c++ - 如何在 Qt 中等待线程完成而不阻塞其执行？

Question

我有一个函数可以创建一堆 QThreads 来加速长时间的计算，但是当我尝试休眠直到计算完成时，后台线程由于某种原因永远不会执行。

我无法弄清楚为什么在我调用 thread->start() 后线程不执行。这是我的代码:

multithread.run_multithread(run_function, thread_count);
while(multithread.running)
    QThread::msleep(100);
qDebug() << "done";  // Never reaches this point

以及多线程函数:

void Multithread::run_multithread(std::function<void
 (int)>run_function_in, int thread_count) {
    running = true;
    // Create workers and threads
    int thread_idx;
    for(thread_idx=0; thread_idx<thread_count; thread_idx++) {
        ThreadWorker *worker = new ThreadWorker(this, run_function_in);
        QThread *thread = new QThread();
        // Set workers and threads to delete when done
        worker->moveToThread(thread);
        connect(worker, &ThreadWorker::finished, this, &Multithread::check_progress);
        connect(thread, &QThread::started, worker, &ThreadWorker::run);
        connect(worker, &ThreadWorker::finished, thread, &QThread::quit);
        connect(worker, &ThreadWorker::finished, worker, &ThreadWorker::deleteLater);
        connect(thread, &QThread::finished, thread, &QThread::deleteLater);
        // Start thread
        thread->start();
    }
}

running 在 Multithread::check_progress 中被设置为 false 当所有线程完成他们的部分计算时。当我删除 QThread::msleep(100) 时，计算将正常执行，但我需要一些方法来阻止直到它完成。

Answer 1

我建议使用 Qt Concurrent 功能，而不是使用 QThread，它提供了比线程原语更高级别的抽象。您可以使用 QFutureSynchronizer 等待多个并发 future 完成。该对象将等待所有附加的 futures 完成，然后才允许自身被销毁。

如何启动多个线程然后等待它们全部完成的示例是:

#include <QtConcurrent>

void run_multithread(...) {
  // Set up a new synchronizer.
  QFutureSynchronizer<void> synchronizer;

  // Run n tasks in parallel.
  for (int thread_idx = 0; thread_idx < thread_count; ++thread_idx) {
    synchronizer.addFuture(QtConcurrent::run(run_function_in));
  }

  // The synchroniser will wait for all threads to finish before returning.
}