kc3-lang/angle/src/common/Spinlock.h

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• Hash : 44a5c913
  Author :
  Date : 2021-06-17T09:29:29
  

  CL: Make CL front end and back end thread-safe
  
  Add locking to all mutable variables of the CL objects in the
  front end and pass-through back end to make them thread-safe.
  This fixes a crash in a multi-threaded CTS test.
  
  Bug: angleproject:6015
  Change-Id: I1d6471c851217639411c434c82acd32d14035291
  Reviewed-on: https://chromium-review.googlesource.com/c/angle/angle/+/2967468
  Commit-Queue: John Plate <jplate@google.com>
  Reviewed-by: Cody Northrop <cnorthrop@google.com>
  Reviewed-by: Jamie Madill <jmadill@chromium.org>
  

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• src/common/Spinlock.h

• //
  // Copyright 2021 The ANGLE Project Authors. All rights reserved.
  // Use of this source code is governed by a BSD-style license that can be
  // found in the LICENSE file.
  //
  // Spinlock.h:
  //   Spinlock is a lock that loops actively until it gets the resource.
  //   Only use it when the lock will be granted in reasonably short time.
  
  #ifndef COMMON_SPINLOCK_H_
  #define COMMON_SPINLOCK_H_
  
  #include <atomic>
  
  // TODO(jplate) Add pause for ARM, http://anglebug.com:6067
  #if defined(_MSC_VER) && (defined(_M_IX86) || defined(_M_X64))
  extern "C" void _mm_pause();
  #    pragma intrinsic(_mm_pause)
  #    define ANGLE_SMT_PAUSE() _mm_pause()
  #elif defined(__GNUC__) && (defined(__i386__) || defined(__x86_64__))
  #    define ANGLE_SMT_PAUSE() __asm__ __volatile__("pause;")
  #else
  #    define ANGLE_SMT_PAUSE() static_cast<void>(0)
  #endif
  
  namespace angle
  {
  
  class Spinlock
  {
    public:
      Spinlock() noexcept;
  
      bool try_lock() noexcept;
      void lock() noexcept;
      void unlock() noexcept;
  
    private:
      std::atomic_bool mLock;
  };
  
  inline Spinlock::Spinlock() noexcept : mLock(false) {}
  
  inline bool Spinlock::try_lock() noexcept
  {
      // Relaxed check first to prevent unnecessary cache misses.
      return !mLock.load(std::memory_order_relaxed) &&
             !mLock.exchange(true, std::memory_order_acquire);
  }
  
  inline void Spinlock::lock() noexcept
  {
      while (mLock.exchange(true, std::memory_order_acquire))
      {
          // Relaxed wait to prevent unnecessary cache misses.
          while (mLock.load(std::memory_order_relaxed))
          {
              // Optimization for simultaneous multithreading.
              ANGLE_SMT_PAUSE();
          }
      }
  }
  
  inline void Spinlock::unlock() noexcept
  {
      mLock.store(false, std::memory_order_release);
  }
  
  }  // namespace angle
  
  #endif  // COMMON_SPINLOCK_H_
  

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