On Wed, Feb 27, 2019 at 01:38:38PM +0000, Stefan Hajnoczi wrote: > On Fri, Feb 22, 2019 at 02:57:24PM +0800, Peter Xu wrote: > > On Fri, Feb 22, 2019 at 07:37:02AM +0100, Marc-André Lureau wrote: > > > Hi > > > > > > On Fri, Feb 22, 2019 at 4:14 AM Peter Xu <pet...@redhat.com> wrote: > > > > > > > > We were pushing the context until right before running the gmainloop. > > > > Now since we have everything unconditionally, we can move this > > > > earlier. > > > > > > > > One benefit is that now it's done even before init_done_sem, so as > > > > long as the iothread user calls iothread_create() and completes, we > > > > know that the thread stack is ready. > > > > > > > > > > This will change the default context in the iothread, for code running > > > there. This may not be a good idea. Until now, only sources dispatched > > > from iothread_get_g_main_context() would have default context > > > associated to it. > > > > > > I don't know if the current behaviour is intentional, but it has some > > > logic. With this change, you may create hidden races, by changing the > > > default context of sources to the iothread. > > > > Yes I agree that the behavior will be changed in this patch that even > > if the iothread user does not use the gcontext they'll also have the > > context set. I would think it should be ok because IMHO events hooked > > onto the aio context should not depend on the gcontext, but indeed I'd > > like to get some confirmation from others, especially the block layer. > > I don't understand why Patch 4 is desirable. The comment about > init_done_sem isn't clear to me but I also wondered the same thing as > Marc-André. > > Can you explain why we should apply this patch?
Hi, Stefan, The patch 4 itself does not help much for current QEMU, but it should be required to replace the patch that Marc-Andre proposed below: https://lists.gnu.org/archive/html/qemu-devel/2019-02/msg05460.html [1] And IMHO patch 4 along with this whole series should be a cleaner approach comparing to the one proposed in [1]. Here if my understanding is correct the problem is that g_main_context_push_thread_default() is really designed to be called at the very beginning of a thread creation but not dynamically called during the execution of a thread (prove is that it even does not have any error to return when failed to acquire the context so the caller will never know if it failed! see [2] below), in that sense this patch 4 can be seen as a tiny cleanup too. g_main_context_push_thread_default (GMainContext *context) { GQueue *stack; gboolean acquired_context; acquired_context = g_main_context_acquire (context); g_return_if_fail (acquired_context); <------------- [2] ... } Regards, -- Peter Xu
