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java.lang.Objectcom.trolltech.qt.internal.QSignalEmitterInternal
com.trolltech.qt.QSignalEmitter
com.trolltech.qt.QtJambiObject
com.trolltech.qt.core.QMutex
public class QMutex
The QMutex
class provides access serialization between threads. The purpose of a QMutex
is to protect an object, data structure or section of code so that only one thread can access it at a time (this is similar to the Java synchronized keyword). It is usually best to use a mutex with a QMutexLocker since this makes it easy to ensure that locking and unlocking are performed consistently.
For example, say there is a method that prints a message to the user on two lines:
int number = 6; public void method1() { number *= 5; number /= 4; } public void method2() { number *= 3; number /= 2; }If these two methods are called in succession, the following happens:
// method1() number *= 5; // number is now 30 number /= 4; // number is now 7 // method2() number *= 3; // number is now 21 number /= 2; // number is now 10If these two methods are called simultaneously from two threads then the following sequence could result:
// Thread 1 calls method1() number *= 5; // number is now 30 // Thread 2 calls method2(). // // Most likely Thread 1 has been put to sleep by the operating // system to allow Thread 2 to run. number *= 3; // number is now 90 number /= 2; // number is now 45 // Thread 1 finishes executing. number /= 4; // number is now 11, instead of 10If we add a mutex, we should get the result we want:
QMutex mutex = new QMutex(); int number = 6; public void method1() { mutex.lock(); number *= 5; number /= 4; mutex.unlock(); } public void method2() { mutex.lock(); number *= 3; number /= 2; mutex.unlock(); }Then only one thread can modify number at any given time and the result is correct. This is a trivial example, of course, but applies to any other case where things need to happen in a particular sequence.
When you call lock()
in a thread, other threads that try to call lock()
in the same place will block until the thread that got the lock calls unlock()
. A non-blocking alternative to lock()
is tryLock()
.
QReadWriteLock
, QSemaphore
, and QWaitCondition
.
Nested Class Summary | |
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static class |
QMutex.RecursionMode
|
Nested classes/interfaces inherited from class com.trolltech.qt.QSignalEmitter |
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QSignalEmitter.AbstractSignal, QSignalEmitter.Signal0, QSignalEmitter.Signal1, QSignalEmitter.Signal2, QSignalEmitter.Signal3, QSignalEmitter.Signal4, QSignalEmitter.Signal5, QSignalEmitter.Signal6, QSignalEmitter.Signal7, QSignalEmitter.Signal8, QSignalEmitter.Signal9 |
Nested classes/interfaces inherited from class com.trolltech.qt.internal.QSignalEmitterInternal |
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com.trolltech.qt.internal.QSignalEmitterInternal.AbstractSignalInternal |
Field Summary |
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Fields inherited from class com.trolltech.qt.internal.QSignalEmitterInternal |
---|
currentSender |
Constructor Summary | |
---|---|
QMutex()
Constructs a new mutex. |
|
QMutex(QMutex.RecursionMode mode)
Constructs a new mutex. |
Method Summary | |
---|---|
void |
lock()
Locks the mutex. |
boolean |
tryLock()
Attempts to lock the mutex. |
boolean |
tryLock(int timeout)
Attempts to lock the mutex. |
void |
unlock()
Unlocks the mutex. |
Methods inherited from class com.trolltech.qt.QtJambiObject |
---|
dispose, disposed, equals, finalize, reassignNativeResources, tr, tr, tr |
Methods inherited from class com.trolltech.qt.QSignalEmitter |
---|
blockSignals, disconnect, disconnect, signalsBlocked, signalSender, thread |
Methods inherited from class com.trolltech.qt.internal.QSignalEmitterInternal |
---|
__qt_signalInitialization |
Methods inherited from class java.lang.Object |
---|
clone, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait |
Methods inherited from interface com.trolltech.qt.QtJambiInterface |
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disableGarbageCollection, nativeId, nativePointer, reenableGarbageCollection, setJavaOwnership |
Constructor Detail |
---|
public QMutex()
If mode is QMutex::Recursive
, a thread can lock the same mutex multiple times and the mutex won't be unlocked until a corresponding number of unlock()
calls have been made. The default is QMutex::NonRecursive
.
lock()
, and unlock()
.
public QMutex(QMutex.RecursionMode mode)
If mode is QMutex::Recursive
, a thread can lock the same mutex multiple times and the mutex won't be unlocked until a corresponding number of unlock()
calls have been made. The default is QMutex::NonRecursive
.
lock()
, and unlock()
.
Method Detail |
---|
public final void lock()
Calling this function multiple times on the same mutex from the same thread is allowed if this mutex is a recursive mutex
. If this mutex is a non-recursive mutex
, this function will dead-lock when the mutex is locked recursively.
unlock()
.
public final boolean tryLock()
If the lock was obtained, the mutex must be unlocked with unlock()
before another thread can successfully lock it.
Calling this function multiple times on the same mutex from the same thread is allowed if this mutex is a recursive mutex
. If this mutex is a non-recursive mutex
, this function will always return false when attempting to lock the mutex recursively.
lock()
, and unlock()
.
public final boolean tryLock(int timeout)
Note: Passing a negative number as the timeout is equivalent to calling lock()
, i.e. this function will wait forever until mutex can be locked if timeout is negative.
If the lock was obtained, the mutex must be unlocked with unlock()
before another thread can successfully lock it.
Calling this function multiple times on the same mutex from the same thread is allowed if this mutex is a recursive mutex
. If this mutex is a non-recursive mutex
, this function will always return false when attempting to lock the mutex recursively.
lock()
, and unlock()
.
public final void unlock()
lock()
.
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