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POQt Event processing problem due to QWaitCondition
 

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  1. POQt Event processing problem due to QWaitCondition
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    <p>I am working on a multithread QT project. The main problem is on a serial controller class. This class uses QMutex and QWaitCondition to shyncronize write and read methods.</p> <p>The problem is about a signal blocked in a children class due to qwaitcondition wait method in the parent. Once the wait method returns, the signal in the children class is emmited (the receiver is also the children class).</p> <p>I think this method (qwaitcondition - wait) is blocking any signal emission in my entire application.</p> <p>The problem is something like that:</p> <pre><code>constructor() { anotherclass = new MyClass; } void run() { forever { if(readmethod()) waitcondition.wakeall(); } } void method1() { sendpacket(); mutex.lock(); if(waitcondition.wait(&amp;mutex,10000)) //somecode; mutex.unlock(); } class MyClass { someObject sobj; MyClass() { connect(sobj,SIGNAL(somesignal),this,SLOT(someslot)); } void someslot() { //some code } } </code></pre> <p>My slot called someslot only is called once the qwaitcondition returns due to the timeout (10 seconds in this case).</p> <p>I just want to use mutex and the qwaitcondition in this class, not in the entire application. I tried to instantiate the children class in the main thread but I got the same behavior.</p> <p><strong>CONCEPTUAL TEST</strong></p> <p>I made a test project and I published it at this link: <a href="http://inotechcorp.com/images/files/testwaitcondition.tar.gz" rel="nofollow">testwaitconditionproject</a></p> <p>the test project works in this way: A waitcondition is iniated with timeout equal to 10 seconds in the parent thread. A children thread emit a signal every 2 seconds, an internal slot must emit a signal captured by the parent. Once the parent slot is called, a flag is set to true. This flag should fire a wakeall to finish de waitcondition.</p> <p>BUT NOT, the children's internal signals only are fired after the waitcondition timeout. THIS IS MY MAIN PROBLEM, the parent waitcondition is blocking my children's signals.</p> <p><strong>EDIT:</strong></p> <p>I solved the problem in the test project, calling the method with waitcondition in another thread. It is not possible to me to replicate the issue because the asynchronous call to the method occurs in the thread 1 (via dbus). I am wondering the dbus call is emitted in the thread 1, so my events in the children class are not going to be emitted while the instance belongs to the same thread.</p> <p><strong>EDIT 2:</strong></p> <p>I solved my problem putting the pparent and the children in an intermediate class qthread. they were instantiated in the run method, and an exec call was used too.</p>
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    1. USJuan E. Delgado
    1. USJuan E. Delgado
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    1. COHow are you creating your new thread? Are you sure the wait is in the new thread and not the primary thread? I've found that checking this by setting the objectName of the UI thread and the new thread, then checking thread()->objectName() in the various calls helps verify things like this.
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      1. POQt Event processing problem due to QWaitCondition
      1. USBrett Stottlemyer
    2. COI am using the waitcondition to synchronize two methods in the same thread, the run method and other one called asynchronously. The children thread is instantiated in the constructor of its parent, but I tried to instantiate it from the main thread without any result. I tried the objectName to verify it and the children is another thread. Do you know why it is working this way?
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      1. POQt Event processing problem due to QWaitCondition
      1. USJuan E. Delgado
    3. COThe run method should be running in the newly constructed thread. Then method1 needs to be called from a different thread (probably the UI thread). That will cause the thread that called method1 to wait until the run method wakes it up. It won't work if the waitcondition and the wait are called from the same thread. Can you post a working sample?
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      1. POQt Event processing problem due to QWaitCondition
      1. USBrett Stottlemyer
 

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