Add handling of `Play`, `Pause` and `Close` stream events to emscripten

src/emscripten/mod.rs

@@ -1,7 +1,7 @@
 use std::mem;
 use std::os::raw::c_void;
 use std::slice::from_raw_parts;
-use std::sync::Mutex;
+use std::sync::{Arc, Mutex};
 use stdweb;
 use stdweb::Reference;
 use stdweb::unstable::TryInto;
@@ -16,6 +16,7 @@ use Format;
 use PauseStreamError;
 use PlayStreamError;
 use SupportedFormatsError;
+use StreamCloseCause;
 use StreamData;
 use StreamEvent;
 use SupportedFormat;
@@ -32,20 +33,62 @@ use UnknownTypeOutputBuffer;
 
 pub struct EventLoop {
     streams: Mutex<Vec<Option<Reference>>>,
+    // The `EventLoop` requires a handle to the callbacks in order to be able to emit necessary
+    // events for `Play`, `Pause` and `Close`.
+    user_callback: Arc<Mutex<UserCallback>>
+}
+
+enum UserCallback {
+    // When `run` is called with a callback, that callback will be stored here.
+    //
+    // It is essential for the safety of the program that this callback is removed before `run`
+    // returns (not possible with the current CPAL API).
+    Active(&'static mut (dyn FnMut(StreamId, StreamEvent) + Send)),
+    // A queue of events that have occurred but that have not yet been emitted to the user as we
+    // don't yet have a callback to do so.
+    Inactive {
+        pending_events: Vec<(StreamId, StreamEvent<'static>)>
+    },
 }
 
 impl EventLoop {
     #[inline]
     pub fn new() -> EventLoop {
         stdweb::initialize();
-
-        EventLoop { streams: Mutex::new(Vec::new()) }
+        EventLoop {
+            streams: Mutex::new(Vec::new()),
+            user_callback: Arc::new(Mutex::new(UserCallback::Inactive { pending_events: vec![] })),
+        }
     }
 
     #[inline]
-    pub fn run<F>(&self, callback: F) -> !
-        where F: FnMut(StreamId, StreamEvent)
+    pub fn run<F>(&self, mut callback: F) -> !
+        where F: FnMut(StreamId, StreamEvent) + Send,
     {
+        // Retrieve and process any pending events.
+        //
+        // Then, set the callback ready to be shared between audio processing and the event loop
+        // handle.
+        {
+            let mut guard = self.user_callback.lock().unwrap();
+            let pending_events = match *guard {
+                UserCallback::Inactive { ref mut pending_events } => {
+                    mem::replace(pending_events, vec![])
+                }
+                UserCallback::Active(_) => {
+                    panic!("`EventLoop::run` was called when the event loop was already running");
+                }
+            };
+
+            let callback: &mut (dyn FnMut(StreamId, StreamEvent) + Send) = &mut callback;
+            for (stream_id, event) in pending_events {
+                callback(stream_id, event);
+            }
+
+            *guard = UserCallback::Active(unsafe { mem::transmute(callback) });
+        }
+
+
         // The `run` function uses `set_timeout` to invoke a Rust callback repeatidely. The job
         // of this callback is to fill the content of the audio buffers.
 
@@ -79,10 +122,10 @@ impl EventLoop {
 
                     let typed_array = {
                         let f32_slice = temporary_buffer.as_slice();
-                        let u8_slice: &[u8] = unsafe {
-                            from_raw_parts(f32_slice.as_ptr() as *const _,
-                                        f32_slice.len() * mem::size_of::<f32>())
-                        };
+                        let u8_slice: &[u8] = from_raw_parts(
+                            f32_slice.as_ptr() as *const _,
+                            f32_slice.len() * mem::size_of::<f32>(),
+                        );
                         let typed_array: TypedArray<u8> = u8_slice.into();
                         typed_array
                     };
@@ -121,6 +164,9 @@ impl EventLoop {
         set_timeout(|| callback_fn::<F>(user_data_ptr as *mut _), 10);
 
         stdweb::event_loop();
+
+        // It is critical that we remove the callback before returning (currently not possible).
+        // *self.user_callback.lock().unwrap() = UserCallback::Inactive { pending_events: vec![] };
     }
 
     #[inline]
@@ -145,9 +191,19 @@ impl EventLoop {
         Ok(StreamId(stream_id))
     }
 
+    fn emit_or_enqueue_event(&self, id: StreamId, event: StreamEvent<'static>) {
+        let mut guard = self.user_callback.lock().unwrap();
+        match *guard {
+            UserCallback::Active(ref mut callback) => callback(id, event),
+            UserCallback::Inactive { ref mut pending_events } => pending_events.push((id, event)),
+        }
+    }
+
     #[inline]
     pub fn destroy_stream(&self, stream_id: StreamId) {
         self.streams.lock().unwrap()[stream_id.0] = None;
+        let event = StreamEvent::Close(StreamCloseCause::UserDestroyed);
+        self.emit_or_enqueue_event(stream_id, event);
     }
 
     #[inline]
@@ -157,6 +213,7 @@ impl EventLoop {
             .get(stream_id.0)
             .and_then(|v| v.as_ref())
             .expect("invalid stream ID");
+        self.emit_or_enqueue_event(stream_id, StreamEvent::Play);
         js!(@{stream}.resume());
         Ok(())
     }
@@ -169,6 +226,7 @@ impl EventLoop {
             .and_then(|v| v.as_ref())
             .expect("invalid stream ID");
         js!(@{stream}.suspend());
+        self.emit_or_enqueue_event(stream_id, StreamEvent::Pause);
         Ok(())
     }
 }