBFBD>ʱ<EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD>ҳ<EFBFBD><EFBFBD><EFBFBD><EFBFBD>ҳ<EFBFBD><EFBFBD><EFBFBD>Ŵ<EFBFBD>ջ<EFBFBD>Ƴ<EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD>ѹ<EFBFBD><EFBFBD>ջ<EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD>ʵ<EFBFBD>ҳ<EFBFBD><EFBFBD><EFBFBD><EFBFBD>ҳ<EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD>ջ<EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD>δʹ<EFBFBD>õ<EFBFBD>ҳ<EFBFBD><EFBFBD><EFBFBD><EFBFBD>ҳ<EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD>ջ<EFBFBD>ס<EFBFBD>
可以用栈来实现该算法，栈中存储页面的页面号。当进程访问一个页面时，将该页面的页面号从栈移除，并将它压入栈顶。这样，最近被访问的页面的页面号总是在栈顶，而最近最久未使用的页面的页面号总是在栈底。
4<EFBFBD><EFBFBD>7<EFBFBD><EFBFBD>0<EFBFBD><EFBFBD>7<EFBFBD><EFBFBD>1<EFBFBD><EFBFBD>0<EFBFBD><EFBFBD>1<EFBFBD><EFBFBD>2<EFBFBD><EFBFBD>1<EFBFBD><EFBFBD>2<EFBFBD><EFBFBD>6
4，7，0，7，1，0，1，2，1，2，6
![](https://github.com/CyC2018/InterviewNotes/blob/master/pics/eb859228-c0f2-4bce-910d-d9f76929352b.png)
![](https://github.com/CyC2018/InterviewNotes/blob/master/pics//eb859228-c0f2-4bce-910d-d9f76929352b.png)
### 4. ʱ<EFBFBD>ӣ<EFBFBD>Clock<EFBFBD><EFBFBD>
### 4. 时钟（Clock）
Clock ҳ<EFBFBD><EFBFBD><EFBFBD>û<EFBFBD><EFBFBD>㷨<EFBFBD><EFBFBD>Ҫ<EFBFBD>õ<EFBFBD>һ<EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD>λ<EFBFBD><EFBFBD><EFBFBD><EFBFBD>һ<EFBFBD><EFBFBD>ҳ<EFBFBD>汻<EFBFBD><EFBFBD><EFBFBD><EFBFBD>ʱ<EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD>Ϊ<EFBFBD><EFBFBD>Ϊ 1<><31>
Clock 页面置换算法需要用到一个访问位，当一个页面被访问时，将访问为置为 1。
<EFBFBD><EFBFBD><EFBFBD>ȣ<EFBFBD><EFBFBD><EFBFBD><EFBFBD>ڴ<EFBFBD><EFBFBD>е<EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD>ҳ<EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD>ӳ<EFBFBD>һ<EFBFBD><EFBFBD>ѭ<EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD>У<EFBFBD><EFBFBD><EFBFBD>ȱҳ<EFBFBD>жϷ<EFBFBD><EFBFBD><EFBFBD>ʱ<EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD>鵱ǰָ<EFBFBD><EFBFBD><EFBFBD><EFBFBD>ָ<EFBFBD><EFBFBD>ҳ<EFBFBD><EFBFBD><EFBFBD>ķ<EFBFBD><EFBFBD><EFBFBD>λ<EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD>λΪ 0<><30><EFBFBD>ͽ<EFBFBD><CDBD><EFBFBD>ҳ<EFBFBD>滻<EFBFBD><E6BBBB><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD>򽫸<EFBFBD>ҳ<EFBFBD>ķ<EFBFBD><C4B7><EFBFBD>λ<EFBFBD><CEBB><EFBFBD><EFBFBD>Ϊ 0<><30><EFBFBD><EFBFBD><EFBFBD><EFBFBD>ҳ<EFBFBD><D2B3><EFBFBD>ڶ<EFBFBD><DAB6>εĻ<CEB5><C4BB>ᣬ<EFBFBD>ƶ<EFBFBD>ָ<EFBFBD><D6B8><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD>顣
首先，将内存中的所有页面链接成一个循环队列，当缺页中断发生时，检查当前指针所指向页面的访问位，如果访问位为 0，就将该页面换出；否则将该页的访问位设置为 0，给该页面第二次的机会，移动指针继续检查。
# <EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD> <20>豸<EFBFBD><E8B1B8><EFBFBD><EFBFBD>
# 第五章 设备管理
## <EFBFBD><EFBFBD><EFBFBD>̵<EFBFBD><EFBFBD><EFBFBD><EFBFBD>㷨
## 磁盘调度算法
<EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD>ͬʱ<EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD>ʴ<EFBFBD><EFBFBD><EFBFBD>ʱ<EFBFBD><EFBFBD><EFBFBD><EFBFBD>Ҫ<EFBFBD><EFBFBD><EFBFBD>д<EFBFBD><EFBFBD>̵<EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD>ƶԴ<EFBFBD><EFBFBD>̵ķ<EFBFBD><EFBFBD>ʡ<EFBFBD><EFBFBD><EFBFBD><EFBFBD>̵<EFBFBD><EFBFBD>ȵ<EFBFBD><EFBFBD><EFBFBD>ҪĿ<EFBFBD><EFBFBD><EFBFBD><EFBFBD>ʹ<EFBFBD><EFBFBD><EFBFBD>̵<EFBFBD>ƽ<EFBFBD><EFBFBD>Ѱ<EFBFBD><EFBFBD>ʱ<EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD>١<EFBFBD>
当多个进程同时请求访问磁盘时，需要进行磁盘调度来控制对磁盘的访问。磁盘调度的主要目标是使磁盘的平均寻道时间最少。
### 1. <EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD>ȷ<EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD>FCFS, First Come First Serverd<EFBFBD><EFBFBD>
### 1. 先来先服务（FCFS, First Come First Serverd）
<EFBFBD><EFBFBD><EFBFBD>ݽ<EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD>ʴ<EFBFBD><EFBFBD>̵<EFBFBD><EFBFBD>Ⱥ<EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD>е<EFBFBD><EFBFBD>ȡ<EFBFBD><EFBFBD>ŵ<EFBFBD><EFBFBD>ǹ<EFBFBD>ƽ<EFBFBD>ͼ򵥣<EFBFBD>ȱ<EFBFBD><EFBFBD>Ҳ<EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD>ԣ<EFBFBD><EFBFBD><EFBFBD>Ϊδ<EFBFBD><EFBFBD>Ѱ<EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD>κ<EFBFBD><EFBFBD>Ż<EFBFBD><EFBFBD><EFBFBD>ʹƽ<EFBFBD><EFBFBD>Ѱ<EFBFBD><EFBFBD>ʱ<EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD>ܽϳ<EFBFBD><EFBFBD><EFBFBD>
根据进程请求访问磁盘的先后次序来进行调度。优点是公平和简单，缺点也很明显，因为未对寻道做任何优化，使平均寻道时间可能较长。
### 2. <EFBFBD><EFBFBD><EFBFBD><EFBFBD>Ѱ<EFBFBD><EFBFBD>ʱ<EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD>ȣ<EFBFBD>SSTF, Shortest Seek Time First<EFBFBD><EFBFBD>
### 2. 最短寻道时间优先（SSTF, Shortest Seek Time First）
Ҫ<EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD>ʵĴŵ<EFBFBD><EFBFBD>뵱ǰ<EFBFBD><EFBFBD>ͷ<EFBFBD><EFBFBD><EFBFBD>ڴŵ<EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD>Ƚ<EFBFBD><EFBFBD>е<EFBFBD><EFBFBD>ȡ<EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD>㷨<EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD>ܱ<EFBFBD>֤ƽ<EFBFBD><EFBFBD>Ѱ<EFBFBD><EFBFBD>ʱ<EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD>̣<EFBFBD><EFBFBD><EFBFBD><EFBFBD>DZ<EFBFBD> FCFS <EFBFBD>úܶࡣ
要求访问的磁道与当前磁头所在磁道距离最近的优先进行调度。这种算法并不能保证平均寻道时间最短，但是比 FCFS 好很多。
### 3. ɨ<EFBFBD><EFBFBD><EFBFBD>㷨<EFBFBD><EFBFBD>SCAN<EFBFBD><EFBFBD>
### 3. 扫描算法（SCAN）
SSTF <EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD>ֽ<EFBFBD><EFBFBD>м<EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD>󡣿<EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD>½<EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD>ʵĴŵ<EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD>ͷ<EFBFBD><EFBFBD><EFBFBD>ڴŵ<EFBFBD><EFBFBD>ľ<EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD>DZ<EFBFBD>һ<EFBFBD><EFBFBD><EFBFBD>ڵȴ<EFBFBD><EFBFBD>Ľ<EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD>Ľ<EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD>ô<EFBFBD>ȴ<EFBFBD><EFBFBD>Ľ<EFBFBD><EFBFBD>̻<EFBFBD>һֱ<EFBFBD>ȴ<EFBFBD><EFBFBD><EFBFBD>ȥ<EFBFBD><EFBFBD>
SSTF 会出现进行饥饿现象。考虑以下情况，新进程请求访问的磁道与磁头所在磁道的距离总是比一个在等待的进程来的近，那么等待的进程会一直等待下去。
SCAN <EFBFBD>㷨<EFBFBD><EFBFBD> SSTF <EFBFBD>㷨֮<EFBFBD>Ͽ<EFBFBD><EFBFBD><EFBFBD><EFBFBD>˴<EFBFBD>ͷ<EFBFBD><EFBFBD><EFBFBD>ƶ<EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD>Ҫ<EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD>ʵĴŵ<EFBFBD><EFBFBD>ڴ<EFBFBD>ͷ<EFBFBD><EFBFBD>ǰ<EFBFBD>ƶ<EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD>ϲ<EFBFBD><EFBFBD>ܹ<EFBFBD><EFBFBD>õ<EFBFBD><EFBFBD><EFBFBD><EFBFBD>ȡ<EFBFBD><EFBFBD><EFBFBD>Ϊ<EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD>ƶ<EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD>ôһ<EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD>ʵĴŵ<EFBFBD>һ<EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD>õ<EFBFBD><EFBFBD><EFBFBD><EFBFBD>ȡ<EFBFBD>
SCAN 算法在 SSTF 算法之上考虑了磁头的移动方向，要求所请求访问的磁道在磁头当前移动方向上才能够得到调度。因为考虑了移动方向，那么一个进程请求访问的磁道一定会得到调度。
<EFBFBD><EFBFBD>һ<EFBFBD><EFBFBD><EFBFBD><EFBFBD>ͷ<EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD>ƶ<EFBFBD>ʱ<EFBFBD><EFBFBD><EFBFBD>Ƶ<EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD>ı<EFBFBD><EFBFBD>ƶ<EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD>Ϊ<EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD>ƶ<EFBFBD><EFBFBD>Ĺ<EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD>ڵ<EFBFBD><EFBFBD>ݵ<EFBFBD><EFBFBD><EFBFBD><EFBFBD>У<EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD>ֳ<EFBFBD><EFBFBD><EFBFBD> SCAN <20>㷨Ϊ<E3B7A8><CEAA><EFBFBD>ݵ<EFBFBD><DDB5><EFBFBD><EFBFBD>㷨<EFBFBD><E3B7A8>
当一个磁头自里向外移动时，移到最外侧会改变移动方向为自外向里，这种移动的规律类似于电梯的运行，因此又常称 SCAN 算法为电梯调度算法。
### 4. ѭ<EFBFBD><EFBFBD>ɨ<EFBFBD><EFBFBD><EFBFBD>㷨<EFBFBD><EFBFBD>CSCAN<EFBFBD><EFBFBD>
### 4. 循环扫描算法（CSCAN）
CSCAN <EFBFBD><EFBFBD> SCAN <EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD>˸Ķ<EFBFBD><EFBFBD><EFBFBD>Ҫ<EFBFBD><EFBFBD><EFBFBD><EFBFBD>ͷʼ<EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD>һ<EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD>ƶ<EFBFBD><EFBFBD><EFBFBD>
CSCAN 对 SCAN 进行了改动，要求磁头始终沿着一个方向移动。
# <EFBFBD>ο<EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD>
# 参考资料
- Tanenbaum A S, Bos H. Modern operating systems[M]. Prentice Hall Press, 2014.
- <EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD>, <20>ܷ<EFBFBD><DCB7><EFBFBD>, <20><>С<EFBFBD><D0A1>. <20><><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD>ϵͳ[M]. <20><><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD>ӿƼ<D3BF><C6BC><EFBFBD>ѧ<EFBFBD><D1A7><EFBFBD><EFBFBD><EFBFBD><EFBFBD>, 2001.
- Bryant, R. E., & O<EFBFBD><EFBFBD>Hallaron, D. R. (2004). <EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD>ϵͳ.
- [<EFBFBD><EFBFBD><EFBFBD>̼<EFBFBD><EFBFBD>ļ<EFBFBD><EFBFBD><EFBFBD>ͨ<EFBFBD>ŷ<EFBFBD>ʽ](http://blog.csdn.net/yufaw/article/details/7409596)
- 汤子瀛, 哲凤屏, 汤小丹. 计算机操作系统[M]. 西安电子科技大学出版社, 2001.
- Bryant, R. E., & O’Hallaron, D. R. (2004). 深入理解计算机系统.
- [进程间的几种通信方式](http://blog.csdn.net/yufaw/article/details/7409596)