<div dir="ltr"><div class="markdown-here-wrapper" style><p style="margin:1.2em 0px!important">All,</p>

<p style="margin:1.2em 0px!important">Pardon the double post. I saw a few obvious bugs after hitting send. My apologies. Here is the improved version.</p>

<p style="margin:1.2em 0px!important">Bryan</p>

<pre style="font-size:0.85em;font-family:Consolas,Inconsolata,Courier,monospace;font-size:1em;line-height:1.2em;margin:1.2em 0px"><code style="font-size:0.85em;font-family:Consolas,Inconsolata,Courier,monospace;margin:0px 0.15em;padding:0px 0.3em;white-space:pre-wrap;border:1px solid rgb(234,234,234);border-top-left-radius:3px;border-top-right-radius:3px;border-bottom-right-radius:3px;border-bottom-left-radius:3px;display:inline;background-color:rgb(248,248,248);white-space:pre;overflow:auto;border-top-left-radius:3px;border-top-right-radius:3px;border-bottom-right-radius:3px;border-bottom-left-radius:3px;border:1px solid rgb(204,204,204);padding:0.5em 0.7em;display:block!important"># Test program to ask about destructors and PyQt4.

import sys, time

from PyQt4.QtGui import QApplication

from PyQt4.QtCore import QThread, QTimer, QObject, pyqtSignal

class Worker(QObject):

    def onStartWork(self):

        time.sleep(1)

class ThreadController(QObject):

    startWork = pyqtSignal()

    def __init__(self, parent):

        QObject.__init__(self, parent)

        # No parent object provided; if so, we get the error

        # "QObject::moveToThread: Cannot move objects with a parent".

        # Likewise, calling setParent after moving the object produces

        # "QObject::setParent: Cannot set parent, new parent is in a different

        # thread". Who will deallocate this object, since it has no parent? I

        # assume the answer is "Python, maybe". Is that good enough?

        self.worker = Worker()

        self.workerThread = QThread(self)

        self.worker.moveToThread(self.workerThread)

        # Use method #2 below. Commnet out for an ominous warning which will

        # crash in a more complex program: "QThread: Destroyed while thread is

        # still running".

        #parent.aboutToQuit.connect(self.del_)

        self.startWork.connect(self.worker.onStartWork)

        self.workerThread.start()

    # I'd like to run when when ~ThreadController is invoked. That's quite

    # differentfrom when __del__ is invoked. How?

    #

    # 1. Give up. Just invoke it manually. However, this is error-prone (i.e.

    #    I'll forget to do it at some point).

    # 2. Connect app.aboutToQuit to this. This seems fairly reasonable, but

    #    it would feel cleaner to invoke when the destructor is invoked,

    #    rather than earlier. Also, this means that the QApplication would

    #    need to be passed to every thread, which might involve awkwardness

    #    in passing it through several intervening subclasses.

    # 3. Connect destroyed(), which doesn't work -- this isn't emitted until

    #    the object is mostly dead, far after ~ThreadController was invoked,

    #    and won't be executed.

    # 4. Have __del__ invoke this, which doesn't work -- it only happens after

    #    ~ThreadController has finihed.

    def del_(self):

        print('del_')

        self.workerThread.quit()

        self.workerThread.wait()

    def __del__(self):

        print('__del__')

        # Crash when uncommented.

        #self.del_()

if __name__ == '__main__':

    app = QApplication(sys.argv)

    # Exit the program shortly after the event loop starts up, but before the

    # thread finishes.

    QTimer.singleShot(200, app.exit)

    # Start a thread

    tm = ThreadController(app)

    # Run the main event loop.

    ret = app.exec_()

    print('done')

    sys.exit(ret)

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eXMuZXhpdChyZXQpPC9kaXY+PGRpdj4mbmJzcDsgJm5ic3A7Jm5ic3A7PC9kaXY+PC9kaXY+" style="height:0;font-size:0em;padding:0;margin:0"></div></div></div><div class="gmail_extra"><br><div class="gmail_quote">On Mon, Nov 3, 2014 at 3:59 PM, Bryan A. Jones <span dir="ltr"><<a href="mailto:bjones@ece.msstate.edu" target="_blank">bjones@ece.msstate.edu</a>></span> wrote:<br><blockquote class="gmail_quote" style="margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex"><div dir="ltr"><div><p style="margin:1.2em 0px!important">All,</p>

<p style="margin:1.2em 0px!important">I’m confused when it comes to the proper way to mesh Qt’s model of creating a tree of parented objects which destroy themselves when no longer used with Python’s “delete it when I feel like it” garbage collector. In particular, I’d like to shut down threads when the underlying Qt objects are destroyed, but I can’t figure out how to do that. Any advice and wisdom would be appreciated. I've attached same code with my thoughts.</p>

<p style="margin:1.2em 0px!important">Bryan</p>

<pre style="font-size:0.85em;font-family:Consolas,Inconsolata,Courier,monospace;font-size:1em;line-height:1.2em;margin:1.2em 0px"><code style="font-size:0.85em;font-family:Consolas,Inconsolata,Courier,monospace;margin:0px 0.15em;padding:0px 0.3em;white-space:pre-wrap;border:1px solid rgb(234,234,234);border-top-left-radius:3px;border-top-right-radius:3px;border-bottom-right-radius:3px;border-bottom-left-radius:3px;display:inline;background-color:rgb(248,248,248);white-space:pre-wrap;overflow:auto;border-top-left-radius:3px;border-top-right-radius:3px;border-bottom-right-radius:3px;border-bottom-left-radius:3px;border:1px solid rgb(204,204,204);padding:0.5em 0.7em;display:block!important"># Test program to ask about destructors and PyQt4.

import sys, time

from PyQt4.QtGui import QApplication

from PyQt4.QtCore import QThread, QTimer, QObject

class Worker(QObject):

    def run(self):

        time.sleep(1)

class ThreadController(QObject):

    def __init__(self, parent):

        QObject.__init__(self, parent)

        # No parent object provided; if so, we get the error