[xlib] Add locking around GC cache.

The per-screen cached of most-recently freed GCs lacks suitable locking
for it to be threadsafe.
(cherry picked from commit dc714106e156cb7901e376c0935922446ae9bcdf)

1 files changed, 1 insertions, 0 deletions

diff --git a/src/cairo-xlib-private.h b/src/cairo-xlib-private.h
index 5bfc2ec5..2d9737d9 100644
--- a/src/cairo-xlib-private.h
+++ b/src/cairo-xlib-private.h
@@ -79,6 +79,7 @@ typedef struct _cairo_xlib_visual_info {
 struct _cairo_xlib_screen_info {
     cairo_xlib_screen_info_t *next;
     cairo_reference_count_t ref_count;
+    cairo_mutex_t mutex;
 
     cairo_xlib_display_t *display;
     Screen *screen;