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我正在尝试为 Qt 编写一个类似屏障的同步原语，以确保在某个点启动多个线程。但是，当我没有得到信号（例如，started()）为我工作时，我似乎遇到了这种情况。

我试图缩小代码以编译一个最小（非）工作示例。

========
main.cpp
========
#include <QtCore>
#include <QCoreApplication>

#include "qmultithreadwaiter.hpp"
#include <QSignalMapper>
#include <qdebug.h>

#define dlog qDebug()

class Test: public QThread {

public:
   virtual void run( ) {
      QThread::sleep( 500 );
   }
};

int main( int argc, char *argv[ ] ) {
   QCoreApplication a( argc, argv );
   Test t1, t2;
   QMultiThreadWaiter w;
   w.addThread(1, &t1);
   w.addThread(2, &t2);

   t1.start();
   t2.start();

   w.wait4all();
   dlog << "Wait completed";

   return 0;
}

=========================
qmultithreadwaiter.hpp
=========================    
// Qt includes
#include <QSignalMapper>
#include <QMap>
#include <QThread>

class QMultiThreadWaiter: public QThread {
Q_OBJECT

   QMap < int, bool > started;
   QSignalMapper sm;

private slots:
   void threadStarted( int id );
   void someThreadStarted();

signals:
   void allStarted( );

public:
   QMultiThreadWaiter( );

   void addThread( int id, QThread* t );
   void wait4all( );

};
=================
qmultithreadwaiter.cpp
=================
#include "qmultithreadwaiter.hpp"

// Qt includes
#include <QThread>
// Debug includes
#include <qdebug.h>

#define dlog qDebug()

// Project includes

void QMultiThreadWaiter::threadStarted( int id ) {
   dlog << "Thread #" << id << " started!";
   started[ id ] = true;
   QMapIterator < int, bool > mi( started );
   while ( mi.hasNext( ) ) {
      mi.next( );
      if ( !mi.value( ) )
         return;
   }

   dlog << "All threads started!";

   // All threads are started
   emit allStarted( );
}

void QMultiThreadWaiter::addThread( int id, QThread* t ) {
   dlog << "Adding thread " << t << " with id " << id;
   sm.setMapping( t, id );
   connect( t, SIGNAL(started()), &sm, SLOT(map()), Qt::QueuedConnection );
   connect( t, SIGNAL(started()), this, SLOT(someThreadStarted()),
            Qt::QueuedConnection );
}
void QMultiThreadWaiter::wait4all( ) {
   dlog << "Starting this thread";
   start( );
   dlog << "Going to wait";
   wait( );
   dlog << "Wait finished";
}

QMultiThreadWaiter::QMultiThreadWaiter( ) {
   sm.moveToThread( this );
   connect( &sm, SIGNAL(mapped(int)), this, SLOT(threadStarted(int)),
            Qt::QueuedConnection );
   connect( this, SIGNAL(allStarted()), this, SLOT(quit()),
            Qt::QueuedConnection );
   connect( this, SIGNAL(started()), this, SLOT( someThreadStarted()),
            Qt::QueuedConnection );
}

void QMultiThreadWaiter::someThreadStarted( ) {
   dlog << "Some thread started!";
}

输出：

Adding thread  QThread(0x28fefc)  with id  1 
Adding thread  QThread(0x28fef4)  with id  2 
Starting this thread 
Going to wait
<stuck>

奇怪的是，竟然someThreadStarted()不叫this。请指教。

4

1 回答 1

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您的所有线程都没有运行事件循环。当你w.wait4all();从你main()的调用时，主线程在执行到达时阻塞wait()。使用Qt::QueuedConnection连接信号意味着当目标线程上的控制返回事件循环时将调用您的插槽，这永远不会用于您的测试线程。同时，您的主线程在 处被阻塞wait()，并且还缺少事件循环（QCoreApplication::exec()从不调用）。主线程也无法处理它接收到的排队信号，这就是this线程似乎也没有发出的原因started()。

于 2012-11-20T04:21:01.727 回答