* generic/tclIO.c (UpdateInterest): When dropping interest in

	  TCL_READABLE now dropping interest in TCL_EXCEPTION too. This
	  fixes a bug where Expect detects eof on a file prematurely on
	  solaris 2.6 and higher. A much more complete explanation is in
	  the code itself (40 lines of comments for a one-line change :)

1 files changed, 44 insertions, 1 deletions

diff --git a/generic/tclIO.c b/generic/tclIO.c
index accf020..e4e8532 100644
--- a/generic/tclIO.c
+++ b/generic/tclIO.c
@@ -10,7 +10,7 @@
  * See the file "license.terms" for information on usage and redistribution
  * of this file, and for a DISCLAIMER OF ALL WARRANTIES.
  *
- * RCS: @(#) $Id: tclIO.c,v 1.66 2003/03/06 20:14:51 mdejong Exp $
+ * RCS: @(#) $Id: tclIO.c,v 1.67 2003/04/11 17:39:51 andreas_kupries Exp $
  */
 
 #include "tclInt.h"
@@ -6870,6 +6870,49 @@ UpdateInterest(chanPtr)
 		&& (statePtr->inQueueHead->nextRemoved <
 			statePtr->inQueueHead->nextAdded)) {
 	    mask &= ~TCL_READABLE;
+
+	    /*
+	     * Andreas Kupries, April 11, 2003
+	     *
+	     * Some operating systems (Solaris 2.6 and higher (but not
+	     * Solaris 2.5, go figure)) generate READABLE and
+	     * EXCEPTION events when select()'ing [*] on a plain file,
+	     * even if EOF was not yet reached. This is a problem in
+	     * the following situation:
+	     *
+	     * - An extension asks to get both READABLE and EXCEPTION
+	     *   events.
+	     * - It reads data into a buffer smaller than the buffer
+	     *   used by Tcl itself.
+	     * - It does not process all events in the event queue, but
+	     *   only only one, at least in some situations.
+	     *
+	     * In that case we can get into a situation where
+	     *
+	     * - Tcl drops READABLE here, because it has data in its own
+	     *   buffers waiting to be read by the extension.
+	     * - A READABLE event is syntesized via timer.
+	     * - The OS still reports the EXCEPTION condition on the file.
+	     * - And the extension gets the EXCPTION event first, and
+	     *   handles this as EOF.
+	     *
+	     * End result ==> Premature end of reading from a file.
+	     *
+	     * The concrete example is 'Expect', and its [expect]
+	     * command (and at the C-level, deep in the bowels of
+	     * Expect, 'exp_get_next_event'. See marker 'SunOS' for
+	     * commentary in that function too).
+	     *
+	     * [*] As the Tcl notifier does. See also for marker
+	     * 'SunOS' in file 'exp_event.c' of Expect.
+	     *
+	     * Our solution here is to drop the interest in the
+	     * EXCEPTION events too. This compiles on all platforms,
+	     * and also passes the testsuite on all of them.
+	     */
+
+	    mask &= ~TCL_EXCEPTION;
+
 	    if (!statePtr->timer) {
 		statePtr->timer = Tcl_CreateTimerHandler(0, ChannelTimerProc,
 			(ClientData) chanPtr);