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// Copyright 2016 Google Inc. All Rights Reserved.
//
// 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.
// Module Overview: Starboard Spin Lock module
//
// Defines a C++-only spin-lock implementation, built entirely on top of
// Starboard atomics and threads. It can be safely used by both clients and
// implementations.
#ifndef STARBOARD_SPIN_LOCK_H_
#define STARBOARD_SPIN_LOCK_H_
#include "starboard/atomic.h"
#include "starboard/thread.h"
#ifndef __cplusplus
#error "Only C++ files can include this header."
#endif
namespace starboard {
const SbAtomic32 kSpinLockStateReleased = 0;
const SbAtomic32 kSpinLockStateAcquired = 1;
inline void SpinLockAcquire(SbAtomic32* atomic) {
while (SbAtomicAcquire_CompareAndSwap(atomic, kSpinLockStateReleased,
kSpinLockStateAcquired) ==
kSpinLockStateAcquired) {
SbThreadYield();
}
}
inline void SpinLockRelease(SbAtomic32* atomic) {
SbAtomicRelease_Store(atomic, kSpinLockStateReleased);
}
class SpinLock {
public:
SpinLock() : atomic_(kSpinLockStateReleased) {}
~SpinLock() {}
void Acquire() { SpinLockAcquire(&atomic_); }
void Release() { SpinLockRelease(&atomic_); }
private:
SbAtomic32 atomic_;
friend class ScopedSpinLock;
};
class ScopedSpinLock {
public:
explicit ScopedSpinLock(SbAtomic32* atomic) : atomic_(atomic) {
SpinLockAcquire(atomic_);
}
explicit ScopedSpinLock(SpinLock& spin_lock) : atomic_(&spin_lock.atomic_) {
SpinLockAcquire(atomic_);
}
~ScopedSpinLock() { SpinLockRelease(atomic_); }
private:
SbAtomic32* atomic_;
};
} // namespace starboard
#endif // STARBOARD_SPIN_LOCK_H_