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subprocess2.py
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subprocess2.py
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# coding=utf8
# Copyright (c) 2011 The Chromium Authors. All rights reserved.
# Use of this source code is governed by a BSD-style license that can be
# found in the LICENSE file.
"""Collection of subprocess wrapper functions.
In theory you shouldn't need anything else in subprocess, or this module failed.
"""
from __future__ import with_statement
import errno
import logging
import os
import subprocess
import sys
import tempfile
import time
import threading
# Constants forwarded from subprocess.
PIPE = subprocess.PIPE
STDOUT = subprocess.STDOUT
# Sends stdout or stderr to os.devnull.
VOID = object()
# Error code when a process was killed because it timed out.
TIMED_OUT = -2001
# Globals.
# Set to True if you somehow need to disable this hack.
SUBPROCESS_CLEANUP_HACKED = False
class CalledProcessError(subprocess.CalledProcessError):
"""Augment the standard exception with more data."""
def __init__(self, returncode, cmd, cwd, stdout, stderr):
super(CalledProcessError, self).__init__(returncode, cmd)
self.stdout = stdout
self.stderr = stderr
self.cwd = cwd
def __str__(self):
out = 'Command %s returned non-zero exit status %s' % (
' '.join(self.cmd), self.returncode)
if self.cwd:
out += ' in ' + self.cwd
return '\n'.join(filter(None, (out, self.stdout, self.stderr)))
class CygwinRebaseError(CalledProcessError):
"""Occurs when cygwin's fork() emulation fails due to rebased dll."""
## Utility functions
def kill_pid(pid):
"""Kills a process by its process id."""
try:
# Unable to import 'module'
# pylint: disable=E1101,F0401
import signal
return os.kill(pid, signal.SIGKILL)
except ImportError:
pass
def kill_win(process):
"""Kills a process with its windows handle.
Has no effect on other platforms.
"""
try:
# Unable to import 'module'
# pylint: disable=F0401
import win32process
# Access to a protected member _handle of a client class
# pylint: disable=W0212
return win32process.TerminateProcess(process._handle, -1)
except ImportError:
pass
def add_kill():
"""Adds kill() method to subprocess.Popen for python <2.6"""
if hasattr(subprocess.Popen, 'kill'):
return
if sys.platform == 'win32':
subprocess.Popen.kill = kill_win
else:
subprocess.Popen.kill = lambda process: kill_pid(process.pid)
def hack_subprocess():
"""subprocess functions may throw exceptions when used in multiple threads.
See http://bugs.python.org/issue1731717 for more information.
"""
global SUBPROCESS_CLEANUP_HACKED
if not SUBPROCESS_CLEANUP_HACKED and threading.activeCount() != 1:
# Only hack if there is ever multiple threads.
# There is no point to leak with only one thread.
subprocess._cleanup = lambda: None
SUBPROCESS_CLEANUP_HACKED = True
def get_english_env(env):
"""Forces LANG and/or LANGUAGE to be English.
Forces encoding to utf-8 for subprocesses.
Returns None if it is unnecessary.
"""
if sys.platform == 'win32':
return None
env = env or os.environ
# Test if it is necessary at all.
is_english = lambda name: env.get(name, 'en').startswith('en')
if is_english('LANG') and is_english('LANGUAGE'):
return None
# Requires modifications.
env = env.copy()
def fix_lang(name):
if not is_english(name):
env[name] = 'en_US.UTF-8'
fix_lang('LANG')
fix_lang('LANGUAGE')
return env
def Popen(args, **kwargs):
"""Wraps subprocess.Popen() with various workarounds.
Returns a subprocess.Popen object.
- Forces English output since it's easier to parse the stdout if it is always
in English.
- Sets shell=True on windows by default. You can override this by forcing
shell parameter to a value.
- Adds support for VOID to not buffer when not needed.
Note: Popen() can throw OSError when cwd or args[0] doesn't exist. Translate
exceptions generated by cygwin when it fails trying to emulate fork().
"""
# Make sure we hack subprocess if necessary.
hack_subprocess()
add_kill()
env = get_english_env(kwargs.get('env'))
if env:
kwargs['env'] = env
if kwargs.get('shell') is None:
# *Sigh*: Windows needs shell=True, or else it won't search %PATH% for the
# executable, but shell=True makes subprocess on Linux fail when it's called
# with a list because it only tries to execute the first item in the list.
kwargs['shell'] = bool(sys.platform=='win32')
tmp_str = ' '.join(args)
if kwargs.get('cwd', None):
tmp_str += '; cwd=%s' % kwargs['cwd']
logging.debug(tmp_str)
def fix(stream):
if kwargs.get(stream) in (VOID, os.devnull):
# Replaces VOID with handle to /dev/null.
# Create a temporary file to workaround python's deadlock.
# http://docs.python.org/library/subprocess.html#subprocess.Popen.wait
# When the pipe fills up, it will deadlock this process. Using a real file
# works around that issue.
kwargs[stream] = open(os.devnull, 'w')
fix('stdout')
fix('stderr')
try:
return subprocess.Popen(args, **kwargs)
except OSError, e:
if e.errno == errno.EAGAIN and sys.platform == 'cygwin':
# Convert fork() emulation failure into a CygwinRebaseError().
raise CygwinRebaseError(
e.errno,
args,
kwargs.get('cwd'),
None,
'Visit '
'http://code.google.com/p/chromium/wiki/CygwinDllRemappingFailure to '
'learn how to fix this error; you need to rebase your cygwin dlls')
# Popen() can throw OSError when cwd or args[0] doesn't exist. Let it go
# through
raise
def communicate(args, timeout=None, **kwargs):
"""Wraps subprocess.Popen().communicate().
Returns ((stdout, stderr), returncode).
- The process will be killed after |timeout| seconds and returncode set to
TIMED_OUT.
- Automatically passes stdin content as input so do not specify stdin=PIPE.
"""
stdin = kwargs.pop('stdin', None)
if stdin is not None:
if stdin is VOID:
kwargs['stdin'] = open(os.devnull, 'r')
stdin = None
else:
assert isinstance(stdin, basestring)
# When stdin is passed as an argument, use it as the actual input data and
# set the Popen() parameter accordingly.
kwargs['stdin'] = PIPE
if not timeout:
# Normal workflow.
proc = Popen(args, **kwargs)
if stdin is not None:
return proc.communicate(stdin), proc.returncode
else:
return proc.communicate(), proc.returncode
# Create a temporary file to workaround python's deadlock.
# http://docs.python.org/library/subprocess.html#subprocess.Popen.wait
# When the pipe fills up, it will deadlock this process. Using a real file
# works around that issue.
with tempfile.TemporaryFile() as buff:
start = time.time()
kwargs['stdout'] = buff
proc = Popen(args, **kwargs)
if stdin is not None:
proc.stdin.write(stdin)
while proc.returncode is None:
proc.poll()
if timeout and (time.time() - start) > timeout:
proc.kill()
proc.wait()
# It's -9 on linux and 1 on Windows. Standardize to TIMED_OUT.
proc.returncode = TIMED_OUT
time.sleep(0.001)
# Now that the process died, reset the cursor and read the file.
buff.seek(0)
out = [buff.read(), None]
return out, proc.returncode
def call(args, **kwargs):
"""Emulates subprocess.call().
Automatically convert stdout=PIPE or stderr=PIPE to VOID.
In no case they can be returned since no code path raises
subprocess2.CalledProcessError.
"""
if kwargs.get('stdout') == PIPE:
kwargs['stdout'] = VOID
if kwargs.get('stderr') == PIPE:
kwargs['stderr'] = VOID
return communicate(args, **kwargs)[1]
def check_call_out(args, **kwargs):
"""Improved version of subprocess.check_call().
Returns (stdout, stderr), unlike subprocess.check_call().
"""
out, returncode = communicate(args, **kwargs)
if returncode:
raise CalledProcessError(
returncode, args, kwargs.get('cwd'), out[0], out[1])
return out
def check_call(args, **kwargs):
"""Emulate subprocess.check_call()."""
check_call_out(args, **kwargs)
return 0
def capture(args, **kwargs):
"""Captures stdout of a process call and returns it.
Returns stdout.
- Discards returncode.
- Blocks stdin by default if not specified since no output will be visible.
"""
kwargs.setdefault('stdin', VOID)
# Like check_output, deny the caller from using stdout arg.
return communicate(args, stdout=PIPE, **kwargs)[0][0]
def check_output(args, **kwargs):
"""Emulates subprocess.check_output().
Captures stdout of a process call and returns stdout only.
- Throws if return code is not 0.
- Works even prior to python 2.7.
- Blocks stdin by default if not specified since no output will be visible.
- As per doc, "The stdout argument is not allowed as it is used internally."
"""
kwargs.setdefault('stdin', VOID)
return check_call_out(args, stdout=PIPE, **kwargs)[0]