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#!/usr/bin/env python
# Copyright 2011 Facebook
# Licensed under the Apache License, Version 2.0 (the "License"); you may
# not use this file except in compliance with the License. You may obtain
# a copy of the License at
# Unless required by applicable law or agreed to in writing, software
# distributed under the License is distributed on an "AS IS" BASIS, WITHOUT
# WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the
# License for the specific language governing permissions and limitations
# under the License.
"""Utilities for working with multiple processes."""
from __future__ import absolute_import, division, with_statement
import errno
import functools
import os
import signal
import subprocess
import sys
import time
from binascii import hexlify
from tornado import ioloop
from tornado.iostream import PipeIOStream
from tornado.log import gen_log
from tornado import stack_context
import multiprocessing # Python 2.6+
except ImportError:
multiprocessing = None
def cpu_count():
"""Returns the number of processors on this machine."""
if multiprocessing is not None:
return multiprocessing.cpu_count()
except NotImplementedError:
return os.sysconf("SC_NPROCESSORS_CONF")
except ValueError:
gen_log.error("Could not detect number of processors; assuming 1")
return 1
def _reseed_random():
if 'random' not in sys.modules:
import random
# If os.urandom is available, this method does the same thing as
# random.seed (at least as of python 2.6). If os.urandom is not
# available, we mix in the pid in addition to a timestamp.
seed = long(hexlify(os.urandom(16)), 16)
except NotImplementedError:
seed = int(time.time() * 1000) ^ os.getpid()
_task_id = None
def fork_processes(num_processes, max_restarts=100):
"""Starts multiple worker processes.
If ``num_processes`` is None or <= 0, we detect the number of cores
available on this machine and fork that number of child
processes. If ``num_processes`` is given and > 0, we fork that
specific number of sub-processes.
Since we use processes and not threads, there is no shared memory
between any server code.
Note that multiple processes are not compatible with the autoreload
module (or the debug=True option to `tornado.web.Application`).
When using multiple processes, no IOLoops can be created or
referenced until after the call to ``fork_processes``.
In each child process, ``fork_processes`` returns its *task id*, a
number between 0 and ``num_processes``. Processes that exit
abnormally (due to a signal or non-zero exit status) are restarted
with the same id (up to ``max_restarts`` times). In the parent
process, ``fork_processes`` returns None if all child processes
have exited normally, but will otherwise only exit by throwing an
global _task_id
assert _task_id is None
if num_processes is None or num_processes <= 0:
num_processes = cpu_count()
if ioloop.IOLoop.initialized():
raise RuntimeError("Cannot run in multiple processes: IOLoop instance "
"has already been initialized. You cannot call "
"IOLoop.instance() before calling start_processes()")"Starting %d processes", num_processes)
children = {}
def start_child(i):
pid = os.fork()
if pid == 0:
# child process
global _task_id
_task_id = i
return i
children[pid] = i
return None
for i in range(num_processes):
id = start_child(i)
if id is not None:
return id
num_restarts = 0
while children:
pid, status = os.wait()
except OSError, e:
if e.errno == errno.EINTR:
if pid not in children:
id = children.pop(pid)
if os.WIFSIGNALED(status):
gen_log.warning("child %d (pid %d) killed by signal %d, restarting",
id, pid, os.WTERMSIG(status))
elif os.WEXITSTATUS(status) != 0:
gen_log.warning("child %d (pid %d) exited with status %d, restarting",
id, pid, os.WEXITSTATUS(status))
else:"child %d (pid %d) exited normally", id, pid)
num_restarts += 1
if num_restarts > max_restarts:
raise RuntimeError("Too many child restarts, giving up")
new_id = start_child(id)
if new_id is not None:
return new_id
# All child processes exited cleanly, so exit the master process
# instead of just returning to right after the call to
# fork_processes (which will probably just start up another IOLoop
# unless the caller checks the return value).
def task_id():
"""Returns the current task id, if any.
Returns None if this process was not created by `fork_processes`.
global _task_id
return _task_id
class Subprocess(object):
"""Wraps ``subprocess.Popen`` with IOStream support.
The constructor is the same as ``subprocess.Popen`` with the following
* ``stdin``, ``stdout``, and ``stderr`` may have the value
`tornado.process.Subprocess.STREAM`, which will make the corresponding
attribute of the resulting Subprocess a `PipeIOStream`.
* A new keyword argument ``io_loop`` may be used to pass in an IOLoop.
STREAM = object()
_initialized = False
_waiting = {}
def __init__(self, *args, **kwargs):
self.io_loop = kwargs.pop('io_loop', None)
to_close = []
if kwargs.get('stdin') is Subprocess.STREAM:
in_r, in_w = os.pipe()
kwargs['stdin'] = in_r
self.stdin = PipeIOStream(in_w, io_loop=self.io_loop)
if kwargs.get('stdout') is Subprocess.STREAM:
out_r, out_w = os.pipe()
kwargs['stdout'] = out_w
self.stdout = PipeIOStream(out_r, io_loop=self.io_loop)
if kwargs.get('stderr') is Subprocess.STREAM:
err_r, err_w = os.pipe()
kwargs['stderr'] = err_w
self.stdout = PipeIOStream(err_r, io_loop=self.io_loop)
self.proc = subprocess.Popen(*args, **kwargs)
for fd in to_close:
for attr in ['stdin', 'stdout', 'stderr', 'pid']:
if not hasattr(self, attr): # don't clobber streams set above
setattr(self, attr, getattr(self.proc, attr))
self._exit_callback = None
self.returncode = None
def set_exit_callback(self, callback):
"""Runs ``callback`` when this process exits.
The callback takes one argument, the return code of the process.
This method uses a ``SIGCHILD`` handler, which is a global setting
and may conflict if you have other libraries trying to handle the
same signal. If you are using more than one ``IOLoop`` it may
be necessary to call `Subprocess.initialize` first to designate
one ``IOLoop`` to run the signal handlers.
In many cases a close callback on the stdout or stderr streams
can be used as an alternative to an exit callback if the
signal handler is causing a problem.
self._exit_callback = stack_context.wrap(callback)
Subprocess._waiting[] = self
def initialize(cls, io_loop=None):
"""Initializes the ``SIGCHILD`` handler.
The signal handler is run on an IOLoop to avoid locking issues.
Note that the IOLoop used for signal handling need not be the
same one used by individual Subprocess objects (as long as the
IOLoops are each running in separate threads).
if cls._initialized:
if io_loop is None:
io_loop = ioloop.IOLoop.instance()
cls._old_sigchld = signal.signal(
lambda sig, frame: io_loop.add_callback_from_signal(cls._cleanup))
cls._initialized = True
def uninitialize(cls):
"""Removes the ``SIGCHILD`` handler."""
if not cls._initialized:
signal.signal(signal.SIGCHLD, cls._old_sigchld)
cls._initialized = False
def _cleanup(cls):
for pid in cls._waiting.keys():
def _try_cleanup_process(cls, pid):
ret_pid, status = os.waitpid(pid, os.WNOHANG)
except OSError, e:
if e.args[0] == errno.ECHILD:
if ret_pid == 0:
assert ret_pid == pid
subproc = cls._waiting.pop(pid)
functools.partial(subproc._set_returncode, status))
def _set_returncode(self, status):
if os.WIFSIGNALED(status):
self.returncode = -os.WTERMSIG(status)
assert os.WIFEXITED(status)
self.returncode = os.WEXITSTATUS(status)
if self._exit_callback:
callback = self._exit_callback
self._exit_callback = None
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