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Message-Id: <199910050417.VAA27657@herra.corp.netapp.com>
To: cygwin AT sourceware DOT cygnus DOT com
Subject: make_pipe() can sometimes fail to grow file descriptors
Date: Mon, 04 Oct 1999 21:17:34 -0700
From: Lincoln Myers <lincoln AT netapp DOT com>


In looking around to find why a perl program of mine is being limited
to about 60 file descriptors, I think I've found what might be the
problem (by inspection only so far, so I still have to convince you
with words rather than deeds :)) an off-by-one error in how
make_pipe() calls hinfo::find_unused_inode().  I'm using B20.1, but I
see the same code in the 1999/10/03 winsup snapshot.

make_pipe contains:

  if ((fdr = dtable.find_unused_handle ()) < 0)
    set_errno (ENMFILE);
  else if ((fdw = dtable.find_unused_handle (fdr + 1)) < 0)
    set_errno ( ENMFILE);
  else
    ...

In make_pipe, 

	fdr = dtable.find_unused_handle()

might return fdr to be be the last currently allocated handle (which
would be dtable.size-1).  But then

	dtable.find_unused_handle(fdr+1)

would be equivalent to

	dtable.find_unused_handle(dtable.size)

which as can be seen in hinfo::find_unused_handle():

  if ((size_t)start >= size)
    return -1;

would return -1, and thus make_pipe() returns ENMFILE when Win32 and
memory would still allow more files and file descriptors.  Unless this
would upset one of its other callers, I think a good fix would be to
change the test in hinfo::find_unused_handle() to this:

  if ((size_t)start > size)
    return -1;

-----

Lincoln

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