Ensure audio keeps playing when AudioContext goes out of scope

Fixes #464

Author: orottier

examples/roundtrip_latency_test.rs

@@ -138,7 +138,7 @@ fn main() {
 
     let estimated_latency = Arc::new(AtomicF64::new(0.));
 
-    let _context = if test {
+    if test {
         // emulate loopback
         let latency: f32 = 0.017;
         println!(
@@ -169,8 +169,6 @@ fn main() {
 
         latency_tester.connect(&delay);
         delay.connect(&latency_tester);
-
-        context
     } else {
         // full round trip
         let devices = enumerate_devices_sync();
@@ -221,8 +219,6 @@ fn main() {
         // create media stream source node with mic stream
         let stream_source = context.create_media_stream_source(&mic);
         stream_source.connect(&latency_tester);
-
-        context
     };
 
     loop {

src/context/online.rs

@@ -4,7 +4,7 @@ use std::sync::Mutex;
 
 use crate::context::{AudioContextState, BaseAudioContext, ConcreteBaseAudioContext};
 use crate::events::{EventDispatch, EventHandler, EventPayload, EventType};
-use crate::io::{self, AudioBackendManager, ControlThreadInit, RenderThreadInit};
+use crate::io::{self, AudioBackendManager, ControlThreadInit, NoneBackend, RenderThreadInit};
 use crate::media_devices::{enumerate_devices_sync, MediaDeviceInfoKind};
 use crate::media_streams::{MediaStream, MediaStreamTrack};
 use crate::message::{ControlMessage, OneshotNotify};
@@ -129,6 +129,17 @@ impl std::fmt::Debug for AudioContext {
     }
 }
 
+impl Drop for AudioContext {
+    fn drop(&mut self) {
+        // Continue playing the stream if the AudioContext goes out of scope
+        if self.state() == AudioContextState::Running {
+            let tombstone = Box::new(NoneBackend::void());
+            let original = std::mem::replace(self.backend_manager.get_mut().unwrap(), tombstone);
+            Box::leak(original);
+        }
+    }
+}
+
 impl BaseAudioContext for AudioContext {
     fn base(&self) -> &ConcreteBaseAudioContext {
         &self.base

src/io/mod.rs

@@ -14,6 +14,7 @@ use crate::message::ControlMessage;
 use crate::{AudioRenderCapacityLoad, RENDER_QUANTUM_SIZE};
 
 mod none;
+pub(crate) use none::NoneBackend;
 
 #[cfg(feature = "cpal")]
 mod cpal;
@@ -91,7 +92,7 @@ pub(crate) fn build_output(
     render_thread_init: RenderThreadInit,
 ) -> Box<dyn AudioBackendManager> {
     if options.sink_id == "none" {
-        let backend = none::NoneBackend::build_output(options, render_thread_init);
+        let backend = NoneBackend::build_output(options, render_thread_init);
         return Box::new(backend);
     }
 
@@ -222,12 +223,12 @@ fn buffer_size_for_latency_category(
 pub(crate) fn enumerate_devices_sync() -> Vec<MediaDeviceInfo> {
     #[cfg(feature = "cubeb")]
     {
-        crate::io::cubeb::CubebBackend::enumerate_devices_sync()
+        cubeb::CubebBackend::enumerate_devices_sync()
     }
 
     #[cfg(all(not(feature = "cubeb"), feature = "cpal"))]
     {
-        crate::io::cpal::CpalBackend::enumerate_devices_sync()
+        cpal::CpalBackend::enumerate_devices_sync()
     }
 
     #[cfg(all(not(feature = "cubeb"), not(feature = "cpal")))]

src/io/none.rs

@@ -23,6 +23,16 @@ pub(crate) struct NoneBackend {
     sample_rate: f32,
 }
 
+impl NoneBackend {
+    /// Creates a mock backend to be used as tombstones
+    pub(crate) fn void() -> Self {
+        Self {
+            sample_rate: 0.,
+            sender: crossbeam_channel::bounded(0).0,
+        }
+    }
+}
+
 struct Callback {
     receiver: Receiver<NoneBackendMessage>,
     render_thread: RenderThread,