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Re: Problem with parallel make

From: Paul D. Smith
Subject: Re: Problem with parallel make
Date: Tue, 1 Aug 2006 17:49:52 -0400

%% David Boyce <address@hidden> writes:

  db> At 10:02 AM 7/30/2006, Paul D. Smith wrote:
  >> %% Lee Killough <address@hidden> writes:
  lk> Perhaps a larger filehandle number, less likely to occur in common
  lk> shell redirection idioms, should be used for the jobserver.
  >> Well, pipe(2) doesn't allow you to choose your own file descriptors: it
  >> just uses the lowest available descriptors.  I could use dup2(2) to
  >> force different ones after the pipe has been created, but there's no
  >> portable way in POSIX (that I know of) to find the maximum valid file
  >> descriptor.  I guess we could just use OPEN_MAX, if we can figure it
  >> out.

  db> I have something like this in my code. What I chose to do, rather 
  db> than try to determine the max fd, was to pick a number north of (say) 
  db> 50 and south of 256. I try to dup to that and then, if it fails, the 
  db> next 10 values or so (or I guess you could go to 257 or 1025 if so 
  db> inclined). If none of them works, I just drop back to using what the 
  db> OS gave me. ISTM the odds of of this not working are very low and 
  db> even if it doesn't you're no worse off.

This seems like a useful thing to do.  This is not the first time we've
seen people confused by the way make steals low-numbered FDs.

Can someone (Lee?) create an enhancement bug request for this in the GNU
make project on Savannah so it won't get lost?

 Paul D. Smith <address@hidden>          Find some GNU make tips at:            
 "Please remain calm...I may be mad, but I am a professional." --Mad Scientist

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