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GeezerVison is showing github.com — bpo-35537: subprocess can now use os.posix_spawnp by vstinner · Pull Request #11579 · python/cpython

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@vstinner

@vstinner vstinner commented Jan 16, 2019 •
edited by bedevere-bot
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The subprocess module can now use the os.posix_spawnp() function if
it is available to locate the program in the PATH.

https://bugs.python.org/issue35537

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@vstinner
bpo-35537: subprocess can now use os.posix_spawnp
e120153 
The subprocess module can now use the os.posix_spawnp() function if
it is available to locate the program in the PATH.
@vstinner vstinner added the skip news label Jan 16, 2019
@vstinner
vstinner requested a review from gpshead as a code owner January 16, 2019 14:07
@the-knights-who-say-ni the-knights-who-say-ni added the CLA signed label Jan 16, 2019
@bedevere-bot bedevere-bot added the awaiting merge label Jan 16, 2019
@vstinner
vstinner merged commit 0785889 into python:master Jan 16, 2019
@bedevere-bot bedevere-bot removed the awaiting merge label Jan 16, 2019
@vstinner
vstinner deleted the subprocess_spawnp branch January 16, 2019 14:26
@vstinner vstinner mentioned this pull request Jan 16, 2019
bpo-35537: subprocess can use posix_spawn with pipes #11575
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izbyshev
izbyshev reviewed Jan 16, 2019
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Comment thread Lib/subprocess.py

self.pid = os.posix_spawn(executable, args, env, **kwargs)
if _HAVE_POSIX_SPAWNP:
self.pid = os.posix_spawnp(executable, args, env, **kwargs)

@izbyshev izbyshev Jan 16, 2019

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Please keep in mind that _posixsubprocess is likely to use a different algorithm for searching in PATH compared to posix_spawnp implementations (and, moreover, posix_spawnp implementations differ between libcs and even between versions of the same libc). For example, musl uses execvpe as a "backend" for posix_spawnp, which skips only 3 kinds of errors, while _posixsubprocess skips all errors. Also, EACCES is treated in a special way by both glibc and musl.

Also, the default PATH if the environment variable is not set is likely to differ (e.g., glibc uses /bin:/usr/bin, musl uses /usr/local/bin:/bin:/usr/bin, and Python uses :/bin:/usr/bin).

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@vstinner vstinner Jan 16, 2019

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"... glibc uses /bin:/usr/bin ... and Python uses :/bin:/usr/bin"

Oh. ":" at the start of posixpath.defpath is surprising. Is it a bug? What's the point of putting an empty string in the list of default search paths? It doesn't help to locate an executable...

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@izbyshev izbyshev Jan 16, 2019

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It's not a bug: empty entries in PATH mean "the current directory". See also NOTES in man execvp about glibc dropping this empty entry.

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@vstinner vstinner Jan 16, 2019

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I created https://bugs.python.org/issue35755 to propose to remove it :-)

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@vstinner vstinner mentioned this pull request Jan 16, 2019
Revert "bpo-35537: subprocess can now use os.posix_spawnp (GH-11579)" #11582
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@vstinner

vstinner commented Jan 16, 2019

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I'm not sure that the exact list of errors catched or nor by subprocess when locating the executable is a major blocker issue, but I didn't notice that subprocess build a list of executable using the PATH computed from its env argument. Using the env argument is a major difference. The devil is in the details...

I'm no longer sure that using posix_spawnp() in subprocess is appropriate. In case of doubt, I prefer to revert this change to have more time to decide what is the best option. I wrote PR #11582 to revert this change.
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vstinner added a commit that referenced this pull request Jan 16, 2019
@vstinner
Revert "bpo-35537: subprocess can now use os.posix_spawnp (GH-11579)" (…
8c34956 
…GH-11582)

This reverts commit 0785889.
@izbyshev izbyshev mentioned this pull request Feb 18, 2019
bpo-35537: Change subprocess to use posix_spawnp instead of posix_spawn #11917
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@gpshead gpshead Awaiting requested review from gpshead
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@izbyshev izbyshev izbyshev left review comments
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4 participants

@vstinner @izbyshev @the-knights-who-say-ni @bedevere-bot
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