The thread does not want to finish because of the “TestDestroy” always return false.

[lionking]

This is the first time I have used threads and after I read a little from the documentation on threads I am still confused.
in my example, I want to do a very simple example just Increasing a progress bar (wxGauge) to reach 100% by using a thread.

Code: Select all

// mainFrm.cpp (Main Window)

void mainFrm::button_OnClick(wxCommandEvent & event) {
    thread = new CThread;
    if (thread->Run() != wxTHREAD_NO_ERROR) {
        wxLogError("Can't create the thread!");
        delete thread;
        thread = NULL;
    }
}
// CThread.cpp

CThread::CThread() : wxThread(wxTHREAD_DETACHED) {
}

Code: Select all

wxThread::ExitCode CThread::Entry() {
    int counter = 0;
    progressbar = (wxGauge*)wxWindow::FindWindowByName("progressbar");
    button = (wxButton*)wxWindow::FindWindowByName("button");
    textbox = (wxTextCtrl*)wxWindow::FindWindowByName("textbox");
    button->Enable(false);
    while (!TestDestroy()) {
        while (counter <= 100) {
            progressbar->SetValue(counter);
            counter += 10;
            textbox->SetValue(wxString::Format("%i", progressbar->GetValue()));
            wxThread::Sleep(200);
        }
    }
    button->Enable(true);
    wxMessageOutputDebug().Printf("%s", "The operation was compeleted.");
    return (wxThread::ExitCode)0;
}

Also, another code without using GUI (the same problem is still):

Code: Select all

wxThread::ExitCode CThread::Entry() {
    int counter = 0;
    while (!TestDestroy()) {
        while (counter <= 100) {
            counter += 10;
            wxMessageOutputDebug().Printf("%i", counter);
            wxThread::Sleep(200);
        }
        wxMessageOutputDebug().Printf("%i", this->IsAlive()); // prints "1"
    }
    wxMessageOutputDebug().Printf("%s", "The operation was compeleted.");
    return (wxThread::ExitCode)0;
}

The problem is that it does not want to come out of "while (!TestDestroy())" loop, so, the thread continues and does not finish.

Is there something wrong with my code?

[doublemax]

First of all: You're not allowed to make GUI calls from inside a secondary thread, so you'll need a different approach for something like this. The sample code in the documentation shows how: https://docs.wxwidgets.org/trunk/classwx_thread.html

Regarding the TestDestroy(): This will only return true after you call wxThread::Delete, usually you do this from the main thread in order to stop the thread while it's still running. If you have job that just does a limited amount of work, you can exit the loop as soon as it's done.

[lionking]

Thank you for your response.
Unfortunately, I have seen that documentation link before and still don't understand it well.
If you answer my following questions you will facilitate me to understand some things that I don't understand.

After I call wxThread::Delete from outside a runtime error occurred "Read access violation".
is that error because I use wxTHREAD_DETACHED kind but when using wxTHREAD_JOINABLE wxThread::Delete will be worked fine, right?

Also, when using wxThread::Delete from outside it deletes the object that I have created previously (ex: CThread *thread = new CThread) or deletes something internally?

Finally, I want to use the threads with GUI controls like the progress bar to increasing or decreasing its value, How can I do that?

[alys666]

if you want just test how the thread works, do your diagnostics via printf(...), or std::cout<<"text".
as doubleMax said you cannot use visual objects of wxWidgets from secondary threads, you can only send messsges of wxThreadMessage class to main frame(or any window of wxWidgets).

[PB]

You can see an example how to update the UI from thread e.g. here
viewtopic.php?f=1&t=46485#p194840

if you want just test how the thread works, do your diagnostics via printf(...), or std::cout<<"text".

I would recommend using wxLog instead, e.g. wxLogDebug. This should work everywhere, including Windows.

[alys666]

Thank you for your response.
Unfortunately, I have seen that documentation link before and still don't understand it well.
If you answer my following questions you will facilitate me to understand some things that I don't understand.

After I call wxThread::Delete from outside a runtime error occurred "Read access violation".
is that error because I use wxTHREAD_DETACHED kind but when using wxTHREAD_JOINABLE wxThread::Delete will be worked fine, right?

Also, when using wxThread::Delete from outside it deletes the object that I have created previously (ex: CThread *thread = new CThread) or deletes something internally?

Finally, I want to use the threads with GUI controls like the progress bar to increasing or decreasing its value, How can I do that?

1. to interact with GUI you must send messages to... for example.. this progress bar or any window, which can access this bar and set it's new value .
2. thread.Delete just sets internal thread's bool variable to true. and TestDestroy checks it for true value, and exits the body according to your exit from loop in the thread body. Delete does not delete the thread, thread deletes himself in finalization code, as i guess.

[doublemax]

After I call wxThread::Delete from outside a runtime error occurred "Read access violation".

A detached thread destroys itself when it's done. So, this error will happen when the thread is already destroyed. That's why the demo code from the page i linked uses a wxCriticalSection to protect the variable that contains the thread pointer.

[lionking]

I thank everyone who responded to me.
Now I have understood some things that I did not understand.

Really, the threads are not easy like I was thinking.

[ONEEYEMAN]

Hi,
Threads are not easy, but they are easy at the same time.

Also, as I pointed out in the SO - to update progress bar you don't need a thread. Look at how it is done inside the dialogs sample.

Thank you.

[lionking]

I want to use the threads with GUI because I have a method that does several steps and I want when it finished from each step increase the progress bar and so on until finish all the steps. the following figure explains my idea:



and for that, I want to use a thread to increase the progress bar after each step.

[ONEEYEMAN]

Hi,
As I said - just look at the wxProgressDialogs.

Thank you.