xcb: Remove free XID cache

cairo-xcb kept a cache of free xid to avoid calling xcb_generate_id()
later. However, this is unsafe: When libxcb runs out of ids, it asks the
X11 server for an empty range of ids to use. The X11 server of course
does not know about cairo's cache and could hand out an id that cairo
will use again later. This would then result in BadIdChoice errors
later.

Fix this by simply removing the whole cache.

Fixes: https://gitlab.freedesktop.org/cairo/cairo/-/issues/434
Signed-off-by: Uli Schlachter <psychon@znc.in>

src/cairo-xcb-connection-core.c

@@ -42,7 +42,7 @@ _cairo_xcb_connection_create_pixmap (cairo_xcb_connection_t *connection,
 				     uint16_t width,
 				     uint16_t height)
 {
-    xcb_pixmap_t pixmap = _cairo_xcb_connection_get_xid (connection);
+    xcb_pixmap_t pixmap = xcb_generate_id (connection->xcb_connection);
 
     assert (width > 0);
     assert (height > 0);
@@ -57,7 +57,6 @@ _cairo_xcb_connection_free_pixmap (cairo_xcb_connection_t *connection,
 				   xcb_pixmap_t pixmap)
 {
     xcb_free_pixmap (connection->xcb_connection, pixmap);
-    _cairo_xcb_connection_put_xid (connection, pixmap);
 }
 
 xcb_gcontext_t
@@ -66,7 +65,7 @@ _cairo_xcb_connection_create_gc (cairo_xcb_connection_t *connection,
 				 uint32_t value_mask,
 				 uint32_t *values)
 {
-    xcb_gcontext_t gc = _cairo_xcb_connection_get_xid (connection);
+    xcb_gcontext_t gc = xcb_generate_id (connection->xcb_connection);
     xcb_create_gc (connection->xcb_connection, gc, drawable,
 		   value_mask, values);
     return gc;
@@ -77,7 +76,6 @@ _cairo_xcb_connection_free_gc (cairo_xcb_connection_t *connection,
 			       xcb_gcontext_t gc)
 {
     xcb_free_gc (connection->xcb_connection, gc);
-    _cairo_xcb_connection_put_xid (connection, gc);
 }
 
 void

src/cairo-xcb-connection-render.c

@@ -79,7 +79,6 @@ _cairo_xcb_connection_render_free_picture (cairo_xcb_connection_t *connection,
 {
     assert (connection->flags & CAIRO_XCB_HAS_RENDER);
     xcb_render_free_picture (connection->xcb_connection, picture);
-    _cairo_xcb_connection_put_xid (connection, picture);
 }
 
 void
@@ -133,7 +132,6 @@ _cairo_xcb_connection_render_free_glyph_set (cairo_xcb_connection_t      *connec
 {
     assert (connection->flags & CAIRO_XCB_HAS_RENDER);
     xcb_render_free_glyph_set (connection->xcb_connection, glyphset);
-    _cairo_xcb_connection_put_xid (connection, glyphset);
 }
 
 void

src/cairo-xcb-connection-shm.c

@@ -43,7 +43,7 @@ _cairo_xcb_connection_shm_attach (cairo_xcb_connection_t *connection,
 				  uint32_t id,
 				  cairo_bool_t readonly)
 {
-    uint32_t segment = _cairo_xcb_connection_get_xid (connection);
+    uint32_t segment = xcb_generate_id (connection->xcb_connection);
     assert (connection->flags & CAIRO_XCB_HAS_SHM);
     xcb_shm_attach (connection->xcb_connection, segment, id, readonly);
     return segment;
@@ -109,7 +109,6 @@ _cairo_xcb_connection_shm_detach (cairo_xcb_connection_t *connection,
 {
     assert (connection->flags & CAIRO_XCB_HAS_SHM);
     xcb_shm_detach (connection->xcb_connection, segment);
-    _cairo_xcb_connection_put_xid (connection, segment);
 }
 
 #endif /* CAIRO_HAS_XCB_SHM_FUNCTIONS */

src/cairo-xcb-connection.c

@@ -255,7 +255,7 @@ pixmap_depths_usable (cairo_xcb_connection_t *connection,
     cairo_bool_t success = TRUE;
     int depth, i, j;
 
-    pixmap = _cairo_xcb_connection_get_xid (connection);
+    pixmap = xcb_generate_id (connection->xcb_connection);
 
     for (depth = 1, i = 0; depth <= 32; depth++) {
 	if (missing & DEPTH_MASK(depth)) {
@@ -275,8 +275,6 @@ pixmap_depths_usable (cairo_xcb_connection_t *connection,
 	free (create_error);
     }
 
-    _cairo_xcb_connection_put_xid (connection, pixmap);
-
     return success;
 }
 
@@ -462,10 +460,9 @@ can_use_shm (cairo_xcb_connection_t *connection)
 	return FALSE;
     }
 
-    shmseg = _cairo_xcb_connection_get_xid (connection);
+    shmseg = xcb_generate_id (connection->xcb_connection);
     cookie[0] = xcb_shm_attach_checked (c, shmseg, shmid, FALSE);
     cookie[1] = xcb_shm_detach_checked (c, shmseg);
-    _cairo_xcb_connection_put_xid (connection, shmseg);
 
     error = xcb_request_check (c, cookie[0]);
     if (error != NULL)
@@ -586,8 +583,6 @@ _device_destroy (void *device)
 #endif
     _cairo_freepool_fini (&connection->shm_info_freelist);
 
-    _cairo_freepool_fini (&connection->xid_pool);
-
     CAIRO_MUTEX_FINI (connection->shm_mutex);
     CAIRO_MUTEX_FINI (connection->screens_mutex);
 
@@ -662,10 +657,6 @@ _cairo_xcb_connection_get (xcb_connection_t *xcb_connection)
 	goto unlock;
     }
 
-    cairo_list_init (&connection->free_xids);
-    _cairo_freepool_init (&connection->xid_pool,
-			  sizeof (cairo_xcb_xid_t));
-
     cairo_list_init (&connection->shm_pools);
     cairo_list_init (&connection->shm_pending);
     _cairo_freepool_init (&connection->shm_info_freelist,
@@ -766,43 +757,6 @@ _cairo_xcb_connection_get_xrender_format_for_visual (cairo_xcb_connection_t *con
     return format ? format->xrender_format : XCB_NONE;
 }
 
-void
-_cairo_xcb_connection_put_xid (cairo_xcb_connection_t *connection,
-			       uint32_t xid)
-{
-    cairo_xcb_xid_t *cache;
-
-    assert (CAIRO_MUTEX_IS_LOCKED (connection->device.mutex));
-    cache = _cairo_freepool_alloc (&connection->xid_pool);
-    if (likely (cache != NULL)) {
-	cache->xid = xid;
-	cairo_list_add (&cache->link, &connection->free_xids);
-    }
-}
-
-uint32_t
-_cairo_xcb_connection_get_xid (cairo_xcb_connection_t *connection)
-{
-    uint32_t xid;
-
-    assert (CAIRO_MUTEX_IS_LOCKED (connection->device.mutex));
-    if (! cairo_list_is_empty (&connection->free_xids)) {
-	cairo_xcb_xid_t *cache;
-
-	cache = cairo_list_first_entry (&connection->free_xids,
-					cairo_xcb_xid_t,
-					link);
-	xid = cache->xid;
-
-	cairo_list_del (&cache->link);
-	_cairo_freepool_free (&connection->xid_pool, cache);
-    } else {
-	xid = xcb_generate_id (connection->xcb_connection);
-    }
-
-    return xid;
-}
-
 /**
  * cairo_xcb_device_get_connection:
  * @device: a #cairo_device_t for the XCB backend

src/cairo-xcb-private.h

@@ -226,9 +226,6 @@ struct _cairo_xcb_connection {
     const xcb_query_extension_reply_t *shm;
     xcb_render_sub_pixel_t *subpixel_orders;
 
-    cairo_list_t free_xids;
-    cairo_freepool_t xid_pool;
-
     cairo_mutex_t shm_mutex;
     cairo_list_t shm_pools;
     cairo_list_t shm_pending;
@@ -323,13 +320,6 @@ _cairo_xcb_connection_acquire (cairo_xcb_connection_t *connection)
     return cairo_device_acquire (&connection->device);
 }
 
-cairo_private uint32_t
-_cairo_xcb_connection_get_xid (cairo_xcb_connection_t *connection);
-
-cairo_private void
-_cairo_xcb_connection_put_xid (cairo_xcb_connection_t *connection,
-			       uint32_t xid);
-
 static inline void
 _cairo_xcb_connection_release (cairo_xcb_connection_t *connection)
 {

src/cairo-xcb-surface-render.c

@@ -128,7 +128,7 @@ _cairo_xcb_picture_create (cairo_xcb_screen_t *screen,
     cairo_list_add (&surface->link, &screen->pictures);
 
     surface->screen = screen;
-    surface->picture = _cairo_xcb_connection_get_xid (screen->connection);
+    surface->picture = xcb_generate_id (screen->connection->xcb_connection);
     surface->pixman_format = pixman_format;
     surface->xrender_format = xrender_format;
 
@@ -308,7 +308,7 @@ _cairo_xcb_surface_ensure_picture (cairo_xcb_surface_t *surface)
 	    values[0] = surface->precision;
 	}
 
-	surface->picture = _cairo_xcb_connection_get_xid (surface->connection);
+	surface->picture = xcb_generate_id (surface->connection->xcb_connection);
 	_cairo_xcb_connection_render_create_picture (surface->connection,
 						     surface->picture,
 						     surface->drawable,
@@ -4232,7 +4232,7 @@ _cairo_xcb_scaled_font_get_glyphset_info_for_format (cairo_xcb_connection_t *c,
 
     info = &priv->glyphset_info[glyphset_index];
     if (info->glyphset == XCB_NONE) {
-	info->glyphset = _cairo_xcb_connection_get_xid (c);
+	info->glyphset = xcb_generate_id (c->xcb_connection);
 	info->xrender_format = c->standard_formats[info->format];
 
 	_cairo_xcb_connection_render_create_glyph_set (c,