transcriberbin: relink transcriber more thoroughly

* Remove old transcriber from correct bin
* Remove old unsynced ghost pads and expose new ones
* Fix potential deadlock where State was locked after PadState

Part-of: <https://gitlab.freedesktop.org/gstreamer/gst-plugins-rs/-/merge_requests/1925>

video/closedcaption/src/transcriberbin/imp.rs

@@ -139,7 +139,7 @@ pub struct TranscriberBin {
 }
 
 impl TranscriberBin {
-    fn construct_channel_bin(
+    fn construct_transcription_channel(
         &self,
         lang: &str,
         mux_method: MuxMethod,
@@ -794,7 +794,7 @@ impl TranscriberBin {
      * be called in READY */
     fn relink_transcriber(
         &self,
-        state: &mut State,
+        state: &State,
         pad_state: &TranscriberSinkPadState,
         old_transcriber: Option<&gst::Element>,
     ) -> Result<(), Error> {
@@ -814,9 +814,9 @@ impl TranscriberBin {
             );
             pad_state.transcriber_aconv.unlink(old_transcriber);
             for channel in pad_state.transcription_channels.values() {
-                old_transcriber.unlink(&channel.bin);
+                pad_state.unlink_transcriber_pads(self.obj().as_ref(), state, channel);
             }
-            let _ = state.transcription_bin.remove(old_transcriber);
+            let _ = pad_state.transcription_bin.remove(old_transcriber);
             old_transcriber.set_state(gst::State::Null).unwrap();
         }
 
@@ -827,7 +827,8 @@ impl TranscriberBin {
             pad_state.transcriber_aconv.link(transcriber)?;
 
             for channel in pad_state.transcription_channels.values() {
-                channel.link_transcriber(transcriber)?;
+                let srcpad_name = channel.link_transcriber(transcriber)?;
+                pad_state.expose_unsynced_pads(self.obj().as_ref(), state, &srcpad_name)?;
             }
         }
 
@@ -883,7 +884,11 @@ impl TranscriberBin {
 
                 transcription_channels.insert(
                     language_code.to_owned(),
-                    self.construct_channel_bin(&language_code, mux_method, caption_streams)?,
+                    self.construct_transcription_channel(
+                        &language_code,
+                        mux_method,
+                        caption_streams,
+                    )?,
                 );
             }
         } else {
@@ -893,7 +898,7 @@ impl TranscriberBin {
             };
             transcription_channels.insert(
                 "transcript".to_string(),
-                self.construct_channel_bin("transcript", mux_method, caption_streams)?,
+                self.construct_transcription_channel("transcript", mux_method, caption_streams)?,
             );
         }
         Ok(())
@@ -966,36 +971,7 @@ impl TranscriberBin {
             }
 
             for channel in pad_state.transcription_channels.values() {
-                let sinkpad = channel.bin.static_pad("sink").unwrap();
+                pad_state.unlink_transcriber_pads(self.obj().as_ref(), state, channel);
-                if let Some(peer) = sinkpad.peer() {
-                    peer.unlink(&sinkpad)?;
-                    if let Some(ref transcriber) = pad_state.transcriber {
-                        if channel.language != "transcript" {
-                            transcriber.release_request_pad(&peer);
-                        }
-                        let mut unsynced_pad_name = format!("unsynced_{}", peer.name().as_str());
-                        if transcriber.static_pad(&unsynced_pad_name).is_some() {
-                            let srcpad = pad_state
-                                .transcription_bin
-                                .static_pad(&unsynced_pad_name)
-                                .unwrap();
-                            let _ = pad_state.transcription_bin.remove_pad(&srcpad);
-                            if let Some(serial) = pad_state.serial {
-                                unsynced_pad_name = format!("{}_{}", unsynced_pad_name, serial);
-                            }
-                            let srcpad = state
-                                .transcription_bin
-                                .static_pad(&unsynced_pad_name)
-                                .unwrap();
-                            let _ = state.transcription_bin.remove_pad(&srcpad);
-
-                            let srcpad = state.internal_bin.static_pad(&unsynced_pad_name).unwrap();
-                            let _ = state.internal_bin.remove_pad(&srcpad);
-                            let srcpad = self.obj().static_pad(&unsynced_pad_name).unwrap();
-                            let _ = self.obj().remove_pad(&srcpad);
-                        }
-                    }
-                }
 
                 let srcpad = pad_state
                     .transcription_bin
@@ -1950,12 +1926,60 @@ impl TranscriberSinkPadState {
         })
     }
 
-    fn link_transcriber_pads(
+    fn remove_unsynced_pads(
         &self,
-        elem: &super::TranscriberBin,
+        topbin: &super::TranscriberBin,
-        srcpad_name: &str,
-        channel: &TranscriptionChannel,
         state: &State,
+        srcpad_name: &str,
+    ) {
+        let Some(ref transcriber) = self.transcriber else {
+            return;
+        };
+
+        let mut unsynced_pad_name = format!("unsynced_{}", srcpad_name);
+
+        if transcriber.static_pad(&unsynced_pad_name).is_some() {
+            let srcpad = self
+                .transcription_bin
+                .static_pad(&unsynced_pad_name)
+                .unwrap();
+            let _ = self.transcription_bin.remove_pad(&srcpad);
+            if let Some(serial) = self.serial {
+                unsynced_pad_name = format!("{}_{}", unsynced_pad_name, serial);
+            }
+            let srcpad = state
+                .transcription_bin
+                .static_pad(&unsynced_pad_name)
+                .unwrap();
+            let _ = state.transcription_bin.remove_pad(&srcpad);
+
+            let srcpad = state.internal_bin.static_pad(&unsynced_pad_name).unwrap();
+            let _ = state.internal_bin.remove_pad(&srcpad);
+            let srcpad = topbin.static_pad(&unsynced_pad_name).unwrap();
+            let _ = topbin.remove_pad(&srcpad);
+        }
+    }
+
+    fn unlink_transcriber_pads(
+        &self,
+        topbin: &super::TranscriberBin,
+        state: &State,
+        channel: &TranscriptionChannel,
+    ) {
+        let sinkpad = channel.bin.static_pad("sink").unwrap();
+        let Some(srcpad) = sinkpad.peer() else {
+            return;
+        };
+        srcpad.unlink(&sinkpad).unwrap();
+
+        self.remove_unsynced_pads(topbin, state, srcpad.name().as_str());
+    }
+
+    fn expose_unsynced_pads(
+        &self,
+        topbin: &super::TranscriberBin,
+        state: &State,
+        srcpad_name: &str,
     ) -> Result<(), Error> {
         let Some(ref transcriber) = self.transcriber else {
             return Ok(());
@@ -1984,9 +2008,21 @@ impl TranscriberSinkPadState {
             state.internal_bin.add_pad(&srcpad)?;
 
             let srcpad = gst::GhostPad::with_target(&srcpad).unwrap();
-            elem.add_pad(&srcpad)?;
+            topbin.add_pad(&srcpad)?;
         }
 
+        Ok(())
+    }
+
+    fn link_transcriber_pads(
+        &self,
+        topbin: &super::TranscriberBin,
+        srcpad_name: &str,
+        channel: &TranscriptionChannel,
+        state: &State,
+    ) -> Result<(), Error> {
+        self.expose_unsynced_pads(topbin, state, srcpad_name)?;
+
         let srcpad = gst::GhostPad::builder_with_target(&channel.bin.static_pad("src").unwrap())
             .unwrap()
             .name(format!("src_{}", channel.language))
@@ -2159,6 +2195,8 @@ impl ObjectImpl for TranscriberSinkPad {
                 }
             }
             "transcriber" => {
+                if let Some(this) = self.obj().parent().and_downcast::<super::TranscriberBin>() {
+                    let mut s = this.imp().state.lock().unwrap();
                     let mut ps = self.state.lock().unwrap();
                     let Ok(pad_state) = ps.as_mut() else {
                         return;
@@ -2168,8 +2206,6 @@ impl ObjectImpl for TranscriberSinkPad {
                         value.get().expect("type checked upstream");
                     pad_state.transcriber.clone_from(&new_transcriber);
 
-                if let Some(this) = self.obj().parent().and_downcast::<super::TranscriberBin>() {
-                    let mut s = this.imp().state.lock().unwrap();
                     if old_transcriber != new_transcriber {
                         if let Some(ref mut state) = s.as_mut() {
                             match this.imp().relink_transcriber(