test: add retry logic for eventloopdelay histogram sampling

On some build configurations (e.g., sharedlibs), the histogram may not
record valid samples (min > 0) after the initial spinning period. This
adds a retry mechanism that will spin the event loop additional times
if valid samples haven't been recorded yet.

This helps ensure the test passes on slower or differently-configured
systems where event loop delay sampling may take longer to produce
measurable results.

Refs: nodejs/reliability#1461

Author: mcollina

test/sequential/test-performance-eventloopdelay.js

@@ -3,7 +3,6 @@
 
 const common = require('../common');
 const assert = require('assert');
-const os = require('os');
 const {
   monitorEventLoopDelay,
 } = require('perf_hooks');
@@ -52,59 +51,77 @@ const { sleep } = require('internal/util');
 }
 
 {
-  const s390x = os.arch() === 's390x';
   const histogram = monitorEventLoopDelay({ resolution: 1 });
   histogram.enable();
-  let m = 5;
-  if (s390x) {
-    m = m * 2;
+
+  // Check if histogram has recorded valid samples (min > 0 indicates real delays measured)
+  function hasValidSamples() {
+    return histogram.count > 0 && histogram.min > 0 && histogram.max > 0;
   }
+
+  // Spin the event loop with blocking work to generate measurable delays.
+  // Some configurations (s390x, sharedlibs) need more iterations.
+  let spinsRemaining = 5;
+  const maxRetries = 3;
+  let retries = 0;
+
   function spinAWhile() {
     sleep(1000);
-    if (--m > 0) {
+    if (--spinsRemaining > 0) {
       setTimeout(spinAWhile, common.platformTimeout(500));
     } else {
-      // Give the histogram a chance to record final samples before disabling.
-      // This helps on slower systems where sampling may be delayed.
-      setImmediate(common.mustCall(() => {
-        histogram.disable();
-        // The values are non-deterministic, so we just check that a value is
-        // present, as opposed to a specific value.
-        assert(histogram.count > 0, `Expected samples to be recorded, got count=${histogram.count}`);
-        assert(histogram.min > 0);
-        assert(histogram.max > 0);
-        assert(histogram.stddev > 0);
-        assert(histogram.mean > 0);
-        assert(histogram.percentiles.size > 0);
-        for (let n = 1; n < 100; n = n + 0.1) {
-          assert(histogram.percentile(n) >= 0);
+      // Give the histogram a chance to record final samples before checking.
+      setImmediate(() => {
+        // If we don't have valid samples yet, retry with more spinning.
+        // This handles slower configurations like sharedlibs builds.
+        if (!hasValidSamples() && retries < maxRetries) {
+          retries++;
+          spinsRemaining = 5;
+          setTimeout(spinAWhile, common.platformTimeout(500));
+          return;
         }
-        histogram.reset();
-        assert.strictEqual(histogram.min, 9223372036854776000);
-        assert.strictEqual(histogram.max, 0);
-        assert(Number.isNaN(histogram.stddev));
-        assert(Number.isNaN(histogram.mean));
-        assert.strictEqual(histogram.percentiles.size, 1);
 
-        ['a', false, {}, []].forEach((i) => {
-          assert.throws(
-            () => histogram.percentile(i),
-            {
-              name: 'TypeError',
-              code: 'ERR_INVALID_ARG_TYPE',
-            }
-          );
-        });
-        [-1, 0, 101, NaN].forEach((i) => {
-          assert.throws(
-            () => histogram.percentile(i),
-            {
-              name: 'RangeError',
-              code: 'ERR_OUT_OF_RANGE',
-            }
-          );
-        });
-      }));
+        // Wrap final assertions in mustCall to ensure they run
+        common.mustCall(() => {
+          histogram.disable();
+          // The values are non-deterministic, so we just check that a value is
+          // present, as opposed to a specific value.
+          assert(histogram.count > 0, `Expected samples to be recorded, got count=${histogram.count}`);
+          assert(histogram.min > 0, `Expected min > 0, got ${histogram.min}`);
+          assert(histogram.max > 0);
+          assert(histogram.stddev > 0);
+          assert(histogram.mean > 0);
+          assert(histogram.percentiles.size > 0);
+          for (let n = 1; n < 100; n = n + 0.1) {
+            assert(histogram.percentile(n) >= 0);
+          }
+          histogram.reset();
+          assert.strictEqual(histogram.min, 9223372036854776000);
+          assert.strictEqual(histogram.max, 0);
+          assert(Number.isNaN(histogram.stddev));
+          assert(Number.isNaN(histogram.mean));
+          assert.strictEqual(histogram.percentiles.size, 1);
+
+          ['a', false, {}, []].forEach((i) => {
+            assert.throws(
+              () => histogram.percentile(i),
+              {
+                name: 'TypeError',
+                code: 'ERR_INVALID_ARG_TYPE',
+              }
+            );
+          });
+          [-1, 0, 101, NaN].forEach((i) => {
+            assert.throws(
+              () => histogram.percentile(i),
+              {
+                name: 'RangeError',
+                code: 'ERR_OUT_OF_RANGE',
+              }
+            );
+          });
+        })();
+      });
     }
   }
   spinAWhile();