use pipe for mpv wakeup callback

hopefully works better with the gtk main loop but idk lol

src/playbin.vala

@@ -57,9 +57,6 @@ public class Playbin : GLib.Object {
     public ListStore _play_queue;
     public ListModel play_queue { get { return this._play_queue; } }
 
-    // try to prevent wait_event to be called twice
-    private bool is_handling_event = false;
-
     private async Mpv.Error mpv_command_async (string[] args) {
         CommandCallback cc = {};
 
@@ -70,6 +67,9 @@ public class Playbin : GLib.Object {
         return cc.error;
     }
 
+    // should be Mpv.WakeupCallback, but i think there's a vala bug here
+    private SourceOnceFunc wakeup_callback; // anchor reference here, mpv won't remind us
+
     public Playbin () {
         this._play_queue = new ListStore (typeof (Subsonic.Song));
 
@@ -83,10 +83,39 @@ public class Playbin : GLib.Object {
         assert (this.mpv.observe_property (2, "playlist-pos", Mpv.Format.INT64) >= 0);
         assert (this.mpv.observe_property (3, "pause", Mpv.Format.FLAG) >= 0);
 
-        this.mpv.wakeup_callback = () => {
-            Idle.add (() => {
-                if (this.is_handling_event) return false;
-                this.is_handling_event = true;
+        int wakeup_fds[2];
+        try {
+            assert (Unix.open_pipe (wakeup_fds, 0));
+        } catch (Error e) {
+            error (@"could not open pipe for mpv wakeup: $(e.message)");
+        }
+
+        IOChannel wakeup_read = new IOChannel.unix_new (wakeup_fds[0]);
+        IOChannel wakeup_write = new IOChannel.unix_new (wakeup_fds[1]);
+
+        try {
+            wakeup_read.set_encoding (null);
+            wakeup_write.set_encoding (null);
+            wakeup_write.set_buffered (false);
+        } catch (Error e) {
+            error (@"could not set up pipes for mpv wakeup: $(e.message)");
+        }
+
+        this.wakeup_callback = () => {
+            try {
+                wakeup_write.write_chars ({0}, null);
+            } catch (Error e) {
+                error (@"could not write to mpv wakeup pipe: $(e.message)");
+            }
+        };
+        this.mpv.wakeup_callback = this.wakeup_callback;
+
+        assert (0 < wakeup_read.add_watch (IOCondition.IN, (source, condition) => {
+            try {
+                wakeup_read.read_chars ({0}, null);
+            } catch (Error e) {
+                error (@"could not read from mpv wakeup pipe: $(e.message)");
+            }
 
             while (true) {
                 var event = this.mpv.wait_event (0.0);
@@ -196,10 +225,8 @@ public class Playbin : GLib.Object {
                 }
             }
             
-                this.is_handling_event = false;
-                return false;
-            });
-        };
+            return true;
+        }));
     }
 
     public void seek (double position) {

src/vapi/mpv.vapi

@@ -43,7 +43,7 @@ namespace Mpv {
         [CCode (cname = "mpv_wait_event")]
         public unowned Event? wait_event (double timeout);
 
-        public WakeupCallback wakeup_callback {
+        public unowned WakeupCallback wakeup_callback {
             [CCode (cname = "mpv_set_wakeup_callback")] set;
         }