Re: [PATCH][RFC] Pollable /proc/<pid>/ - avoid SIGCHLD/poll() races

[John Alvord <jalvo@mbay.net>]

On Sat, 13 Oct 2001 17:36:19 +0200, Jamie Lokier
<lk@tantalophile.demon.co.uk> wrote:

>Mattias Engdegård wrote:
>> I don't think it's contrived --- writing not a byte, but the pid and
>> return status of the dead child to a pipe is an old but useful trick.
>> It gives a natural serialisation of child deaths, and also eliminates
>> the common race where a child dies before its parent has recorded its
>> pid in a data structure. See it as a safe way of converting an
>> asynchronous signal to a queued event.
>>
>> Using pipes to wake up blocking select()s is a useful thing in general,
>> and often a lot cleaner than using signals when dealing with threads.
>
>This mistake is exactly the reason that Netscape 4.x freezes from time
>to time on Linux.
>
>It tries to write too many things to a pipe, making the assumption that
>this will never happen.

At one point a few years ago, someone implemented a loadable library
which "fixed" the Netscape problem by knowing what the bug was, doing
things the right way, and presenting the interface Netscape expected.

john