child_process: add callback parameter to .send()

Add an optional callback parameter to `ChildProcess.prototype.send()`
that is invoked when the message has been sent.

Juggle the control channel's reference count so that in-flight messages
keep the event loop (and therefore the process) alive until they have
been sent.

`ChildProcess.prototype.send()` and `process.send()` used to operate
synchronously but became asynchronous in commit libuv/libuv@393c1c5
("unix: set non-block mode in uv_{pipe,tcp,udp}_open"), which landed
in io.js in commit 07bd05b ("deps: update libuv to 1.2.1").

Fixes: https://github.com/nodejs/node/issues/760
PR-URL: https://github.com/nodejs/node/pull/2620
Reviewed-By: trevnorris - Trevor Norris <trev.norris@gmail.com>
Reviewed-By: jasnell - James M Snell <jasnell@gmail.com>

1 files changed, 19 insertions, 0 deletions

diff --git a/test/parallel/test-child-process-send-cb.js b/test/parallel/test-child-process-send-cb.js
new file mode 100644
index 0000000000..d65a1abd20
--- /dev/null
+++ b/test/parallel/test-child-process-send-cb.js
@@ -0,0 +1,19 @@
+'use strict';
+const common = require('../common');
+const assert = require('assert');
+const fork = require('child_process').fork;
+
+if (process.argv[2] === 'child') {
+  process.send('ok', common.mustCall(function(err) {
+    assert.strictEqual(err, null);
+  }));
+} else {
+  const child = fork(process.argv[1], ['child']);
+  child.on('message', common.mustCall(function(message) {
+    assert.strictEqual(message, 'ok');
+  }));
+  child.on('exit', common.mustCall(function(exitCode, signalCode) {
+    assert.strictEqual(exitCode, 0);
+    assert.strictEqual(signalCode, null);
+  }));
+}