xlib: Fix screen device handling

Add a _cairo_xlib_device_create() function that could easily be exported
as a replacement for _cairo_xlib_display_get(). This function returns a
cairo_device_t instead of a cairo_xlib_display_t because the display
isn't acquired.

src/cairo-xlib-display.c

@@ -254,15 +254,22 @@ static const cairo_device_backend_t _cairo_xlib_device_backend = {
     _cairo_xlib_display_destroy,
 };
 
-cairo_status_t
-_cairo_xlib_display_get (Display *dpy,
-			 cairo_xlib_display_t **out)
+/**
+ * cairo_xlib_device_create:
+ * @dpy: the display to create the device for
+ *
+ * Gets the device belonging to @dpy, or creates it if it doesn't exist yet.
+ *
+ * Returns: the device belonging to @dpy
+ **/
+cairo_device_t *
+_cairo_xlib_device_create (Display *dpy)
 {
     cairo_xlib_display_t *display;
     cairo_xlib_display_t **prev;
+    cairo_device_t *device;
     XExtCodes *codes;
     const char *env;
-    cairo_status_t status = CAIRO_STATUS_SUCCESS;
 
     /* There is an apparent deadlock between this mutex and the
      * mutex for the display, but it's actually safe. For the
@@ -284,18 +291,14 @@ _cairo_xlib_display_get (Display *dpy,
 		display->next = _cairo_xlib_display_list;
 		_cairo_xlib_display_list = display;
 	    }
-	    break;
+            device = cairo_device_reference (&display->base);
+	    goto UNLOCK;
 	}
     }
 
-    if (display != NULL) {
-        cairo_device_reference (&display->base);
-	goto UNLOCK;
-    }
-
     display = malloc (sizeof (cairo_xlib_display_t));
     if (unlikely (display == NULL)) {
-	status = _cairo_error (CAIRO_STATUS_NO_MEMORY);
+	device = _cairo_device_create_in_error (CAIRO_STATUS_NO_MEMORY);
 	goto UNLOCK;
     }
 
@@ -326,9 +329,8 @@ _cairo_xlib_display_get (Display *dpy,
 
     codes = XAddExtension (dpy);
     if (unlikely (codes == NULL)) {
-	status = _cairo_error (CAIRO_STATUS_NO_MEMORY);
+	device = _cairo_device_create_in_error (CAIRO_STATUS_NO_MEMORY);
 	free (display);
-	display = NULL;
 	goto UNLOCK;
     }
 
@@ -433,10 +435,11 @@ _cairo_xlib_display_get (Display *dpy,
     display->next = _cairo_xlib_display_list;
     _cairo_xlib_display_list = display;
 
+    device = &display->base;
+
 UNLOCK:
     CAIRO_MUTEX_UNLOCK (_cairo_xlib_display_mutex);
-    *out = display;
-    return status;
+    return device;
 }
 
 void

src/cairo-xlib-private.h

@@ -112,8 +112,8 @@ struct _cairo_xlib_screen {
     cairo_array_t visuals;
 };
 
-cairo_private cairo_status_t
-_cairo_xlib_display_get (Display *display, cairo_xlib_display_t **out);
+cairo_private cairo_device_t *
+_cairo_xlib_device_create (Display *display);
 
 cairo_private void
 _cairo_xlib_display_add_screen (cairo_xlib_display_t *display,

src/cairo-xlib-screen.c

@@ -307,7 +307,6 @@ _cairo_xlib_screen_destroy (cairo_xlib_screen_t *info)
 
         cairo_device_release (&display->base);
     }
-    cairo_device_destroy (info->device);
 
     _cairo_array_fini (&info->visuals);
 
@@ -320,12 +319,20 @@ _cairo_xlib_screen_get (Display *dpy,
 			cairo_xlib_screen_t **out)
 {
     cairo_xlib_display_t *display;
+    cairo_device_t *device;
     cairo_xlib_screen_t *info;
     cairo_status_t status;
 
-    status = _cairo_xlib_display_get (dpy, &display);
-    if (likely (status == CAIRO_STATUS_SUCCESS))
-	status = _cairo_xlib_display_get_screen (display, screen, &info);
+    device = _cairo_xlib_device_create (dpy);
+    status = device->status;
+    if (unlikely (status))
+        goto CLEANUP_DEVICE;
+
+    status =  _cairo_xlib_display_acquire (device, &display);
+    if (unlikely (status))
+        goto CLEANUP_DEVICE;
+
+    status = _cairo_xlib_display_get_screen (display, screen, &info);
     if (unlikely (status))
 	goto CLEANUP_DISPLAY;
 
@@ -341,7 +348,7 @@ _cairo_xlib_screen_get (Display *dpy,
     }
 
     CAIRO_REFERENCE_COUNT_INIT (&info->ref_count, 2); /* Add one for display cache */
-    info->device = &display->base;
+    info->device = device;
     info->screen = screen;
     info->has_render = FALSE;
     info->has_font_options = FALSE;
@@ -366,10 +373,12 @@ _cairo_xlib_screen_get (Display *dpy,
     _cairo_xlib_display_add_screen (display, info);
 
     *out = info;
-    return CAIRO_STATUS_SUCCESS;
 
   CLEANUP_DISPLAY:
-    cairo_device_destroy ((cairo_device_t *) display);
+    cairo_device_release (&display->base);
+
+  CLEANUP_DEVICE:
+    cairo_device_destroy (device);
     return status;
 }