console.log / console.error are supposedly synchronous, but huge amounts of trailing data can be lost on process.exit

[ghost]

• Version: v6.3.0
• Platform: Linux cyberman 4.5.5-300.fc24.x86_64 deps: update openssl to 1.0.1j #1 SMP Thu May 19 13:05:32 UTC 2016 x86_64 x86_64 x86_64 GNU/Linux
• Subsystem: ???

I read on various sites that console.log is supposed to be synchronous in recent node.js versions. I just want to write a simple application that writes things to the terminal and exits.

However, as you can see with this simple example, huge amounts of output can be missing when simply using console.log and exiting:

var s = "Lorem ipsum dolor sit amet, consectetur adipiscing elit, sed do eiusmod tempor incididunt ut labore et dolore magna aliqua. Ut enim ad minim veniam, quis nostrud exercitation ullamco laboris nisi ut aliquip ex ea commodo consequat. Duis aute irure dolor in reprehenderit in voluptate velit esse cillum dolore eu fugiat nulla pariatur. Excepteur sint occaecat cupidatat non proident, sunt in culpa qui officia deserunt mollit anim id est laborum."

for (var i = 0; i < 99999; i++) {
    console.log (i + "  " + s);
}
console.log ("pink");
console.error ("punk");
process.exit(0);

If you run it multiple times, you'll also get very random cutoffs for the stdout data. That goes completely against my expectations of a supposedly synchronous function..

How can console.log be used for safe output that actually arrives even when exiting the program? I would do a flush before exit, if I knew how..

[mscdex]

I believe the changes made were only for OS X.

/cc @Fishrock123

[Fishrock123]

@nodejs/ctc and here's another report on why we definitely need to do #6816 ...

[ghost]

Since #6816 was closed, I believe this is now also solved.

[buckles1170]

I'm still getting this issue on node 10.9.0

[buckles1170]

pinging @graingert

[refack]

Hello @buckles1170 and thank you for the report.
Could you provide more information on the circumstances in which you experience this issue. Possibly open a new bug report?
Helpful information might be, OS, some minimal code, are you running with NODE_TTY_UNSAFE_ASYNC and are your STDOUT/ERR connected to TTYs?

[graingert]

We're running on gitlab CI with the node:10 docker image, I can't repeat it locally.

I've not configured anything like NODE_TTY_UNSAFE_ASYNC

[refack]

@graingert, my guess is that running in a CI has STDOUT and STDERR piped into files (or even something more complex), so they are not TTY, and NODE_TTY_UNSAFE_ASYNC is not relevant anyway.
In that case it might not be a Node.js problem but a race in the wrapper. It's possible that node pushed the data out before exiting, but the receiver did not update the log before it detected that the node process exited. I'm not sure that is the case, but it's possible.
I can imagine a workaround with piping STDOUT & STDERR to files, then cating the file to the log (or using tee).

[graingert]

This is running under npm run, and I get the little message from npm too