Non-blocking Read from StdoutPipe and StderrPipe

[Peter Bočan]

Hello Community, 

I am writing a small binary which watches the subprocesses it launches. However, I have noticed that cmd.StdoutPipe and cmd.StderrPipe returns io.ReadCloser/io.File, which also, in itself blocks when reading. 

What is the recommended way of reading whatever is on the buffer and return back without blocking? It looks like a bit of a rabbit hole. Is setting the nonblocking flag using syscall recommended? 

Kindly,
Peter.

[robert engels]

I am not sure that is idiomatic Go. Start a new Go routine to do the reading, and post the results to a channel that the main routine selects on.

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[Nico Braun]

Perhaps you can use a context. It wouldnt be truely nonblocking but maybe it is sufficient to use cancel or deadline. https://cs.opensource.google/go/go/+/refs/tags/go1.23.2:src/os/exec/exec.go;drc=d0146bd85bb6870aa43a498b06ccb473af55cbe3;l=453.

[Brian Candler]

On Monday 14 October 2024 at 22:57:07 UTC+1 Peter Bočan wrote:

What is the recommended way of reading whatever is on the buffer and return back without blocking?

If you just want to poll, and get whatever data is available: set a deadline of "just after now", and read.

https://go.dev/play/p/bFDh7gqpeYc   [Note: doesn't work properly in the playground; I don't know why]

If you want to do other concurrent work and/or select between multiple sources: use a goroutine to read and pass the data down a channel, and closes the channel when done.

[Peter Bočan]

Hey peeps, 

thank you for your input, I will try these options and see how it goes. 

Regards,
Peter.