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@adiroiban adiroiban/spawn.py
Last active Aug 29, 2015

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Spawn with timeout and with the same behaviour across operating systems
"""
Execute external processes.
"""
import os
from twisted.internet import reactor, error, defer
from twisted.internet.protocol import ProcessProtocol
SPAWN_PROCESS_TIMEOUT = 5
class ProcessTimedOut(error.ConnectionLost):
"""
Process was killed as is took to much to execute.
"""
class ProcessSpawnFailed(error.ConnectionLost):
"""
Failed to spawn the process.
"""
def __init__(self, message='Failed to launch the process'):
self.message = message
def __str__(self):
return self.message
class ExecuteWithTimeout(ProcessProtocol):
"""
Allow command to execute, ignoring stdout and stderrr.
Result is returned via the `deferred`.
* Success if command exit code is 0.
* failure if command exit code is not 0.
* ProcessTimedOut failure when command takes more than `timeout`
to execute.
* ProcessSpawnFailed failure when failed to launch the executable
"""
def __init__(self, deferred, scheduler, timeout):
self._timeout = timeout
self._deferred = deferred
self._scheduler = scheduler
self._killed = False
self._timeout_call = None
self._first_err_received = False
self._spawn_failure = None
def errReceived(self, data):
"""
Data was received on standard error.
"""
# To detect spawn errors on Unix, we check the first error message
# and see if it is from execvpe.
if os.name != 'posix':
return
if self._first_err_received:
return
self._first_err_received = True
if not data.startswith('Upon execvpe'):
return
# Keep last error line as error message.
self._spawn_failure = to_unicode(data.splitlines()[-1])
def connectionMade(self):
"""
Called when process was started.
"""
def kill_if_alive():
try:
self.transport.signalProcess('KILL')
except error.ProcessExitedAlready:
pass
else:
self._killed = True
self.transport.loseConnection()
self._timeout_call = self._scheduler.callLater(
self._timeout, kill_if_alive)
def processEnded(self, reason):
"""
Called when process terminates.
"""
exit_code = reason.value.exitCode
try:
self._timeout_call.cancel()
except error.AlreadyCalled:
pass
# Sometimes, even when we kill a process, GetExitCodeProcess
# still returns a zero exit status.
# http://stackoverflow.com/q/2061735/539264
if self._killed and exit_code == 0:
exit_code = 1
if exit_code == 0:
self._deferred.callback(None)
elif self._spawn_failure:
self._deferred.errback(ProcessSpawnFailed(self._spawn_failure))
elif self._killed:
self._deferred.errback(ProcessTimedOut())
else:
self._deferred.errback(reason)
def get_process_exit_code(
command, arguments, reactor=reactor, timeout=SPAWN_PROCESS_TIMEOUT):
"""
Execute `command` with `arguments` and return the exit code.
"""
deferred = defer.Deferred()
protocol = ExecuteWithTimeout(deferred, scheduler=reactor, timeout=timeout)
final_command = command.encode('utf-8')
arguments = [a.encode('utf-8') for a in arguments]
final_arguments = (final_command,) + tuple(arguments)
try:
reactor.spawnProcess(protocol, final_command, final_arguments)
except OSError, error:
deferred.errback(ProcessSpawnFailed(unicode(error)))
return deferred
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