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SubjectRe: PROBLEM: pthread-safety bug in write(2) on Linux 2.6.x
Date
On Apr 13, 2006, at 05:56:08, Andrew Morton wrote:
> Dan Bonachea <bonachead@comcast.net> wrote:
>>
>> This problem arose in the parallel runtime system for a scientific
>> language compiler (nearly a million lines of code total -
>> definitely a "real-world" program) - the example code is merely a
>> pared-down demonstration of the problem. In parallel scientific
>> computing, it's very common for many threads to be writing to
>> stdout (usually for monitoring purposes) and it's expected and
>> normal for output from separate threads to be arbitrarily
>> interleaved, but it's *not* ok for output to be lost entirely.
>> This is essentially equivalent to the real-world example you gave
>> of many threads logging to a file.
>
> Interesting - afaik that's the first time this has been hit in a
> real application.

I would guess that it could also be a problem with a wide variety of
Perl CGIs running under Apache2+mod_perl with the worker threading
model. In fact this may actually explain some odd behavior I got
from one such module that I "fixed" by switching to logging via
syslog. I don't remember which module it was or what the exact
problem was, but I think it seemed similar in nature. That is
somewhat of a surprising and nonintuitive failure mode for logging,
IMHO it would be nice to get fixed. I would imagine that this has
probably been hit a number of times before, mysteriously fixed by
changed userspace locking or subtle thread ordering, and written off
as the mysterious effects of cosmic rays on RAM.

Cheers,
Kyle Moffett

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