clipboard-wayland: create data sources in clipboard thread

Currently, it is done in set_data which is called by core.
It was never meant to do so and it is not thread safe when data
sources are created while a seat is being added/removed.

Fix this by passing a message to clipboard thread instead so that
it is done in a thread safe way.

Author: na-na-hi

player/clipboard/clipboard-wayland.c

@@ -28,6 +28,7 @@
 #include "osdep/threads.h"
 
 static const char MESSAGE_DEATH = 0;
+static const char MESSAGE_CREATE_SOURCES = 1;
 
 struct clipboard_wayland_data_offer {
     struct ext_data_control_offer_v1 *offer;
@@ -435,8 +436,14 @@ static bool clipboard_wayland_dispatch_events(struct clipboard_wayland_priv *wl,
         return false;
     }
 
-    if (fds[1].revents & POLLIN)
-        return false;
+    if (fds[1].revents & POLLIN) {
+        char msg = 0;
+        if (read(wl->message_pipe[0], &msg, 1) == 1 && msg == MESSAGE_CREATE_SOURCES) {
+            create_data_sources(wl);
+        } else {
+            return false;
+        }
+    }
 
     if (fds[2].revents & POLLIN)
         get_selection_data(wl, wl->selection_offer, false);
@@ -570,7 +577,7 @@ static int set_data(struct clipboard_ctx *cl, struct clipboard_access_params *pa
         break;
     }
     mp_mutex_unlock(&priv->lock);
-    create_data_sources(priv);
+    (void)write(priv->message_pipe[1], &(char){MESSAGE_CREATE_SOURCES}, 1);
     return CLIPBOARD_SUCCESS;
 }