1/****************************************************************************
2**
3** Copyright (C) 2015 Konstantin Ritt <ritt.ks@gmail.com>
4** Copyright (C) 2016 The Qt Company Ltd.
5** Copyright (C) 2015 Klarälvdalens Datakonsult AB, a KDAB Group company, info@kdab.com, author Tobias Koenig <tobias.koenig@kdab.com>
6** Contact: https://www.qt.io/licensing/
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40****************************************************************************/
41
42#include "qsystemsemaphore.h"
43#include "qsystemsemaphore_p.h"
44
45#include <qdebug.h>
46#include <qfile.h>
47#include <qcoreapplication.h>
48
49#ifdef QT_POSIX_IPC
50
51#ifndef QT_NO_SYSTEMSEMAPHORE
52
53#include <sys/types.h>
54#include <fcntl.h>
55#include <errno.h>
56
57#include "private/qcore_unix_p.h"
58
59// OpenBSD 4.2 doesn't define EIDRM, see BUGS section:
60// http://www.openbsd.org/cgi-bin/man.cgi?query=semop&manpath=OpenBSD+4.2
61#if defined(Q_OS_OPENBSD) && !defined(EIDRM)
62#define EIDRM EINVAL
63#endif
64
65QT_BEGIN_NAMESPACE
66
67bool QSystemSemaphorePrivate::handle(QSystemSemaphore::AccessMode mode)
68{
69 if (semaphore != SEM_FAILED)
70 return true; // we already have a semaphore
71
72 if (fileName.isEmpty()) {
73 errorString = QCoreApplication::tr("%1: key is empty", "QSystemSemaphore").arg(QLatin1String("QSystemSemaphore::handle"));
74 error = QSystemSemaphore::KeyError;
75 return false;
76 }
77
78 const QByteArray semName = QFile::encodeName(fileName);
79
80 // Always try with O_EXCL so we know whether we created the semaphore.
81 int oflag = O_CREAT | O_EXCL;
82 for (int tryNum = 0, maxTries = 1; tryNum < maxTries; ++tryNum) {
83 do {
84 semaphore = ::sem_open(semName.constData(), oflag, 0600, initialValue);
85 } while (semaphore == SEM_FAILED && errno == EINTR);
86 if (semaphore == SEM_FAILED && errno == EEXIST) {
87 if (mode == QSystemSemaphore::Create) {
88 if (::sem_unlink(semName.constData()) == -1 && errno != ENOENT) {
89 setErrorString(QLatin1String("QSystemSemaphore::handle (sem_unlink)"));
90 return false;
91 }
92 // Race condition: the semaphore might be recreated before
93 // we call sem_open again, so we'll retry several times.
94 maxTries = 3;
95 } else {
96 // Race condition: if it no longer exists at the next sem_open
97 // call, we won't realize we created it, so we'll leak it later.
98 oflag &= ~O_EXCL;
99 maxTries = 2;
100 }
101 } else {
102 break;
103 }
104 }
105
106 if (semaphore == SEM_FAILED) {
107 setErrorString(QLatin1String("QSystemSemaphore::handle"));
108 return false;
109 }
110
111 createdSemaphore = (oflag & O_EXCL) != 0;
112
113 return true;
114}
115
116void QSystemSemaphorePrivate::cleanHandle()
117{
118 if (semaphore != SEM_FAILED) {
119 if (::sem_close(semaphore) == -1) {
120 setErrorString(QLatin1String("QSystemSemaphore::cleanHandle (sem_close)"));
121#if defined QSYSTEMSEMAPHORE_DEBUG
122 qDebug("QSystemSemaphore::cleanHandle sem_close failed.");
123#endif
124 }
125 semaphore = SEM_FAILED;
126 }
127
128 if (createdSemaphore) {
129 if (::sem_unlink(QFile::encodeName(fileName).constData()) == -1 && errno != ENOENT) {
130 setErrorString(QLatin1String("QSystemSemaphore::cleanHandle (sem_unlink)"));
131#if defined QSYSTEMSEMAPHORE_DEBUG
132 qDebug("QSystemSemaphore::cleanHandle sem_unlink failed.");
133#endif
134 }
135 createdSemaphore = false;
136 }
137}
138
139bool QSystemSemaphorePrivate::modifySemaphore(int count)
140{
141 if (!handle())
142 return false;
143
144 if (count > 0) {
145 int cnt = count;
146 do {
147 if (::sem_post(semaphore) == -1) {
148 setErrorString(QLatin1String("QSystemSemaphore::modifySemaphore (sem_post)"));
149#if defined QSYSTEMSEMAPHORE_DEBUG
150 qDebug("QSystemSemaphore::modify sem_post failed %d %d", count, errno);
151#endif
152 // rollback changes to preserve the SysV semaphore behavior
153 for ( ; cnt < count; ++cnt) {
154 int res;
155 EINTR_LOOP(res, ::sem_wait(semaphore));
156 }
157 return false;
158 }
159 --cnt;
160 } while (cnt > 0);
161 } else {
162 int res;
163 EINTR_LOOP(res, ::sem_wait(semaphore));
164 if (res == -1) {
165 // If the semaphore was removed be nice and create it and then modifySemaphore again
166 if (errno == EINVAL || errno == EIDRM) {
167 semaphore = SEM_FAILED;
168 return modifySemaphore(count);
169 }
170 setErrorString(QLatin1String("QSystemSemaphore::modifySemaphore (sem_wait)"));
171#if defined QSYSTEMSEMAPHORE_DEBUG
172 qDebug("QSystemSemaphore::modify sem_wait failed %d %d", count, errno);
173#endif
174 return false;
175 }
176 }
177
178 clearError();
179 return true;
180}
181
182QT_END_NAMESPACE
183
184#endif // QT_NO_SYSTEMSEMAPHORE
185
186#endif // QT_POSIX_IPC
187