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    SubjectRe: PID sequences


    On Mon, 23 Feb 1998, David S. Miller wrote:

    > Date: Mon, 23 Feb 1998 17:49:07 -0500
    > From: Jim Nance <jlnance@avanticorp.com>
    >
    > halfpint> bash -c 'for x in 1 2 3 4 5; do /bin/sh -c '\''echo $$'\''; done'
    > 4476
    > 4300
    > 3707
    > 4243
    > 3843
    >
    > This looks almost random, and it does not seem to break anything.
    > I just wanted to let people know that if we wanted to use some other
    > scheme for generating PIDs, there is some precident for doing so.
    >
    > I did consider this issue when I was optimizing and making SMP safe
    > the current PID allocation scheme. If the above you say is true,
    > there is a fantastically efficient way we can allocate PIDs, and an
    > entire SMP lock in fork.c is removed.

    I have a concern. Whether or not this is valid is for you folks to
    decide. Read the theory that describes apache 1.3's mod_unique_id
    <http://www.apache.org/docs/mod/mod_unique_id.html>. Essentially I make
    an assumption that pid reuse is unlikely to occur within a single second.
    I'm sure I'm not the only one making this assumption (think Message-ID
    generation, tmp filename generation, yadda).

    If you can do this with 15-bit "random" pids that's great. Otherwise
    maybe pids have to go 31-bits. I didn't look at your scheme closely, but
    it didn't seem to be "random".

    Dean



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