child_process: fix data loss with readable event

This commit prevents child process stdio streams from being
automatically flushed on child process exit/close if a 'readable'
event handler has been attached at the time of exit.

Without this, child process stdio data can be lost if the process
exits quickly and a `read()` (e.g. from a 'readable' handler)
hasn't had the chance to get called yet.

Fixes: https://github.com/nodejs/node/issues/5034
PR-URL: https://github.com/nodejs/node/pull/5036
Reviewed-By: Evan Lucas <evanlucas@me.com>
Reviewed-By: Colin Ihrig <cjihrig@gmail.com>
Reviewed-By: Ben Noordhuis <info@bnoordhuis.nl>
Reviewed-By: James M Snell <jasnell@gmail.com>

1 files changed, 15 insertions, 3 deletions

diff --git a/test/parallel/test-child-process-flush-stdio.js b/test/parallel/test-child-process-flush-stdio.js
index 5fd7eb3bc9..dacc1226f3 100644
--- a/test/parallel/test-child-process-flush-stdio.js
+++ b/test/parallel/test-child-process-flush-stdio.js
@@ -8,10 +8,22 @@ const p = cp.spawn('echo');
 p.on('close', common.mustCall(function(code, signal) {
   assert.strictEqual(code, 0);
   assert.strictEqual(signal, null);
+  spawnWithReadable();
 }));
 
 p.stdout.read();
 
-setTimeout(function() {
-  p.kill();
-}, 100);
+function spawnWithReadable() {
+  const buffer = [];
+  const p = cp.spawn('echo', ['123']);
+  p.on('close', common.mustCall(function(code, signal) {
+    assert.strictEqual(code, 0);
+    assert.strictEqual(signal, null);
+    assert.strictEqual(Buffer.concat(buffer).toString().trim(), '123');
+  }));
+  p.stdout.on('readable', function() {
+    let buf;
+    while (buf = this.read())
+      buffer.push(buf);
+  });
+}