uriplaylistbin: fix deadlock when shutting down

The probes on srcpad was not removed which was preventing the element to
reach the NULL state.

utils/uriplaylistbin/src/uriplaylistbin/imp.rs

@@ -607,6 +607,17 @@ impl Item {
             _ => panic!("invalid state: {:?}", inner.state),
         }
     }
+
+    fn sender(&self) -> crossbeam_channel::Sender<bool> {
+        let inner = self.inner.lock().unwrap();
+
+        match &inner.state {
+            ItemState::WaitingForStreamsynchronizerEos { sender, .. } => sender.clone(),
+            ItemState::WaitingForPads { sender, .. } => sender.clone(),
+            ItemState::Blocked { sender, .. } => sender.clone(),
+            _ => panic!("invalid state: {:?}", inner.state),
+        }
+    }
 }
 
 #[derive(Debug, Clone)]
@@ -935,6 +946,24 @@ impl ElementImpl for UriPlaylistBin {
             }
         }
 
+        if transition == gst::StateChange::PausedToReady {
+            let mut state_guard = self.state.lock().unwrap();
+            let state = state_guard.as_mut().unwrap();
+
+            // The probe callback owns a ref on the item and so on the sender as well.
+            // As a result we have to explicitly unblock all receivers as dropping the sender
+            // is not enough.
+            if let Some(item) = state.waiting_for_ss_eos.take() {
+                let _ = item.sender().send(false);
+            }
+            if let Some(item) = state.waiting_for_pads.take() {
+                let _ = item.sender().send(false);
+            }
+            if let Some(item) = state.blocked.take() {
+                let _ = item.sender().send(false);
+            }
+        }
+
         self.parent_change_state(element, transition)
     }
 }