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      1 /*
      2  * Copyright 2015 Google Inc.
      3  *
      4  * Use of this source code is governed by a BSD-style license that can be
      5  * found in the LICENSE file.
      6  */
      7 
      8 // This file is not part of the public Skia API.
      9 
     10 #ifndef SkSpinlock_DEFINED
     11 #define SkSpinlock_DEFINED
     12 
     13 #include "../private/SkAtomics.h"
     14 
     15 #define SK_DECLARE_STATIC_SPINLOCK(name) namespace {} static SkPODSpinlock name
     16 
     17 // This class has no constructor and must be zero-initialized (the macro above does this).
     18 class SK_API SkPODSpinlock {
     19 public:
     20     void acquire() {
     21         // To act as a mutex, we need an acquire barrier if we take the lock.
     22         if (sk_atomic_exchange(&fLocked, true, sk_memory_order_acquire)) {
     23             // Lock was contended.  Fall back to an out-of-line spin loop.
     24             this->contendedAcquire();
     25         }
     26     }
     27 
     28     void release() {
     29         // To act as a mutex, we need a release barrier.
     30         sk_atomic_store(&fLocked, false, sk_memory_order_release);
     31     }
     32 
     33 private:
     34     void contendedAcquire();
     35     bool fLocked;
     36 };
     37 
     38 // For non-global-static use cases, this is normally what you want.
     39 class SkSpinlock : public SkPODSpinlock {
     40 public:
     41     SkSpinlock() { this->release(); }
     42 };
     43 
     44 #endif//SkSpinlock_DEFINED
     45