並發運行

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 框架。

在單獨綫程中運行函數

To run a function in another thread, use QtConcurrent::run():

extern void aFunction();
QFuture<void> future = QtConcurrent::run(aFunction);

這將運行 aFunction in a separate thread obtained from the default QThreadPool 。可以使用 QFuture and QFutureWatcher classes to monitor the status of the function.

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);

把自變量傳遞給函數

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.

從函數返迴值

Any return value from the function is available via QFuture :

extern QString functionReturningAString();
QFuture<QString> future = QtConcurrent::run(functionReturningAString);
...
QString result = future.result();

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();

注意， 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.

額外 API 特徵

使用成員函數

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.

例如：調用 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

使用 Lambda 函數

Calling a lambda function is done like this:

QFuture<void> future = QtConcurrent::run([=]() {
    // Code in this block will run in another thread
});
...