/************************************************************************************

Filename    :   OVR_Atomic.h
Content     :   Contains atomic operations and inline fastest locking
                functionality. Will contain #ifdefs for OS efficiency.
                Have non-thread-safe implementaion if not available.
Created     :   September 19, 2012
Notes       :

Copyright   :   Copyright (c) Facebook Technologies, LLC and its affiliates. All rights reserved.

Licensed under the Oculus Master SDK License Version 1.0 (the "License");
you may not use the Oculus VR Rift SDK except in compliance with the License,
which is provided at the time of installation or download, or which
otherwise accompanies this software in either electronic or hard copy form.

You may obtain a copy of the License at

https://developer.oculus.com/licenses/oculusmastersdk-1.0

Unless required by applicable law or agreed to in writing, the Oculus VR SDK
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.

************************************************************************************/

#ifndef OVR_Atomic_h
#define OVR_Atomic_h

#include "OVR_Types.h"

#include <atomic>

// Include System thread functionality.
#if defined(OVR_OS_MS) && !defined(OVR_OS_MS_MOBILE)
#include "OVR_Win32_IncludeWindows.h"
#else
#include <pthread.h>
#endif

namespace OVR {

//-----------------------------------------------------------------------------------
// ***** Lock

// Lock is a simplest and most efficient mutual-exclusion lock class.
// Unlike Mutex, it cannot be waited on.

class Lock {
#if !defined(OVR_ENABLE_THREADS)

 public:
  // With no thread support, lock does nothing.
  inline Lock() {}
  inline Lock(unsigned) {}
  inline ~Lock() {}
  inline void DoLock() {}
  inline void Unlock() {}

// Windows.
#elif defined(OVR_OS_MS)

  CRITICAL_SECTION cs;

 public:
  Lock(unsigned spinCount = 10000); // Mutexes with non-zero spin counts usually result in better
  // performance.
  ~Lock();
  // Locking functions.
  inline void DoLock() {
    ::EnterCriticalSection(&cs);
  }
  inline void Unlock() {
    ::LeaveCriticalSection(&cs);
  }
  inline bool TryLock() {
    return (::TryEnterCriticalSection(&cs) == TRUE);
  }
#else
  pthread_mutex_t mutex;

 public:
  static pthread_mutexattr_t RecursiveAttr;
  static bool RecursiveAttrInit;

  Lock(unsigned spinCount = 0) // To do: Support spin count, probably via a custom lock
                               // implementation.
  {
    OVR_UNUSED(spinCount);
    if (!RecursiveAttrInit) {
      pthread_mutexattr_init(&RecursiveAttr);
      pthread_mutexattr_settype(&RecursiveAttr, PTHREAD_MUTEX_RECURSIVE);
      RecursiveAttrInit = 1;
    }
    pthread_mutex_init(&mutex, &RecursiveAttr);
  }
  ~Lock() {
    pthread_mutex_destroy(&mutex);
  }
  inline void DoLock() {
    pthread_mutex_lock(&mutex);
  }
  inline void Unlock() {
    pthread_mutex_unlock(&mutex);
  }
  inline bool TryLock() {
    return (pthread_mutex_trylock(&mutex) == 0);
  }

#endif // OVR_ENABLE_THREDS

 public:
  // Locker class, used for automatic locking
  class Locker {
    Lock* pLock;

   public:
    Locker(Lock* plock) {
      pLock = plock;
      if (plock)
        pLock->DoLock();
    }
    ~Locker() {
      Release();
    }

    void Release() {
      if (pLock)
        pLock->Unlock();
      pLock = nullptr;
    }
  };

  // Unlocker class, used for automatic unlocking
  class Unlocker {
    // OVR_NON_COPYABLE(Unlocker);
    Lock* mLock;

   public:
    Unlocker(Lock* lock) : mLock(lock) {}
    ~Unlocker() {
      Release();
    }
    void Release() {
      if (mLock)
        mLock->Unlock();
      mLock = nullptr;
    }
  };
};

//-------------------------------------------------------------------------------------
// Thin locking wrapper around data

template <class T>
class LockedData {
 public:
  LockedData(Lock& lock) : TheLock(lock) {}
  LockedData& operator=(const LockedData& /*rhs*/) {
    OVR_ASSERT(false);
    return *this;
  }

  T Get() {
    Lock::Locker locker(&TheLock);
    return Instance;
  }

  void Set(const T& value) {
    Lock::Locker locker(&TheLock);
    Instance = value;
  }

  // Returns true if the value has changed.
  // Returns false if the value has not changed.
  bool GetIfChanged(T& value) {
    Lock::Locker locker(&TheLock);

    if (value != Instance) {
      value = Instance;
      return true;
    }

    return false;
  }

 protected:
  T Instance;
  Lock& TheLock;
};

} // namespace OVR

#endif