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From: Eric Blake <ebb9@byu.net>
Subject:  Re: Excessive thrashing when popen()ing after a large malloc()
Date: Wed, 15 Nov 2006 16:18:10 +0000 (UTC)
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Eric Blake <ebb9 <at> byu.net> writes:

> >     else
> >       sprintf(cmd, "sh -c '%s' %d>&-", program, pdes[1])
> >   }
> >   pid = spawnl(_P_NOWAIT, _PATH_BSHELL, "sh", "-c", cmd, NULL);
> 
> Why are you going through two levels of sh?  That seems like a waste to
> me; the whole idea of using spawn is to avoid a fork(), but when you
> invoke "sh" "-c" "sh -c 'cmd'", you are right back to a fork.  True, the
> new invocation of sh uses less memory than the 1 GB process that invoked
> popen, so less thrashing will occur, but your whole approach seems
> fundamentally flawed if you are trying to use spawn to avoid a fork.

You know, maybe a better approach to this would be to first implement 
posix_spawn() in cygwin, since that API seems like it would be possible to do 
the necessary fd manipulation in a spawned child process without the penalty of 
a full fork/exec.  Then you could teach popen how to use posix_spawn when it is 
available, which is probably a patch more likely to be accepted in newlib, 
rather than your current idea of having to go through an intermediary sh 
invocation.  But I do not have a copyright on file for cygwin contributions, so 
I am currently unable to work on contributing posix_spawn; you are at the mercy 
of someone willing and able to write such a patch.

-- 
Eric Blake



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