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Date: Wed, 28 Aug 2013 10:49:36 +0200
From: Stefan Hajnoczi <stefanha@gmail.com>
Message-ID: <20130828084936.GF4696@stefanha-thinkpad.muc.redhat.com>
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Subject: Re: [Qemu-devel] [RFC] aio: add aio_context_acquire() and
 aio_context_release()
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To: Wenchao Xia <xiawenc@linux.vnet.ibm.com>
Cc: Kevin Wolf <kwolf@redhat.com>, Paolo Bonzini <pbonzini@redhat.com>, qemu-devel@nongnu.org, Stefan Hajnoczi <stefanha@redhat.com>

On Wed, Aug 28, 2013 at 11:25:33AM +0800, Wenchao Xia wrote:
> > +void aio_context_release(AioContext *ctx)
> > +{
> > +    qemu_mutex_lock(&ctx->acquire_lock);
> > +    assert(ctx->owner && qemu_thread_is_self(ctx->owner));
> > +    ctx->owner = NULL;
> > +    qemu_cond_signal(&ctx->acquire_cond);
> > +    qemu_mutex_unlock(&ctx->acquire_lock);
> > +}
>   if main thread have call bdrv_aio_readv(cb *bdrv_cb), now it
> is possible bdrv_cb will be executed in another thread which
> aio_context_acquire() it. I think there are some ways to solve,
> but leave a comments here now to tip better?

Callbacks, BHs, and timers are executed in the thread that calls
aio_poll().  This is safe since other threads cannot run aio_poll() or
submit new block I/O requests at the same time.

In other words: code should only care which AioContext it runs under,
not which thread ID it runs under.  (I think we talked about this on IRC
a few weeks ago.)

Are there any situations you are worried about?

Stefan