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Re: Signal emission from an object thread




Le sam. 18 mars 2017 à 6:29, Tristan Van Berkom <tristan.vanberkom@xxxxxxxxxxxxxxx> a écrit :
I took a brief look into your code, your thread it calling:

    arv_stream_push_output_buffer()

Which is emitting a gsignal. I'm not going to get a full handle on what
your code is trying to do, but I can only presume that you intend for
that to let your parent thread know that a buffer is ready ?

Thanks a lot to have a look at my code.

Ok, well, here are a few tips I think you can use to correct your code.

  o The `gboolean cancel` is wrong, setting this is not a guaranteed
    atomic operation.

    There are some facilities for atomic integers which you can use,
such as g_atomic_int_set/get(), which act as a memory barrier which
    is less overhead than using mutexes.

I understand the setting of cancel is not atomic, but I fail to see what can possibly go wrong in this particular case. There is always only one thread reading this value, and while this thread is alive, only one event can happen, when the value goes from FALSE to TRUE. I will replace it with an atomic operation, but still, I'd love to have an example where the use of a simple gboolean can lead to a wrong beheviour.

  o Whenever sharing data with your thread, always protect it with
    g_mutex_lock() / g_mutex_unlock(), (there are also reader/writer
    locks available but I dont see you needing this here).

If I have done this correctly, there shouldn't be any data sharing, except for the cancel boolean, when the thread is alive. I will double check.

  o If you want to communicate something back to the thread in which
    your main object was created, from the child worker thread, use
    the GMainLoop for this, that is easiest.

Thanks for the suggestion and the detailed explanation. After more thinking, I'm not completely why I have implemented this signal. It was for the multicast nature of signals, but in real life there souldn't be any interresting use case of this property.

  o There is something relatively new called GTask which has appeared,
    and it might take care of some of the above for you so that there
    are less lines of code overall, I have not really tried working
    with GTask since it's creation.

I know this nice API and already used it in another project. But I can not use it here as I'd like to retain the glib requirement to 2.26, while GTask appeared in glib 2.36.

I hope this was helpful :)

Sure !

Thanks again.

	Cheers,

		Emmanuel.

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