XWin crash after the launch of startkde on a remote Red Hat 5 machine

[Michel Hummel <hummel dot michel at gmail dot com>]

Hello,
I'm using cygwin on Microsoft Windows XP with XWin version :
sh-3.2# XWin.exe -version
Welcome to the XWin X Server
Vendor: The Cygwin/X Project
Release: 1.8.0.0 (10800000)
Build Date: 2010-04-02
Contact: cygwin-xfree@cygwin.com

I think I have found a bug in the XWin reset procedure which leads to
the start of two clipboard thread's and sometime to a crash of the X
server.

The crash can be produced by lauching startkde on a Red Hat 5 remote
machine (The crash should arrive after some minutes of work)
but the bug can simply be produced like this :

On my installation if I launch Xwin with this options :
XWin :0 -ac&
then I do
xsetroot -solid '#FFFF00'

After setting the color, Xwin launches its reset procedure because
there is no more client connected ( the server loses the color but it
is the normal comportment isn't it ?
http://sourceware.org/ml/cygwin-xfree/2002-01/msg00106.html)

The problem comes from the clipboard thread. In this example, when the
server launches its reset procedure, the clipboard is in state
"Launched" but is not in state "Started" (Boolean variable about
clipboard status, see file hw/xwin/winclipboardthread.c).

This particular status of the ClipboardThread during server reset is
normaly managed by two "if" statements :

* An "if" in the file hw/xwin/InitOutput.c disables the exit of the
clipboard thread in this state
Extract of the file hw/xwin/InitOutput.c (with line number) :

?169 winClipboardShutdown (void)
?170 {
?171 ? /* Close down clipboard resources */
?172 ? if (g_fClipboard && g_fClipboardLaunched && g_fClipboardStarted)
?173 ? ? {
?174 ? ? ? /* Synchronously destroy the clipboard window */
?175 ? ? ? if (g_hwndClipboard != NULL)
?176 ? ? ? ? {
?177 ? ? ? ? ? SendMessage (g_hwndClipboard, WM_DESTROY, 0, 0);
?178 ? ? ? ? ? /* NOTE: g_hwndClipboard is set to NULL in
winclipboardthread.c */
?179 ? ? ? ? }
?180 ? ? ? else
?181 ? ? ? ? return;
?182
?183 ? ? ? /* Wait for the clipboard thread to exit */
?184 ? ? ? pthread_join (g_ptClipboardProc, NULL);
?185
?186 ? ? ? g_fClipboardLaunched = FALSE;
?187 ? ? ? g_fClipboardStarted = FALSE;
?188
?189 ? ? ? winDebug ("winClipboardShutdown - Clipboard thread has exited.\n");
?190 ? ? }
?191 }

* An "if" statement in the file hw/xwin/winclipboardwrappers.c
prohibits the launch of clipboard thread if one is already Launched.
Extract of the file hw/xwin/winclipboardwrappers.c (with line number)
256 ? /* If the clipboard client has already been started, abort */
257 ? if (g_fClipboardLaunched)
258 ? ? {
259 ? ? ? ErrorF ("winProcEstablishConnection - Clipboard client already "
260 ? ? ? ? ? ? ? "launched, returning.\n");
261 ? ? ? return iReturn;
262 ? ? }


The problem is that the Boolean variables g_fClipboardLaunched and
g_fClipboardStarted are re-initialized by the server reset procedure
(function winInitializeGlobals of the file ?hw/xwin/winglobals.c)
Extract of the file hw/xwin/winglobals.c (with line number)
128 /*
129 ?* Re-initialize global variables that are invalidated 130 ?* by a
server reset.
131 ?*/
132
133 void
134 winInitializeGlobals (void)
135 {
136 ? g_dwCurrentThreadID = GetCurrentThreadId ();
137 ? g_hwndKeyboardFocus = NULL;
138 #ifdef XWIN_CLIPBOARD
139 ? g_fClipboardLaunched = FALSE;
140 ? g_fClipboardStarted = FALSE;
141 ? g_iClipboardWindow = None;
142 ? g_pClipboardDisplay = NULL;
143 ? g_atomLastOwnedSelection = None;
144 ? g_hwndClipboard = NULL;
145 #endif
146 }

The consequence of this Re-initialization in this particular situation
is that the clipboard thread is launched two times and sometimes leads
to a crash of the X server.
You can see the double launch of the clipboard thread at the end of
the attached log file Xwin.0.log ( 2 times the sentence :
winClipboardProc - XOpenDisplay () returned and successfully opened
the display. )

To fix this bug I purpose to remove the variables g_fClipboardLaunched
and g_fClipboardStarted of the "winInitializeGlobals (void)" function,
as their re-initializations are handled in in the files :
hw/xwin/InitOutput.c.

That what is doing the patch Attached to this email.

Regards,
Michel Hummel

Attachment: XWin_winglobals_ClipboardThread.patch
Description: Binary data

Attachment: XWin.0.log
Description: Binary data

--
Unsubscribe info:      http://cygwin.com/ml/#unsubscribe-simple
Problem reports:       http://cygwin.com/problems.html
Documentation:         http://x.cygwin.com/docs/
FAQ:                   http://x.cygwin.com/docs/faq/