child_process: empty stdout on parallel exec

[legendecas]

• Version: 0.11.5
• Platform: linux
• Subsystem: child_process

var childProcess = require('child_process')
var cmd = `cat /proc/meminfo | grep MemAvailable | awk '{ print $2 }'`

childProcess.exec(cmd, (err, stdout) => {
  console.log(err, stdout) // stdout never empty
})
childProcess.exec(cmd, (err, stdout) => {
  console.log(err, stdout) // stdout *possibly* empty
})

[yorkie]

It seems that exit event is in front of data, I have patched the following on my linux device:

diff --git a/src/js/child_process.js b/src/js/child_process.js
index a7cbf10f..9a40631a 100644
--- a/src/js/child_process.js
+++ b/src/js/child_process.js
@@ -917,6 +917,7 @@ exports.execFile = function(file /* , args, options, callback */) {
       child.stdout.setEncoding(encoding);

     child.stdout.on('data', function onChildStdout(chunk) {
+      console.log('>>>>', chunk);
       stdoutLen += chunk.length;

       if (stdoutLen > options.maxBuffer) {

And got the reason why it's null:

/ # node test.js
>>>> <Buffer 35 33 30 30 30 0a>
null string 53000

>>>> <Buffer 35 32 39 39 32 0a>
null string 52992

/ # node test.js
>>>> <Buffer 35 32 38 36 30 0a>
null string 52860

null string   # the _stdout is null because the data event has not fired yet :(
>>>> <Buffer 35 32 39 33 32 0a>

[yorkie]

I found that pipe can still read the data by uv_stream_t after the onexit callback gets fired, namely the process exits. @lolBig May I ask you chime this in a bit?