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// **********************************************************************
//
// Copyright (c) 2001
// IONA Technologies, Inc.
// Waltham, MA, USA
//
// All Rights Reserved
//
// **********************************************************************
#include <IceUtil/RWRecMutex.h>
#include <IceUtil/Exception.h>
#include <assert.h>
IceUtil::RWRecMutex::RWRecMutex() :
_count(0),
_waitingWriters(0)
{
}
IceUtil::RWRecMutex::~RWRecMutex()
{
}
void
IceUtil::RWRecMutex::readLock()
{
Mutex::Lock lock(_mutex);
//
// Wait while a writer holds the lock or while writers are waiting
// to get the lock.
//
while (_count < 0 || _waitingWriters != 0)
{
_readers.wait(lock);
}
_count++;
}
void
IceUtil::RWRecMutex::tryReadLock()
{
Mutex::Lock lock(_mutex);
//
// Would block if a writer holds the lock or if writers are
// waiting to get the lock.
//
if (_count < 0 || _waitingWriters != 0)
{
throw LockedException(__FILE__, __LINE__);
}
_count++;
}
void
IceUtil::RWRecMutex::writeLock()
{
Mutex::Lock lock(_mutex);
//
// Wait for the lock to become available and increment the number
// of waiting writers.
//
while (_count != 0)
{
_waitingWriters++;
try
{
_writers.wait(lock);
}
catch(...)
{
--_waitingWriters;
throw;
}
_waitingWriters--;
}
//
// Got the lock, indicate it's held by a writer.
//
_count = -1;
}
void
IceUtil::RWRecMutex::tryWriteLock()
{
Mutex::Lock lock(_mutex);
//
// If there are readers or other writers then the call would block.
//
if (_count != 0)
{
throw LockedException(__FILE__, __LINE__);
}
//
// Got the lock, indicate it's held by a writer.
//
_count = -1;
}
void
IceUtil::RWRecMutex::unlock()
{
bool ww;
bool wr;
{
Mutex::Lock lock(_mutex);
assert(_count != 0);
//
// If _count < 0, the calling thread is a writer that holds the
// lock, so release the lock. Otherwise, _count is guaranteed to
// be > 0, so the calling thread is a reader releasing the lock.
//
if (_count < 0)
{
//
// Writer called unlock
//
_count = 0;
}
else
{
//
// Reader called unlock
//
--_count;
}
//
// Writers are waiting (ww) if _waitingWriters > 0. In that
// case, it's OK to let another writer into the region once there
// are no more readers (_count == 0). Otherwise, no writers are
// waiting but readers may be waiting (wr).
//
ww = (_waitingWriters != 0 && _count == 0);
wr = (_waitingWriters == 0);
}
//
// Wake up a waiting writer if there is one. If not, wake up all
// readers (just in case -- there may be none).
//
if (ww)
{
//
// Wake writer
//
_writers.signal();
}
else if (wr)
{
//
// Wake readers
//
_readers.broadcast();
}
}
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