The QtConcurrent::run() function runs a function in a separate thread. The return value of the function is made available through the QFuture API.
This function is a part of the Qt Concurrent framework.
To run a function in another thread, use QtConcurrent::run():
To use a dedicated thread pool, you can pass the QThreadPool as the first argument:
extern void aFunction(); QThreadPool pool; QFuture<void> future = QtConcurrent::run(&pool, aFunction);
Passing arguments to the function is done by adding them to the QtConcurrent::run() call immediately after the function name. For example:
extern void aFunctionWithArguments(int arg1, double arg2, const QString &string); int integer = ...; double floatingPoint = ...; QString string = ...; QFuture<void> future = QtConcurrent::run(aFunctionWithArguments, integer, floatingPoint, string);
A copy of each argument is made at the point where QtConcurrent::run() is called, and these values are passed to the thread when it begins executing the function. Changes made to the arguments after calling QtConcurrent::run() are not visible to the thread.
Any return value from the function is available via QFuture:
extern QString functionReturningAString(); QFuture<QString> future = QtConcurrent::run(functionReturningAString); ... QString result = future.result();
If you don't need the result (for example, because the function returns
void), using the QThreadPool::start() overload taking a function object is more efficient.
As documented above, passing arguments is done like this:
extern QString someFunction(const QByteArray &input); QByteArray bytearray = ...; QFuture<QString> future = QtConcurrent::run(someFunction, bytearray); ... QString result = future.result();
Note that the QFuture::result() function blocks and waits for the result to become available. Use QFutureWatcher to get notification when the function has finished execution and the result is available.
QtConcurrent::run() also accepts pointers to member functions. The first argument must be either a const reference or a pointer to an instance of the class. Passing by const reference is useful when calling const member functions; passing by pointer is useful for calling non-const member functions that modify the instance.
For example, calling QByteArray::split() (a const member function) in a separate thread is done like this:
// call 'QList<QByteArray> QByteArray::split(char sep) const' in a separate thread QByteArray bytearray = "hello world"; QFuture<QList<QByteArray> > future = QtConcurrent::run(bytearray, &QByteArray::split, ','); ... QList<QByteArray> result = future.result();
Calling a non-const member function is done like this:
// call 'void QImage::invertPixels(InvertMode mode)' in a separate thread QImage image = ...; QFuture<void> future = QtConcurrent::run(&image, &QImage::invertPixels, QImage::InvertRgba); ... future.waitForFinished(); // At this point, the pixels in 'image' have been inverted
Calling a lambda function is done like this:
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