CopperSpice API  1.7.2
QThread Class Reference

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

Inheritance diagram for QThread:
QObject

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
 
QAbstractEventDispatchereventDispatcher () 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< QStringdynamicPropertyNames () const
 
virtual bool eventFilter (QObject *watched, QEvent *event)
 
template<typename 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 &objName=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 QMetaObjectmetaObject () const
 
void moveToThread (QThread *targetThread)
 
QString objectName () const
 
QObject * parent () const
 
template<class T = QVariant>
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)
 
QThreadthread () 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)
 
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 QMetaObjectstaticMetaObject ()
 
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
 

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

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

ConstantValueDescription
QThread::IdlePriority0Scheduled only when no other threads are running.
QThread::LowestPriority1Scheduled less often than LowPriority.
QThread::LowPriority2Scheduled less often than NormalPriority.
QThread::NormalPriority3Default priority of the operating system.
QThread::HighPriority4Scheduled more often than NormalPriority.
QThread::HighestPriority5Scheduled more often than HighPriority.
QThread::TimeCriticalPriority6Scheduled as often as possible.
QThread::InheritPriority7Use 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.

Note that deleting a QThread object will not stop the execution of the thread it manages. Deleting a running QThread (i.e. isFinished() returns false) will probably 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

This virtual method receives events to an object and should return true if the event event was recognized and processed. The event() method can be overridden to customize the behavior of an object.

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

Reimplemented from QObject.

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. By convention a returnCode of 0 means success, any non-zero value indicates an error.

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

No QEventLoops will be started anymore 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.

See also
quit(), QEventLoop
void QThread::finished ( )
signal

This signal is emitted when the thread has finished executing.

See also
started(), terminated()
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) {
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. Note that this function 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 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, see http://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(), terminated()
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. Note that the operating system decides to which thread to switch.