qlockfile.cpp

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1/****************************************************************************-
2**-
3** Copyright (C) 2013 David Faure <faure+bluesystems@kde.org>-
4** Copyright (C) 2015 The Qt Company Ltd.-
5** Contact: http://www.qt.io/licensing/-
6**-
7** This file is part of the QtCore module of the Qt Toolkit.-
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33****************************************************************************/-
34-
35#include "qlockfile.h"-
36#include "qlockfile_p.h"-
37-
38#include <QtCore/qthread.h>-
39#include <QtCore/qelapsedtimer.h>-
40#include <QtCore/qdatetime.h>-
41-
42QT_BEGIN_NAMESPACE-
43-
44/*!-
45 \class QLockFile-
46 \inmodule QtCore-
47 \brief The QLockFile class provides locking between processes using a file.-
48 \since 5.1-
49-
50 A lock file can be used to prevent multiple processes from accessing concurrently-
51 the same resource. For instance, a configuration file on disk, or a socket, a port,-
52 a region of shared memory...-
53-
54 Serialization is only guaranteed if all processes that access the shared resource-
55 use QLockFile, with the same file path.-
56-
57 QLockFile supports two use cases:-
58 to protect a resource for a short-term operation (e.g. verifying if a configuration-
59 file has changed before saving new settings), and for long-lived protection of a-
60 resource (e.g. a document opened by a user in an editor) for an indefinite amount of time.-
61-
62 When protecting for a short-term operation, it is acceptable to call lock() and wait-
63 until any running operation finishes.-
64 When protecting a resource over a long time, however, the application should always-
65 call setStaleLockTime(0) and then tryLock() with a short timeout, in order to-
66 warn the user that the resource is locked.-
67-
68 If the process holding the lock crashes, the lock file stays on disk and can prevent-
69 any other process from accessing the shared resource, ever. For this reason, QLockFile-
70 tries to detect such a "stale" lock file, based on the process ID written into the file.-
71 To cover the situation that the process ID got reused meanwhile, the current process name is-
72 compared to the name of the process that corresponds to the process ID from the lock file.-
73 If the process names differ, the lock file is considered stale.-
74 Additionally, the last modification time of the lock file (30s by default, for the use case of a-
75 short-lived operation) is taken into account.-
76 If the lock file is found to be stale, it will be deleted.-
77-
78 For the use case of protecting a resource over a long time, you should therefore call-
79 setStaleLockTime(0), and when tryLock() returns LockFailedError, inform the user-
80 that the document is locked, possibly using getLockInfo() for more details.-
81*/-
82-
83/*!-
84 \enum QLockFile::LockError-
85-
86 This enum describes the result of the last call to lock() or tryLock().-
87-
88 \value NoError The lock was acquired successfully.-
89 \value LockFailedError The lock could not be acquired because another process holds it.-
90 \value PermissionError The lock file could not be created, for lack of permissions-
91 in the parent directory.-
92 \value UnknownError Another error happened, for instance a full partition-
93 prevented writing out the lock file.-
94*/-
95-
96/*!-
97 Constructs a new lock file object.-
98 The object is created in an unlocked state.-
99 When calling lock() or tryLock(), a lock file named \a fileName will be created,-
100 if it doesn't already exist.-
101-
102 \sa lock(), unlock()-
103*/-
104QLockFile::QLockFile(const QString &fileName)-
105 : d_ptr(new QLockFilePrivate(fileName))-
106{-
107}
executed 4198 times by 32 tests: end of block
Executed by:
  • tst_QAbstractItemView
  • tst_QAccessibility
  • tst_QCalendarWidget
  • tst_QColorDialog
  • tst_QCommandLinkButton
  • tst_QCompleter
  • tst_QDateTimeEdit
  • tst_QErrorMessage
  • tst_QFileDialog2
  • tst_QFileIconProvider
  • tst_QFileSystemModel
  • tst_QFiledialog
  • tst_QGraphicsProxyWidget
  • tst_QIcon
  • tst_QLabel
  • tst_QLineEdit
  • tst_QLockFile
  • tst_QMessageBox
  • tst_QPlainTextEdit
  • tst_QPrinter
  • tst_QSettings
  • tst_QSidebar
  • tst_QStyle
  • tst_QStyleSheetStyle
  • tst_QSystemTrayIcon
  • ...
4198
108-
109/*!-
110 Destroys the lock file object.-
111 If the lock was acquired, this will release the lock, by deleting the lock file.-
112*/-
113QLockFile::~QLockFile()-
114{-
115 unlock();-
116}
executed 4198 times by 32 tests: end of block
Executed by:
  • tst_QAbstractItemView
  • tst_QAccessibility
  • tst_QCalendarWidget
  • tst_QColorDialog
  • tst_QCommandLinkButton
  • tst_QCompleter
  • tst_QDateTimeEdit
  • tst_QErrorMessage
  • tst_QFileDialog2
  • tst_QFileIconProvider
  • tst_QFileSystemModel
  • tst_QFiledialog
  • tst_QGraphicsProxyWidget
  • tst_QIcon
  • tst_QLabel
  • tst_QLineEdit
  • tst_QLockFile
  • tst_QMessageBox
  • tst_QPlainTextEdit
  • tst_QPrinter
  • tst_QSettings
  • tst_QSidebar
  • tst_QStyle
  • tst_QStyleSheetStyle
  • tst_QSystemTrayIcon
  • ...
4198
117-
118/*!-
119 Sets \a staleLockTime to be the time in milliseconds after which-
120 a lock file is considered stale.-
121 The default value is 30000, i.e. 30 seconds.-
122 If your application typically keeps the file locked for more than 30 seconds-
123 (for instance while saving megabytes of data for 2 minutes), you should set-
124 a bigger value using setStaleLockTime().-
125-
126 The value of \a staleLockTime is used by lock() and tryLock() in order-
127 to determine when an existing lock file is considered stale, i.e. left over-
128 by a crashed process. This is useful for the case where the PID got reused-
129 meanwhile, so one way to detect a stale lock file is by the fact that-
130 it has been around for a long time.-
131-
132 \sa staleLockTime()-
133*/-
134void QLockFile::setStaleLockTime(int staleLockTime)-
135{-
136 Q_D(QLockFile);-
137 d->staleLockTime = staleLockTime;-
138}
executed 1 time by 1 test: end of block
Executed by:
  • tst_QLockFile
1
139-
140/*!-
141 Returns the time in milliseconds after which-
142 a lock file is considered stale.-
143-
144 \sa setStaleLockTime()-
145*/-
146int QLockFile::staleLockTime() const-
147{-
148 Q_D(const QLockFile);-
149 return d->staleLockTime;
never executed: return d->staleLockTime;
0
150}-
151-
152/*!-
153 Returns \c true if the lock was acquired by this QLockFile instance,-
154 otherwise returns \c false.-
155-
156 \sa lock(), unlock(), tryLock()-
157*/-
158bool QLockFile::isLocked() const-
159{-
160 Q_D(const QLockFile);-
161 return d->isLocked;
executed 3 times by 2 tests: return d->isLocked;
Executed by:
  • tst_QLockFile
  • tst_qlockfile - unknown status
3
162}-
163-
164/*!-
165 Creates the lock file.-
166-
167 If another process (or another thread) has created the lock file already,-
168 this function will block until that process (or thread) releases it.-
169-
170 Calling this function multiple times on the same lock from the same-
171 thread without unlocking first is not allowed. This function will-
172 \e dead-lock when the file is locked recursively.-
173-
174 Returns \c true if the lock was acquired, false if it could not be acquired-
175 due to an unrecoverable error, such as no permissions in the parent directory.-
176-
177 \sa unlock(), tryLock()-
178*/-
179bool QLockFile::lock()-
180{-
181 return tryLock(-1);
executed 574 times by 8 tests: return tryLock(-1);
Executed by:
  • tst_QColorDialog
  • tst_QFileDialog2
  • tst_QFiledialog
  • tst_QGraphicsProxyWidget
  • tst_QLockFile
  • tst_QSettings
  • tst_languageChange
  • tst_qlockfile - unknown status
574
182}-
183-
184/*!-
185 Attempts to create the lock file. This function returns \c true if the-
186 lock was obtained; otherwise it returns \c false. If another process (or-
187 another thread) has created the lock file already, this function will-
188 wait for at most \a timeout milliseconds for the lock file to become-
189 available.-
190-
191 Note: Passing a negative number as the \a timeout is equivalent to-
192 calling lock(), i.e. this function will wait forever until the lock-
193 file can be locked if \a timeout is negative.-
194-
195 If the lock was obtained, it must be released with unlock()-
196 before another process (or thread) can successfully lock it.-
197-
198 Calling this function multiple times on the same lock from the same-
199 thread without unlocking first is not allowed, this function will-
200 \e always return false when attempting to lock the file recursively.-
201-
202 \sa lock(), unlock()-
203*/-
204bool QLockFile::tryLock(int timeout)-
205{-
206 Q_D(QLockFile);-
207 QElapsedTimer timer;-
208 if (timeout > 0)
timeout > 0Description
TRUEevaluated 4 times by 1 test
Evaluated by:
  • tst_QLockFile
FALSEevaluated 580 times by 8 tests
Evaluated by:
  • tst_QColorDialog
  • tst_QFileDialog2
  • tst_QFiledialog
  • tst_QGraphicsProxyWidget
  • tst_QLockFile
  • tst_QSettings
  • tst_languageChange
  • tst_qlockfile - unknown status
4-580
209 timer.start();
executed 4 times by 1 test: timer.start();
Executed by:
  • tst_QLockFile
4
210 int sleepTime = 100;-
211 forever {-
212 d->lockError = d->tryLock_sys();-
213 switch (d->lockError) {-
214 case NoError:
executed 578 times by 8 tests: case NoError:
Executed by:
  • tst_QColorDialog
  • tst_QFileDialog2
  • tst_QFiledialog
  • tst_QGraphicsProxyWidget
  • tst_QLockFile
  • tst_QSettings
  • tst_languageChange
  • tst_qlockfile - unknown status
578
215 d->isLocked = true;-
216 return true;
executed 578 times by 8 tests: return true;
Executed by:
  • tst_QColorDialog
  • tst_QFileDialog2
  • tst_QFiledialog
  • tst_QGraphicsProxyWidget
  • tst_QLockFile
  • tst_QSettings
  • tst_languageChange
  • tst_qlockfile - unknown status
578
217 case PermissionError:
executed 1 time by 1 test: case PermissionError:
Executed by:
  • tst_QLockFile
1
218 case UnknownError:
never executed: case UnknownError:
0
219 return false;
executed 1 time by 1 test: return false;
Executed by:
  • tst_QLockFile
1
220 case LockFailedError:
executed 17 times by 1 test: case LockFailedError:
Executed by:
  • tst_QLockFile
17
221 if (!d->isLocked && d->isApparentlyStale()) {
!d->isLockedDescription
TRUEevaluated 13 times by 1 test
Evaluated by:
  • tst_QLockFile
FALSEevaluated 4 times by 1 test
Evaluated by:
  • tst_QLockFile
d->isApparentlyStale()Description
TRUEevaluated 1 time by 1 test
Evaluated by:
  • tst_QLockFile
FALSEevaluated 12 times by 1 test
Evaluated by:
  • tst_QLockFile
1-13
222 // Stale lock from another thread/process-
223 // Ensure two processes don't remove it at the same time-
224 QLockFile rmlock(d->fileName + QStringLiteral(".rmlock"));
executed 1 time by 1 test: return qstring_literal_temp;
Executed by:
  • tst_QLockFile
1
225 if (rmlock.tryLock()) {
rmlock.tryLock()Description
TRUEevaluated 1 time by 1 test
Evaluated by:
  • tst_QLockFile
FALSEnever evaluated
0-1
226 if (d->isApparentlyStale() && d->removeStaleLock())
d->isApparentlyStale()Description
TRUEevaluated 1 time by 1 test
Evaluated by:
  • tst_QLockFile
FALSEnever evaluated
d->removeStaleLock()Description
TRUEevaluated 1 time by 1 test
Evaluated by:
  • tst_QLockFile
FALSEnever evaluated
0-1
227 continue;
executed 1 time by 1 test: continue;
Executed by:
  • tst_QLockFile
1
228 }
never executed: end of block
0
229 }
never executed: end of block
0
230 break;
executed 16 times by 1 test: break;
Executed by:
  • tst_QLockFile
16
231 }-
232 if (timeout == 0 || (timeout > 0 && timer.hasExpired(timeout)))
timeout == 0Description
TRUEevaluated 3 times by 1 test
Evaluated by:
  • tst_QLockFile
FALSEevaluated 13 times by 1 test
Evaluated by:
  • tst_QLockFile
timeout > 0Description
TRUEevaluated 9 times by 1 test
Evaluated by:
  • tst_QLockFile
FALSEevaluated 4 times by 1 test
Evaluated by:
  • tst_QLockFile
timer.hasExpired(timeout)Description
TRUEevaluated 2 times by 1 test
Evaluated by:
  • tst_QLockFile
FALSEevaluated 7 times by 1 test
Evaluated by:
  • tst_QLockFile
2-13
233 return false;
executed 5 times by 1 test: return false;
Executed by:
  • tst_QLockFile
5
234 QThread::msleep(sleepTime);-
235 if (sleepTime < 5 * 1000)
sleepTime < 5 * 1000Description
TRUEevaluated 11 times by 1 test
Evaluated by:
  • tst_QLockFile
FALSEnever evaluated
0-11
236 sleepTime *= 2;
executed 11 times by 1 test: sleepTime *= 2;
Executed by:
  • tst_QLockFile
11
237 }
executed 11 times by 1 test: end of block
Executed by:
  • tst_QLockFile
11
238 // not reached-
239 return false;
never executed: return false;
0
240}-
241-
242/*!-
243 \fn void QLockFile::unlock()-
244 Releases the lock, by deleting the lock file.-
245-
246 Calling unlock() without locking the file first, does nothing.-
247-
248 \sa lock(), tryLock()-
249*/-
250-
251/*!-
252 Retrieves information about the current owner of the lock file.-
253-
254 If tryLock() returns \c false, and error() returns LockFailedError,-
255 this function can be called to find out more information about the existing-
256 lock file:-
257 \list-
258 \li the PID of the application (returned in \a pid)-
259 \li the \a hostname it's running on (useful in case of networked filesystems),-
260 \li the name of the application which created it (returned in \a appname),-
261 \endlist-
262-
263 Note that tryLock() automatically deleted the file if there is no-
264 running application with this PID, so LockFailedError can only happen if there is-
265 an application with this PID (it could be unrelated though).-
266-
267 This can be used to inform users about the existing lock file and give them-
268 the choice to delete it. After removing the file using removeStaleLockFile(),-
269 the application can call tryLock() again.-
270-
271 This function returns \c true if the information could be successfully retrieved, false-
272 if the lock file doesn't exist or doesn't contain the expected data.-
273 This can happen if the lock file was deleted between the time where tryLock() failed-
274 and the call to this function. Simply call tryLock() again if this happens.-
275*/-
276bool QLockFile::getLockInfo(qint64 *pid, QString *hostname, QString *appname) const-
277{-
278 Q_D(const QLockFile);-
279 return d->getLockInfo(pid, hostname, appname);
executed 1 time by 1 test: return d->getLockInfo(pid, hostname, appname);
Executed by:
  • tst_QLockFile
1
280}-
281-
282bool QLockFilePrivate::getLockInfo(qint64 *pid, QString *hostname, QString *appname) const-
283{-
284 QFile reader(fileName);-
285 if (!reader.open(QIODevice::ReadOnly))
!reader.open(Q...ice::ReadOnly)Description
TRUEnever evaluated
FALSEevaluated 15 times by 1 test
Evaluated by:
  • tst_QLockFile
0-15
286 return false;
never executed: return false;
0
287-
288 QByteArray pidLine = reader.readLine();-
289 pidLine.chop(1);-
290 QByteArray appNameLine = reader.readLine();-
291 appNameLine.chop(1);-
292 QByteArray hostNameLine = reader.readLine();-
293 hostNameLine.chop(1);-
294 if (pidLine.isEmpty())
pidLine.isEmpty()Description
TRUEevaluated 2 times by 1 test
Evaluated by:
  • tst_QLockFile
FALSEevaluated 13 times by 1 test
Evaluated by:
  • tst_QLockFile
2-13
295 return false;
executed 2 times by 1 test: return false;
Executed by:
  • tst_QLockFile
2
296-
297 qint64 thePid = pidLine.toLongLong();-
298 if (pid)
pidDescription
TRUEevaluated 13 times by 1 test
Evaluated by:
  • tst_QLockFile
FALSEnever evaluated
0-13
299 *pid = thePid;
executed 13 times by 1 test: *pid = thePid;
Executed by:
  • tst_QLockFile
13
300 if (appname)
appnameDescription
TRUEevaluated 13 times by 1 test
Evaluated by:
  • tst_QLockFile
FALSEnever evaluated
0-13
301 *appname = QString::fromUtf8(appNameLine);
executed 13 times by 1 test: *appname = QString::fromUtf8(appNameLine);
Executed by:
  • tst_QLockFile
13
302 if (hostname)
hostnameDescription
TRUEevaluated 13 times by 1 test
Evaluated by:
  • tst_QLockFile
FALSEnever evaluated
0-13
303 *hostname = QString::fromUtf8(hostNameLine);
executed 13 times by 1 test: *hostname = QString::fromUtf8(hostNameLine);
Executed by:
  • tst_QLockFile
13
304 return thePid > 0;
executed 13 times by 1 test: return thePid > 0;
Executed by:
  • tst_QLockFile
13
305}-
306-
307/*!-
308 Attempts to forcefully remove an existing lock file.-
309-
310 Calling this is not recommended when protecting a short-lived operation: QLockFile-
311 already takes care of removing lock files after they are older than staleLockTime().-
312-
313 This method should only be called when protecting a resource for a long time, i.e.-
314 with staleLockTime(0), and after tryLock() returned LockFailedError, and the user-
315 agreed on removing the lock file.-
316-
317 Returns \c true on success, false if the lock file couldn't be removed. This happens-
318 on Windows, when the application owning the lock is still running.-
319*/-
320bool QLockFile::removeStaleLockFile()-
321{-
322 Q_D(QLockFile);-
323 if (d->isLocked) {
d->isLockedDescription
TRUEnever evaluated
FALSEnever evaluated
0
324 qWarning("removeStaleLockFile can only be called when not holding the lock");-
325 return false;
never executed: return false;
0
326 }-
327 return d->removeStaleLock();
never executed: return d->removeStaleLock();
0
328}-
329-
330/*!-
331 Returns the lock file error status.-
332-
333 If tryLock() returns \c false, this function can be called to find out-
334 the reason why the locking failed.-
335*/-
336QLockFile::LockError QLockFile::error() const-
337{-
338 Q_D(const QLockFile);-
339 return d->lockError;
executed 14 times by 1 test: return d->lockError;
Executed by:
  • tst_QLockFile
14
340}-
341-
342QT_END_NAMESPACE-
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