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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. The appropriate pthread
* functions should be used instead of these whenever possible.
*
* 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.
*
* 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.
*
* 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
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