Re: [Tarantool-patches] [PATCH 1/5] popen: Introduce a backend engine

[Cyrill Gorcunov <gorcunov@gmail.com>]

On Sat, Nov 30, 2019 at 01:54:54PM +0300, Cyrill Gorcunov wrote:
> 
> Forgot to mention that the example in previous message is
> for pipe opened in blocked mode. If o_nonblock used the
> script fails in "read" action. I think the main target now
> for me is to investigate which mode uses python in subprocess
> module and etc (simply because users are familiar with it and
> will expect us to behave the same I think).

Python opens pipes in blocked mode
--- sub.py
import subprocess

args=["sh", "-c", "prompt=''; read -n 5 prompt; echo $prompt"]
process = subprocess.Popen(args, stdout=subprocess.PIPE)
(stdout_data, stderr_data) = process.communicate()
print(stdout_data)
---

$ python3 sub.py
12345b'12345\n'

So it waited for me to type "12345" on keyboard and echo'ed it back.

If we look into strace output we will see

 | pipe2([3, 4], O_CLOEXEC)          = 0

so I think we should follow the convention and open
pipes in blocking mode. Still we could provide an
option to open in nonblocking mode if user wants.

	Cyrill