1// Copyright (C) 2015 Konstantin Ritt <ritt.ks@gmail.com>
2// Copyright (C) 2016 The Qt Company Ltd.
3// Copyright (C) 2015 Klarälvdalens Datakonsult AB, a KDAB Group company, info@kdab.com, author Tobias Koenig <tobias.koenig@kdab.com>
4// Copyright (C) 2022 Intel Corporation.
5// SPDX-License-Identifier: LicenseRef-Qt-Commercial OR LGPL-3.0-only OR GPL-2.0-only OR GPL-3.0-only
6
7#include "qsystemsemaphore.h"
8#include "qsystemsemaphore_p.h"
9
10#include <qdebug.h>
11#include <qfile.h>
12#include <qcoreapplication.h>
13
14#if QT_CONFIG(posix_sem)
15
16#include <sys/types.h>
17#include <fcntl.h>
18#include <errno.h>
19
20#ifdef Q_OS_UNIX
21# include "private/qcore_unix_p.h"
22#else
23#define EINTR_LOOP_VAL(var, val, cmd) \
24 (void)var; var = cmd
25#define EINTR_LOOP(var, cmd) EINTR_LOOP_VAL(var, -1, cmd)
26#endif
27
28// OpenBSD 4.2 doesn't define EIDRM, see BUGS section:
29// http://www.openbsd.org/cgi-bin/man.cgi?query=semop&manpath=OpenBSD+4.2
30#if defined(Q_OS_OPENBSD) && !defined(EIDRM)
31#define EIDRM EINVAL
32#endif
33
34QT_BEGIN_NAMESPACE
35
36using namespace Qt::StringLiterals;
37
38bool QSystemSemaphorePosix::runtimeSupportCheck()
39{
40 static const bool result = []() {
41 sem_open(name: "/", oflag: 0, 0, 0); // this WILL fail
42 return errno != ENOSYS;
43 }();
44 return result;
45}
46
47bool QSystemSemaphorePosix::handle(QSystemSemaphorePrivate *self, QSystemSemaphore::AccessMode mode)
48{
49 if (semaphore != SEM_FAILED)
50 return true; // we already have a semaphore
51
52 const QByteArray semName = QFile::encodeName(fileName: self->nativeKey.nativeKey());
53 if (semName.isEmpty()) {
54 self->setError(e: QSystemSemaphore::KeyError,
55 message: QSystemSemaphore::tr(sourceText: "%1: key is empty")
56 .arg(a: "QSystemSemaphore::handle"_L1));
57 return false;
58 }
59
60 // Always try with O_EXCL so we know whether we created the semaphore.
61 int oflag = O_CREAT | O_EXCL;
62 for (int tryNum = 0, maxTries = 1; tryNum < maxTries; ++tryNum) {
63 do {
64 semaphore = ::sem_open(name: semName.constData(), oflag: oflag, 0600, self->initialValue);
65 } while (semaphore == SEM_FAILED && errno == EINTR);
66 if (semaphore == SEM_FAILED && errno == EEXIST) {
67 if (mode == QSystemSemaphore::Create) {
68 if (::sem_unlink(name: semName.constData()) == -1 && errno != ENOENT) {
69 self->setUnixErrorString("QSystemSemaphore::handle (sem_unlink)"_L1);
70 return false;
71 }
72 // Race condition: the semaphore might be recreated before
73 // we call sem_open again, so we'll retry several times.
74 maxTries = 3;
75 } else {
76 // Race condition: if it no longer exists at the next sem_open
77 // call, we won't realize we created it, so we'll leak it later.
78 oflag &= ~O_EXCL;
79 maxTries = 2;
80 }
81 } else {
82 break;
83 }
84 }
85
86 if (semaphore == SEM_FAILED) {
87 self->setUnixErrorString("QSystemSemaphore::handle"_L1);
88 return false;
89 }
90
91 createdSemaphore = (oflag & O_EXCL) != 0;
92
93 return true;
94}
95
96void QSystemSemaphorePosix::cleanHandle(QSystemSemaphorePrivate *self)
97{
98 if (semaphore != SEM_FAILED) {
99 if (::sem_close(sem: semaphore) == -1) {
100 self->setUnixErrorString("QSystemSemaphore::cleanHandle (sem_close)"_L1);
101#if defined QSYSTEMSEMAPHORE_DEBUG
102 qDebug("QSystemSemaphore::cleanHandle sem_close failed.");
103#endif
104 }
105 semaphore = SEM_FAILED;
106 }
107
108 if (createdSemaphore) {
109 const QByteArray semName = QFile::encodeName(fileName: self->nativeKey.nativeKey());
110 if (::sem_unlink(name: semName) == -1 && errno != ENOENT) {
111 self->setUnixErrorString("QSystemSemaphore::cleanHandle (sem_unlink)"_L1);
112#if defined QSYSTEMSEMAPHORE_DEBUG
113 qDebug("QSystemSemaphorePosix::cleanHandle sem_unlink failed.");
114#endif
115 }
116 createdSemaphore = false;
117 }
118}
119
120bool QSystemSemaphorePosix::modifySemaphore(QSystemSemaphorePrivate *self, int count)
121{
122 if (!handle(self, mode: QSystemSemaphore::Open))
123 return false;
124
125 if (count > 0) {
126 int cnt = count;
127 do {
128 if (::sem_post(sem: semaphore) == -1) {
129 self->setUnixErrorString("QSystemSemaphore::modifySemaphore (sem_post)"_L1);
130#if defined QSYSTEMSEMAPHORE_DEBUG
131 qDebug("QSystemSemaphorePosix::modify sem_post failed %d %d", count, errno);
132#endif
133 // rollback changes to preserve the SysV semaphore behavior
134 for ( ; cnt < count; ++cnt) {
135 int res;
136 EINTR_LOOP(res, ::sem_wait(semaphore));
137 }
138 return false;
139 }
140 --cnt;
141 } while (cnt > 0);
142 } else {
143 int res;
144 EINTR_LOOP(res, ::sem_wait(semaphore));
145 if (res == -1) {
146 // If the semaphore was removed be nice and create it and then modifySemaphore again
147 if (errno == EINVAL || errno == EIDRM) {
148 semaphore = SEM_FAILED;
149 return modifySemaphore(self, count);
150 }
151 self->setUnixErrorString("QSystemSemaphore::modifySemaphore (sem_wait)"_L1);
152#if defined QSYSTEMSEMAPHORE_DEBUG
153 qDebug("QSystemSemaphorePosix::modify sem_wait failed %d %d", count, errno);
154#endif
155 return false;
156 }
157 }
158
159 self->clearError();
160 return true;
161}
162
163QT_END_NAMESPACE
164
165#endif // QT_CONFIG(posix_sem)
166

source code of qtbase/src/corelib/ipc/qsystemsemaphore_posix.cpp