qlock.cpp

Go to the documentation of this file.

/****************************************************************************
**
** Copyright (C) 2014 Digia Plc and/or its subsidiary(-ies).
** Contact: http://www.qt-project.org/legal
**
** This file is part of the QtGui module of the Qt Toolkit.
**
** $QT_BEGIN_LICENSE:LGPL$
** Commercial License Usage
** Licensees holding valid commercial Qt licenses may use this file in
** accordance with the commercial license agreement provided with the
** Software or, alternatively, in accordance with the terms contained in
** a written agreement between you and Digia.  For licensing terms and
** conditions see http://qt.digia.com/licensing.  For further information
** use the contact form at http://qt.digia.com/contact-us.
**
** GNU Lesser General Public License Usage
** Alternatively, this file may be used under the terms of the GNU Lesser
** General Public License version 2.1 as published by the Free Software
** Foundation and appearing in the file LICENSE.LGPL included in the
** packaging of this file.  Please review the following information to
** ensure the GNU Lesser General Public License version 2.1 requirements
** will be met: http://www.gnu.org/licenses/old-licenses/lgpl-2.1.html.
**
** In addition, as a special exception, Digia gives you certain additional
** rights.  These rights are described in the Digia Qt LGPL Exception
** version 1.1, included in the file LGPL_EXCEPTION.txt in this package.
**
** GNU General Public License Usage
** Alternatively, this file may be used under the terms of the GNU
** General Public License version 3.0 as published by the Free Software
** Foundation and appearing in the file LICENSE.GPL included in the
** packaging of this file.  Please review the following information to
** ensure the GNU General Public License version 3.0 requirements will be
** met: http://www.gnu.org/copyleft/gpl.html.
**
**
** $QT_END_LICENSE$
**
****************************************************************************/

#include "qlock_p.h"

#ifdef QT_NO_QWS_MULTIPROCESS

QT_BEGIN_NAMESPACE

/* no multiprocess - use a dummy */

QLock::QLock(const QString & /*filename*/, char /*id*/, bool /*create*/)
    : type(Read), data(0)
{
}

QLock::~QLock()
{
}

bool QLock::isValid() const
{
    return true;
}

void QLock::lock(Type t)
{
    data = (QLockData *)-1;
    type = t;
}

void QLock::unlock()
{
    data = 0;
}

bool QLock::locked() const
{
    return data;
}

QT_END_NAMESPACE

#else // QT_NO_QWS_MULTIPROCESS

#if defined(Q_OS_DARWIN)
#  define QT_NO_SEMAPHORE
#endif

#include "qwssignalhandler_p.h"

#include <unistd.h>
#include <sys/types.h>
#include <sys/ipc.h>
#if defined(QT_NO_SEMAPHORE)
#  include <sys/stat.h>
#  include <sys/file.h>
#elif !defined(QT_POSIX_IPC)
#  include <sys/sem.h>
#else
#  include <semaphore.h>
#endif
#include <string.h>
#include <errno.h>

#include <private/qcore_unix_p.h> // overrides QT_OPEN

QT_BEGIN_NAMESPACE

#define MAX_LOCKS   200            // maximum simultaneous read locks

class QLockData
{
public:
#if defined(QT_NO_SEMAPHORE) || defined(QT_POSIX_IPC)
    QByteArray file;
#endif
#if !defined(QT_POSIX_IPC)
    int id;
#else
    sem_t *id;    // Read mode resource counter
    sem_t *rsem;  // Read mode lock
    sem_t *wsem;  // Write mode lock
#endif
    int count;
    bool owned;
};


QLock::QLock(const QString &filename, char id, bool create)
{
    data = new QLockData;
    data->count = 0;
#if defined(QT_NO_SEMAPHORE)
    data->file = filename.toLocal8Bit() + id;
    for (int x = 0; x < 2; ++x) {
        data->id = QT_OPEN(data->file.constData(), O_RDWR | (x ? O_CREAT : 0), S_IRWXU);
        if (data->id != -1 || !create) {
            data->owned = x;
            break;
        }
    }
#elif !defined(QT_POSIX_IPC)
    key_t semkey = ftok(filename.toLocal8Bit().constData(), id);
    data->id = semget(semkey, 0, 0);
    data->owned = create;
    if (create) {
        qt_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);
    }
#else
    data->file = filename.toLocal8Bit() + id;
    data->owned = create;

    char ids[3] = { 'c', 'r', 'w' };
    sem_t **sems[3] = { &data->id, &data->rsem, &data->wsem };
    unsigned short initialValues[3] = { MAX_LOCKS, 1, 1 };
    for (int i = 0; i < 3; ++i) {
        QByteArray file = data->file + ids[i];
        do {
            *sems[i] = sem_open(file.constData(), 0, 0666, 0);
        } while (*sems[i] == SEM_FAILED && errno == EINTR);
        if (create) {
            if (*sems[i] != SEM_FAILED) {
                sem_close(*sems[i]);
                sem_unlink(file.constData());
            }
            do {
                *sems[i] = sem_open(file.constData(), O_CREAT, 0666, initialValues[i]);
            } while (*sems[i] == SEM_FAILED && errno == EINTR);
        }
    }
#endif
    if (!isValid()) {
        qWarning("QLock::QLock: Cannot %s semaphore %s '%c' (%d, %s)",
                 (create ? "create" : "get"), qPrintable(filename), id,
                 errno, strerror(errno));
    }

#ifndef QT_NO_QWS_SIGNALHANDLER
    QWSSignalHandler::instance()->addLock(this);
#endif
}

QLock::~QLock()
{
#ifndef QT_NO_QWS_SIGNALHANDLER
    QWSSignalHandler::instance()->removeLock(this);
#endif

    while (locked())
        unlock();

#if defined(QT_NO_SEMAPHORE)
    if (isValid())
        QT_CLOSE(data->id);
#elif defined(QT_POSIX_IPC)
    if (data->id != SEM_FAILED)
        sem_close(data->id);
    if (data->rsem != SEM_FAILED)
        sem_close(data->rsem);
    if (data->wsem != SEM_FAILED)
        sem_close(data->wsem);
#endif

    if (data->owned) {
#if defined(QT_NO_SEMAPHORE)
        unlink(data->file.constData());
#elif !defined(QT_POSIX_IPC)
        qt_semun semval;
        semval.val = 0;
        semctl(data->id, 0, IPC_RMID, semval);
#else
        char ids[3] = { 'c', 'r', 'w' };
        for (int i = 0; i < 3; ++i) {
            QByteArray file = data->file + ids[i];
            sem_unlink(file.constData());
        }
#endif
    }
    delete data;
    data = 0;
}

bool QLock::isValid() const
{
#if !defined(QT_POSIX_IPC)
    return data && data->id != -1;
#else
    return data && data->id != SEM_FAILED && data->rsem != SEM_FAILED && data->wsem != SEM_FAILED;
#endif
}

void QLock::lock(Type t)
{
    if (!isValid())
        return;

    if (!data->count) {
        type = t;

        int rv;
#if defined(QT_NO_SEMAPHORE)
        int op = type == Write ? LOCK_EX : LOCK_SH;

        EINTR_LOOP(rv, flock(data->id, op));
#elif !defined(QT_POSIX_IPC)
        sembuf sops;
        sops.sem_num = 0;
        sops.sem_op = type == Write ? -MAX_LOCKS : -1;
        sops.sem_flg = SEM_UNDO;

        EINTR_LOOP(rv, semop(data->id, &sops, 1));
#else
        if (type == Write) {
            EINTR_LOOP(rv, sem_wait(data->rsem));
            if (rv != -1) {
                EINTR_LOOP(rv, sem_wait(data->wsem));
                if (rv == -1)
                    sem_post(data->rsem);
            }
        } else {
            EINTR_LOOP(rv, sem_wait(data->wsem));
            if (rv != -1) {
                EINTR_LOOP(rv, sem_trywait(data->rsem));
                if (rv != -1 || errno == EAGAIN) {
                    EINTR_LOOP(rv, sem_wait(data->id));
                    if (rv == -1) {
                        int semval;
                        sem_getvalue(data->id, &semval);
                        if (semval == MAX_LOCKS)
                            sem_post(data->rsem);
                    }
                }
                rv = sem_post(data->wsem);
            }
        }
#endif
        if (rv == -1) {
            qDebug("QLock::lock(): %s", strerror(errno));
            return;
        }
    } else if (type == Read && t == Write) {
        qDebug("QLock::lock(): Attempt to lock for write while locked for read");
    }
    data->count++;
}

void QLock::unlock()
{
    if (!isValid())
        return;

    if (data->count > 0) {
        data->count--;
        if (!data->count) {
            int rv;
#if defined(QT_NO_SEMAPHORE)
            EINTR_LOOP(rv, flock(data->id, LOCK_UN));
#elif !defined(QT_POSIX_IPC)
            sembuf sops;
            sops.sem_num = 0;
            sops.sem_op = type == Write ? MAX_LOCKS : 1;
            sops.sem_flg = SEM_UNDO;

            EINTR_LOOP(rv, semop(data->id, &sops, 1));
#else
            if (type == Write) {
                sem_post(data->wsem);
                rv = sem_post(data->rsem);
            } else {
                EINTR_LOOP(rv, sem_wait(data->wsem));
                if (rv != -1) {
                    sem_post(data->id);
                    int semval;
                    sem_getvalue(data->id, &semval);
                    if (semval == MAX_LOCKS)
                        sem_post(data->rsem);
                    rv = sem_post(data->wsem);
                }
            }
#endif
            if (rv == -1)
                qDebug("QLock::unlock(): %s", strerror(errno));
        }
    } else {
        qDebug("QLock::unlock(): Unlock without corresponding lock");
    }
}

bool QLock::locked() const
{
    return isValid() && data->count > 0;
}

QT_END_NAMESPACE

#endif // QT_NO_QWS_MULTIPROCESS