Re: [Qemu-devel] [PATCH 13/14] qio: allow threaded qiotask to switch contexts

[Peter Xu]

On Wed, Feb 28, 2018 at 09:23:56AM +0000, Daniel P. Berrangé wrote:
> On Wed, Feb 28, 2018 at 01:06:32PM +0800, Peter Xu wrote:
> > This is the part of work to allow the QIOTask to use a different
> > gcontext rather than the default main gcontext, by providing
> > qio_task_context_set() API.
> > 
> > We have done some work before on doing similar things to add non-default
> > gcontext support.  The general idea is that we delete the old GSource
> > from the main context, then re-add a new one to the new context when
> > context changed to a non-default one.  However this trick won't work
> > easily for threaded QIOTasks since we can't easily stop a real thread
> > and re-setup the whole thing from the very beginning.
> 
> I think this entire usage pattern is really broken. We should not
> provide a way to change the GMainContext on an existing task. We
> should always just set the correct GMainContxt right from the start.
> This will avoid much of the complexity you're introducing into this
> patch series, and avoid having to expose GTasks to the callers of
> the async methods at all.

Yeah I agree with you that the threaded QIO patches are complicated.
Then how about I introduce:

- qio_task_thread_new(): to create QIO task and its thread (but not
                         running)
- qio_task_thread_run(): to run the thread

Then I can setup the context correctly between the two in some way.

After that, qio_task_run_in_thread() will be two calls of above two
APIs.

Thanks,

-- 
Peter Xu