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SubjectRe: [patch 00/11] ANNOUNCE: "Syslets", generic asynchronous system call support
On Tue, 13 Feb 2007, Ingo Molnar wrote:

> * Davide Libenzi <davidel@xmailserver.org> wrote:
>
> > > If this is going to be a generic AIO subsystem:
> > >
> > > - Cancellation of peding request
> >
> > What about the busy_async_threads list becoming a hash/rb_tree indexed
> > by syslet_atom ptr. A cancel would lookup the thread and send a signal
> > (of course, signal handling of the async threads should be set
> > properly)?
>
> well, each async syslet has a separate TID at the moment, so if we want
> a submitted syslet to be cancellable then we could return the TID of the
> syslet handler (instead of the NULL) in sys_async_exec(). Then
> user-space could send a signal the old-fashioned way, via sys_tkill(),
> if it so wishes.

That works too. I was thinking about identifying syslets with the
userspace ptr, but the TID is fine too.



> the TID could also be used in a sys_async_wait_on() API. I.e. it would
> be a natural, readily accessible 'cookie' for the pending work. TIDs can
> be looked up lockless via RCU, so it's reasonably fast as well.
>
> ( Note that there's already a way to 'signal' pending syslets: do_exit()
> in the user context will signal all async contexts (which results in
> -EINTR of currently executing syscalls, wherever possible) and will
> tear them down. But that's too crude for aio_cancel() i guess. )

Yup.



- Davide


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