tts: initialize piper exactly once

1 files changed, 39 insertions, 42 deletions

diff --git a/src/tts.rs b/src/tts.rs
index 4754054..c65e5cd 100644
--- a/src/tts.rs
+++ b/src/tts.rs
@@ -1,7 +1,7 @@
 use std::io::Cursor;
 use std::path::PathBuf;
 use std::sync::atomic::{AtomicUsize, Ordering};
-use std::sync::{Arc, Mutex, OnceLock};
+use std::sync::{Arc, Mutex};
 use std::time::{Duration, Instant};
 
 use dashmap::DashMap;
@@ -43,7 +43,7 @@ const EVENT_TYPES: &[&str] = &[
 /// Held in poise `Data`. Piper is loaded lazily on first synthesis call.
 /// Cache maps full text string → resampled 48 kHz stereo PCM bytes.
 pub struct TtsState {
-    piper: OnceLock<Arc<Mutex<Piper>>>,
+    piper: tokio::sync::OnceCell<Arc<Mutex<Piper>>>,
     cache: DashMap<String, (Vec<u8>, Instant)>,
     cache_bytes: AtomicUsize,
     model_path: Option<PathBuf>,
@@ -52,7 +52,7 @@ pub struct TtsState {
 impl TtsState {
     pub fn new(model_path: Option<PathBuf>) -> Self {
         Self {
-            piper: OnceLock::new(),
+            piper: tokio::sync::OnceCell::new(),
             cache: DashMap::new(),
             cache_bytes: AtomicUsize::new(0),
             model_path,
@@ -62,46 +62,43 @@ impl TtsState {
     /// Get or initialize the Piper model. Returns error if model path is
     /// unset or model fails to load.
     async fn get_piper(&self) -> Result<Arc<Mutex<Piper>>> {
-        if let Some(piper) = self.piper.get() {
-            return Ok(piper.clone());
-        }
-
-        let path = self
-            .model_path
-            .as_ref()
-            .ok_or_else(|| Error::Custom("TTS_MODEL_PATH is not set".into()))?;
-
-        // Resolve .onnx.json config path from model path
-        let onnx_path = path.clone();
-        let config_path = {
-            let s = path.to_string_lossy();
-            if s.ends_with(".onnx") {
-                PathBuf::from(format!("{}.json", s))
-            } else {
-                path.clone()
-            }
-        };
-
-        debug!(
-            onnx = %onnx_path.display(),
-            config = %config_path.display(),
-            "loading piper model"
-        );
-        // Model loading is CPU/IO heavy; keep it off the async runtime too.
-        let piper = tokio::task::spawn_blocking(move || {
-            Piper::new(&onnx_path, &config_path)
-                .map_err(|e| Error::Custom(format!("Failed to load piper model: {e}")))
-        })
-        .await??;
-        info!("piper model loaded successfully");
-
-        // set() may fail if another task initialized first — that's fine
-        let _ = self.piper.set(Arc::new(Mutex::new(piper)));
-        Ok(self
+        // `get_or_try_init` guarantees only one task loads the model even when
+        // several `/tts` calls arrive at once.
+        let piper = self
             .piper
-            .get()
-            .expect("piper was just initialized")
-            .clone())
+            .get_or_try_init(|| async {
+                let path = self
+                    .model_path
+                    .as_ref()
+                    .ok_or_else(|| Error::Custom("TTS_MODEL_PATH is not set".into()))?;
+
+                // Resolve .onnx.json config path from model path
+                let onnx_path = path.clone();
+                let config_path = {
+                    let s = path.to_string_lossy();
+                    if s.ends_with(".onnx") {
+                        PathBuf::from(format!("{}.json", s))
+                    } else {
+                        path.clone()
+                    }
+                };
+
+                debug!(
+                    onnx = %onnx_path.display(),
+                    config = %config_path.display(),
+                    "loading piper model"
+                );
+                // Model loading is CPU/IO heavy; keep it off the async runtime.
+                let piper = tokio::task::spawn_blocking(move || {
+                    Piper::new(&onnx_path, &config_path)
+                        .map_err(|e| Error::Custom(format!("Failed to load piper model: {e}")))
+                })
+                .await??;
+                info!("piper model loaded successfully");
+                Ok::<_, Error>(Arc::new(Mutex::new(piper)))
+            })
+            .await?;
+        Ok(piper.clone())
     }
 
     /// Look up cached audio for a text string. Returns `None` if uncached