Correctly clean up callback references based on whether Arc remains cloned on drop.

examples/clone_drop.rs

@@ -0,0 +1,89 @@
+use std::io;
+
+#[cfg(target_os = "macos")]
+use cocoa_foundation::base::id;
+#[cfg(target_os = "macos")]
+use cocoa_foundation::foundation::NSRunLoop;
+#[cfg(target_os = "macos")]
+use objc::{msg_send, sel, sel_impl};
+
+use tts::*;
+
+fn main() -> Result<(), Error> {
+    env_logger::init();
+    let tts = Tts::default()?;
+    let mut tts_clone = tts.clone();
+    drop(tts);
+    if Tts::screen_reader_available() {
+        println!("A screen reader is available on this platform.");
+    } else {
+        println!("No screen reader is available on this platform.");
+    }
+    let Features {
+        utterance_callbacks,
+        ..
+    } = tts_clone.supported_features();
+    if utterance_callbacks {
+        tts_clone.on_utterance_begin(Some(Box::new(|utterance| {
+            println!("Started speaking {:?}", utterance)
+        })))?;
+        tts_clone.on_utterance_end(Some(Box::new(|utterance| {
+            println!("Finished speaking {:?}", utterance)
+        })))?;
+        tts_clone.on_utterance_stop(Some(Box::new(|utterance| {
+            println!("Stopped speaking {:?}", utterance)
+        })))?;
+    }
+    let Features { is_speaking, .. } = tts_clone.supported_features();
+    if is_speaking {
+        println!("Are we speaking? {}", tts_clone.is_speaking()?);
+    }
+    tts_clone.speak("Hello, world.", false)?;
+    let Features { rate, .. } = tts_clone.supported_features();
+    if rate {
+        let original_rate = tts_clone.get_rate()?;
+        tts_clone.speak(format!("Current rate: {}", original_rate), false)?;
+        tts_clone.set_rate(tts_clone.max_rate())?;
+        tts_clone.speak("This is very fast.", false)?;
+        tts_clone.set_rate(tts_clone.min_rate())?;
+        tts_clone.speak("This is very slow.", false)?;
+        tts_clone.set_rate(tts_clone.normal_rate())?;
+        tts_clone.speak("This is the normal rate.", false)?;
+        tts_clone.set_rate(original_rate)?;
+    }
+    let Features { pitch, .. } = tts_clone.supported_features();
+    if pitch {
+        let original_pitch = tts_clone.get_pitch()?;
+        tts_clone.set_pitch(tts_clone.max_pitch())?;
+        tts_clone.speak("This is high-pitch.", false)?;
+        tts_clone.set_pitch(tts_clone.min_pitch())?;
+        tts_clone.speak("This is low pitch.", false)?;
+        tts_clone.set_pitch(tts_clone.normal_pitch())?;
+        tts_clone.speak("This is normal pitch.", false)?;
+        tts_clone.set_pitch(original_pitch)?;
+    }
+    let Features { volume, .. } = tts_clone.supported_features();
+    if volume {
+        let original_volume = tts_clone.get_volume()?;
+        tts_clone.set_volume(tts_clone.max_volume())?;
+        tts_clone.speak("This is loud!", false)?;
+        tts_clone.set_volume(tts_clone.min_volume())?;
+        tts_clone.speak("This is quiet.", false)?;
+        tts_clone.set_volume(tts_clone.normal_volume())?;
+        tts_clone.speak("This is normal volume.", false)?;
+        tts_clone.set_volume(original_volume)?;
+    }
+    tts_clone.speak("Goodbye.", false)?;
+    let mut _input = String::new();
+    // The below is only needed to make the example run on MacOS because there is no NSRunLoop in this context.
+    // It shouldn't be needed in an app or game that almost certainly has one already.
+    #[cfg(target_os = "macos")]
+    {
+        let run_loop: id = unsafe { NSRunLoop::currentRunLoop() };
+        unsafe {
+            let _: () = msg_send![run_loop, run];
+        }
+    }
+    io::stdin().read_line(&mut _input)?;
+    Ok(())
+}

src/lib.rs

@@ -656,9 +656,11 @@ impl Tts {
 
 impl Drop for Tts {
     fn drop(&mut self) {
-        if let Some(id) = self.0.read().unwrap().id() {
-            let mut callbacks = CALLBACKS.lock().unwrap();
-            callbacks.remove(&id);
+        if Arc::strong_count(&self.0) <= 1 {
+            if let Some(id) = self.0.read().unwrap().id() {
+                let mut callbacks = CALLBACKS.lock().unwrap();
+                callbacks.remove(&id);
+            }
         }
     }
 }