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, 63 insertions, 0 deletions

diff --git a/src/histogram-inl.h b/src/histogram-inl.h
new file mode 100644
index 00000000000..3135041f738
--- /dev/null
+++ b/src/histogram-inl.h
@@ -0,0 +1,63 @@
+#ifndef SRC_HISTOGRAM_INL_H_
+#define SRC_HISTOGRAM_INL_H_
+
+#if defined(NODE_WANT_INTERNALS) && NODE_WANT_INTERNALS
+
+#include "histogram.h"
+#include "node_internals.h"
+
+namespace node {
+
+inline Histogram::Histogram(int64_t lowest, int64_t highest, int figures) {
+  CHECK_EQ(0, hdr_init(lowest, highest, figures, &histogram_));
+}
+
+inline Histogram::~Histogram() {
+  hdr_close(histogram_);
+}
+
+inline void Histogram::Reset() {
+  hdr_reset(histogram_);
+}
+
+inline bool Histogram::Record(int64_t value) {
+  return hdr_record_value(histogram_, value);
+}
+
+inline int64_t Histogram::Min() {
+  return hdr_min(histogram_);
+}
+
+inline int64_t Histogram::Max() {
+  return hdr_max(histogram_);
+}
+
+inline double Histogram::Mean() {
+  return hdr_mean(histogram_);
+}
+
+inline double Histogram::Stddev() {
+  return hdr_stddev(histogram_);
+}
+
+inline double Histogram::Percentile(double percentile) {
+  CHECK_GT(percentile, 0);
+  CHECK_LE(percentile, 100);
+  return hdr_value_at_percentile(histogram_, percentile);
+}
+
+inline void Histogram::Percentiles(std::function<void(double, double)> fn) {
+  hdr_iter iter;
+  hdr_iter_percentile_init(&iter, histogram_, 1);
+  while (hdr_iter_next(&iter)) {
+    double key = iter.specifics.percentiles.percentile;
+    double value = iter.value;
+    fn(key, value);
+  }
+}
+
+}  // namespace node
+
+#endif  // defined(NODE_WANT_INTERNALS) && NODE_WANT_INTERNALS
+
+#endif  // SRC_HISTOGRAM_INL_H_