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/**************************************************************
*
* Licensed to the Apache Software Foundation (ASF) under one
* or more contributor license agreements. See the NOTICE file
* distributed with this work for additional information
* regarding copyright ownership. The ASF licenses this file
* to you under the Apache License, Version 2.0 (the
* "License"); you may not use this file except in compliance
* with the License. You may obtain a copy of the License at
*
* http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing,
* software distributed under the License is distributed on an
* "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
* KIND, either express or implied. See the License for the
* specific language governing permissions and limitations
* under the License.
*
*************************************************************/
#ifndef __FRAMEWORK_THREADHELP_FAIRRWLOCK_HXX_
#define __FRAMEWORK_THREADHELP_FAIRRWLOCK_HXX_
//_________________________________________________________________________________________________________________
// my own includes
//_________________________________________________________________________________________________________________
#include <threadhelp/inoncopyable.h>
#include <threadhelp/irwlock.h>
#include <macros/debug.hxx>
//_________________________________________________________________________________________________________________
// interface includes
//_________________________________________________________________________________________________________________
#include <com/sun/star/uno/XInterface.hpp>
//_________________________________________________________________________________________________________________
// other includes
//_________________________________________________________________________________________________________________
#include <osl/mutex.hxx>
#include <osl/conditn.hxx>
//_________________________________________________________________________________________________________________
// namespace
//_________________________________________________________________________________________________________________
namespace framework{
//_________________________________________________________________________________________________________________
// const
//_________________________________________________________________________________________________________________
//_________________________________________________________________________________________________________________
// declarations
//_________________________________________________________________________________________________________________
/*-************************************************************************************************************//**
@short implement a read/write lock with fairness between read/write accessors
@descr These implementation never should used as base class! Use it as a member every time.
Use ReadGuard and/or WriteGuard in your methods (which work with these lock)
to make your code threadsafe.
Fair means: All reading or writing threads are synchronized AND serialzed by using one
mutex. For reader this mutex is used to access internal variables of this lock only;
for writer this mutex is used to have an exclusiv access on your class member!
=> It's a multi-reader/single-writer lock, which no preferred accessor.
@implements IRWlock
@base INonCopyable
IRWLock
@devstatus ready to use
*//*-*************************************************************************************************************/
class FairRWLock : public IRWLock
, private INonCopyable
{
//-------------------------------------------------------------------------------------------------------------
// public methods
//-------------------------------------------------------------------------------------------------------------
public:
/*-****************************************************************************************************//**
@short standard ctor
@descr Initialize instance with right start values for correct working.
no reader could exist => m_nReadCount = 0
don't block first coming writer => m_aWriteCondition.set()
@seealso -
@param -
@return -
@onerror -
*//*-*****************************************************************************************************/
inline FairRWLock()
: m_nReadCount( 0 )
{
m_aWriteCondition.set();
}
inline virtual ~FairRWLock()
{
}
/*-****************************************************************************************************//**
@interface IRWLock
@short set lock for reading
@descr A guard should call this method to acquire read access on your member.
Writing isn't allowed then - but nobody could check it for you!
@seealso method releaseReadAccess()
@param -
@return -
@onerror -
*//*-*****************************************************************************************************/
inline virtual void acquireReadAccess()
{
// Put call in "SERIALIZE"-queue!
// After successful acquiring this mutex we are alone ...
::osl::MutexGuard aSerializeGuard( m_aSerializer );
// ... but we should synchronize us with other reader!
// May be - they will unregister himself by using releaseReadAccess()!
::osl::MutexGuard aAccessGuard( m_aAccessLock );
// Now we must register us as reader by increasing counter.
// If this the first writer we must close door for possible writer.
// Other reader don't look for this barrier - they work parallel to us!
if( m_nReadCount == 0 )
{
m_aWriteCondition.reset();
}
++m_nReadCount;
}
/*-****************************************************************************************************//**
@interface IRWLock
@short reset lock for reading
@descr A guard should call this method to release read access on your member.
@seealso method acquireReadAccess()
@param -
@return -
@onerror -
*//*-*****************************************************************************************************/
inline virtual void releaseReadAccess()
{
// The access lock is enough at this point
// because it's not allowed to wait for all reader or writer here!
// That will cause a deadlock!
::osl::MutexGuard aAccessGuard( m_aAccessLock );
// Unregister as reader first!
// Open writer barrier then if it was the last reader.
--m_nReadCount;
if( m_nReadCount == 0 )
{
m_aWriteCondition.set();
}
}
/*-****************************************************************************************************//**
@interface IRWLock
@short set lock for writing
@descr A guard should call this method to acquire write access on your member.
Reading is allowed too - of course.
After successfully calling of this method you are the only writer.
@seealso method releaseWriteAccess()
@param -
@return -
@onerror -
*//*-*****************************************************************************************************/
inline virtual void acquireWriteAccess()
{
// You have to stand in our serialize-queue till all reader
// are registered (not for releasing them!) or writer finished their work!
// Don't use a guard to do so - because you must hold the mutex till
// you call releaseWriteAccess()!
// After succesfull acquire you have to wait for current working reader.
// Used condition will open by last gone reader object.
m_aSerializer.acquire();
m_aWriteCondition.wait();
#ifdef ENABLE_MUTEXDEBUG
// A writer is an exclusiv accessor!
LOG_ASSERT2( m_nReadCount!=0, "FairRWLock::acquireWriteAccess()", "No threadsafe code detected ... : Read count != 0!" )
#endif
}
/*-****************************************************************************************************//**
@interface IRWLock
@short reset lock for writing
@descr A guard should call this method to release write access on your member.
@seealso method acquireWriteAccess()
@param -
@return -
@onerror -
*//*-*****************************************************************************************************/
inline virtual void releaseWriteAccess()
{
// The only one you have to do here is to release
// hold seriliaze-mutex. All other user of these instance are blocked
// by these mutex!
// You don't need any other mutex here - you are the only one in the moment!
#ifdef ENABLE_MUTEXDEBUG
// A writer is an exclusiv accessor!
LOG_ASSERT2( m_nReadCount!=0, "FairRWLock::releaseWriteAccess()", "No threadsafe code detected ... : Read count != 0!" )
#endif
m_aSerializer.release();
}
/*-****************************************************************************************************//**
@interface IRWLock
@short downgrade a write access to a read access
@descr A guard should call this method to change a write to a read access.
New readers can work too - new writer are blocked!
@attention Don't call this method if you are not a writer!
Results are not defined then ...
An upgrade can't be really implemented ... because acquiring new access
will be the same - there no differences!
@seealso -
@param -
@return -
@onerror -
*//*-*****************************************************************************************************/
inline virtual void downgradeWriteAccess()
{
// You must be a writer to call this method!
// We can't check it - but otherwise it's your problem ...
// Thats why you don't need any mutex here.
#ifdef ENABLE_MUTEXDEBUG
// A writer is an exclusiv accessor!
LOG_ASSERT2( m_nReadCount!=0, "FairRWLock::downgradeWriteAccess()", "No threadsafe code detected ... : Read count != 0!" )
#endif
// Register himself as "new" reader.
// This value must be 0 before - because we support single writer access only!
++m_nReadCount;
// Close barrier for other writer!
// Why?
// You hold the serializer mutex - next one can be a reader OR a writer.
// They must blocked then - because you will be a reader after this call
// and writer use this condition to wait for current reader!
m_aWriteCondition.reset();
// Open door for next waiting thread in serialize queue!
m_aSerializer.release();
}
//-------------------------------------------------------------------------------------------------------------
// private member
//-------------------------------------------------------------------------------------------------------------
private:
::osl::Mutex m_aAccessLock ; /// regulate access on internal member of this instance
::osl::Mutex m_aSerializer ; /// serialze incoming read/write access threads
::osl::Condition m_aWriteCondition ; /// a writer must wait till current working reader are gone
sal_Int32 m_nReadCount ; /// every reader is registered - the last one open the door for waiting writer
}; // class FairRWLock
} // namespace framework
#endif // #ifndef __FRAMEWORK_THREADHELP_FAIRRWLOCK_HXX_
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