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    SubjectRe: Synchronous signal delivery..
    Giuliano Pochini wrote:
    > IMHO it's not simply a signal delivery system, it's a message queue.

    Not entirely, because - as I understand it - signals would be
    aggregated, so you'd always get one item, no matter how many
    signals are actually pending at that time.

    For generalizing such mechanisms, it might be useful to have
    an atomic "overwrite" operation for pipes, and maybe also for
    some sockets, e.g. something like this:

    ssize_t overwrite(int fd,
    const void *data_if_empty,size_t size_if_empty,
    const void *data_if_full,size_t size_if_full,
    int *was_empty);

    If there is no data in the pipe/queue, "overwrite" would
    write "data_if_empty", and clear *was_empty. Otherwise, it
    would discard what's there, then write "data_if_full", and
    set *was_empty. The whole operation is atomic with respect
    to readers/pollers.


    static int signal_set = 0;

    ... add_signal(int signum)
    int new_signal = 1 << signum;
    int was_empty;

    signal_set |= new_signal;
    if (was_empty)
    signal_set = new_signal;

    - Werner

    / Werner Almesberger, Buenos Aires, Argentina /
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