source: XMLIO_V2/external/src/POCO/Foundation/RWLock_WIN32.hpp @ 80

//
// RWLock_WIN32.cpp
//
// $Id: //poco/1.3/Foundation/src/RWLock_WIN32.cpp#5 $
//
// Library: Foundation
// Package: Threading
// Module:  RWLock
//
// Copyright (c) 2004-2006, Applied Informatics Software Engineering GmbH.
// and Contributors.
//
// Permission is hereby granted, free of charge, to any person or organization
// obtaining a copy of the software and accompanying documentation covered by
// this license (the "Software") to use, reproduce, display, distribute,
// execute, and transmit the Software, and to prepare derivative works of the
// Software, and to permit third-parties to whom the Software is furnished to
// do so, all subject to the following:
// 
// The copyright notices in the Software and this entire statement, including
// the above license grant, this restriction and the following disclaimer,
// must be included in all copies of the Software, in whole or in part, and
// all derivative works of the Software, unless such copies or derivative
// works are solely in the form of machine-executable object code generated by
// a source language processor.
// 
// THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
// IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
// FITNESS FOR A PARTICULAR PURPOSE, TITLE AND NON-INFRINGEMENT. IN NO EVENT
// SHALL THE COPYRIGHT HOLDERS OR ANYONE DISTRIBUTING THE SOFTWARE BE LIABLE
// FOR ANY DAMAGES OR OTHER LIABILITY, WHETHER IN CONTRACT, TORT OR OTHERWISE,
// ARISING FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER
// DEALINGS IN THE SOFTWARE.
//


#include <Poco/RWLock_WIN32.h>


namespace Poco {


RWLockImpl::RWLockImpl(): _readers(0), _writersWaiting(0), _writers(0)
{
        _mutex = CreateMutexW(NULL, FALSE, NULL);
        if (_mutex == NULL)
                throw SystemException("cannot create reader/writer lock");

        _readEvent = CreateEventW(NULL, TRUE, TRUE, NULL);
        if (_readEvent == NULL)
                throw SystemException("cannot create reader/writer lock");

        _writeEvent = CreateEventW(NULL, TRUE, TRUE, NULL);
        if (_writeEvent == NULL)
                throw SystemException("cannot create reader/writer lock");
}


RWLockImpl::~RWLockImpl()
{
        CloseHandle(_mutex);
        CloseHandle(_readEvent);
        CloseHandle(_writeEvent);
}


inline void RWLockImpl::addWriter()
{
        switch (WaitForSingleObject(_mutex, INFINITE))
        {
        case WAIT_OBJECT_0:
                if (++_writersWaiting == 1) ResetEvent(_readEvent);
                ReleaseMutex(_mutex);
                break;
        default:
                throw SystemException("cannot lock reader/writer lock");
        }
}


inline void RWLockImpl::removeWriter()
{
        switch (WaitForSingleObject(_mutex, INFINITE))
        {
        case WAIT_OBJECT_0:
                if (--_writersWaiting == 0 && _writers == 0) SetEvent(_readEvent);
                ReleaseMutex(_mutex);
                break;
        default:
                throw SystemException("cannot lock reader/writer lock");
        }
}


void RWLockImpl::readLockImpl()
{
        HANDLE h[2];
        h[0] = _mutex;
        h[1] = _readEvent;
        switch (WaitForMultipleObjects(2, h, TRUE, INFINITE))
        {
        case WAIT_OBJECT_0:
        case WAIT_OBJECT_0 + 1:
                ++_readers;
                ResetEvent(_writeEvent);
                ReleaseMutex(_mutex);
                poco_assert_dbg(_writers == 0);
                break;
        default:
                throw SystemException("cannot lock reader/writer lock");
        }
}


bool RWLockImpl::tryReadLockImpl()
{
        for (;;)
        {
                if (_writers != 0 || _writersWaiting != 0)
                        return false;

                DWORD result = tryReadLockOnce();
                switch (result)
                {
                case WAIT_OBJECT_0:
                case WAIT_OBJECT_0 + 1:
                        return true;
                case WAIT_TIMEOUT:
                        continue; // try again
                default:
                        throw SystemException("cannot lock reader/writer lock");
                }
        }
}


void RWLockImpl::writeLockImpl()
{
        addWriter();
        HANDLE h[2];
        h[0] = _mutex;
        h[1] = _writeEvent;
        switch (WaitForMultipleObjects(2, h, TRUE, INFINITE))
        {
        case WAIT_OBJECT_0:
        case WAIT_OBJECT_0 + 1:
                --_writersWaiting;
                ++_readers;
                ++_writers;
                ResetEvent(_readEvent);
                ResetEvent(_writeEvent);
                ReleaseMutex(_mutex);
                poco_assert_dbg(_writers == 1);
                break;
        default:
                removeWriter();
                throw SystemException("cannot lock reader/writer lock");
        }
}


bool RWLockImpl::tryWriteLockImpl()
{
        addWriter();
        HANDLE h[2];
        h[0] = _mutex;
        h[1] = _writeEvent;
        switch (WaitForMultipleObjects(2, h, TRUE, 1))
        {
        case WAIT_OBJECT_0:
        case WAIT_OBJECT_0 + 1:
                --_writersWaiting;
                ++_readers;
                ++_writers;
                ResetEvent(_readEvent);
                ResetEvent(_writeEvent);
                ReleaseMutex(_mutex);
                poco_assert_dbg(_writers == 1);
                return true;
        case WAIT_TIMEOUT:
                removeWriter();
                return false;
        default:
                removeWriter();
                throw SystemException("cannot lock reader/writer lock");
        }
}


void RWLockImpl::unlockImpl()
{
        switch (WaitForSingleObject(_mutex, INFINITE))
        {
        case WAIT_OBJECT_0:
                _writers = 0;
                if (_writersWaiting == 0) SetEvent(_readEvent);
                if (--_readers == 0) SetEvent(_writeEvent);
                ReleaseMutex(_mutex);
                break;
        default:
                throw SystemException("cannot unlock reader/writer lock");
        }
}


DWORD RWLockImpl::tryReadLockOnce()
{
        HANDLE h[2];
        h[0] = _mutex;
        h[1] = _readEvent;
        DWORD result = WaitForMultipleObjects(2, h, TRUE, 1); 
        switch (result)
        {
        case WAIT_OBJECT_0:
        case WAIT_OBJECT_0 + 1:
                ++_readers;
                ResetEvent(_writeEvent);
                ReleaseMutex(_mutex);
                poco_assert_dbg(_writers == 0);
                return result;
        case WAIT_TIMEOUT:
                return result;
        default:
                throw SystemException("cannot lock reader/writer lock");
        }
}


} // namespace Poco