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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
# 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 os
import logging
import select
import time
import traceback
from tornado import stack_context
import signal
except ImportError:
signal = None
import fcntl
except ImportError:
if == 'nt':
from tornado import win32_support
from tornado import win32_support as fcntl
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:
connection, address = sock.accept()
except socket.error, e:
if e.args[0] not in (errno.EWOULDBLOCK, errno.EAGAIN):
handle_connection(connection, address)
sock = socket.socket(socket.AF_INET, socket.SOCK_STREAM, 0)
sock.setsockopt(socket.SOL_SOCKET, socket.SO_REUSEADDR, 1)
sock.bind(("", port))
io_loop = ioloop.IOLoop.instance()
callback = functools.partial(connection_ready, sock)
io_loop.add_handler(sock.fileno(), callback, io_loop.READ)
# 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
def __init__(self, impl=None):
self._impl = impl or _poll()
if hasattr(self._impl, 'fileno'):
self._handlers = {}
self._events = {}
self._callbacks = []
self._timeouts = []
self._running = False
self._stopped = False
self._blocking_signal_threshold = None
# Create a pipe that we send bogus data to when we want to wake
# the I/O loop when it is idle
if != 'nt':
r, w = os.pipe()
self._waker_reader = os.fdopen(r, "rb", 0)
self._waker_writer = os.fdopen(w, "wb", 0)
self._waker_reader = self._waker_writer = win32_support.Pipe()
r = self._waker_writer.reader_fd
self.add_handler(r, self._read_waker, self.READ)
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 initialized(cls):
return hasattr(cls, "_instance")
def add_handler(self, fd, handler, events):
"""Registers the given handler to receive the given events for fd."""
self._handlers[fd] = stack_context.wrap(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)
except (OSError, IOError):
logging.debug("Error deleting fd from IOLoop", exc_info=True)
def set_blocking_signal_threshold(self, seconds, action):
"""Sends a signal if the ioloop is blocked for more than s seconds.
Pass seconds=None to disable. Requires python 2.6 on a unixy
The action parameter is a python signal handler. Read the
documentation for the python 'signal' module for more information.
If action is None, the process will be killed if it is blocked for
too long.
if not hasattr(signal, "setitimer"):
logging.error("set_blocking_signal_threshold requires a signal module "
"with the setitimer method")
self._blocking_signal_threshold = seconds
if seconds is not None:
action if action is not None else signal.SIG_DFL)
def set_blocking_log_threshold(self, seconds):
"""Logs a stack trace if the ioloop is blocked for more than s seconds.
Equivalent to set_blocking_signal_threshold(seconds, self.log_stack)
self.set_blocking_signal_threshold(seconds, self.log_stack)
def log_stack(self, signal, frame):
"""Signal handler to log the stack trace of the current thread.
For use with set_blocking_signal_threshold.
logging.warning('IOLoop blocked for %f seconds in\n%s',
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.
if self._stopped:
self._stopped = False
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 = self._callbacks
self._callbacks = []
for callback in callbacks:
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)
if self._timeouts:
milliseconds = self._timeouts[0].deadline - now
poll_timeout = min(milliseconds, poll_timeout)
if not self._running:
if self._blocking_signal_threshold is not None:
# clear alarm so it doesn't fire while poll is waiting for
# events.
signal.setitimer(signal.ITIMER_REAL, 0, 0)
event_pairs = self._impl.poll(poll_timeout)
except Exception, e:
# Depending on python version and IOLoop implementation,
# different exception types may be thrown and there are
# two ways EINTR might be signaled:
# * e.errno == errno.EINTR
# * e.args is like (errno.EINTR, 'Interrupted system call')
if (getattr(e, 'errno', None) == errno.EINTR or
(isinstance(getattr(e, 'args', None), tuple) and
len(e.args) == 2 and e.args[0] == errno.EINTR)):
if self._blocking_signal_threshold is not None:
self._blocking_signal_threshold, 0)
# 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
while self._events:
fd, events = self._events.popitem()
self._handlers[fd](fd, events)
except (KeyboardInterrupt, SystemExit):
except (OSError, IOError), e:
if e.args[0] == errno.EPIPE:
# Happens when the client closes the connection
logging.error("Exception in I/O handler for fd %d",
fd, exc_info=True)
logging.error("Exception in I/O handler for fd %d",
fd, exc_info=True)
# reset the stopped flag so another start/stop pair can be issued
self._stopped = False
if self._blocking_signal_threshold is not None:
signal.setitimer(signal.ITIMER_REAL, 0, 0)
def stop(self):
"""Stop the loop after the current event loop iteration is complete.
If the event loop is not currently running, the next call to start()
will return immediately.
To use asynchronous methods from otherwise-synchronous code (such as
unit tests), you can start and stop the event loop like this:
ioloop = IOLoop()
async_method(ioloop=ioloop, callback=ioloop.stop)
ioloop.start() will return after async_method has run its callback,
whether that callback was invoked before or after ioloop.start.
self._running = False
self._stopped = True
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.
Returns a handle that may be passed to remove_timeout to cancel.
timeout = _Timeout(deadline, stack_context.wrap(callback))
bisect.insort(self._timeouts, timeout)
return timeout
def remove_timeout(self, timeout):
"""Cancels a pending timeout.
The argument is a handle as returned by add_timeout.
def add_callback(self, callback):
"""Calls the given callback on the next I/O loop iteration.
It is safe to call this method from any thread at any time.
Note that this is the *only* method in IOLoop that makes this
guarantee; all other interaction with the IOLoop must be done
from that IOLoop's thread. add_callback() may be used to transfer
control from other threads to the IOLoop's thread.
def _wake(self):
except IOError:
def _run_callback(self, callback):
except (KeyboardInterrupt, SystemExit):
def handle_callback_exception(self, callback):
"""This method is called whenever a callback run by the IOLoop
throws an exception.
By default simply logs the exception as an error. Subclasses
may override this method to customize reporting of exceptions.
The exception itself is not passed explicitly, but is available
in sys.exc_info.
logging.error("Exception in callback %r", callback, exc_info=True)
def _read_waker(self, fd, events):
while True:
except IOError:
def _set_nonblocking(self, fd):
flags = fcntl.fcntl(fd, fcntl.F_GETFL)
fcntl.fcntl(fd, fcntl.F_SETFL, flags | os.O_NONBLOCK)
def _set_close_exec(self, fd):
flags = fcntl.fcntl(fd, fcntl.F_GETFD)
fcntl.fcntl(fd, fcntl.F_SETFD, flags | fcntl.FD_CLOEXEC)
class _Timeout(object):
"""An IOLoop timeout, a UNIX timestamp and a callback"""
# Reduce memory overhead when there are lots of pending callbacks
__slots__ = ['deadline', '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 PeriodicCallback(object):
"""Schedules the given callback to be called periodically.
The callback is called every callback_time milliseconds.
def __init__(self, callback, callback_time, io_loop=None):
self.callback = callback
self.callback_time = callback_time
self.io_loop = io_loop or IOLoop.instance()
self._running = False
def start(self):
self._running = True
timeout = time.time() + self.callback_time / 1000.0
self.io_loop.add_timeout(timeout, self._run)
def stop(self):
self._running = False
def _run(self):
if not self._running: return
except (KeyboardInterrupt, SystemExit):
logging.error("Error in periodic callback", exc_info=True)
if self._running:
class _EPoll(object):
"""An epoll-based event loop using our C module for Python 2.5 systems"""
def __init__(self):
self._epoll_fd = epoll.epoll_create()
def fileno(self):
return self._epoll_fd
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 _KQueue(object):
"""A kqueue-based event loop for BSD/Mac systems."""
def __init__(self):
self._kqueue = select.kqueue()
self._active = {}
def fileno(self):
return self._kqueue.fileno()
def register(self, fd, events):
self._control(fd, events, select.KQ_EV_ADD)
self._active[fd] = events
def modify(self, fd, events):
self.register(fd, events)
def unregister(self, fd):
events = self._active.pop(fd)
self._control(fd, events, select.KQ_EV_DELETE)
def _control(self, fd, events, flags):
kevents = []
if events & IOLoop.WRITE:
fd, filter=select.KQ_FILTER_WRITE, flags=flags))
if events & IOLoop.READ or not kevents:
# Always read when there is not a write
fd, filter=select.KQ_FILTER_READ, flags=flags))
# Even though control() takes a list, it seems to return EINVAL
# on Mac OS X (10.6) when there is more than one event in the list.
for kevent in kevents:
self._kqueue.control([kevent], 0)
def poll(self, timeout):
kevents = self._kqueue.control(None, 1000, timeout)
events = {}
for kevent in kevents:
fd = kevent.ident
flags = 0
if kevent.filter == select.KQ_FILTER_READ:
events[fd] = events.get(fd, 0) | IOLoop.READ
if kevent.filter == select.KQ_FILTER_WRITE:
events[fd] = events.get(fd, 0) | IOLoop.WRITE
if kevent.flags & select.KQ_EV_ERROR:
events[fd] = events.get(fd, 0) | IOLoop.ERROR
return events.items()
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:
# Closed connections are reported as errors by epoll and kqueue,
# but as zero-byte reads by select, so when errors are requested
# we need to listen for both read and error.
def modify(self, fd, events):
self.register(fd, events)
def unregister(self, fd):
def poll(self, timeout):
readable, writeable, errors =
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
elif hasattr(select, "kqueue"):
# Python 2.6+ on BSD or Mac
_poll = _KQueue
# Linux systems with our C module installed
import epoll
_poll = _EPoll
# All other systems
import sys
if "linux" in sys.platform:
logging.warning("epoll module not found; using select()")
_poll = _Select
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