path: root/src/gui/embedded/qlock.cpp

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#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;
};


/*!
    \class QLock
    \brief The QLock class is a wrapper for a system shared semaphore.

    \ingroup qws

    \internal

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

/*!
    \enum QLock::Type

    \value Read
    \value Write
*/

/*!
    Creates a lock. \a filename is the file path of the Unix-domain
    socket the \l{Qt for Embedded Linux} 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 for Embedded Linux server does); if \a
    create is false the lock should exist already (as the Qt for Embedded Linux
    client expects).
*/
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
}

/*!
    Destroys a lock
*/
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;
}

/*!
    Returns true if the lock constructor was successful; returns false if
    the lock could not be created or was not available to connect to.
*/
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
}

/*!
    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)
{
    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++;
}

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

/*!
    Returns true if the lock is currently held by the current process;
    otherwise returns false.
*/
bool QLock::locked() const
{
    return isValid() && data->count > 0;
}

QT_END_NAMESPACE

#endif // QT_NO_QWS_MULTIPROCESS