Tcl_NotifyChannel (tclIO.c) has been modified in Tcl 8.0.3 to protect
the channel in a fileevent by adding calls to Tcl_RegisterChannel and
Tcl_UnregisterChannel. This modification seems to be related to the
following entry in the changes file:
: 12/8/97 (bug fix) Need to protect the channel in a fileevent so that it
: is not deleted before the fileevent handler returns. (CS, JL)
This fix has a side effect that breaks existing C code, in particular
extensions (for example the scotty extension which I am maintaining)
that use Tcl channels internally. These channels are usually not
registered as the extension knows when to close the channel. The
change in Tcl_NotifyChannel has the effect that the channel gets
registered and later unregistered for a NULL interpreter. The call to
Tcl_UnregisterChannel in Tcl_NotifyChannel now has the side effect
that the channel gets closed when the first event on such a channel
has been processed, which of course is not what one expects.
Solution:
I have no concrete proposal as I am not too familiar with the
internals of the Tcl channel code. However, it might help to not call
Tcl_UnregisterChannel in Tcl_UnregisterChannel and to decrement the
reference counter directly. (I did not test this and there might be
more elegant ways.)
Question:
Do you agree that this is a bug? If yes, when can we expect the next
official patch which corrects the problem? (I have to decide whether I
have to rewrite my code to work around the problem or if I can expect
a fixed version of Tcl and TclPro soon. Thanks,
Juergen
Juergen Schoenwaelder schoenw@ibr.cs.tu-bs.de http://www.cs.tu-bs.de/~schoenw
Technical University Braunschweig, Dept. Operating Systems & Computer Networks
Bueltenweg 74/75, 38106 Braunschweig, Germany. (Tel. +49 531 / 391 3289)
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