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    SubjectRe: [PATCH] POSIX message queues - syscalls & SIGEV_THREAD
    Hash: SHA1

    Krzysztof Benedyczak wrote:
    > In userspace we can assign one futex to
    > every such a queue and pass it to kernel in mq_notify syscall. Then we can
    > use FUTEX_FD to get file descriptors of all futexes and wait on them with
    > poll(). On the kernel side it notification have to be triggered we change
    > futex value and do FUTEX_WAKE.

    Yes, this would be possible if FUTEX_FD wouldn't be useless as it is
    implemented today (see the futex paper I announced here recently). The
    thing which makes FUTEX_WAIT work is the current value of the futex
    which is passed to the kernel and based on which the userlevel code made
    it decisions. This part doesn't exist in case of using FUTEX_FD.

    The main recent I suggested using futexes for the notification is that
    it is flexible. For now, we can use simple waiting by creating the
    thread ahead of time. This could change later when there is a reliable
    multi-futex wait operation.

    - --
    ➧ Ulrich Drepper ➧ Red Hat, Inc. ➧ 444 Castro St ➧ Mountain View, CA ❖
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