QFuture< T > Class Template Reference

The QFuture class represents the result of an asynchronous computation. More...

#include <qfuture.h>

Classes
class	const_iterator
	The QFuture::const_iterator class provides an STL-style const iterator for QFuture. More...

Public Types
typedef const_iterator	ConstIterator
	Qt-style synonym for QFuture::const_iterator. More...

Public Functions
const_iterator	begin () const
	Returns a const STL-style iterator pointing to the first result in the future. More...
void	cancel ()
	Cancels the asynchronous computation represented by this future. More...
const_iterator	constBegin () const
	Returns a const STL-style iterator pointing to the first result in the future. More...
const_iterator	constEnd () const
	Returns a const STL-style iterator pointing to the imaginary result after the last result in the future. More...
const_iterator	end () const
	Returns a const STL-style iterator pointing to the imaginary result after the last result in the future. More...
bool	isCanceled () const
	Returns true if the asynchronous computation has been canceled with the cancel() function; otherwise returns false. More...
bool	isFinished () const
	Returns true if the asynchronous computation represented by this future has finished; otherwise returns false. More...
bool	isPaused () const
	Returns true if the asynchronous computation has been paused with the pause() function; otherwise returns false. More...
bool	isResultReadyAt (int resultIndex) const
	Returns true if the result at index is immediately available; otherwise returns false. More...
bool	isRunning () const
	Returns true if the asynchronous computation represented by this future is currently running; otherwise returns false. More...
bool	isStarted () const
	Returns true if the asynchronous computation represented by this future has been started; otherwise returns false. More...
	operator T () const
	Returns the first result in the future. More...
bool	operator!= (const QFuture &other) const
	Returns true if other is not a copy of this future; otherwise returns false. More...
QFuture &	operator= (const QFuture &other)
	Assigns other to this future and returns a reference to this future. More...
bool	operator== (const QFuture &other) const
	Returns true if other is a copy of this future; otherwise returns false. More...
void	pause ()
	Pauses the asynchronous computation represented by this future. More...
int	progressMaximum () const
	Returns the maximum progressValue(). More...
int	progressMinimum () const
	Returns the minimum progressValue(). More...
QString	progressText () const
	Returns the (optional) textual representation of the progress as reported by the asynchronous computation. More...
int	progressValue () const
	Returns the current progress value, which is between the progressMinimum() and progressMaximum(). More...
	QFuture ()
	Constructs an empty future. More...
	QFuture (QFutureInterface< T > *p)
	QFuture (const QFuture &other)
	Constructs a copy of other. More...
T	result () const
	Returns the first result in the future. More...
T	resultAt (int index) const
	Returns the result at index in the future. More...
int	resultCount () const
	Returns the number of continuous results available in this future. More...
QList< T >	results () const
	Returns all results from the future. More...
void	resume ()
	Resumes the asynchronous computation represented by this future. More...
void	setPaused (bool paused)
	If paused is true, this function pauses the asynchronous computation represented by the future. More...
void	togglePaused ()
	Toggles the paused state of the asynchronous computation. More...
void	waitForFinished ()
	Waits for the asynchronous computation to finish (including cancel()ed computations). More...
	~QFuture ()
	Destroys the future. More...

Public Variables
QFutureInterface< T >	d

Friends
class	const_iterator
class	QFutureWatcher< T >

Detailed Description

template<typename T>
class QFuture< T >

The QFuture class represents the result of an asynchronous computation.

Note

This class or function is threadsafe.

Since

4.4

To start a computation, use one of the APIs in the Concurrent Programming {Qt Concurrent} framework.

QFuture allows threads to be synchronized against one or more results which will be ready at a later point in time. The result can be of any type that has a default constructor and a copy constructor. If a result is not available at the time of calling the result(), resultAt(), or results() functions, QFuture will wait until the result becomes available. You can use the isResultReadyAt() function to determine if a result is ready or not. For QFuture objects that report more than one result, the resultCount() function returns the number of continuous results. This means that it is always safe to iterate through the results from 0 to resultCount().

QFuture provides a Java-style iterators{Java-style iterator} (QFutureIterator) and an STL-style iterators{STL-style iterator} (QFuture::const_iterator). Using these iterators is another way to access results in the future.

QFuture also offers ways to interact with a runnning computation. For instance, the computation can be canceled with the cancel() function. To pause the computation, use the setPaused() function or one of the pause(), resume(), or togglePaused() convenience functions. Be aware that not all asynchronous computations can be canceled or paused. For example, the future returned by QtConcurrent::run() cannot be canceled; but the future returned by QtConcurrent::mappedReduced() can.

Progress information is provided by the progressValue(), progressMinimum(), progressMaximum(), and progressText() functions. The waitForFinished() function causes the calling thread to block and wait for the computation to finish, ensuring that all results are available.

The state of the computation represented by a QFuture can be queried using the isCanceled(), isStarted(), isFinished(), isRunning(), or isPaused() functions.

QFuture is a lightweight reference counted class that can be passed by value.

QFuture<void> is specialized to not contain any of the result fetching functions. Any QFuture<T> can be assigned or copied into a QFuture<void> as well. This is useful if only status or progress information is needed

• not the actual result data.

To interact with running tasks using signals and slots, use QFutureWatcher.

See also

QFutureWatcher, {Concurrent Programming}{Qt Concurrent}

Definition at line 64 of file qfuture.h.

Typedefs

ConstIterator

template<typename T>

QFuture< T >::ConstIterator

Qt-style synonym for QFuture::const_iterator.

Definition at line 150 of file qfuture.h.

Constructors and Destructors

QFuture() [1/3]

template<typename T>

QFuture< T >::QFuture ( )

inline

Constructs an empty future.

Definition at line 67 of file qfuture.h.

Referenced by QFutureInterface< T >::future().

        : d(QFutureInterface<T>::canceledResult())
    { }

QFuture() [2/3]

template<typename T>

QFuture< T >::QFuture ( QFutureInterface< T > *  resultHolder )

inlineexplicit

Warning

This function is not part of the public interface.

Definition at line 70 of file qfuture.h.

        : d(*p)
    { }

QFuture() [3/3]

template<typename T>

QFuture< T >::QFuture ( const QFuture< T > &  other )

inline

Constructs a copy of other.

See also

operator=()

Definition at line 73 of file qfuture.h.

        : d(other.d)
    { }

~QFuture()

template<typename T>

QFuture< T >::~QFuture ( )

inline

Destroys the future.

Note that this neither waits nor cancels the asynchronous computation. Use waitForFinished() or QFutureSynchronizer when you need to ensure that the computation is completed before the future is destroyed.

Definition at line 76 of file qfuture.h.

Referenced by QFutureInterface< T >::future().

    { }

Functions

begin()

template<typename T>

QFuture::const_iterator QFuture< T >::begin ( ) const

inline

Returns a const STL-style iterator pointing to the first result in the future.

See also

constBegin(), end()

Definition at line 152 of file qfuture.h.

{ return  const_iterator(this, 0); }

cancel()

template<typename T>

void QFuture< T >::cancel ( )

inline

Cancels the asynchronous computation represented by this future.

Note that the cancelation is asynchronous. Use waitForFinished() after calling cancel() when you need synchronous cancelation.

Results currently available may still be accessed on a canceled future, but new results will not become available after calling this function. Any QFutureWatcher object that is watching this future will not deliver progress and result ready signals on a canceled future.

Be aware that not all asynchronous computations can be canceled. For example, the future returned by QtConcurrent::run() cannot be canceled; but the future returned by QtConcurrent::mappedReduced() can.

Definition at line 83 of file qfuture.h.

Referenced by QFutureInterface< T >::future().

{ d.cancel(); }

constBegin()

template<typename T>

QFuture::const_iterator QFuture< T >::constBegin ( ) const

inline

Returns a const STL-style iterator pointing to the first result in the future.

See also

begin(), constEnd()

Definition at line 153 of file qfuture.h.

{ return  const_iterator(this, 0); }

constEnd()

template<typename T>

QFuture::const_iterator QFuture< T >::constEnd ( ) const

inline

Returns a const STL-style iterator pointing to the imaginary result after the last result in the future.

See also

constBegin(), end()

Definition at line 155 of file qfuture.h.

{ return const_iterator(this, -1); }

end()

template<typename T>

QFuture::const_iterator QFuture< T >::end ( ) const

inline

Returns a const STL-style iterator pointing to the imaginary result after the last result in the future.

See also

begin(), constEnd()

Definition at line 154 of file qfuture.h.

{ return const_iterator(this, -1); }

isCanceled()

template<typename T>

bool QFuture< T >::isCanceled ( ) const

inline

Returns true if the asynchronous computation has been canceled with the cancel() function; otherwise returns false.

Be aware that the computation may still be running even though this function returns true. See cancel() for more details.

Definition at line 84 of file qfuture.h.

Referenced by QFutureInterface< T >::future().

{ return d.isCanceled(); }

isFinished()

template<typename T>

bool QFuture< T >::isFinished ( ) const

inline

Returns true if the asynchronous computation represented by this future has finished; otherwise returns false.

Definition at line 93 of file qfuture.h.

Referenced by QFutureInterface< T >::future().

{ return d.isFinished(); }

isPaused()

template<typename T>

bool QFuture< T >::isPaused ( ) const

inline

Returns true if the asynchronous computation has been paused with the pause() function; otherwise returns false.

Be aware that the computation may still be running even though this function returns true. See setPaused() for more details.

See also

setPaused(), togglePaused()

Definition at line 87 of file qfuture.h.

Referenced by QFutureInterface< T >::future().

{ return d.isPaused(); }

isResultReadyAt()

template<typename T>

bool QFuture< T >::isResultReadyAt ( int  index ) const

inline

Returns true if the result at index is immediately available; otherwise returns false.

See also

resultAt(), resultCount()

Definition at line 105 of file qfuture.h.

{ return d.isResultReadyAt(resultIndex); }

isRunning()

template<typename T>

bool QFuture< T >::isRunning ( ) const

inline

Returns true if the asynchronous computation represented by this future is currently running; otherwise returns false.

Definition at line 94 of file qfuture.h.

Referenced by QFutureInterface< T >::future(), and QFuture< T >::const_iterator::operator!=().

{ return d.isRunning(); }

isStarted()

template<typename T>

bool QFuture< T >::isStarted ( ) const

inline

Returns true if the asynchronous computation represented by this future has been started; otherwise returns false.

Definition at line 92 of file qfuture.h.

Referenced by QFutureInterface< T >::future().

{ return d.isStarted(); }

operator T()

template<typename T>

QFuture< T >::operator T ( ) const

inline

Returns the first result in the future.

If the result is not immediately available, this function will block and wait for the result to become available. This is a convenience method for calling result() or resultAt(0).

See also

result(), resultAt(), results()

Definition at line 107 of file qfuture.h.

{ return result(); }

operator!=()

template<typename T>

bool QFuture< T >::operator!= ( const QFuture< T > &  other ) const

inline

Returns true if other is not a copy of this future; otherwise returns false.

Definition at line 81 of file qfuture.h.

{ return (d != other.d); }

operator=()

template<typename T >

QFuture< T > & QFuture< T >::operator= ( const QFuture< T > &  other )

inline

Assigns other to this future and returns a reference to this future.

Definition at line 165 of file qfuture.h.

Referenced by QFutureInterface< T >::future(), and QFuture< T >::~QFuture().

{
    d = other.d;
    return *this;
}

operator==()

template<typename T>

bool QFuture< T >::operator== ( const QFuture< T > &  other ) const

inline

Returns true if other is a copy of this future; otherwise returns false.

Definition at line 80 of file qfuture.h.

{ return (d == other.d); }

pause()

template<typename T>

void QFuture< T >::pause ( )

inline

Pauses the asynchronous computation represented by this future.

This is a convenience method that simply calls setPaused(true).

See also

resume()

Definition at line 88 of file qfuture.h.

Referenced by QFutureInterface< T >::future().

{ setPaused(true); }

progressMaximum()

template<typename T>

int QFuture< T >::progressMaximum ( ) const

inline

Returns the maximum progressValue().

See also

progressValue(), progressMinimum()

Definition at line 99 of file qfuture.h.

Referenced by QFutureInterface< T >::future().

{ return d.progressMaximum(); }

progressMinimum()

template<typename T>

int QFuture< T >::progressMinimum ( ) const

inline

Returns the minimum progressValue().

See also

progressValue(), progressMaximum()

Definition at line 98 of file qfuture.h.

Referenced by QFutureInterface< T >::future().

{ return d.progressMinimum(); }

progressText()

template<typename T>

QString QFuture< T >::progressText ( ) const

inline

Returns the (optional) textual representation of the progress as reported by the asynchronous computation.

Be aware that not all computations provide a textual representation of the progress, and as such, this function may return an empty string.

Definition at line 100 of file qfuture.h.

Referenced by QFutureInterface< T >::future().

{ return d.progressText(); }

progressValue()

template<typename T>

int QFuture< T >::progressValue ( ) const

inline

Returns the current progress value, which is between the progressMinimum() and progressMaximum().

See also

progressMinimum(), progressMaximum()

Definition at line 97 of file qfuture.h.

Referenced by QFutureInterface< T >::future().

{ return d.progressValue(); }

result()

template<typename T >

T QFuture< T >::result ( ) const

inline

Returns the first result in the future.

If the result is not immediately available, this function will block and wait for the result to become available. This is a convenience method for calling resultAt(0).

See also

resultAt(), results()

Definition at line 172 of file qfuture.h.

Referenced by QFuture< T >::operator T(), and QFuture< T >::waitForFinished().

{
    d.waitForResult(0);
    return d.resultReference(0);
}

resultAt()

template<typename T >

T QFuture< T >::resultAt ( int  index ) const

inline

Returns the result at index in the future.

If the result is not immediately available, this function will block and wait for the result to become available.

See also

result(), results(), resultCount()

Definition at line 179 of file qfuture.h.

Referenced by QFuture< T >::waitForFinished().

{
    d.waitForResult(index);
    return d.resultReference(index);
}

resultCount()

template<typename T>

int QFuture< T >::resultCount ( ) const

inline

Returns the number of continuous results available in this future.

The real number of results stored might be different from this value, due to gaps in the result set. It is always safe to iterate through the results from 0 to resultCount().

See also

result(), resultAt(), results()

Definition at line 96 of file qfuture.h.

Referenced by QFutureInterface< T >::future(), and QFuture< T >::const_iterator::operator!=().

{ return d.resultCount(); }

results()

template<typename T>

QList< T > QFuture< T >::results ( ) const

inline

Returns all results from the future.

If the results are not immediately available, this function will block and wait for them to become available.

See also

result(), resultAt(), resultCount()

Definition at line 108 of file qfuture.h.

{ return d.results(); }

resume()

template<typename T>

void QFuture< T >::resume ( )

inline

Resumes the asynchronous computation represented by this future.

This is a convenience method that simply calls setPaused(false).

See also

pause()

Definition at line 89 of file qfuture.h.

Referenced by QFutureInterface< T >::future().

{ setPaused(false); }

setPaused()

template<typename T>

void QFuture< T >::setPaused ( bool  paused )

inline

If paused is true, this function pauses the asynchronous computation represented by the future.

If the computation is already paused, this function does nothing. Any QFutureWatcher object that is watching this future will stop delivering progress and result ready signals while the future is paused. Signal delivery will continue once the future is resumed.

If paused is false, this function resumes the asynchronous computation. If the computation was not previously paused, this function does nothing.

Be aware that not all computations can be paused. For example, the future returned by QtConcurrent::run() cannot be paused; but the future returned by QtConcurrent::mappedReduced() can.

See also

pause(), resume(), togglePaused()

Definition at line 86 of file qfuture.h.

Referenced by QFutureInterface< T >::future(), QFuture< T >::pause(), and QFuture< T >::resume().

{ d.setPaused(paused); }

togglePaused()

template<typename T>

void QFuture< T >::togglePaused ( )

inline

Toggles the paused state of the asynchronous computation.

In other words, if the computation is currently paused, calling this function resumes it; if the computation is running, it is paused. This is a convenience method for calling setPaused(!isPaused()).

See also

setPaused(), pause(), resume()

Definition at line 90 of file qfuture.h.

Referenced by QFutureInterface< T >::future().

{ d.togglePaused(); }

waitForFinished()

template<typename T>

void QFuture< T >::waitForFinished ( )

inline

Waits for the asynchronous computation to finish (including cancel()ed computations).

Definition at line 101 of file qfuture.h.

Referenced by QFutureInterface< T >::future().

{ d.waitForFinished(); }

Friends and Related Functions

const_iterator

template<typename T>

friend class const_iterator

friend

Definition at line 149 of file qfuture.h.

QFutureWatcher< T >

template<typename T>

friend class QFutureWatcher< T >

friend

Definition at line 158 of file qfuture.h.

Properties

d

template<typename T>

QFutureInterface<T> QFuture< T >::d

mutable

Definition at line 161 of file qfuture.h.

Referenced by QFuture< T >::cancel(), QFutureInterface< T >::future(), QFutureWatcher< T >::futureInterface(), QFuture< T >::isCanceled(), QFuture< T >::isFinished(), QFuture< T >::isPaused(), QFuture< T >::isResultReadyAt(), QFuture< T >::isRunning(), QFuture< T >::isStarted(), QFuture< T >::operator!=(), QFuture< T >::const_iterator::operator*(), QFuture< T >::const_iterator::operator->(), QFuture< T >::operator=(), QFuture< T >::operator==(), QFuture< T >::progressMaximum(), QFuture< T >::progressMinimum(), QFuture< T >::progressText(), QFuture< T >::progressValue(), qToVoidFuture(), QFuture< T >::result(), QFuture< T >::resultAt(), QFuture< T >::resultCount(), QFuture< T >::results(), QFuture< T >::setPaused(), QFuture< T >::togglePaused(), and QFuture< T >::waitForFinished().

---

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

• /src/corelib/concurrent/qfuture.h
• /src/corelib/concurrent/qfuture.cpp