[PyQt] Any way to run code before each QThread?

Phil Thompson phil at riverbankcomputing.com
Sun Jul 15 16:46:58 BST 2018

On 15 Jul 2018, at 4:24 pm, Ned Batchelder <ned at nedbatchelder.com> wrote:
> On 7/15/18 10:55 AM, Florian Bruhin wrote:
>> On Sun, Jul 15, 2018 at 04:43:41PM +0200, David Boddie wrote:
>>> On Sun Jul 15 12:30:55 BST 2018, Ned Batchelder wrote:
>>>> I maintain coverage.py.  I have an issue
>>>> (https://github.com/nedbat/coveragepy/issues/582) that the code running
>>>> in QThreads aren't measured.  For the stdlib threading module, I have
>>>> code that runs as each thread is created to start the measurement.  Is
>>>> there any way to do the same for QThreads?
>>> Perhaps. See below.
>>>> The stdlib feature is threading.settrace
>>>> (https://docs.python.org/3/library/threading.html#threading.settrace). I
>>>> didn't see anything similar for QThreads, or any other hook that would
>>>> give me control before the thread starts running.  Am I overlooking
>>>> something?
>>> From the threading.settrace docs:
>>>  "Set a trace function for all threads started from the threading module.
>>>  The func will be passed to sys.settrace() for each thread, before its run()
>>>  method is called."
>>> The QThread.started signal docs (https://doc.qt.io/qt-5/qthread.html#started)
>>> say this:
>>>  "This signal is emitted from the associated thread when it starts executing,
>>>  before the run() function is called."
>>> So it looks like almost exactly what you want. Connect this signal to a slot
>>> (function/method) and perform the same setup there.
>> That's only for a given QThread instance though - it'd probably work if
>> you could somehow find out about all QThread instances created in a
>> project, but I can't think of a good way to do that.
> I've only poked around for ten minutes, but that's what I'm seeing also: I could get a signal from a specific thread, but only if I were alerted to its creation and could connect the signal.
> Anyone have any other hacky^H^H^H^H^Hcreative ideas for how to accomplish this? :)

Should I implement QThread.settrace()?

If so can somebody clarify what thread the call to sys.settrace() should be made in? The new thread or the thread from which the new thread is created?


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