Bug 16701

Summary:	xcb-image returns NULL
Product:	XCB	Reporter:	Alexander Kerner <lunohod>
Component:	Utils	Assignee:	Jamey Sharp <jamey>
Status:	CLOSED NOTABUG	QA Contact:
Severity:	normal
Priority:	medium	CC:	dottedmag, x
Version:	1.1
Hardware:	x86 (IA32)
OS:	Linux (All)
Whiteboard:
i915 platform:		i915 features:
Attachments:	testcase

Description Alexander Kerner 2008-07-14 03:36:23 UTC

xcb_image_get returns NULL if called right after the connection is established. 

flames.c from xcb-demo(git version) is a perfect test case. Return value of the xcb_image_get is not being checked and there is a segfailt at the next line. Adding sleep(1) before calling xcb_image_get in flame_draw_flame function solves the problem.


It looks like a timing problem, it depends on the slowness of the machine. There is no problem on a 200mhz arm machine and when it runs in gdb.

Comment 1 Mikhail Gusarov 2008-07-14 04:36:30 UTC

I've found minimal testcase which triggers the problem. Attached.

When any argument is passed to it, it sleeps for a second before obtaining image.

[mag@frontier:~/openinkpot/efl/xcb]% ./test1
(nil)
[mag@frontier:~/openinkpot/efl/xcb]% ./test1 test
0x804c330
[mag@frontier:~/openinkpot/efl/xcb]%

Comment 2 Mikhail Gusarov 2008-07-14 04:37:11 UTC

Created attachment 17663 [details]
testcase

Comment 3 Bart Massey 2008-09-15 10:50:22 UTC

I think this is not a bug.  You can't do a get_image on an unmapped window; the server refuses.  You're supposed to wait for the mapping event before you try to work with the window.  In practice, it suffices to ensure that the MapWindow request completes: using xcb_map_window_checked() instead of the xcb_flush() that was there is sufficient to fix the problem.

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