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From:	Haojun Bao <baohaojun AT gmail DOT com>
To:	cygwin AT cygwin DOT com
Subject:	Re: Emacs can't start-process more than 30~40 processes
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Date:	Wed, 29 Jul 2009 15:32:28 +0800
In-Reply-To:	<20090729023256.GC11458@ednor.casa.cgf.cx> (Christopher Faylor's message of "Tue, 28 Jul 2009 22:32:56 -0400")
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Christopher Faylor <cgf-use-the-mailinglist-please AT cygwin DOT com> writes:

> On Tue, Jul 28, 2009 at 10:52:44AM +0800, Haojun Bao wrote:
>>I have debugged it again, and I think I have more clue. I have read the
>>how-cygheap-works.txt, and this might be a known problem.
>>
>>It's because the cygheap space has been used up. With Procexp, I can see
>>cygwin1.dll is based 0x61000000, with size 0x300000 (3M). When segfault
>>is about to happen, cygheap_max is 0x6164e924, and the _csbrk is called
>>with a increase of 
>>    (gdb) p sbs
>>    $16 = 65544
>>This will increase cyghead to 0x6165e92c, but from Proxexp I can see
>>cygncurses-9.dll is based at 0x61650000.
>>
>>Besides, this code snippet from pipe.cc fhandler_pipe::create didn't
>>check for NULL pointer, and directly caused the segfault.
>>
>>      fhs[0] = (fhandler_pipe *) build_fh_dev (*piper_dev);
>>      fhs[1] = (fhandler_pipe *) build_fh_dev (*pipew_dev);
>>
>>//bhj: we should check NULL here.
>
> Not necessarily.  We don't expect these functions to return NULL.  It
> would be interesting to know how many fds are open at this point.  If it
> is a large number then maybe we have to start enforcing an fd max.  If
> it is a "small" number then something is wrong and we're allocating too
> much of the cygheap.  The cygheap was always supposed to be relatively
> small.  Maybe we're abusing it too much in 1.7.

There are quite some fds. In start-process, emacs will allocate 1 PTY
and 1 pipe for each process it starts.

Each fhandler_base is about 32K, but the _csbrk must allocate 65544
bytes for it.

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