Subject: Re: bug#10641: [2.0.3+] start_signal_delivery_thread failure on x86_64-freebsd8.2

From: Andy Wingo <[email-masked]>
Date: Wed, 13 Mar 2013 11:02:41 +0100

Hi,

On Sun 29 Jan 2012 19:00, [email-masked] (Ludovic Courtès) writes:

> Adding printfs shows that the thread calling scm_spawn_thread leaves
> cond_wait before the signal thread has signaled the condition (in
> really_spawn).

>From http://pubs.opengroup.org/onlinepubs/009604599/functions/pthread_cond_wait.html

  When using condition variables there is always a Boolean predicate
  involving shared variables associated with each condition wait that is
  true if the thread should proceed. Spurious wakeups from the
  pthread_cond_timedwait() or pthread_cond_wait() functions may
  occur. Since the return from pthread_cond_timedwait() or
  pthread_cond_wait() does not imply anything about the value of this
  predicate, the predicate should be re-evaluated upon such return.

It seems this code is not robust in the face of spurious wakeups.  I
pushed a patch that waits for data.thread to become non-false.  That
should fix this issue.

Cheers,

Andy
-- 
http://wingolog.org/