test: correct test-worker-eventlooputil

The active worker check compared the time from sending message till
response arrived from worker with the complete time the worker was
running till it responses to the spin request.

If sending back the message is slow for some reason the test fails.

Adapt the test to compare the time seen inside the worker with the
time read from main thread.

PR-URL: #35891
Fixes: #35844
Refs: #35886
Refs: #35664
Reviewed-By: Gireesh Punathil <gpunathi@in.ibm.com>
Reviewed-By: Rich Trott <rtrott@gmail.com>

Backport-PR-URL: #37163

test/parallel/test-worker-eventlooputil.js

@@ -34,9 +34,10 @@ function workerOnMetricsMsg(msg) {
   }
 
   if (msg.cmd === 'spin') {
+    const elu = eventLoopUtilization();
     const t = now();
     while (now() - t < msg.dur);
-    return this.postMessage(eventLoopUtilization());
+    return this.postMessage(eventLoopUtilization(elu));
   }
 }
 
@@ -50,12 +51,13 @@ let workerELU;
   if (eventLoopUtilization().idle <= 0)
     return setTimeout(mustCall(r), 5);
 
+  mainElu = eventLoopUtilization();
+
   worker = new Worker(__filename, { argv: [ 'iamalive' ] });
   metricsCh = new MessageChannel();
   worker.postMessage({ metricsCh: metricsCh.port1 }, [ metricsCh.port1 ]);
 
   workerELU = worker.performance.eventLoopUtilization;
-  mainElu = eventLoopUtilization();
   metricsCh.port2.once('message', mustCall(checkWorkerIdle));
   metricsCh.port2.postMessage({ cmd: 'elu' });
   // Make sure it's still safe to call eventLoopUtilization() after the worker
@@ -66,15 +68,10 @@ let workerELU;
   }));
 })();
 
-
 function checkWorkerIdle(wElu) {
-  const tmpMainElu = eventLoopUtilization(mainElu);
   const perfWorkerElu = workerELU();
-  const eluDiff = eventLoopUtilization(perfWorkerElu, mainElu);
+  const tmpMainElu = eventLoopUtilization(mainElu);
 
-  assert.strictEqual(idleActive(eluDiff),
-                     (perfWorkerElu.active - mainElu.active) +
-                       (perfWorkerElu.idle - mainElu.idle));
   assert.ok(idleActive(wElu) > 0, `${idleActive(wElu)} <= 0`);
   assert.ok(idleActive(workerELU(wElu)) > 0,
             `${idleActive(workerELU(wElu))} <= 0`);
@@ -104,8 +101,9 @@ function checkWorkerActive() {
     const w2 = workerELU(w);
 
     assert.ok(w2.active >= 50, `${w2.active} < 50`);
-    assert.ok(idleActive(wElu) > idleActive(w2),
-              `${idleActive(wElu)} <= ${idleActive(w2)}`);
+    assert.ok(wElu.active >= 50, `${wElu.active} < 50`);
+    assert.ok(idleActive(wElu) < idleActive(w2),
+              `${idleActive(wElu)} >= ${idleActive(w2)}`);
 
     metricsCh.port2.postMessage({ cmd: 'close' });
   });