0
|
1 |
/****************************************************************************
|
|
2 |
**
|
|
3 |
** Copyright (C) 2009 Nokia Corporation and/or its subsidiary(-ies).
|
|
4 |
** All rights reserved.
|
|
5 |
** Contact: Nokia Corporation (qt-info@nokia.com)
|
|
6 |
**
|
|
7 |
** This file is part of the QtCore module of the Qt Toolkit.
|
|
8 |
**
|
|
9 |
** $QT_BEGIN_LICENSE:LGPL$
|
|
10 |
** No Commercial Usage
|
|
11 |
** This file contains pre-release code and may not be distributed.
|
|
12 |
** You may use this file in accordance with the terms and conditions
|
|
13 |
** contained in the Technology Preview License Agreement accompanying
|
|
14 |
** this package.
|
|
15 |
**
|
|
16 |
** GNU Lesser General Public License Usage
|
|
17 |
** Alternatively, this file may be used under the terms of the GNU Lesser
|
|
18 |
** General Public License version 2.1 as published by the Free Software
|
|
19 |
** Foundation and appearing in the file LICENSE.LGPL included in the
|
|
20 |
** packaging of this file. Please review the following information to
|
|
21 |
** ensure the GNU Lesser General Public License version 2.1 requirements
|
|
22 |
** will be met: http://www.gnu.org/licenses/old-licenses/lgpl-2.1.html.
|
|
23 |
**
|
|
24 |
** In addition, as a special exception, Nokia gives you certain additional
|
|
25 |
** rights. These rights are described in the Nokia Qt LGPL Exception
|
|
26 |
** version 1.1, included in the file LGPL_EXCEPTION.txt in this package.
|
|
27 |
**
|
|
28 |
** If you have questions regarding the use of this file, please contact
|
|
29 |
** Nokia at qt-info@nokia.com.
|
|
30 |
**
|
|
31 |
**
|
|
32 |
**
|
|
33 |
**
|
|
34 |
**
|
|
35 |
**
|
|
36 |
**
|
|
37 |
**
|
|
38 |
** $QT_END_LICENSE$
|
|
39 |
**
|
|
40 |
****************************************************************************/
|
|
41 |
|
|
42 |
#include "qplatformdefs.h"
|
|
43 |
#include "qmutex.h"
|
|
44 |
|
|
45 |
#ifndef QT_NO_THREAD
|
|
46 |
#include "qatomic.h"
|
|
47 |
#include "qthread.h"
|
|
48 |
#include "qmutex_p.h"
|
|
49 |
|
|
50 |
QT_BEGIN_NAMESPACE
|
|
51 |
|
|
52 |
/*!
|
|
53 |
\class QMutex
|
|
54 |
\brief The QMutex class provides access serialization between threads.
|
|
55 |
|
|
56 |
\threadsafe
|
|
57 |
|
|
58 |
\ingroup thread
|
|
59 |
|
|
60 |
The purpose of a QMutex is to protect an object, data structure or
|
|
61 |
section of code so that only one thread can access it at a time
|
|
62 |
(this is similar to the Java \c synchronized keyword). It is
|
|
63 |
usually best to use a mutex with a QMutexLocker since this makes
|
|
64 |
it easy to ensure that locking and unlocking are performed
|
|
65 |
consistently.
|
|
66 |
|
|
67 |
For example, say there is a method that prints a message to the
|
|
68 |
user on two lines:
|
|
69 |
|
|
70 |
\snippet doc/src/snippets/code/src_corelib_thread_qmutex.cpp 0
|
|
71 |
|
|
72 |
If these two methods are called in succession, the following happens:
|
|
73 |
|
|
74 |
\snippet doc/src/snippets/code/src_corelib_thread_qmutex.cpp 1
|
|
75 |
|
|
76 |
If these two methods are called simultaneously from two threads then the
|
|
77 |
following sequence could result:
|
|
78 |
|
|
79 |
\snippet doc/src/snippets/code/src_corelib_thread_qmutex.cpp 2
|
|
80 |
|
|
81 |
If we add a mutex, we should get the result we want:
|
|
82 |
|
|
83 |
\snippet doc/src/snippets/code/src_corelib_thread_qmutex.cpp 3
|
|
84 |
|
|
85 |
Then only one thread can modify \c number at any given time and
|
|
86 |
the result is correct. This is a trivial example, of course, but
|
|
87 |
applies to any other case where things need to happen in a
|
|
88 |
particular sequence.
|
|
89 |
|
|
90 |
When you call lock() in a thread, other threads that try to call
|
|
91 |
lock() in the same place will block until the thread that got the
|
|
92 |
lock calls unlock(). A non-blocking alternative to lock() is
|
|
93 |
tryLock().
|
|
94 |
|
|
95 |
\sa QMutexLocker, QReadWriteLock, QSemaphore, QWaitCondition
|
|
96 |
*/
|
|
97 |
|
|
98 |
/*!
|
|
99 |
\enum QMutex::RecursionMode
|
|
100 |
|
|
101 |
\value Recursive In this mode, a thread can lock the same mutex
|
|
102 |
multiple times and the mutex won't be unlocked
|
|
103 |
until a corresponding number of unlock() calls
|
|
104 |
have been made.
|
|
105 |
|
|
106 |
\value NonRecursive In this mode, a thread may only lock a mutex
|
|
107 |
once.
|
|
108 |
|
|
109 |
\sa QMutex()
|
|
110 |
*/
|
|
111 |
|
|
112 |
/*!
|
|
113 |
Constructs a new mutex. The mutex is created in an unlocked state.
|
|
114 |
|
|
115 |
If \a mode is QMutex::Recursive, a thread can lock the same mutex
|
|
116 |
multiple times and the mutex won't be unlocked until a
|
|
117 |
corresponding number of unlock() calls have been made. The
|
|
118 |
default is QMutex::NonRecursive.
|
|
119 |
|
|
120 |
\sa lock(), unlock()
|
|
121 |
*/
|
|
122 |
QMutex::QMutex(RecursionMode mode)
|
|
123 |
: d(new QMutexPrivate(mode))
|
|
124 |
{ }
|
|
125 |
|
|
126 |
/*!
|
|
127 |
Destroys the mutex.
|
|
128 |
|
|
129 |
\warning Destroying a locked mutex may result in undefined behavior.
|
|
130 |
*/
|
|
131 |
QMutex::~QMutex()
|
|
132 |
{ delete d; }
|
|
133 |
|
|
134 |
/*!
|
|
135 |
Locks the mutex. If another thread has locked the mutex then this
|
|
136 |
call will block until that thread has unlocked it.
|
|
137 |
|
|
138 |
Calling this function multiple times on the same mutex from the
|
|
139 |
same thread is allowed if this mutex is a
|
|
140 |
\l{QMutex::Recursive}{recursive mutex}. If this mutex is a
|
|
141 |
\l{QMutex::NonRecursive}{non-recursive mutex}, this function will
|
|
142 |
\e dead-lock when the mutex is locked recursively.
|
|
143 |
|
|
144 |
\sa unlock()
|
|
145 |
*/
|
|
146 |
void QMutex::lock()
|
|
147 |
{
|
|
148 |
Qt::HANDLE self;
|
|
149 |
|
|
150 |
if (d->recursive) {
|
|
151 |
self = QThread::currentThreadId();
|
|
152 |
if (d->owner == self) {
|
|
153 |
++d->count;
|
|
154 |
Q_ASSERT_X(d->count != 0, "QMutex::lock", "Overflow in recursion counter");
|
|
155 |
return;
|
|
156 |
}
|
|
157 |
|
|
158 |
bool isLocked = d->contenders.fetchAndAddAcquire(1) == 0;
|
|
159 |
if (!isLocked) {
|
|
160 |
#ifndef QT_NO_DEBUG
|
|
161 |
if (d->owner == self)
|
|
162 |
qWarning("QMutex::lock: Deadlock detected in thread %ld",
|
|
163 |
long(d->owner));
|
|
164 |
#endif
|
|
165 |
|
|
166 |
// didn't get the lock, wait for it
|
|
167 |
isLocked = d->wait();
|
|
168 |
Q_ASSERT_X(isLocked, "QMutex::lock",
|
|
169 |
"Internal error, infinite wait has timed out.");
|
|
170 |
|
|
171 |
// don't need to wait for the lock anymore
|
|
172 |
d->contenders.deref();
|
|
173 |
}
|
|
174 |
|
|
175 |
d->owner = self;
|
|
176 |
++d->count;
|
|
177 |
Q_ASSERT_X(d->count != 0, "QMutex::lock", "Overflow in recursion counter");
|
|
178 |
return;
|
|
179 |
}
|
|
180 |
|
|
181 |
#ifndef QT_NO_DEBUG
|
|
182 |
self = QThread::currentThreadId();
|
|
183 |
#endif
|
|
184 |
|
|
185 |
bool isLocked = d->contenders == 0 && d->contenders.testAndSetAcquire(0, 1);
|
|
186 |
if (!isLocked) {
|
|
187 |
int spinCount = 0;
|
|
188 |
int lastSpinCount = d->lastSpinCount;
|
|
189 |
|
|
190 |
enum { AdditionalSpins = 20, SpinCountPenalizationDivisor = 4 };
|
|
191 |
const int maximumSpinCount = lastSpinCount + AdditionalSpins;
|
|
192 |
|
|
193 |
do {
|
|
194 |
if (spinCount++ > maximumSpinCount) {
|
|
195 |
// puts("spinning useless, sleeping");
|
|
196 |
isLocked = d->contenders.fetchAndAddAcquire(1) == 0;
|
|
197 |
if (!isLocked) {
|
|
198 |
#ifndef QT_NO_DEBUG
|
|
199 |
if (d->owner == self)
|
|
200 |
qWarning("QMutex::lock: Deadlock detected in thread %ld",
|
|
201 |
long(d->owner));
|
|
202 |
#endif
|
|
203 |
|
|
204 |
// didn't get the lock, wait for it
|
|
205 |
isLocked = d->wait();
|
|
206 |
Q_ASSERT_X(isLocked, "QMutex::lock",
|
|
207 |
"Internal error, infinite wait has timed out.");
|
|
208 |
|
|
209 |
// don't need to wait for the lock anymore
|
|
210 |
d->contenders.deref();
|
|
211 |
}
|
|
212 |
// decrease the lastSpinCount since we didn't actually get the lock by spinning
|
|
213 |
spinCount = -d->lastSpinCount / SpinCountPenalizationDivisor;
|
|
214 |
break;
|
|
215 |
}
|
|
216 |
|
|
217 |
isLocked = d->contenders == 0 && d->contenders.testAndSetAcquire(0, 1);
|
|
218 |
} while (!isLocked);
|
|
219 |
|
|
220 |
// adjust the last spin lock count
|
|
221 |
lastSpinCount = d->lastSpinCount;
|
|
222 |
d->lastSpinCount = spinCount >= 0
|
|
223 |
? qMax(lastSpinCount, spinCount)
|
|
224 |
: lastSpinCount + spinCount;
|
|
225 |
}
|
|
226 |
|
|
227 |
#ifndef QT_NO_DEBUG
|
|
228 |
d->owner = self;
|
|
229 |
#endif
|
|
230 |
}
|
|
231 |
|
|
232 |
/*!
|
|
233 |
Attempts to lock the mutex. If the lock was obtained, this function
|
|
234 |
returns true. If another thread has locked the mutex, this
|
|
235 |
function returns false immediately.
|
|
236 |
|
|
237 |
If the lock was obtained, the mutex must be unlocked with unlock()
|
|
238 |
before another thread can successfully lock it.
|
|
239 |
|
|
240 |
Calling this function multiple times on the same mutex from the
|
|
241 |
same thread is allowed if this mutex is a
|
|
242 |
\l{QMutex::Recursive}{recursive mutex}. If this mutex is a
|
|
243 |
\l{QMutex::NonRecursive}{non-recursive mutex}, this function will
|
|
244 |
\e always return false when attempting to lock the mutex
|
|
245 |
recursively.
|
|
246 |
|
|
247 |
\sa lock(), unlock()
|
|
248 |
*/
|
|
249 |
bool QMutex::tryLock()
|
|
250 |
{
|
|
251 |
Qt::HANDLE self;
|
|
252 |
|
|
253 |
if (d->recursive) {
|
|
254 |
self = QThread::currentThreadId();
|
|
255 |
if (d->owner == self) {
|
|
256 |
++d->count;
|
|
257 |
Q_ASSERT_X(d->count != 0, "QMutex::tryLock", "Overflow in recursion counter");
|
|
258 |
return true;
|
|
259 |
}
|
|
260 |
|
|
261 |
bool isLocked = d->contenders == 0 && d->contenders.testAndSetAcquire(0, 1);
|
|
262 |
if (!isLocked) {
|
|
263 |
// some other thread has the mutex locked, or we tried to
|
|
264 |
// recursively lock an non-recursive mutex
|
|
265 |
return isLocked;
|
|
266 |
}
|
|
267 |
|
|
268 |
d->owner = self;
|
|
269 |
++d->count;
|
|
270 |
Q_ASSERT_X(d->count != 0, "QMutex::tryLock", "Overflow in recursion counter");
|
|
271 |
return isLocked;
|
|
272 |
}
|
|
273 |
|
|
274 |
#ifndef QT_NO_DEBUG
|
|
275 |
self = QThread::currentThreadId();
|
|
276 |
#endif
|
|
277 |
bool isLocked = d->contenders == 0 && d->contenders.testAndSetAcquire(0, 1);
|
|
278 |
if (!isLocked) {
|
|
279 |
// some other thread has the mutex locked, or we tried to
|
|
280 |
// recursively lock an non-recursive mutex
|
|
281 |
return isLocked;
|
|
282 |
}
|
|
283 |
#ifndef QT_NO_DEBUG
|
|
284 |
d->owner = self;
|
|
285 |
#endif
|
|
286 |
return isLocked;
|
|
287 |
}
|
|
288 |
|
|
289 |
/*! \overload
|
|
290 |
|
|
291 |
Attempts to lock the mutex. This function returns true if the lock
|
|
292 |
was obtained; otherwise it returns false. If another thread has
|
|
293 |
locked the mutex, this function will wait for at most \a timeout
|
|
294 |
milliseconds for the mutex to become available.
|
|
295 |
|
|
296 |
Note: Passing a negative number as the \a timeout is equivalent to
|
|
297 |
calling lock(), i.e. this function will wait forever until mutex
|
|
298 |
can be locked if \a timeout is negative.
|
|
299 |
|
|
300 |
If the lock was obtained, the mutex must be unlocked with unlock()
|
|
301 |
before another thread can successfully lock it.
|
|
302 |
|
|
303 |
Calling this function multiple times on the same mutex from the
|
|
304 |
same thread is allowed if this mutex is a
|
|
305 |
\l{QMutex::Recursive}{recursive mutex}. If this mutex is a
|
|
306 |
\l{QMutex::NonRecursive}{non-recursive mutex}, this function will
|
|
307 |
\e always return false when attempting to lock the mutex
|
|
308 |
recursively.
|
|
309 |
|
|
310 |
\sa lock(), unlock()
|
|
311 |
*/
|
|
312 |
bool QMutex::tryLock(int timeout)
|
|
313 |
{
|
|
314 |
Qt::HANDLE self;
|
|
315 |
|
|
316 |
if (d->recursive) {
|
|
317 |
self = QThread::currentThreadId();
|
|
318 |
if (d->owner == self) {
|
|
319 |
++d->count;
|
|
320 |
Q_ASSERT_X(d->count != 0, "QMutex::tryLock", "Overflow in recursion counter");
|
|
321 |
return true;
|
|
322 |
}
|
|
323 |
|
|
324 |
bool isLocked = d->contenders.fetchAndAddAcquire(1) == 0;
|
|
325 |
if (!isLocked) {
|
|
326 |
// didn't get the lock, wait for it
|
|
327 |
isLocked = d->wait(timeout);
|
|
328 |
|
|
329 |
// don't need to wait for the lock anymore
|
|
330 |
d->contenders.deref();
|
|
331 |
if (!isLocked)
|
|
332 |
return false;
|
|
333 |
}
|
|
334 |
|
|
335 |
d->owner = self;
|
|
336 |
++d->count;
|
|
337 |
Q_ASSERT_X(d->count != 0, "QMutex::tryLock", "Overflow in recursion counter");
|
|
338 |
return true;
|
|
339 |
}
|
|
340 |
|
|
341 |
#ifndef QT_NO_DEBUG
|
|
342 |
self = QThread::currentThreadId();
|
|
343 |
#endif
|
|
344 |
bool isLocked = d->contenders.fetchAndAddAcquire(1) == 0;
|
|
345 |
if (!isLocked) {
|
|
346 |
// didn't get the lock, wait for it
|
|
347 |
isLocked = d->wait(timeout);
|
|
348 |
|
|
349 |
// don't need to wait for the lock anymore
|
|
350 |
d->contenders.deref();
|
|
351 |
if (!isLocked)
|
|
352 |
return false;
|
|
353 |
}
|
|
354 |
#ifndef QT_NO_DEBUG
|
|
355 |
d->owner = self;
|
|
356 |
#endif
|
|
357 |
return true;
|
|
358 |
}
|
|
359 |
|
|
360 |
|
|
361 |
/*!
|
|
362 |
Unlocks the mutex. Attempting to unlock a mutex in a different
|
|
363 |
thread to the one that locked it results in an error. Unlocking a
|
|
364 |
mutex that is not locked results in undefined behavior.
|
|
365 |
|
|
366 |
\sa lock()
|
|
367 |
*/
|
|
368 |
void QMutex::unlock()
|
|
369 |
{
|
|
370 |
Q_ASSERT_X(d->owner == QThread::currentThreadId(), "QMutex::unlock()",
|
|
371 |
"A mutex must be unlocked in the same thread that locked it.");
|
|
372 |
|
|
373 |
if (d->recursive) {
|
|
374 |
if (!--d->count) {
|
|
375 |
d->owner = 0;
|
|
376 |
if (!d->contenders.testAndSetRelease(1, 0))
|
|
377 |
d->wakeUp();
|
|
378 |
}
|
|
379 |
} else {
|
|
380 |
#ifndef QT_NO_DEBUG
|
|
381 |
d->owner = 0;
|
|
382 |
#endif
|
|
383 |
if (!d->contenders.testAndSetRelease(1, 0))
|
|
384 |
d->wakeUp();
|
|
385 |
}
|
|
386 |
}
|
|
387 |
|
|
388 |
/*!
|
|
389 |
\fn bool QMutex::locked()
|
|
390 |
|
|
391 |
Returns true if the mutex is locked by another thread; otherwise
|
|
392 |
returns false.
|
|
393 |
|
|
394 |
It is generally a bad idea to use this function, because code
|
|
395 |
that uses it has a race condition. Use tryLock() and unlock()
|
|
396 |
instead.
|
|
397 |
|
|
398 |
\oldcode
|
|
399 |
bool isLocked = mutex.locked();
|
|
400 |
\newcode
|
|
401 |
bool isLocked = true;
|
|
402 |
if (mutex.tryLock()) {
|
|
403 |
mutex.unlock();
|
|
404 |
isLocked = false;
|
|
405 |
}
|
|
406 |
\endcode
|
|
407 |
*/
|
|
408 |
|
|
409 |
/*!
|
|
410 |
\class QMutexLocker
|
|
411 |
\brief The QMutexLocker class is a convenience class that simplifies
|
|
412 |
locking and unlocking mutexes.
|
|
413 |
|
|
414 |
\threadsafe
|
|
415 |
|
|
416 |
\ingroup thread
|
|
417 |
|
|
418 |
Locking and unlocking a QMutex in complex functions and
|
|
419 |
statements or in exception handling code is error-prone and
|
|
420 |
difficult to debug. QMutexLocker can be used in such situations
|
|
421 |
to ensure that the state of the mutex is always well-defined.
|
|
422 |
|
|
423 |
QMutexLocker should be created within a function where a
|
|
424 |
QMutex needs to be locked. The mutex is locked when QMutexLocker
|
|
425 |
is created. You can unlock and relock the mutex with \c unlock()
|
|
426 |
and \c relock(). If locked, the mutex will be unlocked when the
|
|
427 |
QMutexLocker is destroyed.
|
|
428 |
|
|
429 |
For example, this complex function locks a QMutex upon entering
|
|
430 |
the function and unlocks the mutex at all the exit points:
|
|
431 |
|
|
432 |
\snippet doc/src/snippets/code/src_corelib_thread_qmutex.cpp 4
|
|
433 |
|
|
434 |
This example function will get more complicated as it is
|
|
435 |
developed, which increases the likelihood that errors will occur.
|
|
436 |
|
|
437 |
Using QMutexLocker greatly simplifies the code, and makes it more
|
|
438 |
readable:
|
|
439 |
|
|
440 |
\snippet doc/src/snippets/code/src_corelib_thread_qmutex.cpp 5
|
|
441 |
|
|
442 |
Now, the mutex will always be unlocked when the QMutexLocker
|
|
443 |
object is destroyed (when the function returns since \c locker is
|
|
444 |
an auto variable).
|
|
445 |
|
|
446 |
The same principle applies to code that throws and catches
|
|
447 |
exceptions. An exception that is not caught in the function that
|
|
448 |
has locked the mutex has no way of unlocking the mutex before the
|
|
449 |
exception is passed up the stack to the calling function.
|
|
450 |
|
|
451 |
QMutexLocker also provides a \c mutex() member function that returns
|
|
452 |
the mutex on which the QMutexLocker is operating. This is useful
|
|
453 |
for code that needs access to the mutex, such as
|
|
454 |
QWaitCondition::wait(). For example:
|
|
455 |
|
|
456 |
\snippet doc/src/snippets/code/src_corelib_thread_qmutex.cpp 6
|
|
457 |
|
|
458 |
\sa QReadLocker, QWriteLocker, QMutex
|
|
459 |
*/
|
|
460 |
|
|
461 |
/*!
|
|
462 |
\fn QMutexLocker::QMutexLocker(QMutex *mutex)
|
|
463 |
|
|
464 |
Constructs a QMutexLocker and locks \a mutex. The mutex will be
|
|
465 |
unlocked when the QMutexLocker is destroyed. If \a mutex is zero,
|
|
466 |
QMutexLocker does nothing.
|
|
467 |
|
|
468 |
\sa QMutex::lock()
|
|
469 |
*/
|
|
470 |
|
|
471 |
/*!
|
|
472 |
\fn QMutexLocker::~QMutexLocker()
|
|
473 |
|
|
474 |
Destroys the QMutexLocker and unlocks the mutex that was locked
|
|
475 |
in the constructor.
|
|
476 |
|
|
477 |
\sa QMutex::unlock()
|
|
478 |
*/
|
|
479 |
|
|
480 |
/*!
|
|
481 |
\fn QMutex *QMutexLocker::mutex() const
|
|
482 |
|
|
483 |
Returns a pointer to the mutex that was locked in the
|
|
484 |
constructor.
|
|
485 |
*/
|
|
486 |
|
|
487 |
/*!
|
|
488 |
\fn void QMutexLocker::unlock()
|
|
489 |
|
|
490 |
Unlocks this mutex locker. You can use \c relock() to lock
|
|
491 |
it again. It does not need to be locked when destroyed.
|
|
492 |
|
|
493 |
\sa relock()
|
|
494 |
*/
|
|
495 |
|
|
496 |
/*!
|
|
497 |
\fn void QMutexLocker::relock()
|
|
498 |
|
|
499 |
Relocks an unlocked mutex locker.
|
|
500 |
|
|
501 |
\sa unlock()
|
|
502 |
*/
|
|
503 |
|
|
504 |
/*!
|
|
505 |
\fn QMutex::QMutex(bool recursive)
|
|
506 |
|
|
507 |
Use the constructor that takes a RecursionMode parameter instead.
|
|
508 |
*/
|
|
509 |
|
|
510 |
QT_END_NAMESPACE
|
|
511 |
|
|
512 |
#endif // QT_NO_THREAD
|