Question

我正在尝试为Qt编写类似屏障的同步原语，以确保在某个点启动多个线程。但是，当我没有获得为我工作的信号（例如，启动（））时，我似乎遇到了这种情况。

我试图缩小代码以编译最小（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，即使someThreadStarted()没有被this调用。请建议。

Answer 1

您的所有线程都没有运行事件循环。当您从w.wait4all();调用main()时，主线程会在执行到达wait()时阻塞。使用Qt::QueuedConnection连接信号意味着当目标线程上的控件返回到事件循环时，将调用您的插槽，这对于测试线程永远不会。同时，您的主线程在wait()处被阻止，并且还缺少事件循环（永远不会调用QCoreApplication::exec()）。主线程也无法处理它收到的排队信号，这就是this线程似乎也不会发出started()的原因。

等待多个线程启动，启动（）没有被捕获

1 个答案: