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Date: Wed, 17 Oct 2001 10:12:47 +0200
From: Frederic Devernay <Frederic DOT Devernay AT sophia DOT inria DOT fr>
To: cygwin AT cygwin DOT com
Subject: another poll() patch
Message-ID: <20011017101247.A19306@perf.inria.fr>
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Hello,

Jason's patch
(http://www.cygwin.com/ml/cygwin-patches/2001-q3/msg00109.html)
had the following problems:
- it used FD_ISSET with a fd that could possibly be completely out of
range... Sun RPC for example uses fd=-1 in its poll() calls (which
made my server crash when the client quits).
- even when there's _some_ invalid fds, cygwin_select() should be
called. But it should not be called if _all_ are invalid.
- the return value from cygwin_select should not be modified if it's
negative (can it be negative?).
- In brief, it only worked if all fds were valid, or if all were
invalid but within the valid range.

Here's another try:
Index: poll.cc
===================================================================
RCS file: /cvs/src/src/winsup/cygwin/poll.cc,v
retrieving revision 1.20
diff -u -r1.20 poll.cc
--- poll.cc	2001/10/01 04:10:07	1.20
+++ poll.cc	2001/10/15 12:43:29
@@ -51,10 +51,12 @@
   memset (write_fds, 0, fds_size);
   memset (except_fds, 0, fds_size);
 
-  bool invalid_fds = false;
+  bool valid_fds = false;
   for (unsigned int i = 0; i < nfds; ++i)
     if (!cygheap->fdtab.not_open (fds[i].fd))
       {
+	valid_fds = true;
+	fds[i].revents = 0;	
 	FD_SET (fds[i].fd, open_fds);
 	if (fds[i].events & POLLIN)
 	  FD_SET (fds[i].fd, read_fds);
@@ -64,20 +66,17 @@
 	  FD_SET (fds[i].fd, except_fds);
       }
       else
-	invalid_fds = true;
+	fds[i].revents = POLLNVAL;
 
   int ret = 0;
-  if (!invalid_fds)
+  if (valid_fds)
     ret = cygwin_select (max_fd + 1, read_fds, write_fds, except_fds,
 			 timeout < 0 ? NULL : &tv);
 
   for (unsigned int i = 0; i < nfds; ++i)
     {
-      if (!FD_ISSET (fds[i].fd, open_fds))
-	{
-	  fds[i].revents = POLLNVAL;
-	  ret++;
-	}
+      if (fds[i].revents == POLLNVAL && ret >= 0)
+	ret++;
       else if (cygheap->fdtab.not_open(fds[i].fd))
 	fds[i].revents = POLLHUP;
       else if (ret < 0)

----- End forwarded message -----

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