c++ - Qt 异步调用 : how to run something after an async call has finished its job

Question

我有如下代码进行异步调用:

QMetaObject::invokeMethod(this, "endSelectionHandling", Qt::QueuedConnection);

我想这样修改代码:

QMetaObject::invokeMethod(this, "endSelectionHandling", Qt::QueuedConnection);

// I want to add statements here which depend on the result of the above async call.
// How can I wait for the above async call to finish its jobs?

如何等待 Qt asycn 调用完成它的工作？有没有更好的方法？

Answer 1

在您的问题中，您似乎根本不需要异步调用，因为您在进行异步调用后立即等待结果。

但是，如果中间有一些代码，您可以使用 C++11 的 std::async异步调用该函数，然后等待其 std::future无论何时何地，您在完成其他操作后需要它的结果。

这是一个例子:

#include <iostream>
#include <future>
#include <thread>
#include <chrono>

#define LOG()    std::cout << __func__ << " : "

void test()
{
    LOG() << "IN\n";

    using namespace std::chrono_literals;
    std::this_thread::sleep_for( 1s );

    LOG() << "OUT\n";
}

int main()
{
    LOG() << "Calling test()...\n";

    auto f = std::async( std::launch::async, test );

    LOG() << "Running test()...\n";

    // ...                             ...
    // ... You can do other stuff here ...
    // ...                             ...

    f.wait(); // Blocking call to wait for the result to be available

    LOG() << "Exiting...\n";

    return 0;
}

这是输出:

main : Calling test()...
main : Running test()...
test : IN
test : OUT
main : Exiting...

这是实际示例:https://ideone.com/OviYU6

更新:

但是，在 Qt 领域，您可能想要使用 QtConcurrent::run和 QFuture以 Qt 方式做事。

例子如下:

#include <QDebug>
#include <QtConcurrent>
#include <QFuture>
#include <QThread>

#define LOG()    qDebug() << __func__ << ": "

void test()
{
    LOG() << "IN";

    QThread::sleep( 1 );

    LOG() << "OUT";
}

int main()
{
    LOG() << "Calling test()...";

    auto f = QtConcurrent::run( test );

    LOG() << "Running test()...";

    // ...                             ...
    // ... You can do other stuff here ...
    // ...                             ...

    f.waitForFinished(); // Blocking call to wait for function to finish

    LOG() << "Exiting...";

    return 0;
}

这是输出:

main : Calling test()...
main : Running test()...
test : IN
test : OUT
main : Exiting...