Qt 5.6 | Qt Core | C++ Classes | QFutureSynchronizer

Qt 5.6.2 Reference Documentation

# QFutureSynchronizer Class

The QFutureSynchronizer class is a convenience class that simplifies QFuture synchronization. More...

Header: | #include <QFutureSynchronizer>
qmake: | QT += core
Since: | Qt 4.4

- List of all members, including inherited members

## Public Functions

| QFutureSynchronizer()
| QFutureSynchronizer(const QFuture<T> &future)
| ~QFutureSynchronizer()
void | addFuture(const QFuture<T> &future)
bool | cancelOnWait() const
void | clearFutures()
QList<QFuture<T> > | futures() const
void | setCancelOnWait(bool enabled)
void | setFuture(const QFuture<T> &future)
void | waitForFinished()

## Detailed Description

The QFutureSynchronizer class is a convenience class that simplifies QFuture synchronization.

QFutureSynchronizer is a template class that simplifies synchronization of one or more QFuture objects. Futures are added using the addFuture() or setFuture() functions. The futures() function returns a list of futures. Use clearFutures() to remove all futures from the QFutureSynchronizer.

The waitForFinished() function waits for all futures to finish. The destructor of QFutureSynchronizer calls waitForFinished(), providing an easy way to ensure that all futures have finished before returning from a function:

      void someFunction()
      {
          QFutureSynchronizer<void> synchronizer;

          ...

          synchronizer.addFuture(QtConcurrent::run(anotherFunction));
          synchronizer.addFuture(QtConcurrent::map(list, mapFunction));

          return; // QFutureSynchronizer waits for all futures to finish
      }

The behavior of waitForFinished() can be changed using the setCancelOnWait() function. Calling setCancelOnWait(true) will cause waitForFinished() to cancel all futures before waiting for them to finish. You can query the status of the cancel-on-wait feature using the cancelOnWait() function.

See also QFuture, QFutureWatcher, and Qt Concurrent.

## Member Function Documentation

### QFutureSynchronizer::QFutureSynchronizer()

Constructs a QFutureSynchronizer.

### QFutureSynchronizer::QFutureSynchronizer(const QFuture<T> &future)

Constructs a QFutureSynchronizer and begins watching future by calling addFuture().

See also addFuture().

### QFutureSynchronizer::~QFutureSynchronizer()

Calls waitForFinished() function to ensure that all futures have finished before destroying this QFutureSynchronizer.

See also waitForFinished().

### void QFutureSynchronizer::addFuture(const QFuture<T> &future)

Adds future to the list of managed futures.

See also futures().

### bool QFutureSynchronizer::cancelOnWait() const

Returns `true` if the cancel-on-wait feature is enabled; otherwise returns false. If cancel-on-wait is enabled, the waitForFinished() function will cancel all futures before waiting for them to finish.

See also setCancelOnWait() and waitForFinished().

### void QFutureSynchronizer::clearFutures()

Removes all managed futures from this QFutureSynchronizer.

See also addFuture() and setFuture().

### QList<QFuture<T> > QFutureSynchronizer::futures() const

Returns a list of all managed futures.

See also addFuture() and setFuture().

### void QFutureSynchronizer::setCancelOnWait(bool enabled)

Enables or disables the cancel-on-wait feature based on the enabled argument. If enabled is true, the waitForFinished() function will cancel all futures before waiting for them to finish.

See also cancelOnWait() and waitForFinished().

### void QFutureSynchronizer::setFuture(const QFuture<T> &future)

Sets future to be the only future managed by this QFutureSynchronizer. This is a convenience function that calls waitForFinished(), then clearFutures(), and finally passes future to addFuture().

See also addFuture(), waitForFinished(), and clearFutures().

### void QFutureSynchronizer::waitForFinished()

Waits for all futures to finish. If cancelOnWait() returns `true`, each future is canceled before waiting for them to finish.

See also cancelOnWait() and setCancelOnWait().