tqt3/src/tools/qmutexpool.cpp

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#include "qmutexpool_p.h"

#ifdef QT_THREAD_SUPPORT

#include <ntqthread.h>

Q_EXPORT TQMutexPool *tqt_global_mutexpool = 0;


/*!
    \class TQMutexPool qmutexpool_p.h
    \brief The TQMutexPool class provides a pool of TQMutex objects.

    \internal

    \ingroup thread

    TQMutexPool is a convenience class that provides access to a fixed
    number of TQMutex objects.

    Typical use of a TQMutexPool is in situations where it is not
    possible or feasible to use one TQMutex for every protected object.
    The mutex pool will return a mutex based on the address of the
    object that needs protection.

    For example, consider this simple class:

    \code
    class Number {
    public:
	Number( double n ) : num ( n ) { }

	void setNumber( double n ) { num = n; }
	double number() const { return num; }

    private:
	double num;
    };
    \endcode

    Adding a TQMutex member to the Number class does not make sense,
    because it is so small. However, in order to ensure that access to
    each Number is protected, you need to use a mutex. In this case, a
    TQMutexPool would be ideal.

    Code to calculate the square of a number would then look something
    like this:

    \code
    void calcSquare( Number *num )
    {
	TQMutexLocker locker( mutexpool.get( num ) );
	num.setNumber( num.number() * num.number() );
    }
    \endcode

    This function will safely calculate the square of a number, since
    it uses a mutex from a TQMutexPool. The mutex is locked and
    unlocked automatically by the TQMutexLocker class. See the
    TQMutexLocker documentation for more details.
*/

/*!
    Constructs  a TQMutexPool, reserving space for \a size TQMutexes. If
    \a recursive is TRUE, all TQMutexes in the pool will be recursive
    mutexes; otherwise they will all be non-recursive (the default).

    The TQMutexes are created when needed, and deleted when the
    TQMutexPool is destructed.
*/
TQMutexPool::TQMutexPool( bool recursive, int size )
    : mutex( FALSE ), count( size ), recurs( recursive )
{
    mutexes = new TQMutex*[count];
    for ( int index = 0; index < count; ++index ) {
	mutexes[index] = 0;
    }
}

/*!
    Destructs a TQMutexPool. All TQMutexes that were created by the pool
    are deleted.
*/
TQMutexPool::~TQMutexPool()
{
    TQMutexLocker locker( &mutex );
    for ( int index = 0; index < count; ++index ) {
	delete mutexes[index];
	mutexes[index] = 0;
    }
    delete [] mutexes;
    mutexes = 0;
}

/*!
    Returns a TQMutex from the pool. TQMutexPool uses the value \a
    address to determine which mutex is retured from the pool.
*/
TQMutex *TQMutexPool::get( void *address )
{
    int index = (int) ( (unsigned long) address % count );

    if ( ! mutexes[index] ) {
	// mutex not created, create one

	TQMutexLocker locker( &mutex );
	// we need to check once again that the mutex hasn't been created, since
	// 2 threads could be trying to create a mutex as the same index...
	if ( ! mutexes[index] ) {
	    mutexes[index] = new TQMutex( recurs );
	}
    }

    return mutexes[index];
}

#endif