[New-bugs-announce] [issue24763] asyncio.BaseSubprocessTransport triggers an unavoidable ResourceWarning if process doesn't start

[Martin Richard]

New submission from Martin Richard:

An exception can be raised in SubprocessTransport.__init__() from SubprocessTransport._start() - for instance because an exception is raised in the preexec_fn callback.

In this case, the calling function never gets a reference to the transport object, and cannot close the transport. Hence, when the object is deleted, an "unclosed transport" ResourceWarning is always triggered.

Here is a test case showing this behavior:
import asyncio

loop = asyncio.get_event_loop()
try:
    loop.run_until_complete(asyncio.create_subprocess_exec('/doesntexist'))
except FileNotFoundError:
    pass
finally:
    loop.close()


I propose the attached patch as a solution, which call SubprocessTransport.close() when an exception is raised in SubprocessTransport._start() in the constructor.

----------
components: asyncio
files: transport_close_when_exception_init.patch
keywords: patch
messages: 247746
nosy: gvanrossum, haypo, martius, yselivanov
priority: normal
severity: normal
status: open
title: asyncio.BaseSubprocessTransport triggers an unavoidable ResourceWarning if process doesn't start
type: resource usage
versions: Python 3.4, Python 3.5
Added file: http://bugs.python.org/file40082/transport_close_when_exception_init.patch

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<http://bugs.python.org/issue24763>
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