screen_xcb: run in a thread - remove input control latency

modules/access/screen/xcb.c

@@ -91,11 +91,14 @@ vlc_module_end ()
 /*
  * Local prototypes
  */
-static int Demux (demux_t *);
+static void *Thread (void *);
 static int Control (demux_t *, int, va_list);
 
 struct demux_sys_t
 {
+    /* WARNING: Control() is concurrent with Thread()/Demux().
+     * Currently, the thread owns everything in read/write, if it exists.
+     * We destroy it on pause, and re-create it on resume. */
     xcb_connection_t *conn;
     es_out_id_t      *es;
     es_format_t       fmt;
@@ -103,6 +106,10 @@ struct demux_sys_t
     xcb_window_t      root, window;
     int16_t           x, y;
     uint16_t          w, h;
+
+    /* Thread does not use. This is for input thread only: */
+    vlc_thread_t      thread;
+    bool              running;
 };
 
 /**
@@ -116,6 +123,7 @@ static int Open (vlc_object_t *obj)
     if (p_sys == NULL)
         return VLC_ENOMEM;
     demux->p_sys = p_sys;
+    p_sys->running = false;
 
     /* Connect to X server */
     char *display = var_CreateGetNonEmptyString (obj, "x11-display");
@@ -237,9 +245,12 @@ static int Open (vlc_object_t *obj)
     p_sys->fmt.video.i_frame_rate_base = 1000;
     p_sys->es = NULL;
     p_sys->pts = VLC_TS_INVALID;
+    if (vlc_clone (&p_sys->thread, Thread, demux, VLC_THREAD_PRIORITY_INPUT))
+        goto error;
+    p_sys->running = true;
 
     /* Initializes demux */
-    demux->pf_demux   = Demux;
+    demux->pf_demux   = NULL;
     demux->pf_control = Control;
     return VLC_SUCCESS;
 
@@ -257,6 +268,11 @@ static void Close (vlc_object_t *obj)
     demux_t *demux = (demux_t *)obj;
     demux_sys_t *p_sys = demux->p_sys;
 
+    if (p_sys->running)
+    {
+        vlc_cancel (p_sys->thread);
+        vlc_join (p_sys->thread, NULL);
+    }
     xcb_disconnect (p_sys->conn);
     free (p_sys);
 }
@@ -305,11 +321,23 @@ static int Control (demux_t *demux, int query, va_list args)
         case DEMUX_SET_PAUSE_STATE:
         {
             bool pausing = va_arg (args, int);
+
+            if (pausing != p_sys->running)
+                return VLC_SUCCESS; /* No-op. FIXME: is it needed? */
             if (!pausing)
             {
                 p_sys->pts = VLC_TS_INVALID;
                 es_out_Control (demux->out, ES_OUT_RESET_PCR);
+                if (vlc_clone (&p_sys->thread, Thread, demux,
+                               VLC_THREAD_PRIORITY_INPUT))
+                    return VLC_EGENERIC;
             }
+            else
+            {
+                vlc_cancel (p_sys->thread);
+                vlc_join (p_sys->thread, NULL);
+            }
+            p_sys->running = !pausing;
             return VLC_SUCCESS;
         }
 
@@ -330,7 +358,7 @@ static int Control (demux_t *demux, int query, va_list args)
 /**
  * Processing callback
  */
-static int Demux (demux_t *demux)
+static void Demux (demux_t *demux)
 {
     demux_sys_t *p_sys = demux->p_sys;
     xcb_connection_t *conn = p_sys->conn;
@@ -341,6 +369,8 @@ static int Demux (demux_t *demux)
     else
         p_sys->pts = now;
 
+    int canc = vlc_savecancel ();
+
     /* Update capture region (if needed) */
     xcb_get_geometry_cookie_t gc = xcb_get_geometry (conn, p_sys->window);
     int16_t x = p_sys->x, y = p_sys->y;
@@ -354,7 +384,7 @@ static int Demux (demux_t *demux)
     if (geo == NULL)
     {
         msg_Err (demux, "bad X11 drawable 0x%08"PRIx32, p_sys->window);
-        return 0;
+        goto out;
     }
 
     uint16_t w = geo->width - x;
@@ -380,7 +410,7 @@ static int Demux (demux_t *demux)
         xcb_translate_coordinates_reply_t *coords =
              xcb_translate_coordinates_reply (conn, tc, NULL);
         if (coords == NULL)
-            return 1;
+            goto out;
         x = coords->dst_x;
         y = coords->dst_y;
         free (coords);
@@ -388,24 +418,31 @@ static int Demux (demux_t *demux)
 
     /* Capture screen */
     if (p_sys->es == NULL)
-        return 1;
+        goto out;
 
     xcb_get_image_reply_t *img;
     img = xcb_get_image_reply (conn,
         xcb_get_image (conn, XCB_IMAGE_FORMAT_Z_PIXMAP, p_sys->root,
                        x, y, w, h, ~0), NULL);
     if (img == NULL)
-        return 1;
+        goto out;
 
     /* Send block - zero copy */
     block_t *block = block_heap_Alloc (img, xcb_get_image_data (img),
                                        xcb_get_image_data_length (img));
     if (block == NULL)
-        return 0;
+        goto out;
     block->i_pts = block->i_dts = now;
 
     es_out_Control (demux->out, ES_OUT_SET_PCR, now);
     es_out_Send (demux->out, p_sys->es, block);
     p_sys->pts += p_sys->interval;
-    return 1;
+out:
+    vlc_restorecancel (canc);
+}
+
+static void *Thread (void *data)
+{
+    for (;;)
+         Demux (data);
 }