Hello everyone,

libxcb will crash if you try to view some Java stuff in your web browser(Epiphany and Firefox tested). This happens on an up-to-date Arch Linux i686 system with Sun Java 1.6.0_05-b13 installed.
Example Java thing: http://streaming.linux-magazin.de/events/lmo/helmbrecht/frames-java.htm (a video)

Console output:
lisa@myhost:~$ epiphany

** (epiphany:4306): WARNING **: No word lists can be found for the language "de".
** Message: GetValue variable 1 (1)
** Message: GetValue variable 2 (2)
** Message: GetValue variable 1 (1)
** Message: GetValue variable 2 (2)
** Message: GetValue variable 1 (1)
** Message: GetValue variable 2 (2)
** Message: GetValue variable 1 (1)
** Message: GetValue variable 2 (2)
** Message: GetValue variable 1 (1)
** Message: GetValue variable 2 (2)
** Message: GetValue variable 1 (1)
** Message: GetValue variable 2 (2)
//At this point I will open the page containing the embedded Java video
Locking assertion failure. Backtrace:
#0 /usr/lib/libxcb-xlib.so.0 [0xb7d23767]
#1 /usr/lib/libxcb-xlib.so.0(xcb_xlib_unlock+0x31) [0xb7d238b1]
#2 /usr/lib/libX11.so.6(_XReply+0xfd) [0xb5389a8d]
#3 /opt/java/jre/lib/i386/xawt/libmawt.so [0xb549b8ce]
#4 /opt/java/jre/lib/i386/xawt/libmawt.so [0xb5478067]
#5 /opt/java/jre/lib/i386/xawt/libmawt.so [0xb5478318]
#6 /opt/java/jre/lib/i386/xawt/libmawt.so(Java_sun_awt_X11GraphicsEnvironment_initDisplay+0x2f) [0xb547861f]
#7 [0xb5ceae9d]
#8 [0xb5ce3edd]
#9 [0xb5ce3edd]
#10 [0xb5ce1249]
#11 /opt/java/jre/lib/i386/client/libjvm.so [0x621c40d]
#12 /opt/java/jre/lib/i386/client/libjvm.so [0x6310378]
#13 /opt/java/jre/lib/i386/client/libjvm.so [0x621c2a0]
#14 /opt/java/jre/lib/i386/client/libjvm.so(JVM_DoPrivileged+0x363) [0x6272153]
#15 /opt/java/jre/lib/i386/libjava.so(Java_java_security_AccessController_doPrivileged__Ljava_security_PrivilegedAction_2+0x3d) [0xb7cfc96d]
#16 [0xb5ceae9d]
#17 [0xb5ce3d77]
#18 [0xb5ce1249]
#19 /opt/java/jre/lib/i386/client/libjvm.so [0x621c40d]
Locking assertion failure. Backtrace:
#0 /usr/lib/libxcb-xlib.so.0 [0xb7d23767]
#1 /usr/lib/libxcb-xlib.so.0(xcb_xlib_lock+0x2e) [0xb7d2381e]
#2 /usr/lib/libX11.so.6 [0xb5388e08]
#3 /usr/lib/libX11.so.6(XGetVisualInfo+0x26) [0xb537fb76]
#4 /opt/java/jre/lib/i386/xawt/libmawt.so [0xb5477319]
#5 /opt/java/jre/lib/i386/xawt/libmawt.so [0xb5477565]
#6 /opt/java/jre/lib/i386/xawt/libmawt.so [0xb54783c9]
#7 /opt/java/jre/lib/i386/xawt/libmawt.so(Java_sun_awt_X11GraphicsEnvironment_initDisplay+0x2f) [0xb547861f]
#8 [0xb5ceae9d]
#9 [0xb5ce3edd]
#10 [0xb5ce3edd]
#11 [0xb5ce1249]
#12 /opt/java/jre/lib/i386/client/libjvm.so [0x621c40d]
#13 /opt/java/jre/lib/i386/client/libjvm.so [0x6310378]
#14 /opt/java/jre/lib/i386/client/libjvm.so [0x621c2a0]
#15 /opt/java/jre/lib/i386/client/libjvm.so(JVM_DoPrivileged+0x363) [0x6272153]
#16 /opt/java/jre/lib/i386/libjava.so(Java_java_security_AccessController_doPrivileged__Ljava_security_PrivilegedAction_2+0x3d) [0xb7cfc96d]
#17 [0xb5ceae9d]
#18 [0xb5ce3d77]
#19 [0xb5ce1249]

This happens everytime. My browser(Epiphany and Firefox) will not crash, just the lib/Java.
On my test machine with Ubuntu Gutsy(and Java 1.5.something) the video plays absolutely correctly.

Workaround:
I don't know a working workaround. However, you can prevent crashing libxcb by applying the patch included in the PKGBUILD by hand. The patch is deprecated, and for libxcb 1.0(we have 1.1). Apply the patch by hand, recompile and update to that package. Libxcb won't crash anymore, but the video will not play.
The same happens with 1.1 and Ubuntu Hardy patches.
I also tried downgrading to libxcb 1.0 and applying the patch included with the PKGBUILD: libxcb will crash. I tried 1.0 with Ubuntu Gutsy patch:Java VM won't start. With both patches the same behavior like 1.1 with Archlinux patch will happen(nothing).