diff --git a/server.py b/server.py
index 6cfa1a3..8e71c9b 100644
--- a/server.py
+++ b/server.py
@@ -37,6 +37,7 @@ class TTSService:
         self._shutdown_event: asyncio.Event | None = None
         self._worker_task: asyncio.Task | None = None
         self._cookies: dict[str, str] | None = None
+        self._lifecycle_lock = asyncio.Lock()
         self.running = False
         self.start_time: float = 0
         self.messages_processed = 0
@@ -48,49 +49,51 @@ class TTSService:
         self._cookies = cookies
 
     async def start(self, config: dict) -> None:
-        if self.running:
-            raise RuntimeError("Already running")
-        room_id = config["room_id"]
-        voice = config.get("voice", "f1")
-        speed = config.get("speed", 100)
-        self._volume = config.get("volume", 100)
-        message_format = config.get("format", "{uname}\u8bf4\u3001 {msg}")
-        convert_numbers = config.get("convert_numbers", True)
-        self.current_config = config
-        self.recent_messages = []
-        self.messages_processed = 0
-        self.start_time = time.time()
-        self._queue = asyncio.Queue(maxsize=256)
-        self._shutdown_event = asyncio.Event()
-        self._bridge = TTSBridge(voice=voice, speed=speed)
-        await self._bridge.start()
-        self._danmaku_client = DanmakuClient(
-            room_id=room_id, queue=self._queue,
-            cookies=self._cookies, message_format=message_format,
-        )
-        await self._danmaku_client.start()
-        self.running = True
-        self._worker_task = asyncio.create_task(self._tts_worker(convert_numbers))
+        async with self._lifecycle_lock:
+            if self.running:
+                raise RuntimeError("Already running")
+            room_id = config["room_id"]
+            voice = config.get("voice", "f1")
+            speed = config.get("speed", 100)
+            self._volume = config.get("volume", 100)
+            message_format = config.get("format", "{uname}\u8bf4\u3001 {msg}")
+            convert_numbers = config.get("convert_numbers", True)
+            self.current_config = config
+            self.recent_messages = []
+            self.messages_processed = 0
+            self.start_time = time.time()
+            self._queue = asyncio.Queue(maxsize=256)
+            self._shutdown_event = asyncio.Event()
+            self._bridge = TTSBridge(voice=voice, speed=speed)
+            await self._bridge.start()
+            self._danmaku_client = DanmakuClient(
+                room_id=room_id, queue=self._queue,
+                cookies=self._cookies, message_format=message_format,
+            )
+            await self._danmaku_client.start()
+            self.running = True
+            self._worker_task = asyncio.create_task(self._tts_worker(convert_numbers))
 
     async def stop(self) -> None:
-        if not self.running:
-            return
-        self.running = False
-        if self._shutdown_event:
-            self._shutdown_event.set()
-        if self._worker_task:
-            self._worker_task.cancel()
-            try:
-                await self._worker_task
-            except asyncio.CancelledError:
-                pass
-        if self._danmaku_client:
-            await self._danmaku_client.stop()
-        if self._bridge:
-            await self._bridge.stop()
-        self._queue = None
-        self._bridge = None
-        self._danmaku_client = None
+        async with self._lifecycle_lock:
+            if not self.running:
+                return
+            self.running = False
+            if self._shutdown_event:
+                self._shutdown_event.set()
+            if self._worker_task:
+                self._worker_task.cancel()
+                try:
+                    await self._worker_task
+                except asyncio.CancelledError:
+                    pass
+            if self._danmaku_client:
+                await self._danmaku_client.stop()
+            if self._bridge:
+                await self._bridge.stop()
+            self._queue = None
+            self._bridge = None
+            self._danmaku_client = None
 
     async def _tts_worker(self, convert_numbers: bool) -> None:
         total_in = 0
diff --git a/tts.py b/tts.py
index 533fab0..bfa6dc9 100644
--- a/tts.py
+++ b/tts.py
@@ -46,6 +46,7 @@ class TTSBridge:
         self._bridge_script = bridge_script or _resolve_path("tts_bridge.js")
         self._node_exe = _get_node_exe()
         self._stderr_task: asyncio.Task | None = None
+        self._io_lock = asyncio.Lock()
 
     async def start(self) -> None:
         if not pathlib.Path(self._bridge_script).exists():
@@ -96,39 +97,40 @@ class TTSBridge:
         if self._process is None or self._process.stdin is None:
             raise RuntimeError("Bridge not started. Call start() first.")
 
-        tmpdir = pathlib.Path(tempfile.mkdtemp(prefix="tts_"))
-        try:
-            input_path = tmpdir / "input.txt"
-            output_path = tmpdir / "output.wav"
+        async with self._io_lock:
+            tmpdir = pathlib.Path(tempfile.mkdtemp(prefix="tts_"))
+            try:
+                input_path = tmpdir / "input.txt"
+                output_path = tmpdir / "output.wav"
 
-            input_path.write_text(kana_text, encoding="utf-8")
+                input_path.write_text(kana_text, encoding="utf-8")
 
-            cmd_line = f"{input_path}|{output_path}\n"
-            self._process.stdin.write(cmd_line.encode("utf-8"))
-            await self._process.stdin.drain()
+                cmd_line = f"{input_path}|{output_path}\n"
+                self._process.stdin.write(cmd_line.encode("utf-8"))
+                await self._process.stdin.drain()
 
-            line = await asyncio.wait_for(self._process.stdout.readline(), timeout=120)
-            line_str = line.decode("utf-8").strip()
+                line = await asyncio.wait_for(self._process.stdout.readline(), timeout=120)
+                line_str = line.decode("utf-8").strip()
 
-            if line_str.startswith("ERR:"):
-                raise RuntimeError(f"TTS synthesis error: {line_str[4:]}")
+                if line_str.startswith("ERR:"):
+                    raise RuntimeError(f"TTS synthesis error: {line_str[4:]}")
 
-            if not line_str.startswith("OK:") or line_str[3:] != str(output_path):
-                raise RuntimeError(f"Unexpected bridge response: {line_str}")
+                if not line_str.startswith("OK:") or line_str[3:] != str(output_path):
+                    raise RuntimeError(f"Unexpected bridge response: {line_str}")
 
-            wav_data = output_path.read_bytes()
-            return wav_data
+                wav_data = output_path.read_bytes()
+                return wav_data
 
-        finally:
-            for f in tmpdir.iterdir():
+            finally:
+                for f in tmpdir.iterdir():
+                    try:
+                        f.unlink()
+                    except OSError:
+                        pass
                 try:
-                    f.unlink()
+                    tmpdir.rmdir()
                 except OSError:
                     pass
-            try:
-                tmpdir.rmdir()
-            except OSError:
-                pass
 
     async def stop(self) -> None:
         if self._process is not None: