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    SubjectRe: ioevent queues (was Re: Proposed new poll2() syscall)

    On Sat, 23 Aug 1997, Erik Corry wrote:

    > > Yeah I know of the "self pipe" trick, I haven't benchmarked it yet. But I
    > > suspect that the need to start taking EINTRs all over the place might
    > > hurt. Especially since you'll take an EINTR while in select() because of
    > > the SIGCHLD, then restart the select(), then find out it's a dead child,
    > > and read(). So it costs a signal, a write(), a select() and a read().
    > Hmm. The EINTRs rather ruin the point. After I sent the
    > previous mail I started having serious doubts about doing IO
    > (even to a pipe or message queue) in a signal handler. Does
    > it work? What is and isn't allowed?

    What am I smoking ... child deaths don't happen often enough to worry
    about EINTR causing performance problems. Instead of paying for a
    wait/select on every iteration I can just pay for a select(). Duh. I'll
    go benchmark that.

    > Posix.1b also has a neat feature (which I didn't see before)
    > which is that you can run with the interesting signals
    > blocked, and then do a sigwaitinfo(). This syscall waits
    > until one of a set of signals appears, and then doesn't call
    > the handler at all, but rather returns, and lets you call it
    > synchronously. This seems very cool, as it allows you to
    > avoid all that troublesome (slow!) setting up of a signal
    > handler stack etc. You don't have to do any pipe tricks, you
    > can just get on with it. In combination with SIGIO and
    > signals delivered on AIO completion, it should be just what
    > you need.

    Yes this does sound cool, and right on the money... as long as multiple
    threads can block and only one thread gets each queued signal ;)


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