process: improve process.hrtime

* Add benchmarks for diffing a previous result
* Improvements to the documentation, including type annotation
* Update the outdated comments in src/node.cc, improve comments
  in lib/internal/process.js
* Check the argument is an Array Tuple with length 2

PR-URL: https://github.com/nodejs/node/pull/10764
Reviewed-By: James M Snell <jasnell@gmail.com>
Reviewed-By: Anna Henningsen <anna@addaleax.net>
Reviewed-By: Brian White <mscdex@mscdex.net>

1 files changed, 6 insertions, 6 deletions

diff --git a/src/node.cc b/src/node.cc
index b6dd9b59d5..721c4d097a 100644
--- a/src/node.cc
+++ b/src/node.cc
@@ -2274,18 +2274,18 @@ void Kill(const FunctionCallbackInfo<Value>& args) {
 
 // Hrtime exposes libuv's uv_hrtime() high-resolution timer.
 // The value returned by uv_hrtime() is a 64-bit int representing nanoseconds,
-// so this function instead returns an Array with 2 entries representing seconds
-// and nanoseconds, to avoid any integer overflow possibility.
-// Pass in an Array from a previous hrtime() call to instead get a time diff.
+// so this function instead fills in an Uint32Array with 3 entries,
+// to avoid any integer overflow possibility.
+// The first two entries contain the second part of the value
+// broken into the upper/lower 32 bits to be converted back in JS,
+// because there is no Uint64Array in JS.
+// The third entry contains the remaining nanosecond part of the value.
 void Hrtime(const FunctionCallbackInfo<Value>& args) {
   uint64_t t = uv_hrtime();
 
   Local<ArrayBuffer> ab = args[0].As<Uint32Array>()->Buffer();
   uint32_t* fields = static_cast<uint32_t*>(ab->GetContents().Data());
 
-  // These three indices will contain the values for the hrtime tuple. The
-  // seconds value is broken into the upper/lower 32 bits and stored in two
-  // uint32 fields to be converted back in JS.
   fields[0] = (t / NANOS_PER_SEC) >> 32;
   fields[1] = (t / NANOS_PER_SEC) & 0xffffffff;
   fields[2] = t % NANOS_PER_SEC;