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ioloop.py
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ioloop.py
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#!/usr/bin/env python
#
# Copyright 2009 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.
"""A level-triggered I/O loop for non-blocking sockets."""
import bisect
import errno
import fcntl
import logging
import os
import select
import time
class IOLoop(object):
"""A level-triggered I/O loop.
We use epoll if it is available, or else we fall back on select(). If
you are implementing a system that needs to handle 1000s of simultaneous
connections, you should use Linux and either compile our epoll module or
use Python 2.6+ to get epoll support.
Example usage for a simple TCP server:
import errno
import functools
import ioloop
import socket
def connection_ready(sock, fd, events):
while True:
try:
connection, address = sock.accept()
except socket.error, e:
if e[0] not in (errno.EWOULDBLOCK, errno.EAGAIN):
raise
return
connection.setblocking(0)
handle_connection(connection, address)
sock = socket.socket(socket.AF_INET, socket.SOCK_STREAM, 0)
sock.setsockopt(socket.SOL_SOCKET, socket.SO_REUSEADDR, 1)
sock.setblocking(0)
sock.bind(("", port))
sock.listen(128)
io_loop = ioloop.IOLoop.instance()
callback = functools.partial(connection_ready, sock)
io_loop.add_handler(sock.fileno(), callback, io_loop.READ)
io_loop.start()
"""
# Constants from the epoll module
_EPOLLIN = 0x001
_EPOLLPRI = 0x002
_EPOLLOUT = 0x004
_EPOLLERR = 0x008
_EPOLLHUP = 0x010
_EPOLLRDHUP = 0x2000
_EPOLLONESHOT = (1 << 30)
_EPOLLET = (1 << 31)
# Our events map exactly to the epoll events
NONE = 0
READ = _EPOLLIN
WRITE = _EPOLLOUT
ERROR = _EPOLLERR | _EPOLLHUP | _EPOLLRDHUP
def __init__(self, impl=None):
self._impl = impl or _poll()
self._handlers = {}
self._events = {}
self._callbacks = set()
self._timeouts = []
self._running = False
# Create a pipe that we send bogus data to when we want to wake
# the I/O loop when it is idle
r, w = os.pipe()
self._set_nonblocking(r)
self._set_nonblocking(w)
self._waker_reader = os.fdopen(r, "r", 0)
self._waker_writer = os.fdopen(w, "w", 0)
self.add_handler(r, self._read_waker, self.WRITE)
@classmethod
def instance(cls):
"""Returns a global IOLoop instance.
Most single-threaded applications have a single, global IOLoop.
Use this method instead of passing around IOLoop instances
throughout your code.
A common pattern for classes that depend on IOLoops is to use
a default argument to enable programs with multiple IOLoops
but not require the argument for simpler applications:
class MyClass(object):
def __init__(self, io_loop=None):
self.io_loop = io_loop or IOLoop.instance()
"""
if not hasattr(cls, "_instance"):
cls._instance = cls()
return cls._instance
def add_handler(self, fd, handler, events):
"""Registers the given handler to receive the given events for fd."""
self._handlers[fd] = handler
self._impl.register(fd, events | self.ERROR)
def update_handler(self, fd, events):
"""Changes the events we listen for fd."""
self._impl.modify(fd, events | self.ERROR)
def remove_handler(self, fd):
"""Stop listening for events on fd."""
self._handlers.pop(fd, None)
self._events.pop(fd, None)
try:
self._impl.unregister(fd)
except OSError:
logging.debug("Error deleting fd from IOLoop", exc_info=True)
def start(self):
"""Starts the I/O loop.
The loop will run until one of the I/O handlers calls stop(), which
will make the loop stop after the current event iteration completes.
"""
self._running = True
while True:
# Never use an infinite timeout here - it can stall epoll
poll_timeout = 0.2
# Prevent IO event starvation by delaying new callbacks
# to the next iteration of the event loop.
callbacks = list(self._callbacks)
for callback in callbacks:
# A callback can add or remove other callbacks
if callback in self._callbacks:
self._callbacks.remove(callback)
self._run_callback(callback)
if self._callbacks:
poll_timeout = 0.0
if self._timeouts:
now = time.time()
while self._timeouts and self._timeouts[0].deadline <= now:
timeout = self._timeouts.pop(0)
self._run_callback(timeout.callback)
if self._timeouts:
milliseconds = self._timeouts[0].deadline - now
poll_timeout = min(milliseconds, poll_timeout)
if not self._running:
break
try:
event_pairs = self._impl.poll(poll_timeout)
except Exception, e:
if e.args == (4, "Interrupted system call"):
logging.warning("Interrupted system call", exc_info=1)
continue
else:
raise
# Pop one fd at a time from the set of pending fds and run
# its handler. Since that handler may perform actions on
# other file descriptors, there may be reentrant calls to
# this IOLoop that update self._events
self._events.update(event_pairs)
while self._events:
fd, events = self._events.popitem()
try:
self._handlers[fd](fd, events)
except KeyboardInterrupt:
raise
except OSError, e:
if e[0] == errno.EPIPE:
# Happens when the client closes the connection
pass
else:
logging.error("Exception in I/O handler for fd %d",
fd, exc_info=True)
except:
logging.error("Exception in I/O handler for fd %d",
fd, exc_info=True)
def stop(self):
"""Stop the loop after the current event loop iteration is complete."""
self._running = False
self._wake()
def running(self):
"""Returns true if this IOLoop is currently running."""
return self._running
def add_timeout(self, deadline, callback):
"""Calls the given callback at the time deadline from the I/O loop."""
timeout = _Timeout(deadline, callback)
bisect.insort(self._timeouts, timeout)
return timeout
def remove_timeout(self, timeout):
self._timeouts.remove(timeout)
def add_callback(self, callback):
"""Calls the given callback on the next I/O loop iteration."""
self._callbacks.add(callback)
self._wake()
def remove_callback(self, callback):
"""Removes the given callback from the next I/O loop iteration."""
self._callbacks.pop(callback)
def _wake(self):
try:
self._waker_writer.write("x")
except IOError:
pass
def _run_callback(self, callback):
try:
callback()
except (KeyboardInterrupt, SystemExit):
raise
except:
logging.error("Exception in callback %r", callback, exc_info=True)
def _read_waker(self, fd, events):
try:
while True:
self._waker_reader.read()
except IOError:
pass
def _set_nonblocking(self, fd):
flags = fcntl.fcntl(fd, fcntl.F_GETFL)
fcntl.fcntl(fd, fcntl.F_SETFL, flags | os.O_NONBLOCK)
class _Timeout(object):
"""An IOLoop timeout, a UNIX timestamp and a callback"""
def __init__(self, deadline, callback):
self.deadline = deadline
self.callback = callback
def __cmp__(self, other):
return cmp((self.deadline, id(self.callback)),
(other.deadline, id(other.callback)))
class _EPoll(object):
"""An epoll-based event loop using our C module for Python 2.5 systems"""
_EPOLL_CTL_ADD = 1
_EPOLL_CTL_DEL = 2
_EPOLL_CTL_MOD = 3
def __init__(self):
self._epoll_fd = epoll.epoll_create()
def register(self, fd, events):
epoll.epoll_ctl(self._epoll_fd, self._EPOLL_CTL_ADD, fd, events)
def modify(self, fd, events):
epoll.epoll_ctl(self._epoll_fd, self._EPOLL_CTL_MOD, fd, events)
def unregister(self, fd):
epoll.epoll_ctl(self._epoll_fd, self._EPOLL_CTL_DEL, fd, 0)
def poll(self, timeout):
return epoll.epoll_wait(self._epoll_fd, int(timeout * 1000))
class _Select(object):
"""A simple, select()-based IOLoop implementation for non-Linux systems"""
def __init__(self):
self.read_fds = set()
self.write_fds = set()
self.error_fds = set()
self.fd_sets = (self.read_fds, self.write_fds, self.error_fds)
def register(self, fd, events):
if events & IOLoop.READ: self.read_fds.add(fd)
if events & IOLoop.WRITE: self.write_fds.add(fd)
if events & IOLoop.ERROR: self.error_fds.add(fd)
def modify(self, fd, events):
self.unregister(fd)
self.register(fd, events)
def unregister(self, fd):
self.read_fds.discard(fd)
self.write_fds.discard(fd)
self.error_fds.discard(fd)
def poll(self, timeout):
readable, writeable, errors = select.select(
self.read_fds, self.write_fds, self.error_fds, timeout)
events = {}
for fd in readable:
events[fd] = events.get(fd, 0) | IOLoop.READ
for fd in writeable:
events[fd] = events.get(fd, 0) | IOLoop.WRITE
for fd in errors:
events[fd] = events.get(fd, 0) | IOLoop.ERROR
return events.items()
# Choose a poll implementation. Use epoll if it is available, fall back to
# select() for non-Linux platforms
if hasattr(select, "epoll"):
# Python 2.6+ on Linux
_poll = select.epoll
else:
try:
# Linux systems with our C module installed
import epoll
_poll = _EPoll
except:
# All other systems
import sys
if "linux" in sys.platform:
logging.warning("epoll module not found; using select()")
_poll = _Select