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From Matt Braithwaite <...@alink.net>
Subject os-bsdi/2227: serializing access to accept with fcntl works better than flock under BSDI
Date Wed, 13 May 1998 21:17:09 GMT

>Number:         2227
>Category:       os-bsdi
>Synopsis:       serializing access to accept with fcntl works better than flock under
BSDI
>Confidential:   no
>Severity:       serious
>Priority:       medium
>Responsible:    apache
>State:          open
>Class:          change-request
>Submitter-Id:   apache
>Arrival-Date:   Wed May 13 14:20:01 PDT 1998
>Last-Modified:
>Originator:     mab@alink.net
>Organization:
apache
>Release:        1.2.6
>Environment:
BSDI/OS 2.1 and 3.1 with the standard compiler
>Description:
in the interest of honesty i have to tell you that we added the
apache/SSL patch, and started using multiple `Listen' directives, at
the same time.  but, after we did so, our HTTP test program started
having problems (seldom; a few times a day) with the servers so
upgraded.  the problem was that requests would sometimes time out
after 30 seconds.  since the requests (1) are distinctive; i can
distinguish the test program's requests from other programs' requests
and (2) occur at very regular intervals, i was able to determine that
requests that timed out were actually logged by the server like a
minute or two after they were issued, and at the exact same instant as
another request came in to the server---as though the first request
had gotten stuck, and the second one jarred it loose.

anyway, since we'd never used multiple listen directives before, i
tried switching the servers in question from the default flock locking
to fcntl locking, for synchronization of calls to accept.  this worked
fine; the test program has not noted any problems since i made the
change.
>How-To-Repeat:
no guarantee that you can; but i would be surprised if whatever conditions you
customarily use to tickle the accept synchronization problem do not produce it
with flock locking under vanilla BSDI 2.1 or 3.1.
>Fix:
switch BSDI to fcntl locking.
>Audit-Trail:
>Unformatted:
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