Source code for tornado.process

#!/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
#
#     http://www.apache.org/licenses/LICENSE-2.0
#
# 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, including both forking
the server into multiple processes and managing subprocesses.
"""

from __future__ import absolute_import, division, print_function, with_statement

import errno
import multiprocessing
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.platform.auto import set_close_exec
from tornado import stack_context

try:
    long  # py2
except NameError:
    long = int  # py3


[docs]def cpu_count(): """Returns the number of processors on this machine.""" try: return multiprocessing.cpu_count() except NotImplementedError: pass try: return os.sysconf("SC_NPROCESSORS_CONF") except ValueError: pass gen_log.error("Could not detect number of processors; assuming 1") return 1
def _reseed_random(): if 'random' not in sys.modules: return 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. try: seed = long(hexlify(os.urandom(16)), 16) except NotImplementedError: seed = int(time.time() * 1000) ^ os.getpid() random.seed(seed) def _pipe_cloexec(): r, w = os.pipe() set_close_exec(r) set_close_exec(w) return r, w _task_id = None
[docs]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 exception. """ 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()") gen_log.info("Starting %d processes", num_processes) children = {} def start_child(i): pid = os.fork() if pid == 0: # child process _reseed_random() global _task_id _task_id = i return i else: 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: try: pid, status = os.wait() except OSError as e: if e.errno == errno.EINTR: continue raise if pid not in children: continue 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: gen_log.info("child %d (pid %d) exited normally", id, pid) continue 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). sys.exit(0)
[docs]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
[docs]class Subprocess(object): """Wraps ``subprocess.Popen`` with IOStream support. The constructor is the same as ``subprocess.Popen`` with the following additions: * ``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) or ioloop.IOLoop.current() to_close = [] if kwargs.get('stdin') is Subprocess.STREAM: in_r, in_w = _pipe_cloexec() kwargs['stdin'] = in_r to_close.append(in_r) self.stdin = PipeIOStream(in_w, io_loop=self.io_loop) if kwargs.get('stdout') is Subprocess.STREAM: out_r, out_w = _pipe_cloexec() kwargs['stdout'] = out_w to_close.append(out_w) self.stdout = PipeIOStream(out_r, io_loop=self.io_loop) if kwargs.get('stderr') is Subprocess.STREAM: err_r, err_w = _pipe_cloexec() kwargs['stderr'] = err_w to_close.append(err_w) self.stderr = PipeIOStream(err_r, io_loop=self.io_loop) self.proc = subprocess.Popen(*args, **kwargs) for fd in to_close: os.close(fd) 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
[docs] 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.initialize(self.io_loop) Subprocess._waiting[self.pid] = self Subprocess._try_cleanup_process(self.pid)
@classmethod
[docs] 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: return if io_loop is None: io_loop = ioloop.IOLoop.current() cls._old_sigchld = signal.signal( signal.SIGCHLD, lambda sig, frame: io_loop.add_callback_from_signal(cls._cleanup)) cls._initialized = True
@classmethod
[docs] def uninitialize(cls): """Removes the ``SIGCHILD`` handler.""" if not cls._initialized: return signal.signal(signal.SIGCHLD, cls._old_sigchld) cls._initialized = False
@classmethod def _cleanup(cls): for pid in list(cls._waiting.keys()): # make a copy cls._try_cleanup_process(pid) @classmethod def _try_cleanup_process(cls, pid): try: ret_pid, status = os.waitpid(pid, os.WNOHANG) except OSError as e: if e.args[0] == errno.ECHILD: return if ret_pid == 0: return assert ret_pid == pid subproc = cls._waiting.pop(pid) subproc.io_loop.add_callback_from_signal( subproc._set_returncode, status) def _set_returncode(self, status): if os.WIFSIGNALED(status): self.returncode = -os.WTERMSIG(status) else: assert os.WIFEXITED(status) self.returncode = os.WEXITSTATUS(status) if self._exit_callback: callback = self._exit_callback self._exit_callback = None callback(self.returncode)

This Page