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include/hardware/system/cutils/atomic.h

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+/*
+ * Copyright (C) 2007 The Android Open Source Project
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *      http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+#ifndef ANDROID_CUTILS_ATOMIC_H
+#define ANDROID_CUTILS_ATOMIC_H
+
+#include <stdint.h>
+#include <sys/types.h>
+
+#ifdef __cplusplus
+extern "C" {
+#endif
+
+/*
+ * A handful of basic atomic operations.
+ * THESE ARE HERE FOR LEGACY REASONS ONLY.  AVOID.
+ *
+ * PREFERRED ALTERNATIVES:
+ * - Use C++/C/pthread locks/mutexes whenever there is not a
+ *   convincing reason to do otherwise.  Note that very clever and
+ *   complicated, but correct, lock-free code is often slower than
+ *   using locks, especially where nontrivial data structures
+ *   are involved.
+ * - C11 stdatomic.h.
+ * - Where supported, C++11 std::atomic<T> .
+ *
+ * PLEASE STOP READING HERE UNLESS YOU ARE TRYING TO UNDERSTAND
+ * OR UPDATE OLD CODE.
+ *
+ * The "acquire" and "release" terms can be defined intuitively in terms
+ * of the placement of memory barriers in a simple lock implementation:
+ *   - wait until compare-and-swap(lock-is-free --> lock-is-held) succeeds
+ *   - barrier
+ *   - [do work]
+ *   - barrier
+ *   - store(lock-is-free)
+ * In very crude terms, the initial (acquire) barrier prevents any of the
+ * "work" from happening before the lock is held, and the later (release)
+ * barrier ensures that all of the work happens before the lock is released.
+ * (Think of cached writes, cache read-ahead, and instruction reordering
+ * around the CAS and store instructions.)
+ *
+ * The barriers must apply to both the compiler and the CPU.  Note it is
+ * legal for instructions that occur before an "acquire" barrier to be
+ * moved down below it, and for instructions that occur after a "release"
+ * barrier to be moved up above it.
+ *
+ * The ARM-driven implementation we use here is short on subtlety,
+ * and actually requests a full barrier from the compiler and the CPU.
+ * The only difference between acquire and release is in whether they
+ * are issued before or after the atomic operation with which they
+ * are associated.  To ease the transition to C/C++ atomic intrinsics,
+ * you should not rely on this, and instead assume that only the minimal
+ * acquire/release protection is provided.
+ *
+ * NOTE: all int32_t* values are expected to be aligned on 32-bit boundaries.
+ * If they are not, atomicity is not guaranteed.
+ */
+
+/*
+ * Basic arithmetic and bitwise operations.  These all provide a
+ * barrier with "release" ordering, and return the previous value.
+ *
+ * These have the same characteristics (e.g. what happens on overflow)
+ * as the equivalent non-atomic C operations.
+ */
+int32_t android_atomic_inc(volatile int32_t* addr);
+int32_t android_atomic_dec(volatile int32_t* addr);
+int32_t android_atomic_add(int32_t value, volatile int32_t* addr);
+int32_t android_atomic_and(int32_t value, volatile int32_t* addr);
+int32_t android_atomic_or(int32_t value, volatile int32_t* addr);
+
+/*
+ * Perform an atomic load with "acquire" or "release" ordering.
+ *
+ * Note that the notion of a "release" ordering for a load does not
+ * really fit into the C11 or C++11 memory model.  The extra ordering
+ * is normally observable only by code using memory_order_relaxed
+ * atomics, or data races.  In the rare cases in which such ordering
+ * is called for, use memory_order_relaxed atomics and a leading
+ * atomic_thread_fence (typically with memory_order_acquire,
+ * not memory_order_release!) instead.  If you do not understand
+ * this comment, you are in the vast majority, and should not be
+ * using release loads or replacing them with anything other than
+ * locks or default sequentially consistent atomics.
+ *
+ * This is only necessary if you need the memory barrier.  A 32-bit read
+ * from a 32-bit aligned address is atomic on all supported platforms.
+ */
+int32_t android_atomic_acquire_load(volatile const int32_t* addr);
+int32_t android_atomic_release_load(volatile const int32_t* addr);
+
+/*
+ * Perform an atomic store with "acquire" or "release" ordering.
+ *
+ * Note that the notion of a "acquire" ordering for a store does not
+ * really fit into the C11 or C++11 memory model.  The extra ordering
+ * is normally observable only by code using memory_order_relaxed
+ * atomics, or data races.  In the rare cases in which such ordering
+ * is called for, use memory_order_relaxed atomics and a trailing
+ * atomic_thread_fence (typically with memory_order_release,
+ * not memory_order_acquire!) instead.
+ *
+ * This is only necessary if you need the memory barrier.  A 32-bit write
+ * to a 32-bit aligned address is atomic on all supported platforms.
+ */
+void android_atomic_acquire_store(int32_t value, volatile int32_t* addr);
+void android_atomic_release_store(int32_t value, volatile int32_t* addr);
+
+/*
+ * Compare-and-set operation with "acquire" or "release" ordering.
+ *
+ * This returns zero if the new value was successfully stored, which will
+ * only happen when *addr == oldvalue.
+ *
+ * (The return value is inverted from implementations on other platforms,
+ * but matches the ARM ldrex/strex result.)
+ *
+ * Implementations that use the release CAS in a loop may be less efficient
+ * than possible, because we re-issue the memory barrier on each iteration.
+ */
+int android_atomic_acquire_cas(int32_t oldvalue, int32_t newvalue,
+                               volatile int32_t* addr);
+int android_atomic_release_cas(int32_t oldvalue, int32_t newvalue,
+                               volatile int32_t* addr);
+
+/*
+ * Aliases for code using an older version of this header.  These are now
+ * deprecated and should not be used.  The definitions will be removed
+ * in a future release.
+ */
+#define android_atomic_write android_atomic_release_store
+#define android_atomic_cmpxchg android_atomic_release_cas
+
+#ifdef __cplusplus
+} // extern "C"
+#endif
+
+#endif // ANDROID_CUTILS_ATOMIC_H

include/hardware/system/cutils/bitops.h

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+/*
+ * Copyright (C) 2011 The Android Open Source Project
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *      http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+#ifndef __CUTILS_BITOPS_H
+#define __CUTILS_BITOPS_H
+
+#include <stdbool.h>
+#include <string.h>
+#include <strings.h>
+#include <sys/cdefs.h>
+
+__BEGIN_DECLS
+
+/*
+ * Bitmask Operations
+ *
+ * Note this doesn't provide any locking/exclusion, and isn't atomic.
+ * Additionally no bounds checking is done on the bitmask array.
+ *
+ * Example:
+ *
+ * int num_resources;
+ * unsigned int resource_bits[BITS_TO_WORDS(num_resources)];
+ * bitmask_init(resource_bits, num_resources);
+ * ...
+ * int bit = bitmask_ffz(resource_bits, num_resources);
+ * bitmask_set(resource_bits, bit);
+ * ...
+ * if (bitmask_test(resource_bits, bit)) { ... }
+ * ...
+ * bitmask_clear(resource_bits, bit);
+ *
+ */
+
+#define BITS_PER_WORD    (sizeof(unsigned int) * 8)
+#define BITS_TO_WORDS(x) (((x) + BITS_PER_WORD - 1) / BITS_PER_WORD)
+#define BIT_IN_WORD(x)   ((x) % BITS_PER_WORD)
+#define BIT_WORD(x)      ((x) / BITS_PER_WORD)
+#define BIT_MASK(x)      (1 << BIT_IN_WORD(x))
+
+static inline void bitmask_init(unsigned int *bitmask, int num_bits)
+{
+    memset(bitmask, 0, BITS_TO_WORDS(num_bits)*sizeof(unsigned int));
+}
+
+static inline int bitmask_ffz(unsigned int *bitmask, int num_bits)
+{
+    int bit, result;
+    size_t i;
+    for (i = 0; i < BITS_TO_WORDS(num_bits); i++)
+    {
+        bit = ffs(~bitmask[i]);
+        if (bit)
+        {
+            // ffs is 1-indexed, return 0-indexed result
+            bit--;
+            result = BITS_PER_WORD * i + bit;
+            if (result >= num_bits)
+                return -1;
+            return result;
+        }
+    }
+    return -1;
+}
+
+static inline int bitmask_weight(unsigned int *bitmask, int num_bits)
+{
+    size_t i;
+    int weight = 0;
+    for (i = 0; i < BITS_TO_WORDS(num_bits); i++)
+        weight += __builtin_popcount(bitmask[i]);
+    return weight;
+}
+
+static inline void bitmask_set(unsigned int *bitmask, int bit)
+{
+    bitmask[BIT_WORD(bit)] |= BIT_MASK(bit);
+}
+
+static inline void bitmask_clear(unsigned int *bitmask, int bit)
+{
+    bitmask[BIT_WORD(bit)] &= ~BIT_MASK(bit);
+}
+
+static inline bool bitmask_test(unsigned int *bitmask, int bit)
+{
+    return bitmask[BIT_WORD(bit)] & BIT_MASK(bit);
+}
+
+static inline int popcount(unsigned int x)
+{
+    return __builtin_popcount(x);
+}
+
+static inline int popcountl(unsigned long x)
+{
+    return __builtin_popcountl(x);
+}
+
+static inline int popcountll(unsigned long long x)
+{
+    return __builtin_popcountll(x);
+}
+
+__END_DECLS
+
+#endif /* __CUTILS_BITOPS_H */

include/hardware/system/cutils/native_handle.h

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+/*
+ * Copyright (C) 2009 The Android Open Source Project
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *      http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+#ifndef NATIVE_HANDLE_H_
+#define NATIVE_HANDLE_H_
+
+#ifdef __cplusplus
+extern "C" {
+#endif
+
+typedef struct native_handle
+{
+    int version;        /* sizeof(native_handle_t) */
+    int numFds;         /* number of file-descriptors at &data[0] */
+    int numInts;        /* number of ints at &data[numFds] */
+    int data[0];        /* numFds + numInts ints */
+} native_handle_t;
+
+/*
+ * native_handle_close
+ *
+ * closes the file descriptors contained in this native_handle_t
+ *
+ * return 0 on success, or a negative error code on failure
+ *
+ */
+int native_handle_close(const native_handle_t* h);
+
+
+/*
+ * native_handle_create
+ *
+ * creates a native_handle_t and initializes it. must be destroyed with
+ * native_handle_delete().
+ *
+ */
+native_handle_t* native_handle_create(int numFds, int numInts);
+
+/*
+ * native_handle_delete
+ *
+ * frees a native_handle_t allocated with native_handle_create().
+ * This ONLY frees the memory allocated for the native_handle_t, but doesn't
+ * close the file descriptors; which can be achieved with native_handle_close().
+ *
+ * return 0 on success, or a negative error code on failure
+ *
+ */
+int native_handle_delete(native_handle_t* h);
+
+
+#ifdef __cplusplus
+}
+#endif
+
+#endif /* NATIVE_HANDLE_H_ */