The QThread class provides a platform independent way to manage threads. More...

Inheritance diagram for QThread:

Public Types
enum	Priority

Public Signals
void	finished ()

void	started ()

Public Signals inherited from QObject
void	destroyed (QObject *obj=nullptr)

void	objectNameChanged (const QString &objectName)

Public Slots
void	quit ()

void	start (Priority priority=InheritPriority)

void	terminate ()

Public Slots inherited from QObject
void	deleteLater ()

Public Methods
	QThread (QObject *parent=nullptr)

	~QThread ()

bool	event (QEvent *event) override

QAbstractEventDispatcher *	eventDispatcher () const

void	exit (int returnCode=0)

bool	isFinished () const

bool	isInterruptionRequested () const

bool	isRunning () const

int	loopLevel () const

Priority	priority () const

void	requestInterruption ()

void	setEventDispatcher (QAbstractEventDispatcher *eventDispatcher)

void	setPriority (Priority priority)

void	setStackSize (uint stackSize)

uint	stackSize () const

bool	wait (unsigned long time=ULONG_MAX)

Public Methods inherited from QObject
	QObject (QObject *parent=nullptr)

	~QObject ()

bool	blockSignals (bool block)

const QList< QObject * > &	children () const

bool	connect (const QObject *sender, const QString &signalMethod, const QString &location, const QString &slotMethod, Qt::ConnectionType type=Qt::AutoConnection)

bool	connect (const QObject *sender, const QString &signalMethod, const QString &slotMethod, Qt::ConnectionType type=Qt::AutoConnection)

bool	disconnect (const QObject *receiver, const QString &slotMethod=QString ()) const

bool	disconnect (const QString &signalMethod, const QString &location, const QObject *receiver=nullptr, const QString &slotMethod=QString ()) const

bool	disconnect (const QString &signalMethod=QString (), const QObject *receiver=nullptr, const QString &slotMethod=QString ()) const

void	dumpObjectInfo ()

void	dumpObjectTree ()

QList< QString >	dynamicPropertyNames () const

virtual bool	eventFilter (QObject watched, QEvent event)

template<typename T >
T	findChild (const QString &childName=QString ()) const

template<class T >
QList< T >	findChildren (const QRegularExpression &regExp, Qt::FindChildOptions options=Qt::FindChildrenRecursively) const

template<class T >
QList< T >	findChildren (const QString &childName=QString (), Qt::FindChildOptions options=Qt::FindChildrenRecursively) const

bool	inherits (const QString &className) const

void	installEventFilter (QObject *filterObj)

bool	isWidgetType () const

bool	isWindowType () const

void	killTimer (int id)

const QMetaObject *	metaObject () const

void	moveToThread (QThread *targetThread)

QString	objectName () const

QObject *	parent () const

template<class T = QVariant>
T	property (const QString &name) const

void	removeEventFilter (QObject *obj)

void	setObjectName (const QString &name)

void	setParent (QObject *parent)

bool	setProperty (const QString &name, const QVariant &value)

bool	signalsBlocked () const

int	startTimer (int interval, Qt::TimerType timerType=Qt::CoarseTimer)

QThread *	thread () const

Static Public Methods
static QThread *	currentThread ()

static Qt::HANDLE	currentThreadId ()

static int	idealThreadCount ()

static void	msleep (unsigned long msecs)

static void	sleep (unsigned long secs)

static void	usleep (unsigned long usecs)

static void	yieldCurrentThread ()

Static Public Methods inherited from QObject
static bool	connect (const QObject sender, const QMetaMethod &signalMethod, const QObject receiver, const QMetaMethod &slotMethod, Qt::ConnectionType type=Qt::AutoConnection)

static bool	connect (const QObject sender, const QString &signalMethod, const QObject receiver, const QString &slotMethod, Qt::ConnectionType type=Qt::AutoConnection, const QString &location=QString ())

static bool	connect (const QObject sender, const QString &signalMethod, const QString &location, const QObject receiver, const QString &slotMethod, Qt::ConnectionType type=Qt::AutoConnection)

template<class Sender , class SignalClass , class... SignalArgs, class Receiver , class SlotClass , class... SlotArgs, class SlotReturn >
static bool	connect (const Sender sender, void (SignalClass::signalMethod)(SignalArgs...), const Receiver receiver, SlotReturn (SlotClass::slotMethod)(SlotArgs...), Qt::ConnectionType type=Qt::AutoConnection)

template<class Sender , class SignalClass , class... SignalArgs, class Receiver , class T >
static bool	connect (const Sender sender, void (SignalClass::signalMethod)(SignalArgs...), const Receiver *receiver, T slotLambda, Qt::ConnectionType type=Qt::AutoConnection)

static bool	disconnect (const QObject sender, const QMetaMethod &signalMethod, const QObject receiver, const QMetaMethod &slotMethod)

static bool	disconnect (const QObject sender, const QString &signalMethod, const QObject receiver, const QString &slotMethod)

static bool	disconnect (const QObject sender, const QString &signalMethod, const QString &location, const QObject receiver, const QString &slotMethod)

static bool	disconnect (const QObject sender, std::nullptr_t, const QObject receiver, std::nullptr_t)

template<class Sender , class SignalClass , class... SignalArgs, class Receiver , class SlotClass , class... SlotArgs, class SlotReturn >
static bool	disconnect (const Sender sender, void (SignalClass::signalMethod)(SignalArgs...), const Receiver receiver, SlotReturn (SlotClass::slotMethod)(SlotArgs...))

template<class Sender , class SignalClass , class... SignalArgs, class Receiver >
static bool	disconnect (const Sender sender, void (SignalClass::signalMethod)(SignalArgs...), const Receiver *receiver, std::nullptr_t slotMethod=nullptr)

template<class Sender , class SignalClass , class... SignalArgs, class Receiver , class T >
static bool	disconnect (const Sender sender, void (SignalClass::signalMethod)(SignalArgs...), const Receiver *receiver, T slotMethod)

static QMetaObject &	staticMetaObject ()

static QString	tr (const char text, const char comment=nullptr, std::optional< int > numArg=std::optional< int >())

Protected Methods
int	exec ()

virtual void	run ()

Protected Methods inherited from QObject
virtual void	childEvent (QChildEvent *event)

virtual void	connectNotify (const QMetaMethod &signalMethod) const

virtual void	customEvent (QEvent *event)

virtual void	disconnectNotify (const QMetaMethod &signalMethod) const

bool	isSignalConnected (const QMetaMethod &signalMethod) const

int	receivers (const QString &signal) const

QObject *	sender () const

int	senderSignalIndex () const

virtual void	timerEvent (QTimerEvent *event)

Static Protected Methods
static void	setTerminationEnabled (bool enabled=true)

Friends
class	QCoreApplication

Additional Inherited Members
Properties inherited from QObject
	objectName

Related Functions inherited from QObject
T	qobject_cast (QObject *object)

	QObjectList

Detailed Description

The QThread class provides a platform independent way to manage threads. A QThread object manages one thread of control within the program. QThreads begin executing in run(). By default, run() starts the event loop by calling exec() and runs a CopperSpice event loop inside the thread.

You can use worker objects by moving them to the thread using QObject::moveToThread().

class Worker : public QObject
{
    CS_OBJECT(Worker)
 
    QThread workerThread;
 
    public:
       CS_SIGNAL_1(Public, void resultReady(const QString &result))
       CS_SIGNAL_2(resultReady, result)
 
       CS_SLOT_1(Public, void doWork(const QString &parameter) { emit resultReady(result);})
       CS_SLOT_2(doWork)
};
 
class Controller : public QObject
{
    CS_OBJECT(Controller)
 
    QThread workerThread;
 
    public:
       Controller() {
           Worker *worker = new Worker;
           worker->moveToThread(&workerThread);
           connect(workerThread, SIGNAL(finished()), worker, SLOT(deleteLater()));
           connect(this, SIGNAL(operate(QString)),   worker, SLOT(doWork(QString)));
           connect(worker, SIGNAL(resultReady(QString)), this, SLOT(handleResults(QString)));
           workerThread.start();
       }
 
       ~Controller() {
           workerThread.quit();
           workerThread.wait();
       }
 
    public:
       CS_SIGNAL_1(Public, void operate(const QString &data))
       CS_SIGNAL_2(operate, data)
 
       CS_SLOT_1(Public, void handleResults(const QString &))
       CS_SLOT_2(handleResults)
};

The code inside the Worker's slot would then execute in a separate thread. However, you can connect the Worker's slots to any signal, from any object, in any thread. It is safe to connect signals and slots across different threads due to the queued connection mechanism. Refer to Qt::ConnectionType for additional information.

Another way to make code run in a separate thread, is to subclass QThread and reimplement run().

class WorkerThread : public QThread
{
    CS_OBJECT(WorkerThread)
 
    void run() {
        QString result;
 
        /* expensive or blocking operation  */
        emit resultReady(result);
    }
 
    public:
       CS_SIGNAL_1(Public, void resultReady(const QString &s))
       CS_SIGNAL_2(operate, s)
};
 
void MyObject::startWorkInAThread()
{
    WorkerThread *workerThread = new WorkerThread(this);
    connect(workerThread, SIGNAL(resultReady(QString)), this, SLOT(handleResults(QString)));
    connect(workerThread, SIGNAL(finished()), workerThread, SLOT(deleteLater()));
    workerThread->start();
}

In that example the thread will exit after the run function has returned. There will not be any event loop running in the thread unless you call exec().

It is important to remember that a QThread instance lives in the old thread that instantiated it, not in the new thread that calls run(). This means that all of QThread's queued slots will execute in the old thread. Thus, a developer who wishes to invoke slots in the new thread must use the worker-object approach; new slots should not be implemented directly into a subclassed QThread.

When subclassing QThread, keep in mind that the constructor executes in the old thread while run() executes in the new thread. If a member variable is accessed from both functions, then the variable is accessed from two different threads. Check that it is safe to do so.

Care must be taken when interacting with objects across different threads. Refer to Synchronizing Threads for details.

Managing Threads

QThread will notify you via a signal when the thread is started(), finished(), and terminated(), or you can use isFinished() and isRunning() to query the state of the thread.

You can stop the thread by calling exit() or quit(). In extreme cases you may want to forcibly terminate() an executing thread. However doing so is dangerous and discouraged. Please read the documentation for terminate() and setTerminationEnabled() for detailed information.

It is possible to deallocate objects that live in a thread that has just ended by connecting the finished() signal to QObject::deleteLater().

The static functions currentThreadId() and currentThread() return identifiers for the currently executing thread. The former returns a platform specific ID for the thread, the latter returns a QThread pointer.

To choose the name that your thread will be given (as identified by the command ps -L on Linux, for example), you can call setObjectName() before starting the thread. If you do not call setObjectName(), the name given to your thread will be the class name of the runtime type of your thread object. This feature is not available with release builds on Windows.

Blocking Threads

Use wait() to block the calling thread, until the other thread has finished execution (or until a specified time has passed). QThread also provides static, platform independent sleep functions: sleep(), msleep(), and usleep() allow full second, millisecond, and microsecond resolution respectively.

Note: The wait() and sleep() methods should be avoided since CopperSpice is an event driven system. Instead of wait(), consider listening for the finished() signal. Instead of the sleep() methods consider using QTimer.

See also: Multithreading, QThreadStorage, Synchronizing Threads

Member Enumeration Documentation

enum QThread::Priority

This enum type indicates how the operating system should schedule newly created threads.

Constant	Value	Description
`QThread::IdlePriority`	`0`	Scheduled only when no other threads are running.
`QThread::LowestPriority`	`1`	Scheduled less often than LowPriority.
`QThread::LowPriority`	`2`	Scheduled less often than NormalPriority.
`QThread::NormalPriority`	`3`	Default priority of the operating system.
`QThread::HighPriority`	`4`	Scheduled more often than NormalPriority.
`QThread::HighestPriority`	`5`	Scheduled more often than HighPriority.
`QThread::TimeCriticalPriority`	`6`	Scheduled as often as possible.
`QThread::InheritPriority`	`7`	Use the same priority as the creating thread, this is the default.

Constructor & Destructor Documentation

QThread::QThread ( QObject * parent = nullptr )

explicit

Constructs a new QThread to manage a new thread. The parent takes ownership of the QThread. The thread does not begin executing until start() is called.

See also: start()

QThread::~QThread ( )

Destroys the QThread.

Deleting a QThread object will not stop the execution of the thread it manages. Deleting a running QThread, where isFinished() returns false, will most likely result in a program crash. Wait for the finished() signal before deleting the QThread.

Method Documentation

QThread * QThread::currentThread ( )

static

Returns a pointer to a QThread which manages the currently executing thread.

Qt::HANDLE QThread::currentThreadId ( )

static

Returns the thread handle of the currently executing thread.

Warning: The handle returned by this method is used for internal purposes and should not be used in any application code.; On Windows, the returned value is a pseudo-handle for the current thread. It can not be used for numerical comparison. i.e., this function returns the DWORD (Windows-Thread ID) returned by the Win32 function getCurrentThreadId(), not the HANDLE (Windows-Thread HANDLE) returned by the Win32 function getCurrentThread().

bool QThread::event ( QEvent * event )

overridevirtual

Receives events to an object and should return true if the given event was recognized and processed. This method can be overridden to customize the event handling for an object.

See also: installEventFilter(), timerEvent(), QApplication::sendEvent(), QApplication::postEvent(), QWidget::event()

Reimplemented from QObject::event()

QAbstractEventDispatcher * QThread::eventDispatcher ( ) const

Returns a pointer to the event dispatcher object for the thread. If no event dispatcher exists for the thread, this function returns nullptr.

See also: setEventDispatcher()

int QThread::exec ( )

protected

Enters the event loop and waits until exit() is called, returning the value that was passed to exit(). The value returned is 0 if exit() is called via quit(). This method is meant to be called from within run(). It is necessary to call this method to start event handling.

See also: quit(), exit()

void QThread::exit ( int returnCode = 0 )

Instructs the thread's event loop to exit with a return code. After calling this method the thread leaves the event loop and returns from the call to QEventLoop::exec(). The QEventLoop::exec() method returns returnCode. A returnCode of 0 means success, any non-zero value indicates an error.

No QEventLoops will be started in this thread until QThread::exec() has been called again. If the eventloop in QThread::exec() is not running then the next call to QThread::exec() will also return immediately.

Unlike the C library function of the same name this method does return to the caller, it is event processing which stops.

See also: quit(), QEventLoop

void QThread::finished ( )

signal

This signal is emitted when the thread has finished executing.

See also: started()

int QThread::idealThreadCount ( )

static

Returns the ideal number of threads that can be run on the system. This is done querying the number of processor cores, both real and logical, in the system. This method returns -1 if the number of processor cores could not be detected.

bool QThread::isFinished ( ) const

Returns true if the thread is finished, otherwise returns false.

See also: isRunning()

bool QThread::isInterruptionRequested ( ) const

Return true if the task running on this thread should be stopped. An interruption can be requested by requestInterruption().

This method can be used to make long running tasks cleanly interruptible. Never checking or acting on the value returned by this function is safe, however it is advisable do so regularly in long running functions. Take care not to call it too often, to keep the overhead low.

void long_task() {
   while (true) {
      if (QThread::currentThread()->isInterruptionRequested()) {
         return;
      }
   }
}

See also: currentThread(), requestInterruption()

bool QThread::isRunning ( ) const

Returns true if the thread is running, otherwise returns false.

See also: isFinished()

int QThread::loopLevel ( ) const

Returns the current event loop level for the thread.

Note: This method must only be called in the current thread.

void QThread::msleep ( unsigned long msecs )

static

Forces the current thread to sleep for msecs milliseconds.

See also: sleep(), usleep()

Priority QThread::priority ( ) const

Returns the priority for a running thread. If the thread is not running, this function returns InheritPriority.

See also: Priority, setPriority(), start()

void QThread::quit ( )

slot

Tells the thread's event loop to exit with return code 0 (success). Equivalent to calling QThread::exit(0). This method does nothing if the thread does not have an event loop.

See also: exit(), QEventLoop

void QThread::requestInterruption ( )

Request the interruption of the thread. That request is advisory and it is up to code running on the thread to decide if and how it should act upon such request. This method does not stop any event loop running on the thread and does not terminate it in any way.

See also: isInterruptionRequested()

void QThread::run ( )

protectedvirtual

The starting point for the thread. After calling start(), the newly created thread calls this function. The default implementation simply calls exec().

You can reimplement this function to facilitate advanced thread management. Returning from this method will end the execution of the thread.

See also: start(), wait()

void QThread::setEventDispatcher ( QAbstractEventDispatcher * eventDispatcher )

Sets the event dispatcher for the thread to eventDispatcher. This is only possible as long as there is no event dispatcher installed for the thread yet. That is, before the thread has been started with start() or, in case of the main thread, before QCoreApplication has been instantiated. This method takes ownership of the object.

See also: eventDispatcher()

void QThread::setPriority ( Priority priority )

This function sets the priority for a running thread. If the thread is not running, this function does nothing and returns immediately. Use start() to start a thread with a specific priority.

The priority argument can be any value in the QThread::Priority enum except for InheritPriority.

The effect of the priority parameter is dependent on the operating system's scheduling policy. In particular, the priority will be ignored on systems that do not support thread priorities such as on Linux. Refer to http://linux.die.net/man/2/sched_setscheduler for more details.

See also: Priority, priority(), start()

void QThread::setStackSize ( uint stackSize )

Sets the maximum stack size for the thread to stackSize. If stackSize is greater than zero, the maximum stack size is set to stackSize bytes, otherwise the maximum stack size is automatically determined by the operating system.

Warning: Most operating systems place minimum and maximum limits on thread stack sizes. The thread will fail to start if the stack size is outside these limits.

See also: stackSize()

void QThread::setTerminationEnabled ( bool enabled = true )

staticprotected

Enables or disables termination of the current thread based on the enabled parameter. The thread must have been started by QThread. When enabled is false, termination is disabled. Future calls to QThread::terminate() will return immediately without effect. Instead, the termination is deferred until termination is enabled.

When enabled is true, termination is enabled. Future calls to QThread::terminate() will terminate the thread normally. If termination has been deferred (i.e. QThread::terminate() was called with termination disabled), this function will terminate the calling thread immediately This method will not return in this case.

See also: terminate()

void QThread::sleep ( unsigned long secs )

static

Forces the current thread to sleep for secs seconds.

See also: msleep(), usleep()

uint QThread::stackSize ( ) const

Returns the maximum stack size for the thread (if set with setStackSize()), otherwise returns zero.

See also: setStackSize()

void QThread::start ( Priority priority = InheritPriority )

slot

Begins execution of the thread by calling run(). The operating system will schedule the thread according to the priority parameter. If the thread is already running, this function does nothing.

The effect of the given priority is dependent on the operating system's scheduling policy. In particular, the priority will be ignored on systems which do not support thread priorities such as on Linux. Refer to https://linux.die.net/man/2/sched_setscheduler for more details.

See also: run(), terminate()

void QThread::started ( )

signal

This signal is emitted when the thread starts executing.

See also: finished()

void QThread::terminate ( )

slot

Terminates the execution of the thread. The thread may or may not be terminated immediately, depending on the operating system's scheduling policies. Listen for the terminated() signal, or use QThread::wait() after terminate(), to be sure.

When the thread is terminated, all threads waiting for the thread to finish will be woken up.

Termination can be explicitly enabled or disabled by calling QThread::setTerminationEnabled(). Calling this function while termination is disabled results in the termination being deferred, until termination is re-enabled. See the documentation of QThread::setTerminationEnabled() for more information.

Warning: This method is somewhat dangerous and using it is discouraged. The thread can be terminated at any point in its code path. Threads can be terminated while modifying data. There is no chance for the thread to clean up after itself, unlock any held mutexes, etc. In short, use this function only if absolutely necessary.

See also: setTerminationEnabled()

void QThread::usleep ( unsigned long usecs )

static

Forces the current thread to sleep for usecs microseconds.

See also: sleep(), msleep()

bool QThread::wait ( unsigned long time = ULONG_MAX )

Blocks the thread until either of these conditions is met:

The thread associated with this QThread object has finished execution (i.e. when it returns from run()). This method will return true if the thread has finished. It also returns true if the thread has not been started yet.
time milliseconds has elapsed. If time is ULONG_MAX (the default), then the wait will never timeout (the thread must return from run()). This function will return false if the wait timed out.

This provides similar functionality to the POSIX pthread_join() function.

See also: sleep(), terminate()

void QThread::yieldCurrentThread ( )

static

Yields execution of the current thread to another runnable thread, if any. The operating system decides to which thread to switch.

Public Types

Public Signals

Public Slots

Public Methods

Static Public Methods

Protected Methods

Static Protected Methods

Friends

Additional Inherited Members

Detailed Description

Managing Threads

Blocking Threads

Member Enumeration Documentation

Constructor & Destructor Documentation

Method Documentation