path: root/src/kernel/qlock.cpp

/****************************************************************************
**
** Definition of QLock class. This manages interprocess locking
**
** Created : 20000406
**
** Copyright (C) 2000-2008 Trolltech ASA.  All rights reserved.
**
** This file is part of the kernel module of the Qt GUI Toolkit.
**
** This file may be used under the terms of the GNU General
** Public License versions 2.0 or 3.0 as published by the Free
** Software Foundation and appearing in the files LICENSE.GPL2
** and LICENSE.GPL3 included in the packaging of this file.
** Alternatively you may (at your option) use any later version
** of the GNU General Public License if such license has been
** publicly approved by Trolltech ASA (or its successors, if any)
** and the KDE Free Qt Foundation.
**
** Please review the following information to ensure GNU General
** Public Licensing requirements will be met:
** http://trolltech.com/products/qt/licenses/licensing/opensource/.
** If you are unsure which license is appropriate for your use, please
** review the following information:
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**********************************************************************/

#include "qlock_p.h"

#ifndef QT_NO_QWS_MULTIPROCESS

#include <unistd.h>
#include <sys/types.h>
#if defined(Q_OS_MACX)
#define Q_NO_SEMAPHORE
#include <sys/stat.h>
#include <sys/file.h>
#else
#include <sys/sem.h>
#if defined(__GNU_LIBRARY__) && !defined(_SEM_SEMUN_UNDEFINED) \
    || defined(Q_OS_FREEBSD) || defined(Q_OS_OPENBSD) || defined(Q_OS_NETBSD) || defined(Q_OS_BSDI)
/* union semun is defined by including <sys/sem.h> */
#else
/* according to X/OPEN we have to define it ourselves */
union semun {
    int val;                    /* value for SETVAL */
    struct semid_ds *buf;       /* buffer for IPC_STAT, IPC_SET */
    unsigned short *array;      /* array for GETALL, SETALL */
};
#endif
#endif
#include <sys/ipc.h>
#include <string.h>
#include <errno.h>

#define MAX_LOCKS   200	    // maximum simultaneous read locks

class QLockData
{
public:
#ifdef Q_NO_SEMAPHORE
    QCString file;
#endif
    int id;
    int count;
    bool owned;
};

#endif

/*!
    \class QLock qlock_p.h
    \brief The QLock class is a wrapper for a System V shared semaphore.

    \ingroup qws
    \ingroup io

    \internal

    It is used by Qt/Embedded for synchronizing access to the graphics
    card and shared memory region between processes.
*/

/*!
    \enum QLock::Type

    \value Read
    \value Write
*/

/*!
    \fn QLock::QLock( const QString &filename, char id, bool create )

    Creates a lock. \a filename is the file path of the Unix-domain
    socket the Qt/Embedded client is using. \a id is the name of the
    particular lock to be created on that socket. If \a create is TRUE
    the lock is to be created (as the Qt/Embedded server does); if \a
    create is FALSE the lock should exist already (as the Qt/Embedded
    client expects).
*/

QLock::QLock( const QString &filename, char id, bool create )
{
#ifndef QT_NO_QWS_MULTIPROCESS
    data = new QLockData;
    data->count = 0;
#ifdef Q_NO_SEMAPHORE
    data->file = QString(filename+id).local8Bit();
    for(int x = 0; x < 2; x++) {
	data->id = open(data->file, O_RDWR | (x ? O_CREAT : 0), S_IRWXU);
	if(data->id != -1 || !create) {
	    data->owned = x;
	    break;
	}
    }
#else
    key_t semkey = ftok(filename, id);
    data->id = semget(semkey,0,0);
    data->owned = create;
    if ( create ) {
	semun arg; arg.val = 0;
	if ( data->id != -1 )
	    semctl(data->id,0,IPC_RMID,arg);
	data->id = semget(semkey,1,IPC_CREAT|0600);
	arg.val = MAX_LOCKS;
	semctl(data->id,0,SETVAL,arg);
    }
#endif
    if ( data->id == -1 ) {
	qWarning( "Cannot %s semaphore %s \'%c\'",
	    create ? "create" : "get", filename.latin1(), id );
	qDebug("Error %d %s\n",errno,strerror(errno));
    }
#endif
}

/*!
    \fn QLock::~QLock()

    Destroys a lock
*/

QLock::~QLock()
{
#ifndef QT_NO_QWS_MULTIPROCESS
    if ( locked() )
	unlock();
#ifdef Q_NO_SEMAPHORE
    if(isValid()) {
	close(data->id);
	if( data->owned )
	    unlink( data->file );
    }
#else
    if(data->owned) {
	semun arg; arg.val = 0;
	semctl( data->id, 0, IPC_RMID, arg );
    }
#endif
    delete data;
#endif
}

/*!
    \fn bool QLock::isValid() const

    Returns TRUE if the lock constructor was succesful; returns FALSE if
    the lock could not be created or was not available to connect to.
*/

bool QLock::isValid() const
{
#ifndef QT_NO_QWS_MULTIPROCESS
    return (data->id != -1);
#else
    return TRUE;
#endif
}

/*!
    Locks the semaphore with a lock of type \a t. Locks can either be
    \c Read or \c Write. If a lock is \c Read, attempts by other
    processes to obtain \c Read locks will succeed, and \c Write
    attempts will block until the lock is unlocked. If locked as \c
    Write, all attempts to lock by other processes will block until
    the lock is unlocked. Locks are stacked: i.e. a given QLock can be
    locked multiple times by the same process without blocking, and
    will only be unlocked after a corresponding number of unlock()
    calls.
*/

void QLock::lock( Type t )
{
#ifndef QT_NO_QWS_MULTIPROCESS
    if ( !data->count ) {
#ifdef Q_NO_SEMAPHORE
	int op = LOCK_SH;
	if(t == Write)
	    op = LOCK_EX;
	for( int rv=1; rv; ) {
	    rv = flock(data->id, op);
	    if (rv == -1 && errno != EINTR)
		qDebug("Semop lock failure %s",strerror(errno));
	}
#else
	sembuf sops;
	sops.sem_num = 0;
	sops.sem_flg = SEM_UNDO;

	if ( t == Write ) {
	    sops.sem_op = -MAX_LOCKS;
	    type = Write;
	} else {
	    sops.sem_op = -1;
	    type = Read;
	}

	int rv;
	do {
	    rv = semop(data->id,&sops,1);
	    if (rv == -1 && errno != EINTR)
		qDebug("Semop lock failure %s",strerror(errno));
	} while ( rv == -1 && errno == EINTR );
#endif
    }
    data->count++;
#endif
}

/*!
    \fn void QLock::unlock()

    Unlocks the semaphore. If other processes were blocking waiting to
    lock() the semaphore, one of them will wake up and succeed in
    lock()ing.
*/

void QLock::unlock()
{
#ifndef QT_NO_QWS_MULTIPROCESS
    if( data->count ) {
	data->count--;
	if( !data->count ) {
#ifdef Q_NO_SEMAPHORE
	    for( int rv=1; rv; ) {
		rv = flock(data->id, LOCK_UN);
		if (rv == -1 && errno != EINTR)
		    qDebug("Semop lock failure %s",strerror(errno));
	    }
#else
	    sembuf sops;
	    sops.sem_num = 0;
	    sops.sem_op = 1;
	    sops.sem_flg = SEM_UNDO;
	    if ( type == Write )
		sops.sem_op = MAX_LOCKS;

	    int rv;
	    do {
		rv = semop(data->id,&sops,1);
		if (rv == -1 && errno != EINTR)
		    qDebug("Semop unlock failure %s",strerror(errno));
	    } while ( rv == -1 && errno == EINTR );
#endif
	}
    } else {
	qDebug("Unlock without corresponding lock");
    }
#endif
}

/*!
    \fn bool QLock::locked() const

    Returns TRUE if the lock is currently held by the current process;
    otherwise returns FALSE.
*/

bool QLock::locked() const
{
#ifndef QT_NO_QWS_MULTIPROCESS
    return (data->count > 0);
#else
    return FALSE;
#endif
}