atomic_poor_man.cpp

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/** @file
 *  @author Bram de Greve (bram@cocamware.com)
 *  @author Tom De Muer (tom@cocamware.com)
 *
 *  *** BEGIN LICENSE INFORMATION ***
 *  
 *  The contents of this file are subject to the Common Public Attribution License 
 *  Version 1.0 (the "License"); you may not use this file except in compliance with 
 *  the License. You may obtain a copy of the License at 
 *  http://lass.sourceforge.net/cpal-license. The License is based on the 
 *  Mozilla Public License Version 1.1 but Sections 14 and 15 have been added to cover 
 *  use of software over a computer network and provide for limited attribution for 
 *  the Original Developer. In addition, Exhibit A has been modified to be consistent 
 *  with Exhibit B.
 *  
 *  Software distributed under the License is distributed on an "AS IS" basis, WITHOUT 
 *  WARRANTY OF ANY KIND, either express or implied. See the License for the specific 
 *  language governing rights and limitations under the License.
 *  
 *  The Original Code is LASS - Library of Assembled Shared Sources.
 *  
 *  The Initial Developer of the Original Code is Bram de Greve and Tom De Muer.
 *  The Original Developer is the Initial Developer.
 *  
 *  All portions of the code written by the Initial Developer are:
 *  Copyright (C) 2004-2011 the Initial Developer.
 *  All Rights Reserved.
 *  
 *  Contributor(s):
 *
 *  Alternatively, the contents of this file may be used under the terms of the 
 *  GNU General Public License Version 2 or later (the GPL), in which case the 
 *  provisions of GPL are applicable instead of those above.  If you wish to allow use
 *  of your version of this file only under the terms of the GPL and not to allow 
 *  others to use your version of this file under the CPAL, indicate your decision by 
 *  deleting the provisions above and replace them with the notice and other 
 *  provisions required by the GPL License. If you do not delete the provisions above,
 *  a recipient may use your version of this file under either the CPAL or the GPL.
 *  
 *  *** END LICENSE INFORMATION ***
 */
 
#include "lass_common.h"
#include "../atomic.h"
 
#ifdef LASS_UTIL_ATOMIC_HAVE_POOR_MANS_IMPL
 
#if LASS_HAVE_LDREX_STREX || LASS_KUSER_HELPER_VERSION >= 2
#   if LASS_HAVE_LDREXB_STREXB && LASS_HAVE_LDREXH_STREXH
#       if LASS_HAVE_LDREXD_STREXD || LASS_KUSER_HELPER_VERSION >= 5
            // all should be ok (except for 8-byte adjacent CAS, which shouldn't be used anyway, can we protect against that?)
#       else
#           warning "[LASS BUILD MSG] Poor man's implementation of 4-byte adjacent CAS (used in TaggedPtr), and all 8-byte atomics. Performance will suffer!"
#       endif
#   elif LASS_HAVE_LDREXD_STREXD || LASS_KUSER_HELPER_VERSION >= 5
#       warning "[LASS BUILD MSG] Poor man's implementation of 1- and 2-byte atomics (except 2-byte adjacent CAS). All 4- and 8-byte atomics are good."
#   else
#       warning "[LASS BUILD MSG] Poor man's implementation of 1-, 2- and 8-byte atomics, and 4-byte adjacent CAS (used in TaggedPtr). Performance will suffer!"
#   endif
#else
#   warning "[LASS BUILD MSG] Poor man's implementation of ALL atomics using a mutex! performance will SEVERELY suffer!"
#endif
 
#if LASS_KUSER_HELPER_VERSION >= 2
 
namespace
{
    typedef int (kuser_cmpxchg_t)(int oldval, int newval, volatile int *ptr);
    #define kuser_cmpxchg (*(kuser_cmpxchg_t *)0xffff0fc0)
 
    enum
    {
        unlocked = 0,
        locked = 1,
    };
    volatile int globalLock = unlocked;
}
 
namespace lass
{
namespace util
{
namespace impl
{
 
PoorMansGlobalAtomicLock::PoorMansGlobalAtomicLock()
{
    int old;
    do
    {
        old = globalLock;
        if ( old == locked )
        {
            continue;
        }
    }
    while (kuser_cmpxchg(old, locked, &globalLock));
}
 
PoorMansGlobalAtomicLock::~PoorMansGlobalAtomicLock()
{
    LASS_ASSERT(globalLock == locked);
    kuser_cmpxchg(locked, unlocked, &globalLock);
};
 
}
}
}
 
#else
 
#include "../thread.h"
 
namespace
{
 
using ::lass::util::Mutex;
 
Mutex* globalMutex()
{
    static Mutex* mutex = 0;
    if (!mutex)
    {
        mutex = new Mutex;
    }
    return mutex;
}
 
Mutex* const initializeBeforeMain = globalMutex();
 
}
 
namespace lass
{
namespace util
{
namespace impl
{
 
PoorMansGlobalAtomicLock::PoorMansGlobalAtomicLock()
{
    globalMutex()->lock();
}
 
PoorMansGlobalAtomicLock::~PoorMansGlobalAtomicLock()
{
    globalMutex()->unlock();
};
 
}
}
}
 
#endif
 
#endif
 
// EOF