fix(webapp): correctly associate event-loop-blocked spans with parent span context

Author: ericallam

apps/webapp/app/env.server.ts

@@ -1060,6 +1060,8 @@ const EnvironmentSchema = z.object({
 
   // AI Run Filter
   AI_RUN_FILTER_MODEL: z.string().optional(),
+
+  EVENT_LOOP_MONITOR_THRESHOLD_MS: z.coerce.number().int().default(100),
 });
 
 export type Environment = z.infer<typeof EnvironmentSchema>;

apps/webapp/app/eventLoopMonitor.server.ts

@@ -1,10 +1,12 @@
 import { createHook } from "node:async_hooks";
 import { singleton } from "./utils/singleton";
 import { tracer } from "./v3/tracer.server";
+import { env } from "./env.server";
+import { context, Context } from "@opentelemetry/api";
 
-const THRESHOLD_NS = 1e8; // 100ms
+const THRESHOLD_NS = env.EVENT_LOOP_MONITOR_THRESHOLD_MS * 1e6;
 
-const cache = new Map<number, { type: string; start?: [number, number] }>();
+const cache = new Map<number, { type: string; start?: [number, number]; parentCtx?: Context }>();
 
 function init(asyncId: number, type: string, triggerAsyncId: number, resource: any) {
   cache.set(asyncId, {
@@ -26,6 +28,7 @@ function before(asyncId: number) {
   cache.set(asyncId, {
     ...cached,
     start: process.hrtime(),
+    parentCtx: context.active(),
   });
 }
 
@@ -47,13 +50,17 @@ function after(asyncId: number) {
   if (diffNs > THRESHOLD_NS) {
     const time = diffNs / 1e6; // in ms
 
-    const newSpan = tracer.startSpan("event-loop-blocked", {
-      startTime: new Date(new Date().getTime() - time),
-      attributes: {
-        asyncType: cached.type,
-        label: "EventLoopMonitor",
+    const newSpan = tracer.startSpan(
+      "event-loop-blocked",
+      {
+        startTime: new Date(new Date().getTime() - time),
+        attributes: {
+          asyncType: cached.type,
+          label: "EventLoopMonitor",
+        },
       },
-    });
+      cached.parentCtx
+    );
 
     newSpan.end();
   }