win32mutex.cpp

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/* -*-c++-*- OpenThreads library, Copyright (C) 2002 - 2007  The Open Thread Group
 *
 * This library is open source and may be redistributed and/or modified under  
 * the terms of the OpenSceneGraph Public License (OSGPL) version 0.0 or 
 * (at your option) any later version.  The full license is in LICENSE file
 * included with this distribution, and on the openscenegraph.org website.
 * 
 * This library is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the 
 * OpenSceneGraph Public License for more details.
*/

//
//
// Win32Mutex.c++ - C++ Mutex class .
// The idea for it is borrowed from SGI STL
// It looks like it's hard to use win32 CRITICALL_SECTIONS withour introducing race 
// conditions on InitializeCriticalSection() . So we use spin mutex here.
// ~~~~~~~~~~~~~~~~
//

#include <OpenThreads/Mutex>
#include "Win32MutexPrivateData.h"
using namespace OpenThreads;

Win32MutexPrivateData::Win32MutexPrivateData()
{
#ifdef USE_CRITICAL_SECTION
    InitializeCriticalSection( &_cs );
#else
    mutex  = 0;
#endif
}
Win32MutexPrivateData::~Win32MutexPrivateData()
{
#ifdef USE_CRITICAL_SECTION
    DeleteCriticalSection( &_cs );
#endif
}


#ifndef USE_CRITICAL_SECTION

template <int instance>
struct WIN32MutexSpin {

  enum { __low_max = 30, __high_max = 1000 };
  // Low if we suspect uniprocessor, high for multiprocessor.
  static unsigned __max;
  static unsigned __last;
};

template <int instance>
unsigned WIN32MutexSpin <instance>::__max = WIN32MutexSpin <instance>::__low_max;

template <int instance>
unsigned WIN32MutexSpin <instance>::__last = 0;



static void _S_nsec_sleep(int __log_nsec) {

    if (__log_nsec <= 20) {
        SwitchToThread(); //Sleep(0); // adegli replaced it Sleep by SwitchToThread
    } else {
        Sleep(1 << (__log_nsec - 20));
    }
}


#if defined(_MSC_VER) && _MSC_VER <= 1300
    template WIN32MutexSpin <0>;
#endif

#endif // USE_CRITICAL_SECTION

//----------------------------------------------------------------------------
//
// Description: Constructor
//
// Use: public.
//
Mutex::Mutex() {
    Win32MutexPrivateData *pd = new Win32MutexPrivateData();
    _prvData = static_cast<void *>(pd);
}

//----------------------------------------------------------------------------
//
// Description: Destructor
//
// Use: public.
//
Mutex::~Mutex() {
    unlock();
    delete static_cast<Win32MutexPrivateData*>(_prvData);
}
//----------------------------------------------------------------------------
//
// Description: lock the mutex
//
// Use: public.
//
int Mutex::lock() {
    Win32MutexPrivateData *pd =
        static_cast<Win32MutexPrivateData*>(_prvData);

#ifdef USE_CRITICAL_SECTION

    // Block until we can take this lock.
    EnterCriticalSection( &(pd->_cs) );

    return 0;

#else

    volatile unsigned long* lock = &pd->mutex;
    // InterlockedExchange returns old value
    // if old_value  == 0 mutex wasn't locked , now it is
    if( !InterlockedExchange((long*)lock, 1L)) {
       return 0;
    }

    unsigned my_spin_max = WIN32MutexSpin<0>::__max;
    unsigned my_last_spins = WIN32MutexSpin<0>::__last;
    volatile unsigned junk = 17;      
    unsigned i;

    for (i = 0; i < my_spin_max; i++) {
      if (i < my_last_spins/2 || *lock) {
        junk *= junk; junk *= junk;
        junk *= junk; junk *= junk;
        continue;
      }

      if (!InterlockedExchange((long*)lock, 1L)) {
        // got it!
        // Spinning worked.  Thus we're probably not being scheduled
        // against the other process with which we were contending.
        // Thus it makes sense to spin longer the next time.
        WIN32MutexSpin<0>::__last = i;
        WIN32MutexSpin<0>::__max = WIN32MutexSpin<0>::__high_max;
        return 0;
      }
    }
    // We are probably being scheduled against the other process.  Sleep.
    WIN32MutexSpin<0>::__max = WIN32MutexSpin<0>::__low_max;
    for (i = 0 ;; ++i) {
      int __log_nsec = i + 6;
      if (__log_nsec > 27) __log_nsec = 27;
      if (!InterlockedExchange((long*)lock, 1L)) {
        return 0;
      }
      _S_nsec_sleep(__log_nsec);
    }
    return -1;

#endif // USE_CRITICAL_SECTION
}

//----------------------------------------------------------------------------
//
// Description: unlock the mutex
//
// Use: public.
//
int Mutex::unlock() {
    Win32MutexPrivateData *pd =
        static_cast<Win32MutexPrivateData*>(_prvData);

#ifdef USE_CRITICAL_SECTION

    // Release this lock. CRITICAL_SECTION is nested, thus
    //   unlock() calls must be paired with lock() calls.
    LeaveCriticalSection( &(pd->_cs) );

    return 0;

#else

    volatile unsigned long* lock = &pd->mutex;
    *lock = 0;
    // This is not sufficient on many multiprocessors, since
    // writes to protected variables and the lock may be reordered.
    return 0;

#endif // USE_CRITICAL_SECTION
}

//----------------------------------------------------------------------------
//
// Description: test if the mutex may be locked
//
// Use: public.
//
int Mutex::trylock() {
    Win32MutexPrivateData *pd =
        static_cast<Win32MutexPrivateData*>(_prvData);

#ifdef USE_CRITICAL_SECTION

    // Take the lock if we can; regardless don't block.
    // 'result' is FALSE if we took the lock or already held
    //   it amd TRUE if another thread already owns the lock.
    BOOL result = TryEnterCriticalSection( &(pd->_cs) );

    return( (result==TRUE) ? 0 : 1 );

#else

    volatile unsigned long* lock = &pd->mutex;

    if( !InterlockedExchange((long*)lock, 1L)) {
      return 1; // TRUE
    }

    return 0; // FALSE

#endif // USE_CRITICAL_SECTION
}