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xlib/shm: Wrap the detection of shm with locking

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As we access a global error variable, we need to hold a mutex against
simultaneous checking of multiple Displays. This should already be true
as we hold our display mutex to serialize initialisation, so just add an
assertion. As the client may mix use of cairo in one thread with X from
another, we need to hold the Display lock and serialise whilst
manipulating the low-level state of the Display.

Suggested-by: Uli Schlachter <psychon@znc.in>
Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
This commit is contained in:
Chris Wilson 2012-08-18 08:02:42 +01:00
parent 1bc9f673b6
commit ec01c71eca
1 changed files with 6 additions and 0 deletions
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6
src/cairo-xlib-surface-shm.c
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@ -231,6 +231,7 @@ _pqueue_pop (struct pqueue *pq)
}
static cairo_bool_t _x_error_occurred;
static int
_check_error_handler (Display *display,
XErrorEvent *event)
@ -263,7 +264,11 @@ can_use_shm (Display *dpy, int *has_pixmap)
return FALSE;
}
assert (CAIRO_MUTEX_IS_LOCKED (_cairo_xlib_display_mutex));
_x_error_occurred = FALSE;
XLockDisplay (dpy);
XSync (dpy, False);
old_handler = XSetErrorHandler (_check_error_handler);
success = XShmAttach (dpy, &shm);
@ -272,6 +277,7 @@ can_use_shm (Display *dpy, int *has_pixmap)
XSync (dpy, False);
XSetErrorHandler (old_handler);
XUnlockDisplay (dpy);
shmctl (shm.shmid, IPC_RMID, NULL);
shmdt (shm.shmaddr);