qwslock.cpp

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#include "qwslock_p.h"

#ifndef QT_NO_QWS_MULTIPROCESS

#include "qwssignalhandler_p.h"

#include <stdint.h>
#include <stdio.h>
#include <errno.h>
#include <string.h>
#include <sys/types.h>
#include <sys/ipc.h>
#ifndef QT_POSIX_IPC
#include <sys/sem.h>
#endif
#include <sys/time.h>
#include <time.h>
#ifdef Q_OS_LINUX
#include <linux/version.h>
#endif
#include <unistd.h>

#include <private/qcore_unix_p.h>

QT_BEGIN_NAMESPACE

#ifdef QT_NO_SEMAPHORE
#error QWSLock currently requires semaphores
#endif

#ifdef QT_POSIX_IPC
#include <QtCore/QAtomicInt>

static QBasicAtomicInt localUniqueId = Q_BASIC_ATOMIC_INITIALIZER(1);
#endif

QWSLock::QWSLock(int id) : semId(id)
{
    static unsigned short initialValues[3] = { 1, 1, 0 };

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

#ifndef QT_POSIX_IPC
    if (semId == -1) {
        semId = semget(IPC_PRIVATE, 3, IPC_CREAT | 0666);
        if (semId == -1) {
            perror("QWSLock::QWSLock");
            qFatal("Unable to create semaphore");
        }

        qt_semun semval;
        semval.array = initialValues;
        if (semctl(semId, 0, SETALL, semval) == -1) {
            perror("QWSLock::QWSLock");
            qFatal("Unable to initialize semaphores");
        }
    }
#else
    sems[0] = sems[1] = sems[2] = SEM_FAILED;
    owned = false;

    if (semId == -1) {
        // ### generate really unique IDs
        semId = (getpid() << 16) + (localUniqueId.fetchAndAddRelaxed(1) % ushort(-1));
        owned = true;
    }

    QByteArray pfx = "/qwslock_" + QByteArray::number(semId, 16) + '_';
    QByteArray keys[3] = { pfx + "BackingStore", pfx + "Communication", pfx + "RegionEvent" };
    for (int i = 0; i < 3; ++i) {
        if (owned)
            sem_unlink(keys[i].constData());
        do {
            sems[i] = sem_open(keys[i].constData(), (owned ? O_CREAT : 0), 0666, initialValues[i]);
        } while (sems[i] == SEM_FAILED && errno == EINTR);
        if (sems[i] == SEM_FAILED) {
            perror("QWSLock::QWSLock");
            qFatal("Unable to %s semaphore", (owned ? "create" : "open"));
        }
    }
#endif

    lockCount[0] = lockCount[1] = 0;
}

QWSLock::~QWSLock()
{
#ifndef QT_NO_QWS_SIGNALHANDLER
    QWSSignalHandler::instance()->removeWSLock(this);
#endif

    if (semId != -1) {
#ifndef QT_POSIX_IPC
        qt_semun semval;
        semval.val = 0;
        semctl(semId, 0, IPC_RMID, semval);
        semId = -1;
#else
        // emulate the SEM_UNDO behavior for the BackingStore lock
        while (hasLock(BackingStore))
            unlock(BackingStore);

        QByteArray pfx = "/qwslock_" + QByteArray::number(semId, 16) + '_';
        QByteArray keys[3] = { pfx + "BackingStore", pfx + "Communication", pfx + "RegionEvent" };
        for (int i = 0; i < 3; ++i) {
            if (sems[i] != SEM_FAILED) {
                sem_close(sems[i]);
                sems[i] = SEM_FAILED;
            }
            if (owned)
                sem_unlink(keys[i].constData());
        }
#endif
    }
}

bool QWSLock::up(unsigned short semNum)
{
    int ret;

#ifndef QT_POSIX_IPC
    sembuf sops = { semNum, 1, 0 };
    // As the BackingStore lock is a mutex, and only one process may own
    // the lock, it's safe to use SEM_UNDO. On the other hand, the
    // Communication lock is locked by the client but unlocked by the
    // server and therefore can't use SEM_UNDO.
    if (semNum == BackingStore)
        sops.sem_flg |= SEM_UNDO;

    EINTR_LOOP(ret, semop(semId, &sops, 1));
#else
    ret = sem_post(sems[semNum]);
#endif
    if (ret == -1) {
        qDebug("QWSLock::up(): %s", strerror(errno));
        return false;
    }

    return true;
}

bool QWSLock::down(unsigned short semNum, int)
{
    int ret;

#ifndef QT_POSIX_IPC
    sembuf sops = { semNum, -1, 0 };
    // As the BackingStore lock is a mutex, and only one process may own
    // the lock, it's safe to use SEM_UNDO. On the other hand, the
    // Communication lock is locked by the client but unlocked by the
    // server and therefore can't use SEM_UNDO.
    if (semNum == BackingStore)
        sops.sem_flg |= SEM_UNDO;

    EINTR_LOOP(ret, semop(semId, &sops, 1));
#else
    EINTR_LOOP(ret, sem_wait(sems[semNum]));
#endif
    if (ret == -1) {
        qDebug("QWSLock::down(): %s", strerror(errno));
        return false;
    }

    return true;
}

int QWSLock::getValue(unsigned short semNum) const
{
    int ret;
#ifndef QT_POSIX_IPC
    ret = semctl(semId, semNum, GETVAL, 0);
#else
    if (sem_getvalue(sems[semNum], &ret) == -1)
        ret = -1;
#endif
    if (ret == -1)
        qDebug("QWSLock::getValue(): %s", strerror(errno));
    return ret;
}

bool QWSLock::lock(LockType type, int timeout)
{
    if (type == RegionEvent)
        return up(type);

    if (lockCount[type] > 0) {
        ++lockCount[type];
        return true;
    }

    if (down(type, timeout)) {
        ++lockCount[type];
        return true;
    }

    return false;
}

bool QWSLock::hasLock(LockType type)
{
    if (type == RegionEvent)
        return getValue(type) == 0;

    return lockCount[type] > 0;
}

void QWSLock::unlock(LockType type)
{
    if (type == RegionEvent) {
        down(type, -1);
        return;
    }

    if (lockCount[type] > 0) {
        --lockCount[type];
        if (lockCount[type] > 0)
            return;
    }

    up(type);
}

bool QWSLock::wait(LockType type, int timeout)
{
    bool ok = down(type, timeout);
    if (ok)
        unlock(type);
    return ok;
}

QT_END_NAMESPACE

#endif // QT_NO_QWS_MULTIPROCESS