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/*
* Copyright (C) 2015 The Android Open Source Project
* All rights reserved.
*
* Redistribution and use in source and binary forms, with or without
* modification, are permitted provided that the following conditions
* are met:
* * Redistributions of source code must retain the above copyright
* notice, this list of conditions and the following disclaimer.
* * Redistributions in binary form must reproduce the above copyright
* notice, this list of conditions and the following disclaimer in
* the documentation and/or other materials provided with the
* distribution.
*
* THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
* "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
* LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS
* FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE
* COPYRIGHT OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT,
* INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING,
* BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS
* OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED
* AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY,
* OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT
* OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
* SUCH DAMAGE.
*/
#ifndef _BIONIC_LOCK_H
#define _BIONIC_LOCK_H
#include <stdatomic.h>
#include "private/bionic_futex.h"
class Lock {
private:
enum LockState {
Unlocked = 0,
LockedWithoutWaiter,
LockedWithWaiter,
};
_Atomic(LockState) state;
bool process_shared;
public:
Lock(bool process_shared = false) {
init(process_shared);
}
void init(bool process_shared) {
atomic_init(&state, Unlocked);
this->process_shared = process_shared;
}
void lock() {
LockState old_state = Unlocked;
if (__predict_true(atomic_compare_exchange_strong_explicit(&state, &old_state,
LockedWithoutWaiter, memory_order_acquire, memory_order_relaxed))) {
return;
}
while (atomic_exchange_explicit(&state, LockedWithWaiter, memory_order_acquire) != Unlocked) {
// TODO: As the critical section is brief, it is a better choice to spin a few times befor sleeping.
__futex_wait_ex(&state, process_shared, LockedWithWaiter, NULL);
}
return;
}
void unlock() {
if (atomic_exchange_explicit(&state, Unlocked, memory_order_release) == LockedWithWaiter) {
__futex_wake_ex(&state, process_shared, 1);
}
}
};
#endif // _BIONIC_LOCK_H
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