Lib/multiprocessing/process.py

   1 #
   2 # Module providing the `Process` class which emulates `threading.Thread`
   3 #
   4 # multiprocessing/process.py
   5 #
   6 # Copyright (c) 2006-2008, R Oudkerk --- see COPYING.txt
   7 #
   8
   9 __all__ = ['Process', 'current_process', 'active_children']
  10
  11 #
  12 # Imports
  13 #
  14
  15 import os
  16 import sys
  17 import signal
  18 import itertools
  19
  20 #
  21 #
  22 #
  23
  24 try:
  25     ORIGINAL_DIR = os.path.abspath(os.getcwd())
  26 except OSError:
  27     ORIGINAL_DIR = None
  28
  29 #
  30 # Public functions
  31 #
  32
  33 def current_process():
  34     '''
  35     Return process object representing the current process
  36     '''
  37     return _current_process
  38
  39 def active_children():
  40     '''
  41     Return list of process objects corresponding to live child processes
  42     '''
  43     _cleanup()
  44     return list(_current_process._children)
  45
  46 #
  47 #
  48 #
  49
  50 def _cleanup():
  51     # check for processes which have finished
  52     for p in list(_current_process._children):
  53         if p._popen.poll() is not None:
  54             _current_process._children.discard(p)
  55
  56 #
  57 # The `Process` class
  58 #
  59
  60 class Process(object):
  61     '''
  62     Process objects represent activity that is run in a separate process
  63
  64     The class is analagous to `threading.Thread`
  65     '''
  66     _Popen = None
  67
  68     def __init__(self, group=None, target=None, name=None, args=(), kwargs={}):
  69         assert group is None, 'group argument must be None for now'
  70         count = _current_process._counter.next()
  71         self._identity = _current_process._identity + (count,)
  72         self._authkey = _current_process._authkey
  73         self._daemonic = _current_process._daemonic
  74         self._tempdir = _current_process._tempdir
  75         self._parent_pid = os.getpid()
  76         self._popen = None
  77         self._target = target
  78         self._args = tuple(args)
  79         self._kwargs = dict(kwargs)
  80         self._name = name or type(self).__name__ + '-' + \
  81                      ':'.join(str(i) for i in self._identity)
  82
  83     def run(self):
  84         '''
  85         Method to be run in sub-process; can be overridden in sub-class
  86         '''
  87         if self._target:
  88             self._target(*self._args, **self._kwargs)
  89
  90     def start(self):
  91         '''
  92         Start child process
  93         '''
  94         assert self._popen is None, 'cannot start a process twice'
  95         assert self._parent_pid == os.getpid(), \
  96                'can only start a process object created by current process'
  97         assert not _current_process._daemonic, \
  98                'daemonic processes are not allowed to have children'
  99         _cleanup()
 100         if self._Popen is not None:
 101             Popen = self._Popen
 102         else:
 103             from .forking import Popen
 104         self._popen = Popen(self)
 105         _current_process._children.add(self)
 106
 107     def terminate(self):
 108         '''
 109         Terminate process; sends SIGTERM signal or uses TerminateProcess()
 110         '''
 111         self._popen.terminate()
 112
 113     def join(self, timeout=None):
 114         '''
 115         Wait until child process terminates
 116         '''
 117         assert self._parent_pid == os.getpid(), 'can only join a child process'
 118         assert self._popen is not None, 'can only join a started process'
 119         res = self._popen.wait(timeout)
 120         if res is not None:
 121             _current_process._children.discard(self)
 122
 123     def is_alive(self):
 124         '''
 125         Return whether process is alive
 126         '''
 127         if self is _current_process:
 128             return True
 129         assert self._parent_pid == os.getpid(), 'can only test a child process'
 130         if self._popen is None:
 131             return False
 132         self._popen.poll()
 133         return self._popen.returncode is None
 134
 135     @property
 136     def name(self):
 137         return self._name
 138
 139     @name.setter
 140     def name(self, name):
 141         assert isinstance(name, basestring), 'name must be a string'
 142         self._name = name
 143
 144     @property
 145     def daemon(self):
 146         '''
 147         Return whether process is a daemon
 148         '''
 149         return self._daemonic
 150
 151     @daemon.setter
 152     def daemon(self, daemonic):
 153         '''
 154         Set whether process is a daemon
 155         '''
 156         assert self._popen is None, 'process has already started'
 157         self._daemonic = daemonic
 158
 159     @property
 160     def authkey(self):
 161         return self._authkey
 162
 163     @authkey.setter
 164     def authkey(self, authkey):
 165         '''
 166         Set authorization key of process
 167         '''
 168         self._authkey = AuthenticationString(authkey)
 169
 170     @property
 171     def exitcode(self):
 172         '''
 173         Return exit code of process or `None` if it has yet to stop
 174         '''
 175         if self._popen is None:
 176             return self._popen
 177         return self._popen.poll()
 178
 179     @property
 180     def ident(self):
 181         '''
 182         Return indentifier (PID) of process or `None` if it has yet to start
 183         '''
 184         if self is _current_process:
 185             return os.getpid()
 186         else:
 187             return self._popen and self._popen.pid
 188
 189     pid = ident
 190
 191     def __repr__(self):
 192         if self is _current_process:
 193             status = 'started'
 194         elif self._parent_pid != os.getpid():
 195             status = 'unknown'
 196         elif self._popen is None:
 197             status = 'initial'
 198         else:
 199             if self._popen.poll() is not None:
 200                 status = self.exitcode
 201             else:
 202                 status = 'started'
 203
 204         if type(status) is int:
 205             if status == 0:
 206                 status = 'stopped'
 207             else:
 208                 status = 'stopped[%s]' % _exitcode_to_name.get(status, status)
 209
 210         return '<%s(%s, %s%s)>' % (type(self).__name__, self._name,
 211                                    status, self._daemonic and ' daemon' or '')
 212
 213     ##
 214
 215     def _bootstrap(self):
 216         from . import util
 217         global _current_process
 218
 219         try:
 220             self._children = set()
 221             self._counter = itertools.count(1)
 222             try:
 223                 sys.stdin.close()
 224                 sys.stdin = open(os.devnull)
 225             except (OSError, ValueError):
 226                 pass
 227             _current_process = self
 228             util._finalizer_registry.clear()
 229             util._run_after_forkers()
 230             util.info('child process calling self.run()')
 231             try:
 232                 self.run()
 233                 exitcode = 0
 234             finally:
 235                 util._exit_function()
 236         except SystemExit, e:
 237             if not e.args:
 238                 exitcode = 1
 239             elif type(e.args[0]) is int:
 240                 exitcode = e.args[0]
 241             else:
 242                 sys.stderr.write(e.args[0] + '\n')
 243                 sys.stderr.flush()
 244                 exitcode = 1
 245         except:
 246             exitcode = 1
 247             import traceback
 248             sys.stderr.write('Process %s:\n' % self.name)
 249             sys.stderr.flush()
 250             traceback.print_exc()
 251
 252         util.info('process exiting with exitcode %d' % exitcode)
 253         return exitcode
 254
 255 #
 256 # We subclass bytes to avoid accidental transmission of auth keys over network
 257 #
 258
 259 class AuthenticationString(bytes):
 260     def __reduce__(self):
 261         from .forking import Popen
 262         if not Popen.thread_is_spawning():
 263             raise TypeError(
 264                 'Pickling an AuthenticationString object is '
 265                 'disallowed for security reasons'
 266                 )
 267         return AuthenticationString, (bytes(self),)
 268
 269 #
 270 # Create object representing the main process
 271 #
 272
 273 class _MainProcess(Process):
 274
 275     def __init__(self):
 276         self._identity = ()
 277         self._daemonic = False
 278         self._name = 'MainProcess'
 279         self._parent_pid = None
 280         self._popen = None
 281         self._counter = itertools.count(1)
 282         self._children = set()
 283         self._authkey = AuthenticationString(os.urandom(32))
 284         self._tempdir = None
 285
 286 _current_process = _MainProcess()
 287 del _MainProcess
 288
 289 #
 290 # Give names to some return codes
 291 #
 292
 293 _exitcode_to_name = {}
 294
 295 for name, signum in signal.__dict__.items():
 296     if name[:3]=='SIG' and '_' not in name:
 297         _exitcode_to_name[-signum] = name