/*

 * Copyright 2015 Google Inc.

 *

 * Use of this source code is governed by a BSD-style license that can be

 * found in the LICENSE file.

 */

#ifndef SkSpinlock_DEFINED

#define SkSpinlock_DEFINED

#include "include/core/SkTypes.h"

#include "include/private/SkThreadAnnotations.h"

#include <atomic>

class SK_CAPABILITY("mutex") SkSpinlock {

public:

    constexpr SkSpinlock() = default;

    void acquire() SK_ACQUIRE() {

        // To act as a mutex, we need an acquire barrier when we acquire the lock.

        if (fLocked.exchange(true, std::memory_order_acquire)) {

            // Lock was contended.  Fall back to an out-of-line spin loop.

            this->contendedAcquire();

        }

    }

    // Acquire the lock or fail (quickly). Lets the caller decide to do something other than wait.

    bool tryAcquire() SK_TRY_ACQUIRE(true) {

        // To act as a mutex, we need an acquire barrier when we acquire the lock.

        if (fLocked.exchange(true, std::memory_order_acquire)) {

            // Lock was contended. Let the caller decide what to do.

            return false;

        }

        return true;

    }

    void release() SK_RELEASE_CAPABILITY() {

        // To act as a mutex, we need a release barrier when we release the lock.

        fLocked.store(false, std::memory_order_release);

    }

private:

    SK_API void contendedAcquire();

    std::atomic<bool> fLocked{false};

};

class SK_SCOPED_CAPABILITY SkAutoSpinlock {

public:

    SkAutoSpinlock(SkSpinlock& mutex) SK_ACQUIRE(mutex) : fSpinlock(mutex) { fSpinlock.acquire(); }

    ~SkAutoSpinlock() SK_RELEASE_CAPABILITY() { fSpinlock.release(); }

private:

    SkSpinlock& fSpinlock;

};

#endif//SkSpinlock_DEFINED