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// Copyright (C) 2015 Konstantin Ritt <ritt.ks@gmail.com>
// Copyright (C) 2016 The Qt Company Ltd.
// Copyright (C) 2015 Klarälvdalens Datakonsult AB, a KDAB Group company, info@kdab.com, author Tobias Koenig <tobias.koenig@kdab.com>
// Copyright (C) 2022 Intel Corporation.
// SPDX-License-Identifier: LicenseRef-Qt-Commercial OR LGPL-3.0-only OR GPL-2.0-only OR GPL-3.0-only
#include "qsystemsemaphore.h"
#include "qsystemsemaphore_p.h"
#include <qdebug.h>
#include <qfile.h>
#include <qcoreapplication.h>
#if QT_CONFIG(posix_sem)
#include <sys/types.h>
#include <fcntl.h>
#include <errno.h>
#ifdef Q_OS_UNIX
# include "private/qcore_unix_p.h"
#else
# define QT_EINTR_LOOP_VAL(var, val, cmd) \
(void)var; var = cmd
# define QT_EINTR_LOOP(var, cmd) QT_EINTR_LOOP_VAL(var, -1, cmd)
#endif
// OpenBSD 4.2 doesn't define EIDRM, see BUGS section:
// http://www.openbsd.org/cgi-bin/man.cgi?query=semop&manpath=OpenBSD+4.2
#if defined(Q_OS_OPENBSD) && !defined(EIDRM)
#define EIDRM EINVAL
#endif
QT_BEGIN_NAMESPACE
using namespace Qt::StringLiterals;
bool QSystemSemaphorePosix::runtimeSupportCheck()
{
static const bool result = []() {
sem_open("/", 0, 0, 0); // this WILL fail
return errno != ENOSYS;
}();
return result;
}
bool QSystemSemaphorePosix::handle(QSystemSemaphorePrivate *self, QSystemSemaphore::AccessMode mode)
{
if (semaphore != SEM_FAILED)
return true; // we already have a semaphore
const QByteArray semName = QFile::encodeName(self->nativeKey.nativeKey());
if (semName.isEmpty()) {
self->setError(QSystemSemaphore::KeyError,
QSystemSemaphore::tr("%1: key is empty")
.arg("QSystemSemaphore::handle"_L1));
return false;
}
// Always try with O_EXCL so we know whether we created the semaphore.
int oflag = O_CREAT | O_EXCL;
for (int tryNum = 0, maxTries = 1; tryNum < maxTries; ++tryNum) {
do {
semaphore = ::sem_open(semName.constData(), oflag, 0600, self->initialValue);
} while (semaphore == SEM_FAILED && errno == EINTR);
if (semaphore == SEM_FAILED && errno == EEXIST) {
if (mode == QSystemSemaphore::Create) {
if (::sem_unlink(semName.constData()) == -1 && errno != ENOENT) {
self->setUnixErrorString("QSystemSemaphore::handle (sem_unlink)"_L1);
return false;
}
// Race condition: the semaphore might be recreated before
// we call sem_open again, so we'll retry several times.
maxTries = 3;
} else {
// Race condition: if it no longer exists at the next sem_open
// call, we won't realize we created it, so we'll leak it later.
oflag &= ~O_EXCL;
maxTries = 2;
}
} else {
break;
}
}
if (semaphore == SEM_FAILED) {
self->setUnixErrorString("QSystemSemaphore::handle"_L1);
return false;
}
createdSemaphore = (oflag & O_EXCL) != 0;
return true;
}
void QSystemSemaphorePosix::cleanHandle(QSystemSemaphorePrivate *self)
{
if (semaphore != SEM_FAILED) {
if (::sem_close(semaphore) == -1) {
self->setUnixErrorString("QSystemSemaphore::cleanHandle (sem_close)"_L1);
#if defined QSYSTEMSEMAPHORE_DEBUG
qDebug("QSystemSemaphore::cleanHandle sem_close failed.");
#endif
}
semaphore = SEM_FAILED;
}
if (createdSemaphore) {
const QByteArray semName = QFile::encodeName(self->nativeKey.nativeKey());
if (::sem_unlink(semName) == -1 && errno != ENOENT) {
self->setUnixErrorString("QSystemSemaphore::cleanHandle (sem_unlink)"_L1);
#if defined QSYSTEMSEMAPHORE_DEBUG
qDebug("QSystemSemaphorePosix::cleanHandle sem_unlink failed.");
#endif
}
createdSemaphore = false;
}
}
bool QSystemSemaphorePosix::modifySemaphore(QSystemSemaphorePrivate *self, int count)
{
if (!handle(self, QSystemSemaphore::Open))
return false;
if (count > 0) {
int cnt = count;
do {
if (::sem_post(semaphore) == -1) {
#if defined(Q_OS_VXWORKS)
if (errno == EINVAL) {
semaphore = SEM_FAILED;
return modifySemaphore(self, cnt);
}
#endif
self->setUnixErrorString("QSystemSemaphore::modifySemaphore (sem_post)"_L1);
#if defined QSYSTEMSEMAPHORE_DEBUG
qDebug("QSystemSemaphorePosix::modify sem_post failed %d %d", count, errno);
#endif
// rollback changes to preserve the SysV semaphore behavior
for ( ; cnt < count; ++cnt) {
int res;
QT_EINTR_LOOP(res, ::sem_wait(semaphore));
}
return false;
}
--cnt;
} while (cnt > 0);
} else {
int res;
QT_EINTR_LOOP(res, ::sem_wait(semaphore));
if (res == -1) {
// If the semaphore was removed be nice and create it and then modifySemaphore again
if (errno == EINVAL || errno == EIDRM) {
semaphore = SEM_FAILED;
return modifySemaphore(self, count);
}
self->setUnixErrorString("QSystemSemaphore::modifySemaphore (sem_wait)"_L1);
#if defined QSYSTEMSEMAPHORE_DEBUG
qDebug("QSystemSemaphorePosix::modify sem_wait failed %d %d", count, errno);
#endif
return false;
}
}
self->clearError();
return true;
}
QT_END_NAMESPACE
#endif // QT_CONFIG(posix_sem)
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