Understand process tree measurement on each OS

Your command starts other processes, a shell, make, a compiler, and you need to know what the CPU and memory numbers include.

# yaml-language-server: $schema=../../schema/himorime.schema.json
#
# Recipe: understand process tree measurement on each OS.
# https://nao1215.github.io/himorime/cookbook/#understand-process-tree-measurement-on-each-os
version: "1"

name: process tree
description: CPU time of a program that does its work itself, and of one that delegates it to two child processes.

build:
  command: [go, build, -o, "${artifact}", ../tools/sleepy]

defaults:
  warmup: 1
  runs: 6

benchmarks:
  - name: spin 100ms
    metrics:
      # The started process and its descendants. Only process_tree exists.
      cpu: true
    commands:
      alone:
        command: ["${artifact}", -busy, -ms, "100"]
      two-children:
        # The parent only waits; each child spins for 100ms.
        command: ["${artifact}", -busy, -ms, "100", -children, "2"]

$ himorime run examples/process-tree

alone shows about 100ms of CPU time, two-children about 200ms: the CPU time of the two children counts, although the parent itself only waits.

	Linux, macOS, BSD	Windows
CPU time	the process and every descendant its parents waited for (`wait4` usage)	every process that was part of the command’s Job Object
Peak RSS	the largest peak of the process or any descendant its parents waited for	the peak working set of the started process, reported only when it started no child processes
Not included	a descendant still running when the command exits, or orphaned before it exits	a child started in the microseconds before the process joined the job

Neither platform adds up processes that ran at the same time: peak RSS is the largest single process.
Collection happens after the measured interval and uses the operating system’s high-water marks; see Metrics.
shell: true adds the shell process to the tree: its start-up time, CPU time and memory count too.

Example: examples/process-tree