On 01/11/2012 08:13 AM, Adam Jackson wrote:
On Tue, 2012-01-10 at 19:46 -0700, Brian Paul wrote:
From: Brian Paul<bri...@vmware.com>
This is a follow-on to the previous commits. It seems that
XShmQueryVersion() can trigger an X error after the first X
connection is closed and we start using a new connection.
I assume this is when you switch which Display you're talking to as
well.
Yes. It's really weird. I looked at the sources for the XShm
extension code and I didn't see anything obviously wrong there.
If I disabled all use of XShm in the Mesa code the test app worked
fine. Also, If I hard coded the check_for_xshm() function to just
always return true, things ran normally as well.
So the X error handler is a band-aid over the problem, but it seems to
do the job.
I guess another "solution" would be to simply remove the call to
XShmQueryVersion() and assume that if XQueryExtension("MIT-SHM")
passes then the version is acceptable (it's been 1.1 forever, AFAIK).
What do you think about that?
+static int
+xshm_query_version_err_handler( XMesaDisplay* dpy, XErrorEvent* xerr )
+{
+ /* If this function gets called, it's because XShmQuerryVersion()
+ * has failed.
+ */
+ XShmErrorFlag = True;
+ return 0;
+}
Not safe against a process using multiple Display connections, which is
admittedly quite rare. There's a few instances of that kind of bug
already though, I wouldn't call it a blocker.
+ /* Install X error handler before calling XShmQueryVersion() to catch
+ * a spurious X error.
+ */
+ XShmErrorFlag = False;
+ old_handler = XSetErrorHandler(xshm_query_version_err_handler);
+ ok = XShmQueryVersion( display,&major,&minor,&pixmaps );
+ XSetErrorHandler(old_handler);
+ if (XShmErrorFlag)
+ ok = False;
+
+ if (ok) {
Not thread-safe, though it's tough to hit. You want an XLockDisplay
before the first XSetErrorHandler and the matching XUnlockDisplay after
the second, otherwise your handler can get called for errors on other
threads.
I guess I'm not too concerned about that for the time being. As you
said, there's other instances of multi-display and thread safety
issues already.
-Brian
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