lib,doc: return boolean from child.send()

doc/api/child_process.markdown

@@ -266,9 +266,10 @@ argument: `null` on success, or an `Error` object on failure.
 `child.send()` emits an `'error'` event if no callback was given and the message
 cannot be sent, for example because the child process has already exited.
 
-Returns `true` under normal circumstances or `false` when the backlog of
+`child.send()` returns `false` if the channel has closed or when the backlog of
 unsent messages exceeds a threshold that makes it unwise to send more.
-Use the callback mechanism to implement flow control.
+Otherwise, it returns `true`. Use the callback mechanism to implement flow
+control.
 
 #### Example: sending server object
 

lib/internal/child_process.js

@@ -504,15 +504,15 @@ function setupChannel(target, channel) {
  handle = undefined;
  }
  if (this.connected) {
- this._send(message, handle, false, callback);
- return;
+ return this._send(message, handle, false, callback);
  }
  const ex = new Error('channel closed');
  if (typeof callback === 'function') {
  process.nextTick(callback, ex);
  } else {
  this.emit('error', ex); // FIXME(bnoordhuis) Defer to next tick.
  }
+ return false;
  };
 
  target._send = function(message, handle, swallowErrors, callback) {
@@ -577,7 +577,7 @@ function setupChannel(target, channel) {
  handle: null,
  message: message,
  });
- return;
+ return this._handleQueue.length === 1;
  }
 
  var req = new WriteWrap();

test/parallel/test-child-process-send-returns-boolean.js

@@ -0,0 +1,9 @@
+'use strict';
+const common = require('../common');
+const assert = require('assert');
+const fork = require('child_process').fork;
+
+const n = fork(common.fixturesDir + '/empty.js');
+
+const rv = n.send({ hello: 'world' });
+assert.strictEqual(rv, true);