Re: race condition in run-time system

Taylor R Campbell <[email protected]> Fri, 8 May 2009 08:45:45 -0400

Newsgroups	gmane.lisp.scheme.scheme48
Message-ID	<[email protected]>

   Date: Fri, 08 May 2009 08:49:18 +0200
   From: Michael Sperber <[email protected]>

   Could you elaborate a bit on where the race occurs?  I don't see it,
   despite staring at it for a while.  (I see that it may get in the way of
   itself, but only in inconsequential ways.)

Two threads, A and B, call PERIODICALLY-FORCE-OUTPUT! concurrently
(because they both called OPEN-OUTPUT-FILE or something).  Each thread
fetches the cdr of the list of periodically forced ports.  Each thread
conses up a new cdr.  Thread A sets the cdr, and then thread B sets
the cdr again, clobbering the change that thread A made, effectively
removing thread A's port from the list.  Thread A's port will not be
periodically forced.