fix: distinguish idle from program time

ts/src/profilers/time-profiler.ts

@@ -35,10 +35,20 @@ export class TimeProfiler {
    * @param durationMillis - time in milliseconds for which to collect profile.
    */
   async profile(durationMillis: number): Promise<perftools.profiles.IProfile> {
+    // Node.js contains an undocumented API for reporting idle status to V8.
+    // This lets the profiler distinguish idle time from time spent in native
+    // code. Ideally this should be default behavior. Until then, use the
+    // undocumented API.
+    // See https://github.com/nodejs/node/issues/19009#issuecomment-403161559.
+    // tslint:disable-next-line no-any
+    (process as any)._startProfilerIdleNotifier();
     const runName = 'stackdriver-profiler-' + Date.now() + '-' + Math.random();
     profiler.startProfiling(runName);
     await delay(durationMillis);
     const result = profiler.stopProfiling(runName);
-    return serializeTimeProfile(result, this.intervalMicros);
+    // tslint:disable-next-line no-any
+    (process as any)._stopProfilerIdleNotifier();
+    const profile = serializeTimeProfile(result, this.intervalMicros);
+    return profile;
   }
 }

ts/test/test-time-profiler.ts

@@ -27,6 +27,17 @@ const v8TimeProfiler = require('bindings')('time_profiler');
 
 describe('TimeProfiler', () => {
   describe('profile', () => {
+    it('should detect idle time', async () => {
+      const durationMillis = 500;
+      const intervalMicros = 1000;
+      const profiler = new TimeProfiler(intervalMicros);
+      const profile = await profiler.profile(durationMillis);
+      assert.ok(profile.stringTable);
+      assert.notStrictEqual(profile.stringTable!.indexOf('(idle)'), -1);
+    });
+  });
+
+  describe('profile (w/ stubs)', () => {
     const sinonStubs: sinon.SinonStub[] = new Array();
     before(() => {
       sinonStubs.push(sinon.stub(v8TimeProfiler, 'startProfiling'));