[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)

2 files changed, 22 insertions, 10 deletions

diff --git a/src/cairo-xlib-private.h b/src/cairo-xlib-private.h
index 5bfc2ec56..2d9737d93 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;
diff --git a/src/cairo-xlib-screen.c b/src/cairo-xlib-screen.c
index 8a3da6675..fc07fda22 100644
--- a/src/cairo-xlib-screen.c
+++ b/src/cairo-xlib-screen.c
@@ -256,12 +256,14 @@ _cairo_xlib_screen_info_close_display (cairo_xlib_screen_info_t *info)
 {
     int i;
 
+    CAIRO_MUTEX_LOCK (info->mutex);
     for (i = 0; i < ARRAY_LENGTH (info->gc); i++) {
 	if (info->gc[i] != NULL) {
 	    XFreeGC (info->display->display, info->gc[i]);
 	    info->gc[i] = NULL;
 	}
     }
+    CAIRO_MUTEX_UNLOCK (info->mutex);
 }
 
 void
@@ -295,6 +297,8 @@ _cairo_xlib_screen_info_destroy (cairo_xlib_screen_info_t *info)
 
     _cairo_array_fini (&info->visuals);
 
+    CAIRO_MUTEX_FINI (info->mutex);
+
     free (info);
 }
 
@@ -335,6 +339,7 @@ _cairo_xlib_screen_info_get (Display *dpy, Screen *screen)
 	info = malloc (sizeof (cairo_xlib_screen_info_t));
 	if (info != NULL) {
 	    CAIRO_REFERENCE_COUNT_INIT (&info->ref_count, 2); /* Add one for display cache */
+	    CAIRO_MUTEX_INIT (info->mutex);
 	    info->display = _cairo_xlib_display_reference (display);
 	    info->screen = screen;
 	    info->has_render = FALSE;
@@ -385,16 +390,18 @@ GC
 _cairo_xlib_screen_get_gc (cairo_xlib_screen_info_t *info, int depth)
 {
     GC gc;
+    cairo_bool_t needs_reset;
 
     depth = depth_to_index (depth);
 
+    CAIRO_MUTEX_LOCK (info->mutex);
     gc = info->gc[depth];
     info->gc[depth] = NULL;
+    needs_reset = info->gc_needs_clip_reset & (1 << depth);
+    CAIRO_MUTEX_UNLOCK (info->mutex);
 
-    if (info->gc_needs_clip_reset & (1 << depth)) {
+    if (needs_reset)
 	XSetClipMask(info->display->display, gc, None);
-	info->gc_needs_clip_reset &= ~(1 << depth);
-    }
 
     return gc;
 }
@@ -403,21 +410,25 @@ cairo_status_t
 _cairo_xlib_screen_put_gc (cairo_xlib_screen_info_t *info, int depth, GC gc, cairo_bool_t reset_clip)
 {
     cairo_status_t status = CAIRO_STATUS_SUCCESS;
+    GC oldgc;
 
     depth = depth_to_index (depth);
 
-    if (info->gc[depth] != NULL) {
-	status = _cairo_xlib_display_queue_work (info->display,
-		                               (cairo_xlib_notify_func) XFreeGC,
-					       info->gc[depth],
-					       NULL);
-    }
-
+    CAIRO_MUTEX_LOCK (info->mutex);
+    oldgc = info->gc[depth];
     info->gc[depth] = gc;
     if (reset_clip)
 	info->gc_needs_clip_reset |= 1 << depth;
     else
 	info->gc_needs_clip_reset &= ~(1 << depth);
+    CAIRO_MUTEX_UNLOCK (info->mutex);
+
+    if (oldgc != NULL) {
+	status = _cairo_xlib_display_queue_work (info->display,
+		                               (cairo_xlib_notify_func) XFreeGC,
+					       oldgc,
+					       NULL);
+    }
 
     return status;
 }