Qt entry routine (2), qt entry routine

Qt entry routine (2), qt entry routine

This document uses the QtConcurrent: run () function in Qt as an example to describe how to run a function in a separate thread.

1 QtConcurrent: run ()

QtConcurrent is a namespace that provides high-level interface functions (APIs) to automatically adjust the number of running threads of a program based on the actual number of CPU cores in the current computer.

The following is the built-in routines runfunction in Qt, corresponding to the installation directory is D: \ Qt \ Qt5.8.0 \ Examples \ Qt-5.8 \ qtconcurrent \ runfucntion

1.1. pro project file

To use the QtConcurrent module, you must add: QT + = concurrent in. pro.

QT += concurrent widgetsCONFIG += consoleCONFIG -= app_bundleSOURCES += main.cpp

1.2 main. cpp

 1 #include <QApplication> 2 #include <QDebug> 3 #include <QThread> 4  5 #include <QString> 6 #include <QtConcurrent> 7  8 void func(QString name) 9 {10     qDebug() << "Hello" << name << "from" << QThread::currentThread();11 }12 13 int main(int argc, char **argv)14 {15     QApplication app(argc, argv);16 17     QFuture<void> fut1 = QtConcurrent::run(func, QString("Thread 1"));18     QFuture<void> fut2 = QtConcurrent::run(func, QString("Thread 2"));19 20     fut1.waitForFinished();21     fut2.waitForFinished();22 }

As you can see, the QtConcurrent: run () function runs func () in two different threads. The output result is as follows:

Hello "Thread 2" from QThread(0x3597f0, name = "Thread (pooled)")Hello "Thread 1" from QThread(0x337720, name = "Thread (pooled)")

The following is a detailed explanation of the use of QtConcurrent: run (). After reading 2 and 3, let's take a look at the above runfunction routine, which is very easy to understand.

 2. Common functions

2.1 run the function in a thread

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

If you want to specify a thread pool for it, you can pass the pointer of the thread pool as the first parameter.

extern void func();QThreadPool pool;QFuture<void> future = QtConcurrent::run(&pool, func);

2.2 pass parameters to the Function

Parameters to be passed must be added after the function name.

extern void FuncWithArguments(int arg1, const QString &string); int integer = ...; QString string = ...; QFuture<void> future = QtConcurrent::run(FuncWithArguments,integer,string);

2.3 obtain the calculation result of this function

extern QString Func(const QByteArray &input);QByteArray byte_array = ...;QFuture<QString> future = QtConcurrent::run(func, byte_array);...QString result = future.result();

3. member functions

To run a member function in a class in a thread, you can pass the reference or pointer pointing to the class instance as the first parameter of QtConcurrent: run,

Constant member functions generally pass the const reference, while very many member functions generally pass the pointer (pointer)

3.1 constant member functions

In a separate thread, the constant member function split () that calls QByteArray is passed to the run () function. The parameter is bytearray.

  QByteArray bytearray = "hello world";  QFuture<QList<QByteArray> > future = QtConcurrent::run(bytearray, &QByteArray::split, ',');  ...  QList<QByteArray> result = future.result();

3.2 extraordinary member functions

In a separate thread, the invertPixels () function that calls the QImage extraordinary member function is passed to the run () function. The parameter is & image

  QImage image = ...;  QFuture<void> future = QtConcurrent::run(&image, &QImage::invertPixels, QImage::InvertRgba);  ...  future.waitForFinished();
  // At this point, the pixels in 'image' have been inverted

 

References:

Qt assistant | Qt 5.8 | Qt Concurrent | Concurrent Run