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////////////////////////////////////////////////////////////////////////////////
// The Loki Library
// Copyright (c) 2001 by Andrei Alexandrescu
// This code is from the article:
// "Generic<Programming>: volatile — Multithreaded Programmer’s Best Friend
// Volatile-Correctness or How to Have Your Compiler Detect Race Conditions
// for You" by Alexandrescu, Andrei.
// Published in the February 2001 issue of the C/C++ Users Journal.
// http://www.cuj.com/documents/s=7998/cujcexp1902alexandr/
// Permission to use, copy, modify, distribute and sell this software for any
// purpose is hereby granted without fee, provided that the above copyright
// notice appear in all copies and that both that copyright notice and this
// permission notice appear in supporting documentation.
// The author makes no representations about the
// suitability of this software for any purpose. It is provided "as is"
// without express or implied warranty.
// Prepared for Loki library by Richard Sposato
////////////////////////////////////////////////////////////////////////////////
#ifndef LOKI_LOCKING_PTR_INC_
#define LOKI_LOCKING_PTR_INC_
// $Id: LockingPtr.h 840 2008-03-19 19:44:38Z rich_sposato $
#include <loki/ConstPolicy.h>
#include <loki/Threads.h>
namespace Loki
{
/** @class LockingPtr
Locks a volatile object and casts away volatility so that the object
can be safely used in a single-threaded region of code.
Original version of LockingPtr had only one template - for the shared
object, but not the mutex type. This version allows users to specify a
the mutex type as a LockingPolicy class. The only requirements for a
LockingPolicy class are to provide Lock and Unlock methods.
*/
template < typename SharedObject, typename LockingPolicy = LOKI_DEFAULT_MUTEX,
template<class> class ConstPolicy = LOKI_DEFAULT_CONSTNESS >
class LockingPtr
{
public:
typedef typename ConstPolicy<SharedObject>::Type ConstOrNotType;
/** Constructor locks mutex associated with an object.
@param object Reference to object.
@param mutex Mutex used to control thread access to object.
*/
LockingPtr( volatile ConstOrNotType& object, LockingPolicy& mutex )
: pObject_( const_cast< SharedObject* >( &object ) ),
pMutex_( &mutex )
{
mutex.Lock();
}
typedef typename std::pair<volatile ConstOrNotType*, LockingPolicy*> Pair;
/** Constructor locks mutex associated with an object.
@param lockpair a std::pair of pointers to the object and the mutex
*/
LockingPtr( Pair lockpair )
: pObject_( const_cast< SharedObject* >( lockpair.first ) ),
pMutex_( lockpair.second )
{
lockpair.second->Lock();
}
/// Destructor unlocks the mutex.
~LockingPtr()
{
pMutex_->Unlock();
}
/// Star-operator dereferences pointer.
ConstOrNotType& operator * ()
{
return *pObject_;
}
/// Point-operator returns pointer to object.
ConstOrNotType* operator -> ()
{
return pObject_;
}
private:
/// Default constructor is not implemented.
LockingPtr();
/// Copy-constructor is not implemented.
LockingPtr( const LockingPtr& );
/// Copy-assignment-operator is not implemented.
LockingPtr& operator = ( const LockingPtr& );
/// Pointer to the shared object.
ConstOrNotType* pObject_;
/// Pointer to the mutex.
LockingPolicy* pMutex_;
}; // end class LockingPtr
} // namespace Loki
#endif // end file guardian
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