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bpo-35537: use os.posix_spawn in subprocess #11242

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bpo-35537: use os.posix_spawn in subprocess #11242

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6726dac
use os.posix_spawn in subprocess
nanjekyejoannah Dec 18, 2018
f7df9e8
use os.posix_spawn in subprocess
nanjekyejoannah Dec 20, 2018
c05a078
📜🤖 Added by blurb_it.
blurb-it[bot] Dec 20, 2018
1b9357a
Fix test deciding if posix_spawn() can be used
vstinner Dec 20, 2018
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19 changes: 19 additions & 0 deletions Lib/subprocess.py
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Original file line number Diff line number Diff line change
Expand Up @@ -1390,6 +1390,10 @@ def _get_handles(self, stdin, stdout, stderr):
errread, errwrite)


def _posix_spawn(self, args, executable):
"""Execute program using os.posix_spawn()."""
self.pid = os.posix_spawn(executable, args, os.environ)

def _execute_child(self, args, executable, preexec_fn, close_fds,
pass_fds, cwd, env,
startupinfo, creationflags, shell,
Expand All @@ -1414,6 +1418,21 @@ def _execute_child(self, args, executable, preexec_fn, close_fds,

if executable is None:
executable = args[0]

if (os.path.dirname(executable)
and preexec_fn is None
and not close_fds
and not pass_fds
and cwd is None
and env is None
and p2cread == p2cwrite == -1
and c2pread == c2pwrite == -1
and errread == errwrite == -1
and not restore_signals
and not start_new_session):
self._posix_spawn(args, executable)
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Checking self.std* is still not enough. Those fields are for the parent's ends of pipes, but if a caller redirects to a descriptor, there is no such end. For example, subprocess.call(['/bin/sleep', '1000'], stdout=fd, close_fds=False, restore_signals=False) doesn't work properly.

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@izbyshev: Oh right! I fixed the test: test (p2cread, p2cwrite, c2pread, c2pwrite, errread, errwrite) instead of (self.stdin, self.stdout, self.stderr). Is it better now?

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Yes, LGTM now.

There is another potential problem with posix_spawn: asynchronous error notification. _posixsubprocess uses a pipe to notify the parent about all errors up to and including execve errors, so its style is synchronous. Glibc and musl use the pipe-based notification too, but they are not required to do that, and I don't know what other implementations do.

return

orig_executable = executable

# For transferring possible exec failure from child to parent.
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1 change: 1 addition & 0 deletions Misc/NEWS.d/next/Library/2018-12-20-16-24-51.bpo-35537.z4E7aA.rst
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@@ -0,0 +1 @@
subprocess.Popen can now use posix_spawn() in some cases.