Add an event loop monitor

Author: ericallam

apps/webapp/app/entry.server.tsx

@@ -186,3 +186,4 @@ export { apiRateLimiter } from "./services/apiRateLimit.server";
 export { socketIo } from "./v3/handleSocketIo.server";
 export { wss } from "./v3/handleWebsockets.server";
 export { registryProxy } from "./v3/registryProxy.server";
+export { eventLoopMonitor } from "./eventLoopMonitor.server";

apps/webapp/app/eventLoopMonitor.server.ts

@@ -0,0 +1,39 @@
+import { createHook } from "node:async_hooks";
+import { logger } from "./services/logger.server";
+import { singleton } from "./utils/singleton";
+
+const THRESHOLD_NS = 1e8; // 100ms
+
+const cache = new Map<number, [number, number]>();
+
+function before(asyncId: number) {
+  cache.set(asyncId, process.hrtime());
+}
+
+function after(asyncId: number) {
+  const cached = cache.get(asyncId);
+  if (cached == null) {
+    return;
+  }
+  cache.delete(asyncId);
+
+  const diff = process.hrtime(cached);
+  const diffNs = diff[0] * 1e9 + diff[1];
+  if (diffNs > THRESHOLD_NS) {
+    const time = diffNs / 1e6; // in ms
+
+    logger.error(`Event loop was blocked for ${time}ms`, {
+      label: "EventLoopMonitor",
+      startTime: new Date(new Date().getTime() - time),
+      durationMs: time,
+    });
+  }
+}
+
+export const eventLoopMonitor = singleton("eventLoopMonitor", () => {
+  console.log("🥸 Initializing event loop monitor");
+
+  const asyncHook = createHook({ before, after });
+  asyncHook.enable();
+  return asyncHook;
+});