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Diffstat (limited to 'media/omx-plugin/include/ics/cutils/atomic.h')
-rw-r--r-- | media/omx-plugin/include/ics/cutils/atomic.h | 121 |
1 files changed, 121 insertions, 0 deletions
diff --git a/media/omx-plugin/include/ics/cutils/atomic.h b/media/omx-plugin/include/ics/cutils/atomic.h new file mode 100644 index 000000000..ae42eb8a0 --- /dev/null +++ b/media/omx-plugin/include/ics/cutils/atomic.h @@ -0,0 +1,121 @@ +/* + * 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 |