Add `close()` method to `asyncio.StreamReader`

Feature or enhancement

Proposal:

When creating a sub-process using asyncio.create_subprocess_exec(), it returns a Process instance that has a stdout property. This property is intended to be an asyncio version of the stdout property of the Popen instance from the subprocess module.

An important aspect of Popen.stdout property is that you can close it. This is a signal to the sub-process that is generating output that it should cleanly terminate. This is a common pattern in processes used in shell pipelines. Indeed, the object located at Popen.stdout has a close() method. This pattern is demonstrated below:

import subprocess
proc = subprocess.Popen(["yes"], stdout=subprocess.PIPE) # start subprocess
data = proc.stdout.read(4096) # get data
proc.stdout.close() # signal to process to cleanly shutdown
proc.wait() # wait for shutdown

Unfortunately this pattern cannot be reproduced easily with the stdout property of the Process instance returned from asyncio.create_subprocess_exec() because stdout is an instance of StreamReader which does not have the close() method.

I propose adding a close() method to the StreamReader class so that asyncio version of the subprocess module may support this pattern of managing sub-processes. This change is consistent with the asyncio ecosystem as the companion StreamWriter class already has a close() method, along with other methods that expose its inner "transport" object. It's also trivial to implement, since it's essentially a wrapper method around the inner transport object's close() method.

Has this already been discussed elsewhere?

This is a minor feature, which does not need previous discussion elsewhere

Links to previous discussion of this feature:

No response

Linked PRs

• gh-130929

Start by locating the asyncio.StreamReader implementation and the subprocess stdout path used by asyncio.create_subprocess_exec(). Review linked PR gh-130929 for the work already under way, then verify that StreamReader-based subprocess output supports the requested close behavior.