[Boost-build] Patch execunix.c for Darwin PPC hangs

From: K. Noel Belcourt (kbelco_at_[hidden])
Date: 2008-02-07 15:03:35

Hi,

I've been having occasional problems running parallel (-j2) darwin  
trunk regression tests on ppc G5 hardware under Mac OS 10.4.x.  It  
appears that a race condition, or other unsavory interaction,  
randomly occurs between vfork and execvp.  I've tried using execve,  
as documented in the vfork man page, but the race condition still  
occurs.   Simply replacing vfork with fork fixes the occasional hangs  
I've been seeing.  While I am concerned about the increased overhead  
of fork over vfork, I believe a robust parallel bjam is well worth  
the increase in overhead.

Attached is a patch that replaces vfork with fork, only on ppc  
darwin, along with a couple of minor patches.  I've used the  
__APPLE__ and __ppc__ macros to select fork over vfork.  I'm open to  
suggestions if there's a better set of macros to use.

I've tested this patch to ensure that (1) it fixes the darwin ppc  
trunk tests and (2) doesn't break any other unix trunk regression  
tests (Aix, Sun, Intel Darwin, Linux flavors).  If there's no  
objection, I'd like to commit this to the trunk.

Thanks.

-- Noel