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 Q_NO_SEMAPHORE
#endif

#include "qwssignalhandler_p.h"

#include <unistd.h>
#include <sys/types.h>
#include <sys/ipc.h>
#if defined(Q_NO_SEMAPHORE)
#  include <sys/stat.h>
#  include <sys/file.h>
#else
#  include <sys/sem.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:
#ifdef Q_NO_SEMAPHORE
    QByteArray file;
#endif // Q_NO_SEMAPHORE
    int id;
    int count;
    bool owned;
};

/*!
    \class QLock
    \brief The QLock class is a wrapper for a System V 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;
#ifdef Q_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;
        }
    }
#else
    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);
    }
#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();
#ifdef Q_NO_SEMAPHORE
    if (isValid())
        QT_CLOSE(data->id);
#endif
    if (data->owned) {
#ifdef Q_NO_SEMAPHORE
        unlink(data->file.constData());
#else
        qt_semun semval;
        semval.val = 0;
        semctl(data->id, 0, IPC_RMID, semval);
#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
{
    return data && data->id != -1;
}

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

        int rv;
#ifdef Q_NO_SEMAPHORE
        int op = type == Write ? LOCK_EX : LOCK_SH;

        EINTR_LOOP(rv, flock(data->id, op));
#else
        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));
#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 (data->count) {
        data->count--;
        if (!data->count) {
            int rv;
#ifdef Q_NO_SEMAPHORE
            EINTR_LOOP(rv, flock(data->id, LOCK_UN));
#else
            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));
#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