Does libuv guarantee the order in which callbacks associated with an `uv_process_t` will be invoked?

[Thiago Arruda]

When a process is spawned with stdout/stderr connected to pipes, there are three associated callbacks:

- One for stdout data

- One for stderr data

- One for when the process exits.

When a stream reaches EOF, it's read callback will be invoked with an error set. That means when a process exits, all three callbacks will be invoked.

Is it guaranteed that the last callback of a process will be the `uv_process_t.exit_cb`? I need to know this to determine when the process handles can be safely closed.

Thanks in advance

Thiago.

[Saúl Ibarra Corretgé]

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I don't think we guarantee such a thing, and it's actually not that
obvious from the code :-S Fedor, any idea?


- --
Saúl Ibarra Corretgé
bettercallsaghul.com

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[Fedor Indutny]

We do not provide any guarantees, and it'd be hard for us to do so.

Thanks for raising up the question!

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[Thiago Padilha]

I was already handling this by counting callbacks and wondered if it was really necessary. Thanks for the answer anyway

[Bert Belder]

> Is it guaranteed that the last callback of a process will be the `uv_process_t.exit_cb`? I need to know this to determine when the process handles can be safely closed.

You should explicitly close the stdio pipes.

Read callbacks can indeed come in after the exit_cb is fired. Sometimes data may still be lingering in the stdout/stderr pipes which will be flushed after the exit callback.

You have to realize that there are scenarios in which the pipes stay open long after the process exits. This may for example happen when the child process creates another process that inherits the child's stdio pipes. The grand-child may outlive it's parent.

- Bert

[Thiago Padilha]

Bert, thanks for the info.

After adding calls to uv_close on the close_cb of my uv_process_t, all
my problems were fixed!