Qt应用程序中的线程自定义调度

Question

I am a new-comer to Qt and would like to know about recommended approaches towards custom scheduling of threads managed by QThread instances.

I would like to have a scheduler thread which, in response to change in application state, puts certain threads to sleep or changes their priority. The scheduling should be preemptive as in I should be able to put to sleep certain workers (which may be waiting on a mutex) and invoke them later.

What I am particularly curious about is why the QThread::sleep and related functions are protected ?

If the kind of fine grained control over scheduling can't be obtained through Qt threading classes then I would like to know about alternative possibilities.

Answer 1

So do there exist ways to make other threads sleep and later wake them up ?

Making threads sleep when out of work is not usually the most efficient or cleanest way to accomplish what you need. You generally want to keep threads alive when they have work and destroy them when they don't (instead of forcing stagnant threads to sleep repeatedly). The idiomatic way to manage threads in Qt is utilizing the signal /slot interface to facilitate the creation and destruction of threads.

Here is a simple example from the QThread documentation that shows how this feature of Qt can be used to handle thread scheduling with little outside intervention:

 class Worker : public QObject
 {
     Q_OBJECT

 public slots:
     void doWork() {
         ...
     }
 };

 void MyObject::putWorkerInAThread()
 {
     Worker *worker = new Worker;
     QThread *workerThread = new QThread(this);

     connect(workerThread, SIGNAL(started()), worker, SLOT(doWork()));
     connect(workerThread, SIGNAL(finished()), worker, SLOT(deleteLater()));
     worker->moveToThread(workerThread);

     // Starts an event loop, and emits workerThread->started()
     workerThread->start();
 }

For more advanced threading schemes, Qt also provides additional threading mechanisms (that utilize signals & slots) like QThreadPool or anything in the QtConcurrent namespace.