311 lines
14 KiB
C++
311 lines
14 KiB
C++
/*************************************************************************
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*
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* OpenOffice.org - a multi-platform office productivity suite
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*
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* $RCSfile: fairrwlock.hxx,v $
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*
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* $Revision: 1.5 $
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*
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* last change: $Author: rt $ $Date: 2005-09-09 00:35:25 $
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*
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* The Contents of this file are made available subject to
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* the terms of GNU Lesser General Public License Version 2.1.
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*
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*
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* GNU Lesser General Public License Version 2.1
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* =============================================
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* Copyright 2005 by Sun Microsystems, Inc.
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* 901 San Antonio Road, Palo Alto, CA 94303, USA
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*
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* This library is free software; you can redistribute it and/or
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* modify it under the terms of the GNU Lesser General Public
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* License version 2.1, as published by the Free Software Foundation.
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*
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* This library is distributed in the hope that it will be useful,
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* but WITHOUT ANY WARRANTY; without even the implied warranty of
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* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
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* Lesser General Public License for more details.
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*
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* You should have received a copy of the GNU Lesser General Public
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* License along with this library; if not, write to the Free Software
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* Foundation, Inc., 59 Temple Place, Suite 330, Boston,
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* MA 02111-1307 USA
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*
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************************************************************************/
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#ifndef __FRAMEWORK_THREADHELP_FAIRRWLOCK_HXX_
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#define __FRAMEWORK_THREADHELP_FAIRRWLOCK_HXX_
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//_________________________________________________________________________________________________________________
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// my own includes
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//_________________________________________________________________________________________________________________
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#ifndef __FRAMEWORK_THREADHELP_INONCOPYABLE_H_
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#include <threadhelp/inoncopyable.h>
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#endif
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#ifndef __FRAMEWORK_THREADHELP_IRWLOCK_H_
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#include <threadhelp/irwlock.h>
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#endif
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#ifndef __FRAMEWORK_MACROS_DEBUG_HXX_
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#include <macros/debug.hxx>
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#endif
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//_________________________________________________________________________________________________________________
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// interface includes
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//_________________________________________________________________________________________________________________
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#ifndef _COM_SUN_STAR_UNO_XINTERFACE_HPP_
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#include <com/sun/star/uno/XInterface.hpp>
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#endif
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#ifndef _COM_SUN_STAR_LANG_DISPOSEDEXCEPTION_HPP_
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#include <com/sun/star/lang/DisposedException.hpp>
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#endif
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//_________________________________________________________________________________________________________________
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// other includes
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//_________________________________________________________________________________________________________________
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#ifndef _OSL_MUTEX_HXX_
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#include <osl/mutex.hxx>
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#endif
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#ifndef _OSL_CONDITN_HXX_
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#include <osl/conditn.hxx>
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#endif
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//_________________________________________________________________________________________________________________
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// namespace
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//_________________________________________________________________________________________________________________
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namespace framework{
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//_________________________________________________________________________________________________________________
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// const
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//_________________________________________________________________________________________________________________
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//_________________________________________________________________________________________________________________
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// declarations
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//_________________________________________________________________________________________________________________
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/*-************************************************************************************************************//**
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@short implement a read/write lock with fairness between read/write accessors
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@descr These implementation never should used as base class! Use it as a member every time.
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Use ReadGuard and/or WriteGuard in your methods (which work with these lock)
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to make your code threadsafe.
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Fair means: All reading or writing threads are synchronized AND serialzed by using one
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mutex. For reader this mutex is used to access internal variables of this lock only;
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for writer this mutex is used to have an exclusiv access on your class member!
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=> It's a multi-reader/single-writer lock, which no preferred accessor.
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@implements IRWlock
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@base INonCopyable
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IRWLock
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@devstatus ready to use
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*//*-*************************************************************************************************************/
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class FairRWLock : public IRWLock
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, private INonCopyable
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{
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//-------------------------------------------------------------------------------------------------------------
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// public methods
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//-------------------------------------------------------------------------------------------------------------
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public:
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/*-****************************************************************************************************//**
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@short standard ctor
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@descr Initialize instance with right start values for correct working.
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no reader could exist => m_nReadCount = 0
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don't block first comming writer => m_aWriteCondition.set()
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@seealso -
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@param -
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@return -
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@onerror -
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*//*-*****************************************************************************************************/
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inline FairRWLock()
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: m_nReadCount( 0 )
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{
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m_aWriteCondition.set();
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}
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/*-****************************************************************************************************//**
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@interface IRWLock
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@short set lock for reading
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@descr A guard should call this method to acquire read access on your member.
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Writing isn't allowed then - but nobody could check it for you!
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@seealso method releaseReadAccess()
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@param -
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@return -
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@onerror -
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*//*-*****************************************************************************************************/
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inline virtual void acquireReadAccess()
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{
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// Put call in "SERIALIZE"-queue!
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// After successful acquiring this mutex we are alone ...
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::osl::MutexGuard aSerializeGuard( m_aSerializer );
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// ... but we should synchronize us with other reader!
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// May be - they will unregister himself by using releaseReadAccess()!
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::osl::MutexGuard aAccessGuard( m_aAccessLock );
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// Now we must register us as reader by increasing counter.
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// If this the first writer we must close door for possible writer.
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// Other reader don't look for this barrier - they work parallel to us!
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if( m_nReadCount == 0 )
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{
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m_aWriteCondition.reset();
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}
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++m_nReadCount;
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}
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/*-****************************************************************************************************//**
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@interface IRWLock
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@short reset lock for reading
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@descr A guard should call this method to release read access on your member.
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@seealso method acquireReadAccess()
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@param -
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@return -
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@onerror -
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*//*-*****************************************************************************************************/
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inline virtual void releaseReadAccess()
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{
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// The access lock is enough at this point
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// because it's not allowed to wait for all reader or writer here!
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// That will cause a deadlock!
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::osl::MutexGuard aAccessGuard( m_aAccessLock );
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// Unregister as reader first!
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// Open writer barrier then if it was the last reader.
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--m_nReadCount;
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if( m_nReadCount == 0 )
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{
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m_aWriteCondition.set();
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}
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}
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/*-****************************************************************************************************//**
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@interface IRWLock
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@short set lock for writing
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@descr A guard should call this method to acquire write access on your member.
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Reading is allowed too - of course.
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After successfully calling of this method you are the only writer.
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@seealso method releaseWriteAccess()
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@param -
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@return -
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@onerror -
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*//*-*****************************************************************************************************/
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inline virtual void acquireWriteAccess()
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{
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// You have to stand in our serialize-queue till all reader
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// are registered (not for releasing them!) or writer finished their work!
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// Don't use a guard to do so - because you must hold the mutex till
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// you call releaseWriteAccess()!
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// After succesfull acquire you have to wait for current working reader.
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// Used condition will open by last gone reader object.
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m_aSerializer.acquire();
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m_aWriteCondition.wait();
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#ifdef ENABLE_MUTEXDEBUG
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// A writer is an exclusiv accessor!
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LOG_ASSERT2( m_nReadCount!=0, "FairRWLock::acquireWriteAccess()", "No threadsafe code detected ... : Read count != 0!" )
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#endif
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}
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/*-****************************************************************************************************//**
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@interface IRWLock
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@short reset lock for writing
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@descr A guard should call this method to release write access on your member.
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@seealso method acquireWriteAccess()
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@param -
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@return -
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@onerror -
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*//*-*****************************************************************************************************/
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inline virtual void releaseWriteAccess()
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{
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// The only one you have to do here is to release
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// hold seriliaze-mutex. All other user of these instance are blocked
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// by these mutex!
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// You don't need any other mutex here - you are the only one in the moment!
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#ifdef ENABLE_MUTEXDEBUG
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// A writer is an exclusiv accessor!
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LOG_ASSERT2( m_nReadCount!=0, "FairRWLock::releaseWriteAccess()", "No threadsafe code detected ... : Read count != 0!" )
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#endif
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m_aSerializer.release();
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}
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/*-****************************************************************************************************//**
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@interface IRWLock
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@short downgrade a write access to a read access
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@descr A guard should call this method to change a write to a read access.
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New readers can work too - new writer are blocked!
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@attention Don't call this method if you are not a writer!
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Results are not defined then ...
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An upgrade can't be implemented realy ... because acquiring new access
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will be the same - there no differences!
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@seealso -
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@param -
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@return -
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@onerror -
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*//*-*****************************************************************************************************/
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inline virtual void downgradeWriteAccess()
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{
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// You must be a writer to call this method!
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// We can't check it - but otherwise it's your problem ...
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// Thats why you don't need any mutex here.
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#ifdef ENABLE_MUTEXDEBUG
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// A writer is an exclusiv accessor!
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LOG_ASSERT2( m_nReadCount!=0, "FairRWLock::downgradeWriteAccess()", "No threadsafe code detected ... : Read count != 0!" )
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#endif
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// Register himself as "new" reader.
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// This value must be 0 before - because we support single writer access only!
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++m_nReadCount;
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// Close barrier for other writer!
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// Why?
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// You hold the serializer mutex - next one can be a reader OR a writer.
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// They must blocked then - because you will be a reader after this call
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// and writer use this condition to wait for current reader!
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m_aWriteCondition.reset();
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// Open door for next waiting thread in serialize queue!
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m_aSerializer.release();
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}
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//-------------------------------------------------------------------------------------------------------------
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// private member
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//-------------------------------------------------------------------------------------------------------------
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private:
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::osl::Mutex m_aAccessLock ; /// regulate access on internal member of this instance
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::osl::Mutex m_aSerializer ; /// serialze incoming read/write access threads
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::osl::Condition m_aWriteCondition ; /// a writer must wait till current working reader are gone
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sal_Int32 m_nReadCount ; /// every reader is registered - the last one open the door for waiting writer
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}; // class FairRWLock
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} // namespace framework
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#endif // #ifndef __FRAMEWORK_THREADHELP_FAIRRWLOCK_HXX_
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