doc: document vm module limitation with timeouts and async code

[jasnell]

Checklist

• documentation is changed or added
• commit message follows commit guidelines

Affected core subsystem(s)

doc (vm)

Description of change

Fixes: #3020

[bengl]

Hmm, is this accurate?

I put the code snippet in a file and ran it (in v6.3.1). Unable to reproduce. It stops due to timeout as expected.

It fails as documented here if used in the REPL though.

[jasnell]

It fails consistently in the REPL... and, ugh, you're right that it appears to work as expected within a file. Sigh...

[23doors]

If you skip the part outside of Promise, it will never stop though (as expected).

vm.runInNewContext(
  'Promise.resolve().then(()=>{while(1)console.log("foo", Date.now());});',
  {console:{log(){console.log.apply(console,arguments);}}},
  {timeout:5}
);

[targos]

... are not limited by the timeout

[targos]

If you skip the part outside of Promise, it will never stop though (as expected).

That's right. I suggest you just change the example to what @23doors wrote.

[ghost]

It's unfortunate that it wasn't merged, it would have saved me a few hours!