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Re: [PATCH v6 01/33] main-loop.h: introduce qemu_in_main_thread()

From: Kevin Wolf
Subject: Re: [PATCH v6 01/33] main-loop.h: introduce qemu_in_main_thread()
Date: Tue, 1 Feb 2022 12:55:09 +0100

Am 31.01.2022 um 16:49 hat Paolo Bonzini geschrieben:
> > > However, commit 5f50be9b5810293141bb53cfd0cb46e765367d56 changed the
> > > stub to return false for a specific reason.
> > 
> > I must admit I don't really understand the reasoning there:
> > 
> >      With this change, the stub qemu_mutex_iothread_locked() must be changed
> >      from true to false.  The previous value of true was needed because the
> >      main thread did not have an AioContext in the thread-local variable,
> >      but now it does have one.
> > 
> > This explains why it _can_ be changed to false for this caller, but not
> > why it _must_ be changed.
> See above: because it returns the wrong value for all threads except one,
> and there are better ways to do a meaningful check in that one thread: using
> qemu_get_current_aio_context(), which is what aio_co_enter did at the time
> and qemu_in_main_thread() does with Emanuele's change.
> > So is the problem with the unit tests really just that they never call
> > qemu_init_main_loop() and therefore never set the AioContext for the
> > main thread?
> No, most of them do (and if some are missing it we can add it).

But if they do, why doesn't qemu_get_current_aio_context() already
return the right result? In this case, my_aiocontext is set and it
should never even call qemu_mutex_iothread_locked() - at least not in
any case where qemu_in_main_thread() would return true.

So provided that qemu_init_main_loop() is called, both functions should
be equivalent and we wouldn't need a second one.


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