process: adds 'spawn' event

doc/api/process.md

@@ -95,6 +95,13 @@ log, either periodically (probably best for long-running programs, allowing
 you to clear the map, which in the case of a very buggy program could grow
 indefinitely) or upon process exit (more convenient for scripts).
 
+## Event: 'spawn'
+
+Emitted whenever a process calls the internal `child_process.spawn()` and assign
+the child a `pid`. This is useful for bookkeeping - especially for subsequent
+calls to `process.kill()`, in case no reference to `child` was held and hence
+`child.kill()` is not an option.
+
 ## Event: 'uncaughtException'
 
 The `'uncaughtException'` event is emitted when an exception bubbles all the

lib/internal/child_process.js

@@ -303,6 +303,7 @@ ChildProcess.prototype.spawn = function(options) {
   }
 
   this.pid = this._handle.pid;
+  process.emit('spawn', this.pid);
 
   stdio.forEach(function(stdio, i) {
     if (stdio.type === 'ignore') return;

test/parallel/test-process-emit.js

@@ -1,6 +1,7 @@
 'use strict';
 const common = require('../common');
 const assert = require('assert');
+const spawn = require('child_process').spawn
 const sym = Symbol();
 
 process.on('normal', common.mustCall((data) => {
@@ -20,3 +21,7 @@ process.emit(sym, 'symbolData');
 process.emit('SIGPIPE', 'signalData');
 
 assert.strictEqual(isNaN(process._eventsCount), false);
+
+process.on('spawn', common.mustCall((pid) => {
+  assert.strictEqual(isNaN(pid), false);
+}))