QLock Class Reference

The QLock class is a wrapper for a system shared semaphore. More...

#include <qlock_p.h>

Public Types
enum	Type { Read, Write }

Public Functions
bool	isValid () const
	Returns true if the lock constructor was successful; returns false if the lock could not be created or was not available to connect to. More...
void	lock (Type type)
	Locks the semaphore with a lock of type t. More...
bool	locked () const
	Returns true if the lock is currently held by the current process; otherwise returns false. More...
	QLock (const QString &filename, char id, bool create=false)
	Creates a lock. More...
void	unlock ()
	Unlocks the semaphore. More...
	~QLock ()
	Destroys a lock. More...

Properties
QLockData *	data
Type	type

Detailed Description

The QLock class is a wrapper for a system shared semaphore.

Warning

This function is not part of the public interface.

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

Definition at line 62 of file qlock_p.h.

Enumerations

Type

enum QLock::Type

• Read
• Write

Enumerator
Read
Write

Definition at line 68 of file qlock_p.h.

{ Read, Write };

Constructors and Destructors

QLock()

QLock::QLock	(	const QString &	filename,
		char	id,
		bool	create = false
	)

Creates a lock.

filename is the file path of the Unix-domain socket the Qt for Embedded Linux client is using. id is the name of the particular lock to be created on that socket. If create is true the lock is to be created (as the Qt for Embedded Linux server does); if create is false the lock should exist already (as the Qt for Embedded Linux client expects).

Definition at line 158 of file qlock.cpp.

{
    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::~QLock

(

)

Destroys a lock.

Definition at line 221 of file qlock.cpp.

Referenced by QWSSignalHandler::clear().

{
#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;
}

Functions

isValid()

bool QLock::isValid

(

)

const

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

Definition at line 265 of file qlock.cpp.

{
#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
}

lock()

void QLock::lock

(

Type

t

)

Locks the semaphore with a lock of type t.

Locks can either be Read or Write. If a lock is Read, attempts by other processes to obtain Read locks will succeed, and Write attempts will block until the lock is unlocked. If locked as 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.

Definition at line 285 of file qlock.cpp.

{
    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++;
}

locked()

bool QLock::locked

(

)

const

Returns true if the lock is currently held by the current process; otherwise returns false.

Definition at line 391 of file qlock.cpp.

{
    return isValid() && data->count > 0;
}

unlock()

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 locking.

Definition at line 345 of file qlock.cpp.

{
    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");
    }
}

Properties

data

QLockData* QLock::data

private

Definition at line 77 of file qlock_p.h.

type

Type QLock::type

private

Definition at line 76 of file qlock_p.h.

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The documentation for this class was generated from the following files:

• /src/gui/embedded/qlock_p.h
• /src/gui/embedded/qlock.cpp