perf_hooks: implement histogram based api

Add a sampling-based event loop delay monitor.

```js
const { monitorEventLoopDelay } = require('perf_hooks');

const h = monitorEventLoopDelay();

h.enable();

h.disable();

console.log(h.percentiles);
console.log(h.min);
console.log(h.max);
console.log(h.mean);
console.log(h.stddev);
console.log(h.percentile(50));
```

PR-URL: https://github.com/nodejs/node/pull/25378
Reviewed-By: Matteo Collina <matteo.collina@gmail.com>
Reviewed-By: Gireesh Punathil <gpunathi@in.ibm.com>
Reviewed-By: Stephen Belanger <admin@stephenbelanger.com>
Reviewed-By: Richard Lau <riclau@uk.ibm.com>
Reviewed-By: Anna Henningsen <anna@addaleax.net>

1 files changed, 99 insertions, 0 deletions

diff --git a/test/sequential/test-performance-eventloopdelay.js b/test/sequential/test-performance-eventloopdelay.js
new file mode 100644
index 0000000000..82f47b6fb2
--- /dev/null
+++ b/test/sequential/test-performance-eventloopdelay.js
@@ -0,0 +1,99 @@
+'use strict';
+
+const common = require('../common');
+const assert = require('assert');
+const {
+  monitorEventLoopDelay
+} = require('perf_hooks');
+
+{
+  const histogram = monitorEventLoopDelay();
+  assert(histogram);
+  assert(histogram.enable());
+  assert(!histogram.enable());
+  histogram.reset();
+  assert(histogram.disable());
+  assert(!histogram.disable());
+}
+
+{
+  [null, 'a', 1, false, Infinity].forEach((i) => {
+    common.expectsError(
+      () => monitorEventLoopDelay(i),
+      {
+        type: TypeError,
+        code: 'ERR_INVALID_ARG_TYPE'
+      }
+    );
+  });
+
+  [null, 'a', false, {}, []].forEach((i) => {
+    common.expectsError(
+      () => monitorEventLoopDelay({ resolution: i }),
+      {
+        type: TypeError,
+        code: 'ERR_INVALID_ARG_TYPE'
+      }
+    );
+  });
+
+  [-1, 0, Infinity].forEach((i) => {
+    common.expectsError(
+      () => monitorEventLoopDelay({ resolution: i }),
+      {
+        type: RangeError,
+        code: 'ERR_INVALID_OPT_VALUE'
+      }
+    );
+  });
+}
+
+{
+  const histogram = monitorEventLoopDelay({ resolution: 1 });
+  histogram.enable();
+  let m = 5;
+  function spinAWhile() {
+    common.busyLoop(1000);
+    if (--m > 0) {
+      setTimeout(spinAWhile, common.platformTimeout(500));
+    } else {
+      histogram.disable();
+      // The values are non-deterministic, so we just check that a value is
+      // present, as opposed to a specific value.
+      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);
+      }
+      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) => {
+        common.expectsError(
+          () => histogram.percentile(i),
+          {
+            type: TypeError,
+            code: 'ERR_INVALID_ARG_TYPE'
+          }
+        );
+      });
+      [-1, 0, 101].forEach((i) => {
+        common.expectsError(
+          () => histogram.percentile(i),
+          {
+            type: RangeError,
+            code: 'ERR_INVALID_ARG_VALUE'
+          }
+        );
+      });
+    }
+  }
+  spinAWhile();
+}