Bound the /__hot-reload__ long-poll duration

mesop/server/server_debug_routes.py

@@ -5,13 +5,20 @@
 from mesop.runtime import runtime
 from mesop.server.server_utils import prefix_base_url
 
+# Cap how long a single poll can block so that a request can't tie up a
+# server thread/connection indefinitely when no hot reload ever happens
+# during its lifetime. The client detects an unchanged counter and simply
+# polls again.
+_MAX_POLL_SECONDS = 25
+
 
 def configure_debug_routes(flask_app: Flask):
   @flask_app.route(prefix_base_url("/__hot-reload__"))
   def hot_reload() -> Response:
     counter = int(request.args["counter"])
-    while True:
-      if counter < runtime().hot_reload_counter:
+    start_time = time.monotonic()
+    while counter >= runtime().hot_reload_counter:
+      if time.monotonic() - start_time > _MAX_POLL_SECONDS:
         break
       # Sleep a short duration but not too short that we hog up excessive CPU.
       time.sleep(0.1)

mesop/web/src/services/channel.ts

@@ -562,9 +562,15 @@ export class Channel {
         );
         if (response.status === 200) {
           const text = await response.text();
-          this.hotReloadCounter = Number(text);
-          this.hotReload();
+          const newCounter = Number(text);
           this.hotReloadBackoffCounter = 0;
+          // The server may respond without the counter having changed (e.g.
+          // it hit its max poll duration with no reload having happened).
+          // Only trigger a reload when the counter actually advanced.
+          if (newCounter !== this.hotReloadCounter) {
+            this.hotReloadCounter = newCounter;
+            this.hotReload();
+          }
           // Use void to explicitly not await to avoid downstream sync issue.
           void pollHotReloadEndpoint();
         } else {