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Subject: RE: random "fork: Resource temporarily unavailable"
Date: Tue, 20 Jun 2006 07:24:15 -0700
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From: "Mark Bartel" <mbartel AT adobe DOT com>
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Larry Hall wrote:
> Linda Walsh wrote:
> > I've not seen this message except when I've had to rapidly
> > press ^C to break out of a loop shell script.
> >
> > Today, I've seen it twice when there was virtually no cpu load
> > on the system, about 50% virtual memory committed, and 40 processes.
> >
> > Once, was with an "ls" command, the other happened as my shell was
> > starting up by some command invoked in the .rc script.
> >
> > I get suspicious whenever I see behavior on my computers when
> > anomalies crop up.
> >
> > I don't think any of my cygwin libraries have been updated recently.
> >
> > What would cause something like this?  Memory fragmentation?
> > Insufficient real memory to "immediately" fork?  I.e. I wonder
> > if, when NT goes to "fork", if it doesn't have enough free
> > memory, it tells the caller it failed (try again later) and
> > then starts a memory cleanup cycle to free up memory: i.e. rather
> > than the forking process sleeping while memory is made available
> > NT returns it immediately with a failure.
> >
> > Any idea on causes?  Is it as rare as it has been for me?
> > A possible solution would be retry the fork a second time, or
> > sleep for a millisecond and then try fork again. I'm not sure,
> > but I think many *ixy (*='un'|'pos'|'lin'|'ir'...etc) type programs
> > may not retry the fork  but immediately die, as on *ixy systems,
> > a fork failure is less common, and usually only happens when
> > the system really is out of resources.  If that's the case,
> > it _might_ be an aid to smooth *ixy compatibility for the
> > library handling fork, retry the fork (possibly with millisecond
> > sleep) once before returning failure to the application.
> >
> > Not a high priority issue, but just wondering....
> >
> > Linda
> > If it is NT returning failure rather than
> > forking, I wonder if, in order to provide a better "run-time"
> 
> 
> If you can reproduce this problem, I would suggest trying it again
with
> a recent snapshot.

This sounds like the same issue I was encountering.  I can reproduce it
on demand with:

mbartel AT mbartel-t60p ~
$ find * -type f -exec grep foo {} /dev/null \;
      6 [main] find 435884 fhandler_dev_zero::fixup_mmap_after_fork:
requested 0x480000 != 0x0 mem alloc base 0x480000, state 0x2000, size
1040384, Win32 error 487
    272 [main] find 435884 C:\cygwin\bin\find.exe: *** fatal error -
C:\cygwin\bin\find.exe: *** recreate_mmaps_after_fork_failed
     13 [main] find 434720 child_info::sync: wait failed, pid 435884,
Win32 error 0
    344 [main] find 434720 fork: child -1 - died waiting for longjmp
before initialization, retry 10, exit code 0x1000000, errno 11
find: cannot fork: Resource temporarily unavailable

mbartel AT mbartel-t60p ~
$

Unfortunately, it is more than just annoying in my case, as it happens
all the time.  I had to buy MKS Toolkit to get on with my job.

-Mark

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