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Date: Tue, 29 Aug 1995 07:24:08 +1000
From: Bruce Evans <bde@zeta.org.au>
Message-Id: <199508282124.HAA14752@godzilla.zeta.org.au>
To: frank@exit.com, hackers@freefall.FreeBSD.org
Subject: Re: 16-bit pids?  (was Re: 16, 32, and 64bit types?)
Sender: hackers-owner@FreeBSD.org
Precedence: bulk

>Sixteen bits for PID_MAX?  Yukko!  IMHO, this should be at least 32, and
>preferably a black-box type (handled by allocate_pid(), not by an int
>increment, as fast that that might be -- it's still one of the least
>critical bits of fork()).  Some distributed systems need at least 32
>bits for the pid, since they add node information, and a black-box type
>would make this much easier.

>Granted, it's a nontrivial change, but it would be nice to see some system
>do it right.  I don't think there's any inherent reason why pid_t should
>be limited to an int (of any size) in modern Un*ces.

pid_t shall be a signed arithmetic type in POSIX systems (POSIX.1 section
2.5).  The meaning of the bits isn't specified so you can treat it as a
cookie except for the sign bit (which is presumably only required to
encode process groups in kill() etc.).

Does anyone know why POSIX specifies `signed arithmetic' types?  The C
standard specifies that the `arithmetic types' are the signed and
unsigned integral types and the floating point types, so the `signed' in
`signed arithmetic' doesn't add anything, but it suggests that POSIX
really meant to say `integral' instead of `arithmetic'.  Has anyone
written a big portable program that supports dev_t, gid_t, ino_t,
mode_t, nlink_t, off_t, pid_t, ssize_t and uid_t being arbitrary
arithmetic types including long double?

Bruce