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## com.trolltech.qt.core
Class QThreadPool

    java.lang.Object
      com.trolltech.qt.internal.QSignalEmitterInternal
          com.trolltech.qt.QSignalEmitter
              com.trolltech.qt.QtJambiObject
                  com.trolltech.qt.core.QObject
                      com.trolltech.qt.core.QThreadPool

All Implemented Interfaces:
  QtJambiInterface

    public class QThreadPool

extends QObject

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.

See also:
  `QRunnable`.

Nested Class Summary

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

### QThreadPool

    public QThreadPool()

  Constructs a thread pool with the given `parent`.

### QThreadPool

    public QThreadPool(QObject parent)

  Constructs a thread pool with the given `parent`.

Method Detail

### activeThreadCount

    public final int activeThreadCount()

  This property represents the number of active threads in the thread pool.

  Note: It is possible for this function to return a value that is greater than `maxThreadCount()`. See `reserveThread()` for more details.

See also:
  `reserveThread()`, and `releaseThread()`.

### expiryTimeout

    public final int expiryTimeout()

  Threads that are unused for `expiryTimeout` milliseconds are considered to have expired and will exit. Such threads will be restarted as needed. The default `expiryTimeout` is 30000 milliseconds (30 seconds). If `expiryTimeout` is negative, newly created threads will not expire, e.g., they will not exit until the thread pool is destroyed.

  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()`.

### maxThreadCount

    public final int maxThreadCount()

  This property represents the maximum number of threads used by the thread pool.

  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().

### releaseThread

    public final void releaseThread()

  Releases a thread previously reserved by a call to `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()`.

See also:
  `reserveThread()`.

### reserveThread

    public final void reserveThread()

  Reserves one thread, disregarding `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()` .

See also:
  `releaseThread()`.

### setExpiryTimeout

    public final void setExpiryTimeout(int expiryTimeout)

  Threads that are unused for `expiryTimeout` milliseconds are considered to have expired and will exit. Such threads will be restarted as needed. The default `expiryTimeout` is 30000 milliseconds (30 seconds). If `expiryTimeout` is negative, newly created threads will not expire, e.g., they will not exit until the thread pool is destroyed.

  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()`.

### setMaxThreadCount

    public final void setMaxThreadCount(int maxThreadCount)

  This property represents the maximum number of threads used by the thread pool.

  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().

### start

    public final void start(QRunnable runnable)

  Reserves a thread and uses it to run `runnable`, unless this thread will make the current thread count exceed `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.

### start

    public final 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()`. 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.

### tryStart

    public final boolean tryStart(QRunnable runnable)

  Attempts to reserve a thread to run `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.

### waitForDone

    public final void waitForDone()

  Waits for each thread to exit and removes all threads from the thread pool.

### globalInstance

    public static QThreadPool globalInstance()

  Returns the global QThreadPool instance.

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