Re: [PATCH v2 4/7] util: add qemu-co-timeout

[Vladimir Sementsov-Ogievskiy]

01.04.2022 16:13, Hanna Reitz wrote:
> On 01.04.22 11:19, Vladimir Sementsov-Ogievskiy wrote:
> > Add new API, to make a time limited call of the coroutine.
> >
> > Signed-off-by: Vladimir Sementsov-Ogievskiy <vsementsov@openvz.org>
> > ---
> >   include/qemu/coroutine.h | 13 ++++++
> >   util/meson.build         |  1 +
> >   util/qemu-co-timeout.c   | 89 ++++++++++++++++++++++++++++++++++++++++
> >   3 files changed, 103 insertions(+)
> >   create mode 100644 util/qemu-co-timeout.c
>
> I don’t really understand what this does.  Intuitively, I would have assumed 
> this makes the first yield of the respective coroutine not return when the 
> timeout has elapsed, and instead, we switch back to qemu_co_timeout(), which 
> returns to its callers.
>
> But it looks like when this yield happens and we switch back to 
> qemu_co_timeout(), the coroutine actually isn’t cancelled, and will just 
> continue running, actually.  Is that right?  On first look, this looks like 
> it’ll be quite difficult to think about what happens when this is used, because 
> the coroutine in question is no longer run in sequence with its caller, but 
> actually might run in parallel (even though it’s still a coroutine, so it’ll 
> remain cooperative multitasking).

Yes, the coroutine continue execution in parallel. That's a generic interface, and there 
is no way to "cancel" generic coroutine. So, caller should care about it.


--
Best regards,
Vladimir