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SubjectRe: [patch 00/11] ANNOUNCE: "Syslets", generic asynchronous system call support

* 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.

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. )

Ingo
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