fast_mutex.h

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/*
Copyright (c) 2010 Marcus Geelnard

This software is provided 'as-is', without any express or implied
warranty. In no event will the authors be held liable for any damages
arising from the use of this software.

Permission is granted to anyone to use this software for any purpose,
including commercial applications, and to alter it and redistribute it
freely, subject to the following restrictions:

    1. The origin of this software must not be misrepresented; you must not
    claim that you wrote the original software. If you use this software
    in a product, an acknowledgment in the product documentation would be
    appreciated but is not required.

    2. Altered source versions must be plainly marked as such, and must not be
    misrepresented as being the original software.

    3. This notice may not be removed or altered from any source
    distribution.
*/

#ifndef _FAST_MUTEX_H_
#define _FAST_MUTEX_H_


// Which platform are we on?
#if !defined(_TTHREAD_PLATFORM_DEFINED_)
  #if defined(_WIN32) || defined(__WIN32__) || defined(__WINDOWS__)
    #define _TTHREAD_WIN32_
  #else
    #define _TTHREAD_POSIX_
  #endif
  #define _TTHREAD_PLATFORM_DEFINED_
#endif

// Check if we can support the assembly language level implementation (otherwise
// revert to the system API)
#if (defined(__GNUC__) && (defined(__i386__) || defined(__x86_64__))) || \
    (defined(_MSC_VER) && (defined(_M_IX86) || defined(_M_X64))) || \
    (defined(__GNUC__) && (defined(__ppc__)))
  #define _FAST_MUTEX_ASM_
#else
  #define _FAST_MUTEX_SYS_
#endif

#if defined(_TTHREAD_WIN32_)
  #include <windows.h>
#else
  #ifdef _FAST_MUTEX_ASM_
    #include <sched.h>
  #else
    #include <pthread.h>
  #endif
#endif

namespace tthread {

class fast_mutex {
  public:
#if defined(_FAST_MUTEX_ASM_)
    fast_mutex() : mLock(0) {}
#else
    fast_mutex()
    {
  #if defined(_TTHREAD_WIN32_)
      InitializeCriticalSection(&mHandle);
  #elif defined(_TTHREAD_POSIX_)
      pthread_mutex_init(&mHandle, NULL);
  #endif
    }
#endif

#if !defined(_FAST_MUTEX_ASM_)

    ~fast_mutex()
    {
  #if defined(_TTHREAD_WIN32_)
      DeleteCriticalSection(&mHandle);
  #elif defined(_TTHREAD_POSIX_)
      pthread_mutex_destroy(&mHandle);
  #endif
    }
#endif

    inline void lock()
    {
#if defined(_FAST_MUTEX_ASM_)
      bool gotLock;
      do {
        gotLock = try_lock();
        if(!gotLock)
        {
  #if defined(_TTHREAD_WIN32_)
          Sleep(0);
  #elif defined(_TTHREAD_POSIX_)
          sched_yield();
  #endif
        }
      } while(!gotLock);
#else
  #if defined(_TTHREAD_WIN32_)
      EnterCriticalSection(&mHandle);
  #elif defined(_TTHREAD_POSIX_)
      pthread_mutex_lock(&mHandle);
  #endif
#endif
    }

    inline bool try_lock()
    {
#if defined(_FAST_MUTEX_ASM_)
      int oldLock;
  #if defined(__GNUC__) && (defined(__i386__) || defined(__x86_64__))
      asm volatile (
        "movl $1,%%eax\n\t"
        "xchg %%eax,%0\n\t"
        "movl %%eax,%1\n\t"
        : "=m" (mLock), "=m" (oldLock)
        :
        : "%eax", "memory"
      );
  #elif defined(_MSC_VER) && (defined(_M_IX86) || defined(_M_X64))
      int *ptrLock = &mLock;
      __asm {
        mov eax,1
        mov ecx,ptrLock
        xchg eax,[ecx]
        mov oldLock,eax
      }
  #elif defined(__GNUC__) && (defined(__ppc__))
      int newLock = 1;
      asm volatile (
        "\n1:\n\t"
        "lwarx  %0,0,%1\n\t"
        "cmpwi  0,%0,0\n\t"
        "bne-   2f\n\t"
        "stwcx. %2,0,%1\n\t"
        "bne-   1b\n\t"
        "isync\n"
        "2:\n\t"
        : "=&r" (oldLock)
        : "r" (&mLock), "r" (newLock)
        : "cr0", "memory"
      );
  #endif
      return (oldLock == 0);
#else
  #if defined(_TTHREAD_WIN32_)
      return TryEnterCriticalSection(&mHandle) ? true : false;
  #elif defined(_TTHREAD_POSIX_)
      return (pthread_mutex_trylock(&mHandle) == 0) ? true : false;
  #endif
#endif
    }

    inline void unlock()
    {
#if defined(_FAST_MUTEX_ASM_)
  #if defined(__GNUC__) && (defined(__i386__) || defined(__x86_64__))
      asm volatile (
        "movl $0,%%eax\n\t"
        "xchg %%eax,%0\n\t"
        : "=m" (mLock)
        :
        : "%eax", "memory"
      );
  #elif defined(_MSC_VER) && (defined(_M_IX86) || defined(_M_X64))
      int *ptrLock = &mLock;
      __asm {
        mov eax,0
        mov ecx,ptrLock
        xchg eax,[ecx]
      }
  #elif defined(__GNUC__) && (defined(__ppc__))
      asm volatile (
        "sync\n\t"  // Replace with lwsync where possible?
        : : : "memory"
      );
      mLock = 0;
  #endif
#else
  #if defined(_TTHREAD_WIN32_)
      LeaveCriticalSection(&mHandle);
  #elif defined(_TTHREAD_POSIX_)
      pthread_mutex_unlock(&mHandle);
  #endif
#endif
    }

  private:
#if defined(_FAST_MUTEX_ASM_)
    int mLock;
#else
  #if defined(_TTHREAD_WIN32_)
    CRITICAL_SECTION mHandle;
  #elif defined(_TTHREAD_POSIX_)
    pthread_mutex_t mHandle;
  #endif
#endif
};

}

#endif // _FAST_MUTEX_H_

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