The QThreadPool class manages a collection of QThreads. More...

#include <qthreadpool.h>

Inheritance diagram for QThreadPool:

Public Functions
int	activeThreadCount () const

int	expiryTimeout () const

int	maxThreadCount () const

	QThreadPool (QObject *parent=0)
	Constructs a thread pool with the given parent. More...

void	releaseThread ()
	Releases a thread previously reserved by a call to reserveThread(). More...

void	reserveThread ()
	Reserves one thread, disregarding activeThreadCount() and maxThreadCount(). More...

void	setExpiryTimeout (int expiryTimeout)

void	setMaxThreadCount (int maxThreadCount)

void	start (QRunnable *runnable, int priority=0)
	Reserves a thread and uses it to run runnable, unless this thread will make the current thread count exceed maxThreadCount(). More...

bool	tryStart (QRunnable *runnable)
	Attempts to reserve a thread to run runnable. More...

void	waitForDone ()
	Waits for each thread to exit and removes all threads from the thread pool. More...

bool	waitForDone (int msecs)

	~QThreadPool ()
	Destroys the QThreadPool. More...

Public Functions inherited from QObject
bool	blockSignals (bool b)
	If block is true, signals emitted by this object are blocked (i.e., emitting a signal will not invoke anything connected to it). More...

const QObjectList &	children () const
	Returns a list of child objects. More...

bool	connect (const QObject sender, const char signal, const char *member, Qt::ConnectionType type=Qt::AutoConnection) const

bool	disconnect (const char signal=0, const QObject receiver=0, const char *member=0)

bool	disconnect (const QObject receiver, const char member=0)

void	dumpObjectInfo ()
	Dumps information about signal connections, etc. More...

void	dumpObjectTree ()
	Dumps a tree of children to the debug output. More...

QList< QByteArray >	dynamicPropertyNames () const
	Returns the names of all properties that were dynamically added to the object using setProperty(). More...

virtual bool	event (QEvent *)
	This virtual function receives events to an object and should return true if the event e was recognized and processed. More...

virtual bool	eventFilter (QObject , QEvent )
	Filters events if this object has been installed as an event filter for the watched object. More...

template<typename T >
T	findChild (const QString &aName=QString()) const
	Returns the child of this object that can be cast into type T and that is called name, or 0 if there is no such object. More...

template<typename T >
QList< T >	findChildren (const QString &aName=QString()) const
	Returns all children of this object with the given name that can be cast to type T, or an empty list if there are no such objects. More...

template<typename T >
QList< T >	findChildren (const QRegExp &re) const

bool	inherits (const char *classname) const
	Returns true if this object is an instance of a class that inherits className or a QObject subclass that inherits className; otherwise returns false. More...

void	installEventFilter (QObject *)
	Installs an event filter filterObj on this object. More...

bool	isWidgetType () const
	Returns true if the object is a widget; otherwise returns false. More...

void	killTimer (int id)
	Kills the timer with timer identifier, id. More...

virtual const QMetaObject *	metaObject () const
	Returns a pointer to the meta-object of this object. More...

void	moveToThread (QThread *thread)
	Changes the thread affinity for this object and its children. More...

QString	objectName () const

QObject *	parent () const
	Returns a pointer to the parent object. More...

QVariant	property (const char *name) const
	Returns the value of the object's name property. More...

Q_INVOKABLE	QObject (QObject *parent=0)
	Constructs an object with parent object parent. More...

void	removeEventFilter (QObject *)
	Removes an event filter object obj from this object. More...

void	setObjectName (const QString &name)

void	setParent (QObject *)
	Makes the object a child of parent. More...

bool	setProperty (const char *name, const QVariant &value)
	Sets the value of the object's name property to value. More...

void	setUserData (uint id, QObjectUserData *data)

bool	signalsBlocked () const
	Returns true if signals are blocked; otherwise returns false. More...

int	startTimer (int interval)
	Starts a timer and returns a timer identifier, or returns zero if it could not start a timer. More...

QThread *	thread () const
	Returns the thread in which the object lives. More...

QObjectUserData *	userData (uint id) const

virtual	~QObject ()
	Destroys the object, deleting all its child objects. More...

Static Public Functions
static QThreadPool *	globalInstance ()
	Returns the global QThreadPool instance. More...

Static Public Functions inherited from QObject
static bool	connect (const QObject sender, const char signal, const QObject receiver, const char member, Qt::ConnectionType=Qt::AutoConnection)
	Creates a connection of the given type from the signal in the sender object to the method in the receiver object. More...

static bool	connect (const QObject sender, const QMetaMethod &signal, const QObject receiver, const QMetaMethod &method, Qt::ConnectionType type=Qt::AutoConnection)

static bool	disconnect (const QObject sender, const char signal, const QObject receiver, const char member)
	Disconnects signal in object sender from method in object receiver. More...

static bool	disconnect (const QObject sender, const QMetaMethod &signal, const QObject receiver, const QMetaMethod &member)

static uint	registerUserData ()

static QString	tr (const char sourceText, const char comment=0, int n=-1)

static QString	trUtf8 (const char sourceText, const char comment=0, int n=-1)

Properties
int	activeThreadCount
	This property represents the number of active threads in the thread pool. More...

int	expiryTimeout
	Threads that are unused for expiryTimeout milliseconds are considered to have expired and will exit. More...

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

Friends
class	QFutureInterfaceBase

Additional Inherited Members
Public Slots inherited from QObject
void	deleteLater ()
	Schedules this object for deletion. More...

Signals inherited from QObject
void	destroyed (QObject *=0)
	This signal is emitted immediately before the object obj is destroyed, and can not be blocked. More...

Static Public Variables inherited from QObject
static const QMetaObject	staticMetaObject
	This variable stores the meta-object for the class. More...

Protected Functions inherited from QObject
virtual void	childEvent (QChildEvent *)
	This event handler can be reimplemented in a subclass to receive child events. More...

virtual void	connectNotify (const char *signal)
	This virtual function is called when something has been connected to signal in this object. More...

virtual void	customEvent (QEvent *)
	This event handler can be reimplemented in a subclass to receive custom events. More...

virtual void	disconnectNotify (const char *signal)
	This virtual function is called when something has been disconnected from signal in this object. More...

	QObject (QObjectPrivate &dd, QObject *parent=0)

int	receivers (const char *signal) const
	Returns the number of receivers connected to the signal. More...

QObject *	sender () const
	Returns a pointer to the object that sent the signal, if called in a slot activated by a signal; otherwise it returns 0. More...

int	senderSignalIndex () const

virtual void	timerEvent (QTimerEvent *)
	This event handler can be reimplemented in a subclass to receive timer events for the object. More...

Protected Variables inherited from QObject
QScopedPointer< QObjectData >	d_ptr

Static Protected Variables inherited from QObject
static const QMetaObject	staticQtMetaObject

Related Functions inherited from QObject
T	qFindChildqFindChildren (const QObject *obj, const QString &name)()

QList< T >	qFindChildrenqFindChildren (const QObject *obj, const QString &name)()

QList< T >	qFindChildrenqFindChildren (const QObject *obj, const QRegExp &regExp)()

T *	qobject_cast (QObject *object)

	QObjectList

void *	qt_find_obj_child (QObject parent, const char type, const QString &name)
	Returns a pointer to the object named name that inherits type and with a given parent. More...

Detailed Description

The QThreadPool class manages a collection of QThreads.

Since: 4.4

Note: This class or function is threadsafe.

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().

class HelloWorldTask : public QRunnable
{
    void run()
    {
        qDebug() << "Hello world from thread" << QThread::currentThread();
    }
}
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 Concurrent Programming {Qt Concurrent} APIs for higher level alternatives.

See also: QRunnable

Definition at line 58 of file qthreadpool.h.

Constructors and Destructors

◆ QThreadPool()

QThreadPool::QThreadPool ( QObject * parent = 0 )

Constructs a thread pool with the given parent.

Definition at line 439 of file qthreadpool.cpp.

440 : QObject(*new QThreadPoolPrivate, parent)

441 { }

QThreadPoolPrivate

Definition: qthreadpool_p.h:68

QObject::QObject

Q_INVOKABLE QObject(QObject *parent=0)

Constructs an object with parent object parent.

Definition: qobject.cpp:753

◆ ~QThreadPool()

QThreadPool::~QThreadPool ( )

Destroys the QThreadPool.

This function will block until all runnables have been completed.

Definition at line 447 of file qthreadpool.cpp.

 {
     d_func()->waitForDone();
     d_func()->reset();
 }

Functions

◆ activeThreadCount()

int QThreadPool::activeThreadCount ( ) const

Referenced by setMaxThreadCount().

◆ expiryTimeout()

int QThreadPool::expiryTimeout ( ) const

Referenced by setExpiryTimeout(), and tryStart().

◆ globalInstance()

QThreadPool * QThreadPool::globalInstance ( )

static

Returns the global QThreadPool instance.

Definition at line 456 of file qthreadpool.cpp.

Referenced by elapsed(), QFutureInterfaceBase::waitForFinished(), QFutureInterfaceBase::waitForResult(), QFutureInterfaceBase::waitForResume(), and QCoreApplication::~QCoreApplication().

 {
     return theInstance();
 }

◆ maxThreadCount()

int QThreadPool::maxThreadCount ( ) const

Referenced by setExpiryTimeout(), and setMaxThreadCount().

◆ releaseThread()

void QThreadPool::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()

Definition at line 636 of file qthreadpool.cpp.

Referenced by QFutureInterfaceBase::waitForResume().

 {
     Q_D(QThreadPool);
     QMutexLocker locker(&d->mutex);
     --d->reservedThreads;
     d->tryToStartMoreThreads();
 }

◆ reserveThread()

void QThreadPool::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()

Definition at line 617 of file qthreadpool.cpp.

Referenced by QFutureInterfaceBase::waitForResume().

 {
     Q_D(QThreadPool);
     QMutexLocker locker(&d->mutex);
     ++d->reservedThreads;
 }

◆ setExpiryTimeout()

void QThreadPool::setExpiryTimeout ( int expiryTimeout )

Definition at line 545 of file qthreadpool.cpp.

 {
     Q_D(QThreadPool);
     if (d->expiryTimeout == expiryTimeout)
         return;
     d->expiryTimeout = expiryTimeout;
 }

◆ setMaxThreadCount()

void QThreadPool::setMaxThreadCount ( int maxThreadCount )

Definition at line 573 of file qthreadpool.cpp.

Referenced by QHostInfoLookupManager::QHostInfoLookupManager().

 {
     Q_D(QThreadPool);
     QMutexLocker locker(&d->mutex);
 
     if (maxThreadCount == d->maxThreadCount)
         return;
 
     d->maxThreadCount = maxThreadCount;
     d->tryToStartMoreThreads();
 }

◆ start()

void QThreadPool::start	(	QRunnable *	runnable,
		int	priority = `0`
	)

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.

Definition at line 476 of file qthreadpool.cpp.

Referenced by QHostInfoLookupManager::work().

 {
     if (!runnable)
         return;
 
     Q_D(QThreadPool);
     QMutexLocker locker(&d->mutex);
     if (!d->tryStart(runnable)) {
         d->enqueueTask(runnable, priority);
 
         if (!d->waitingThreads.isEmpty())
             d->waitingThreads.takeFirst()->runnableReady.wakeOne();
     }
 }

◆ tryStart()

bool QThreadPool::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.

Definition at line 507 of file qthreadpool.cpp.

 {
     if (!runnable)
         return false;
 
     Q_D(QThreadPool);
 
     QMutexLocker locker(&d->mutex);
 
     if (d->allThreads.isEmpty() == false && d->activeThreadCount() >= d->maxThreadCount)
         return false;
 
     return d->tryStart(runnable);
 }

◆ waitForDone() [1/2]

void QThreadPool::waitForDone ( )

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

Definition at line 647 of file qthreadpool.cpp.

Referenced by QHostInfoLookupManager::clear(), QHostInfoLookupManager::waitForThreadPoolDone(), and QCoreApplication::~QCoreApplication().

 {
     Q_D(QThreadPool);
     d->waitForDone();
     d->reset();
 }

◆ waitForDone() [2/2]

bool QThreadPool::waitForDone ( int msecs )

Definition at line 665 of file qthreadpool.cpp.

 {
     Q_D(QThreadPool);
     bool rc = d->waitForDone(msecs);
     if (rc)
       d->reset();
     return rc;
 }

Friends and Related Functions

◆ QFutureInterfaceBase

friend class QFutureInterfaceBase

friend

Definition at line 65 of file qthreadpool.h.

Properties

◆ activeThreadCount

int QThreadPool::activeThreadCount

private

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(), releaseThread()

Definition at line 64 of file qthreadpool.h.

◆ expiryTimeout

int QThreadPool::expiryTimeout

private

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().

Definition at line 62 of file qthreadpool.h.

◆ maxThreadCount

int QThreadPool::maxThreadCount

private

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().

Definition at line 63 of file qthreadpool.h.

Referenced by QHostInfoLookupManager::work().

The documentation for this class was generated from the following files:

/src/corelib/concurrent/qthreadpool.h
/src/corelib/concurrent/qthreadpool.cpp

Public Functions

Static Public Functions

Properties

Friends

Additional Inherited Members

Detailed Description

Constructors and Destructors

◆ QThreadPool()

◆ ~QThreadPool()

Functions

◆ activeThreadCount()

◆ expiryTimeout()

◆ globalInstance()

◆ maxThreadCount()

◆ releaseThread()

◆ reserveThread()

◆ setExpiryTimeout()

◆ setMaxThreadCount()

◆ start()

◆ tryStart()

◆ waitForDone() [1/2]

◆ waitForDone() [2/2]

Friends and Related Functions

◆ QFutureInterfaceBase

Properties

◆ activeThreadCount

◆ expiryTimeout

◆ maxThreadCount