Re: [Qemu-devel] [RFC] aio: add aio_context_acquire() and aio_context_release()

[Stefan Hajnoczi <stefanha@gmail.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