I want to make a condition in code to wait until all threads are finished in the main thread final slot, following is the test code ..
testClass::testClass()
{
m_count = 0;
m_flag = false;
for( int i = 0; i < 3; i++)
{
QThread *thread = new QThread();
WorkerThread *worker = new WorkerThread();
connect(thread, SIGNAL(started()), worker, SLOT(startThread()));
connect(worker, SIGNAL(workerFinished()), this, SLOT(threadFinished()));
connect(worker, SIGNAL(workerFinished()), thread, SLOT(quit()));
connect(thread, SIGNAL(finished()), worker, SLOT(deleteLater()));
connect(thread, SIGNAL(finished()), thread, SLOT(deleteLater()));
thread->start();
m_workerList.append(worker);
}
}
void testClass::threadFinished()
{
// wait untill all thread are finished, how to achive this ?
if(!m_flag)
{
// print << m_flag;
m_flag = true;
}
}
void WorkerThread::startThread()
{
emit workerFinished();
}
here testClass is in main thread and I want the application to wait in threadFinished slot until all threads I started in testClass constructor to finish, could anyone suggest best way to do this ?
I am using Qt 5.4.0 in Windows 7.
If using boost in addition to Qt is an option, you can use a thread group and call join_all, which waits until all threads in the group are done.
Also, QThreadPool provides the waitForDone() function ("Waits for each thread to exit and removes all threads from the thread pool."), however you might have to restructure your worker objects slightly to comply to the QRunnable interface.
A more basic solution would be to set a QVector or QMap member variable with one entry for each thread and set them to true when the respective thread finishes. Continue program execution in your slot only when all threads have reached "finished = true" state in your member variable.
Related
I know that this is next question about connect signal/slot mechanism between threads. I wrote working Worker application.
Main problem
I have worker class that has been moved to another thread. Second part of application is GUI interface with button. When I click button thread starts:
void MainWindow::startStopThreadA()
{
...
else
{
threadA = new QThread;
workerA = new WorkerObject;
workerA->setMessage("Thread A running");
workerA->moveToThread(threadA);
connect(threadA, SIGNAL(started()), workerA, SLOT(process()), Qt::QueuedConnection);
connect(workerA, SIGNAL(finished()), threadA, SLOT(quit()));
connect(workerA, SIGNAL(finished()), workerA, SLOT(deleteLater()));
connect(threadA, SIGNAL(finished()), threadA, SLOT(deleteLater()));
//Connect signal from thread with slot from MainWindow
connect(workerA, SIGNAL(printMessage(QString)), this, SLOT(printMessage(QString)), Qt::QueuedConnection);
threadA->start();
ui->threadAButton->setText("Stop A");
}
}
When thread starts then emits signal:
void WorkerObject::process(void)
{
//Infinity thread loop
forever
{
//Exit loop part
mutex.lock();
if(m_stop)
{
m_stop = false;
mutex.unlock();
break;
}
mutex.unlock();
//Hold/unhold loop part
mutex.lock();
if(!m_hold)
{
mutex.unlock();
//Here signal is emited
emit printMessage(messageStr); //That not works
//qDebug() << "Thread A test message."; //That works properly
}
mutex.unlock();
}
emit finished();
}
In main GUI thread I have timer for show that GUI thread works. So qDebug() works fine and prints messages from my thread. Also timer from GUI thread works fine and prints message inside textEdit GUI field.
Now when printMessage signal is emited, GUI thread executes slot method:
void MainWindow::printMessage(QString str)
{
ui->textEdit->append(str);
}
And this is most important part of my problem:
When signal printMessage from workerA object is connected with GUI slot printMessage with Qt::QueuedConnection my application hangs up. There is no possible to click something button or even exit app.
When signal/slot are connected with Qt::BlockingQueuedConnection everything works fine. Messages are emitted and received between threads and also GUI timer works fine.
So my question is why connection Qt::QueuedConnection causes that app freezes ?
I figured out this problem with #m7913d help.
You can try to perform a QThread::sleep inside your forever loop (f.e.
1 second) to check if it solves your problem.
So worker's thread emitted signal too frequently. Adding QThread::msleep(5) after emitted signal really helped. There ` also need to be included.
I am trying to write thread poll with QThread.
class ThreadPool: public QObject
{
Q_OBJECT
public:
ThreadPool(int maxThreads);
void addTask(MyTask *task);
private:
int maxThreads;
QMutex mutex;
QVector<QPair<bool, QThread>> threads;
QThread *getFreeThread();
public slots:
void freeThread();
};
void ThreadPool::addTask(MyTask* task)
{
QThread *thread = getFreeThread();
task->moveToThread(thread);
connect(thread, SIGNAL(started()), task, SLOT(doWork()));
connect(task, SIGNAL(workFinished()), thread, SLOT(quit()));
connect(thread, SIGNAL(finished()), task, SLOT(deleteLater()));
connect(thread, SIGNAL(finished()), thread, SLOT(deleteLater()));
connect(thread, SIGNAL(finished()), this, SLOT(freeThread()));
thread->start();
}
I am creating a limited number of threads in which I want to perform tasks.
However, I do not understand how to get the number of the freed thread.
I know about QThreadPool and Qtconcurrent, but I dont want to use it.
Perhaps, it is worth noting at each thread in QPair's vector is it free or not.
you do not really need a QVector<QPair<bool, QThread>> to keep track of all the threads in your Pool, instead use a QList< QThread* > which holds only the pointers to the free threads.
private:
QList<QThread*> freeThreads; // only free threads
QList<QThread*> allThreads; // just to count the number of all threads
In the slot freeThread() use the sender() method from QObject to get the pointer of the signal sender, which in this case will be the QThread, that has become free
void ThreadPool::freeThread()
{
// get the pointer to the thread that sent the signal:
QObject* threadFreed = QObject::sender();
if( ! freeThreads.contains( threadFreed ) )
{
// save the thread pointer in list
freeThreads << threadFreed;
}
}
Finally getFreeThread() can look like this:
QThread* getFreeThread()
{
if( ! freeThreads.isEmpty() )
{
// take the first free thread
return freeThreads.takeFirst();
}
else
{
if(allThreads.size() < maxThreads )
{
// create a new thread
QThread* thread = new QThread(this);
allThreads << thread;
return thread;
}
else
{
// Maximum number of threads exceeded
// and no free thread is available
return NULL;
}
}
}
Also you should handle the case when a NULL pointer is returned in addTask:
void ThreadPool::addTask(MyTask* task)
{
QThread *thread = getFreeThread();
if( ! thread )
{
// do something else
return;
}
// proceed with thread execution ...
}
What is the corrent way to stop threads in Qt?
Suppose that I have a worker (LicenseChecker class) and I want to do some actions every n seconds in the process member function. I need to do it indefinitely, until someone abort my loop.
_worker = new LicenseChecker;
_thread = new QThread;
_worker->moveToThread(_thread);
connect(_thread, SIGNAL(started()), _worker, SLOT(process()));
connect(_worker, SIGNAL(finished()), _thread, SLOT(quit()));
connect(_worker, SIGNAL(finished()), _worker, SLOT(deleteLater()));
connect(_thread, SIGNAL(finished()), _thread, SLOT(deleteLater()));
connect(_worker, SIGNAL(newLicensesActivated(QVector<LicenseInfo>)),
this, SLOT(newLicensesActivated(QVector<LicenseInfo>)));
_thread->start();
What can I do to abort it?
The first idea that I came up with was to define the sleep function as the following:
bool LicenseChecker::sleep(int seconds)
{
QTime end_time = QTime::currentTime().addSecs(seconds);
while (QTime::currentTime() < end_time)
{
QCoreApplication::processEvents(QEventLoop::AllEvents, 100);
QMutexLocker lock(&_abort_sync);
if (_abort)
{
return false;
}
}
return true;
}
and to check the return code of this function in my infinite loop:
while (true)
{
if (!sleep(5))
{
emit finished();
return;
}
// ...
}
And then on MainWindow's close event I need to do the following:
_worker->stop();
_thread->wait();
where stop member function just sets _abort data member to true, but the application hangs on these calls.
What is the right way to accomplish such task?
Seems that you call stop() from another thread (the main thread) but the worker instance is located in the worker thread. You can overcome this problem by carefully writing something like this to invoke a method from another thread:
void Worker::stop()
{
// make thread safe
if(QThread::currentThread() != this->thread())
{
this->metaObject()->invokeMethod(this, "stop", Qt::QueuedConnection);
return;
}
REAL CODE HERE ...
}
Besides that, i would rather use a timer to fire every n seconds to do the licence check. Something like that (example of an database connection checker):
dbCheckerThread = new QThread(this);
dbCheckerTimer = new QTimer();
dbCheckerTimer->setInterval(CHECKDBCONNECTIONINTERVALL);
dbCheckerTimer->moveToThread(dbCheckerThread);
dbChecker->moveToThread(dbCheckerThread);
connect(dbCheckerTimer, &QTimer::timeout, dbChecker, &DbConnectionChecker::checkConnection);
connect(dbCheckerThread, &QThread::started, dbCheckerTimer, static_cast<void (QTimer::*)(void)>(&QTimer::start));
dbCheckerThread->start();
In the Worker Class I have two functions who works and control the thread, start() and abort()
void Worker::requestWork()
{
mutex.lock();
_working = true;
_abort = false;
qDebug()<<"Le thread travail de"<<this->myId<<" "<<thread()->currentThreadId();
mutex.unlock();
emit workRequested();
}
void Worker::abort()
{
mutex.lock();
if(_working) {
_abort = true;
qDebug()<<"Le thread "<<thread()->currentThreadId()<<" s'arrete";
}
mutex.unlock();
}
As you can see the workrequest emit a signal saying to the thread to start to work. And because the Worker Class is in the thread, how can I pause or restore it? From the worker class? from the MainWindow?
and now the Whole code.Mainwindow Class.
MainWindow::MainWindow(QWidget *parent) :
QMainWindow(parent),
ui(new Ui::MainWindow)
{
ui->setupUi(this);
QObject::connect(ui->lineEdit,SIGNAL(textChanged(QString)),this,SLOT(command(QString)));
thread = new QThread();
worker = new Worker();
worker->moveToThread(thread);
connect(worker, SIGNAL(valueChanged(QString)), ui->label, SLOT(setText(QString)));
connect(worker, SIGNAL(workRequested()), thread, SLOT(start()));
connect(thread, SIGNAL(started()), worker, SLOT(doWork()));
connect(worker, SIGNAL(finished()), thread, SLOT(quit()), Qt::DirectConnection);
}
//QLineEdit send signal to slot "command" permit to control the thread
void MainWindow::command(QString text){
qDebug()<<"le message a bien ete intercepte";
qDebug()<<ui->lineEdit->text();
if (text.contains("help"))
qDebug()<<"heeeelp";
if (text.contains("pause")){
worker->Paused();
if(thread->isRunning()){}
//cond.wait()
}
if (text.contains("restart")){
worker->Restarted();
if (!thread->isRunning()){}
//cond.wakeAll();
}
if (text.contains("stopped")){
worker->Paused();
thread->wait();
}
if (text.contains("start")){
worker->requestWork();
}
if (text.contains("destroyed")){
worker->destroyed();
}
}
So my question is: how to pause and restart the thread from the command() slot when the User insert "Pause" ?
I think you mess up the two possible ways of doing work with QThread:
One is to have an object (Worker) moved to a start()ed QThread. This way you do work by calling slots on the Worker, the work is done when the slots execute. You don't pause/resume this - when the slot is done, QThread will wait for new work, the same way QApplication waits for events when it's idle.
Second way is subclassing QThread, reimplementing run() and creating (some sort of) Worker there. Using this way you must create your "work queue" with something similar to your state variables (_working, _done, wait conditions, etc), because the thread will exit if it leaves run(), you must pause/resume yourself.
I get every time the message: QObject::moveToThread: Cannot move objects with a parent
mainwindow.cpp:
QTimer *timer_ = new QTimer(this);
Device* device = new Device(this);
QThread* thread = new QThread(this);
device->moveToThread(thread);
connect(timer_, SIGNAL(timeout()), device, SLOT(checkConnection()));
connect(device, SIGNAL(checkCompleted()), this, SLOT(doSomethingWhenItIsDone()));
timer_->start(3000);
Device.cpp:
Device::Device(QObject *parent) :
QObject(parent)
{
}
void Device::checkConnection() {
qDebug() << "checkConnection:" << QThread::currentThreadId();
//do something
emit checkCompleted();
}
this inside Device constructor means that Device has a parent and this parent in your case lives in main GUI thread, so Qt tells you that you can't move to another thread object which has parent. So try to use next:
QTimer *timer_ = new QTimer(this);
Device* device = new Device;//no parent
QThread* thread = new QThread(this);
Also you should start your thread with:
thread->start();
Also you need delete your object because it has no parent and it is your responsibility now. The most common way is to use some signal to indicate that worker already done all needed work. For example:
connect(worker, SIGNAL(finished()), thread, SLOT(quit()));
connect(worker, SIGNAL(finished()), worker, SLOT(deleteLater()));