Mutex.h

#pragma once
#include <atomic>
 
#include "AudioConfig.h"
 
#ifdef USE_STD_CONCURRENCY
#include <mutex>
#endif
 
namespace audio_tools {
 
class MutexBase {
 public:
  virtual void lock() {}
  virtual void unlock() {}
};
 
class SpinLock : public MutexBase {
  void lock() {
    for (;;) {
      // Optimistically assume the lock is free on the first try
      if (!lock_.exchange(true, std::memory_order_acquire)) {
        return;
      }
      // Wait for lock to be released without generating cache misses
      while (lock_.load(std::memory_order_relaxed)) {
        // Issue X86 PAUSE or ARM YIELD instruction to reduce contention between
        // hyper-threads
        //__builtin_ia32_pause();
        delay(1);
      }
    }
  }
 
  bool try_lock() {
    // First do a relaxed load to check if lock is free in order to prevent
    // unnecessary cache misses if someone does while(!try_lock())
    return !lock_.load(std::memory_order_relaxed) &&
           !lock_.exchange(true, std::memory_order_acquire);
  }
 
  void unlock() { lock_.store(false, std::memory_order_release); }
 
 protected:
  volatile std::atomic<bool> lock_ = {0};
};
 
#if defined(USE_STD_CONCURRENCY)
 
class StdMutex : public MutexBase {
 public:
  void lock() override { std_mutex.lock(); }
  void unlock() override { std_mutex.unlock(); }
 
 protected:
  std::mutex std_mutex;
};
 
#endif
 
}  // namespace audio_tools