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java.lang.Objectcom.trolltech.qt.internal.QSignalEmitterInternal
com.trolltech.qt.QSignalEmitter
com.trolltech.qt.QtJambiObject
com.trolltech.qt.core.QObject
com.trolltech.qt.core.QThreadPool
public class QThreadPool
The QThreadPool
class manages a collection of QThreads. QThreadPool
manages and recyles individual QThread objects to help reduce thread creation costs in programs that use threads. Each Qt application has one global QThreadPool
object, which can be accessed by calling globalInstance()
.
To use one of the QThreadPool
threads, subclass QRunnable
and implement the run() virtual function. Then create an object of that class and pass it to QThreadPool::start()
.
static class HelloWorldTask extends QRunnable { @Override public void run() { System.out.println("Hello world from thread" + QThread.currentThread()); } } public static void main(String args[]) { QCoreApplication.initialize(args); HelloWorldTask hello = new HelloWorldTask(); // QThreadPool takes ownership and deletes 'hello' automatically QThreadPool.globalInstance().start(hello); }
QThreadPool
deletes the QRunnable
automatically by default. Use QRunnable::setAutoDelete()
to change the auto-deletion flag. QThreadPool
supports executing the same QRunnable
more than once by calling tryStart(this) from within QRunnable::run()
. If autoDelete is enabled the QRunnable
will be deleted when the last thread exits the run function. Calling start()
multiple times with the same QRunnable
when autoDelete is enabled creates a race condition and is not recommended.
Threads that are unused for a certain amount of time will expire. The default expiry timeout is 30000 milliseconds (30 seconds). This can be changed using setExpiryTimeout()
. Setting a negative expiry timeout disables the expiry mechanism.
Call maxThreadCount()
to query the maximum number of threads to be used. If needed, you can change the limit with setMaxThreadCount()
. The default maxThreadCount()
is QThread::idealThreadCount(). The activeThreadCount()
function returns the number of threads currently doing work.
The reserveThread()
function reserves a thread for external use. Use releaseThread()
when your are done with the thread, so that it may be reused. Essentially, these functions temporarily increase or reduce the active thread count and are useful when implementing time-consuming operations that are not visible to the QThreadPool
.
Note that QThreadPool
is a low-level class for managing threads, see QtConcurrent::run() or the other Qt Concurrent APIs for higher level alternatives.
QRunnable
.
Nested Class Summary |
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Nested classes/interfaces inherited from class com.trolltech.qt.QSignalEmitter |
---|
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 |
---|
com.trolltech.qt.internal.QSignalEmitterInternal.AbstractSignalInternal |
Field Summary |
---|
Fields inherited from class com.trolltech.qt.internal.QSignalEmitterInternal |
---|
currentSender |
Constructor Summary | |
---|---|
QThreadPool()
Constructs a thread pool with the given parent. |
|
QThreadPool(QObject parent)
Constructs a thread pool with the given parent. |
Method Summary | |
---|---|
int |
activeThreadCount()
This property represents the number of active threads in the thread pool. |
int |
expiryTimeout()
Threads that are unused for expiryTimeout milliseconds are considered to have expired and will exit. |
static QThreadPool |
globalInstance()
Returns the global QThreadPool instance. |
int |
maxThreadCount()
This property represents the maximum number of threads used by the thread pool. |
void |
releaseThread()
Releases a thread previously reserved by a call to reserveThread() . |
void |
reserveThread()
Reserves one thread, disregarding activeThreadCount() and maxThreadCount() . |
void |
setExpiryTimeout(int expiryTimeout)
Threads that are unused for expiryTimeout milliseconds are considered to have expired and will exit. |
void |
setMaxThreadCount(int maxThreadCount)
This property represents the maximum number of threads used by the thread pool. |
void |
start(QRunnable runnable)
Reserves a thread and uses it to run runnable, unless this thread will make the current thread count exceed maxThreadCount() . |
void |
start(QRunnable runnable,
int priority)
Reserves a thread and uses it to run runnable, unless this thread will make the current thread count exceed maxThreadCount() . |
boolean |
tryStart(QRunnable runnable)
Attempts to reserve a thread to run runnable. |
void |
waitForDone()
Waits for each thread to exit and removes all threads from the thread pool. |
Methods inherited from class com.trolltech.qt.core.QObject |
---|
childEvent, children, connectSlotsByName, customEvent, disposeLater, dumpObjectInfo, dumpObjectTree, dynamicPropertyNames, event, eventFilter, findChild, findChild, findChild, findChildren, findChildren, findChildren, findChildren, indexOfProperty, installEventFilter, isWidgetType, killTimer, moveToThread, objectName, parent, properties, property, removeEventFilter, setObjectName, setParent, setProperty, startTimer, timerEvent, toString, userProperty |
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, wait, wait, wait |
Methods inherited from interface com.trolltech.qt.QtJambiInterface |
---|
disableGarbageCollection, nativeId, nativePointer, reenableGarbageCollection, setJavaOwnership |
Constructor Detail |
---|
public QThreadPool()
public QThreadPool(QObject parent)
Method Detail |
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public final int activeThreadCount()
Note: It is possible for this function to return a value that is greater than maxThreadCount()
. See reserveThread()
for more details.
reserveThread()
, and releaseThread()
.
public final int expiryTimeout()
Note that setting expiryTimeout has no effect on already running threads. Only newly created threads will use the new expiryTimeout. We recommend setting the expiryTimeout immediately after creating the thread pool, but before calling start()
.
public final int maxThreadCount()
Note: The thread pool will always use at least 1 thread, even if maxThreadCount limit is zero or negative.
The default maxThreadCount is QThread::idealThreadCount().
public final void releaseThread()
reserveThread()
. Note: Calling this function without previously reserving a thread temporarily increases maxThreadCount()
. This is useful when a thread goes to sleep waiting for more work, allowing other threads to continue. Be sure to call reserveThread()
when done waiting, so that the thread pool can correctly maintain the activeThreadCount()
.
reserveThread()
.
public final void reserveThread()
activeThreadCount()
and maxThreadCount()
. Once you are done with the thread, call releaseThread()
to allow it to be reused.
Note: This function will always increase the number of active threads. This means that by using this function, it is possible for activeThreadCount()
to return a value greater than maxThreadCount()
.
releaseThread()
.
public final void setExpiryTimeout(int expiryTimeout)
Note that setting expiryTimeout has no effect on already running threads. Only newly created threads will use the new expiryTimeout. We recommend setting the expiryTimeout immediately after creating the thread pool, but before calling start()
.
public final void setMaxThreadCount(int maxThreadCount)
Note: The thread pool will always use at least 1 thread, even if maxThreadCount limit is zero or negative.
The default maxThreadCount is QThread::idealThreadCount().
public final void start(QRunnable runnable)
maxThreadCount()
. In that case, runnable is added to a run queue instead. The priority argument can be used to control the run queue's order of execution. Note that the thread pool takes ownership of the runnable if runnable->autoDelete()
returns true, and the runnable will be deleted automatically by the thread pool after the runnable->run()
returns. If runnable->autoDelete()
returns false, ownership of runnable remains with the caller. Note that changing the auto-deletion on runnable after calling this functions results in undefined behavior.
public final void start(QRunnable runnable, int priority)
maxThreadCount()
. In that case, runnable is added to a run queue instead. The priority argument can be used to control the run queue's order of execution. Note that the thread pool takes ownership of the runnable if runnable->autoDelete()
returns true, and the runnable will be deleted automatically by the thread pool after the runnable->run()
returns. If runnable->autoDelete()
returns false, ownership of runnable remains with the caller. Note that changing the auto-deletion on runnable after calling this functions results in undefined behavior.
public final boolean tryStart(QRunnable runnable)
If no threads are available at the time of calling, then this function does nothing and returns false. Otherwise, runnable is run immediately using one available thread and this function returns true.
Note that the thread pool takes ownership of the runnable if runnable->autoDelete()
returns true, and the runnable will be deleted automatically by the thread pool after the runnable->run()
returns. If runnable->autoDelete()
returns false, ownership of runnable remains with the caller. Note that changing the auto-deletion on runnable after calling this function results in undefined behavior.
public final void waitForDone()
public static QThreadPool globalInstance()
QThreadPool
instance.
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