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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.
"""An I/O event loop for non-blocking sockets.
Typical applications will use a single `IOLoop` object, in the
`IOLoop.instance` singleton. The `IOLoop.start` method should usually
be called at the end of the ``main()`` function. Atypical applications may
use more than one `IOLoop`, such as one `IOLoop` per thread, or per `unittest`
In addition to I/O events, the `IOLoop` can also schedule time-based events.
`IOLoop.add_timeout` is a non-blocking alternative to `time.sleep`.
from __future__ import absolute_import, division, with_statement
import datetime
import errno
import functools
import heapq
import logging
import os
import select
import sys
import thread
import threading
import time
import traceback
from tornado.concurrent import DummyFuture
from tornado.log import app_log, gen_log
from tornado import stack_context
from tornado.util import Configurable
import signal
except ImportError:
signal = None
from concurrent import futures
except ImportError:
futures = None
from import set_close_exec, Waker
class IOLoop(Configurable):
"""A level-triggered I/O loop.
We use epoll (Linux) or kqueue (BSD and Mac OS X; requires python
2.6+) if they are available, or else we fall back on select(). If
you are implementing a system that needs to handle thousands of
simultaneous connections, you should use a system that supports either
epoll or queue.
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
# Global lock for creating global IOLoop instance
_instance_lock = threading.Lock()
_current = threading.local()
def instance():
"""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(IOLoop, "_instance"):
with IOLoop._instance_lock:
if not hasattr(IOLoop, "_instance"):
# New instance after double check
IOLoop._instance = IOLoop()
return IOLoop._instance
def initialized():
"""Returns true if the singleton instance has been created."""
return hasattr(IOLoop, "_instance")
def install(self):
"""Installs this IOloop object as the singleton instance.
This is normally not necessary as `instance()` will create
an IOLoop on demand, but you may want to call `install` to use
a custom subclass of IOLoop.
assert not IOLoop.initialized()
IOLoop._instance = self
def current():
current = getattr(IOLoop._current, "instance", None)
if current is None:
raise ValueError("no current IOLoop")
return current
def make_current(self):
IOLoop._current.instance = self
def clear_current(self):
assert IOLoop._current.instance is self
IOLoop._current.instance = None
def configurable_base(cls):
return IOLoop
def configurable_default(cls):
if hasattr(select, "epoll") or sys.platform.startswith('linux'):
from tornado.platform.epoll import EPollIOLoop
return EPollIOLoop
except ImportError:
gen_log.warning("unable to import EPollIOLoop, falling back to SelectIOLoop")
if hasattr(select, "kqueue"):
# Python 2.6+ on BSD or Mac
from tornado.platform.kqueue import KQueueIOLoop
return KQueueIOLoop
from import SelectIOLoop
return SelectIOLoop
def initialize(self):
def close(self, all_fds=False):
"""Closes the IOLoop, freeing any resources used.
If ``all_fds`` is true, all file descriptors registered on the
IOLoop will be closed (not just the ones created by the IOLoop itself).
Many applications will only use a single IOLoop that runs for the
entire lifetime of the process. In that case closing the IOLoop
is not necessary since everything will be cleaned up when the
process exits. `IOLoop.close` is provided mainly for scenarios
such as unit tests, which create and destroy a large number of
An IOLoop must be completely stopped before it can be closed. This
means that `IOLoop.stop()` must be called *and* `IOLoop.start()` must
be allowed to return before attempting to call `IOLoop.close()`.
Therefore the call to `close` will usually appear just after
the call to `start` rather than near the call to `stop`.
raise NotImplementedError()
def add_handler(self, fd, handler, events):
"""Registers the given handler to receive the given events for fd."""
raise NotImplementedError()
def update_handler(self, fd, events):
"""Changes the events we listen for fd."""
raise NotImplementedError()
def remove_handler(self, fd):
"""Stop listening for events on fd."""
raise NotImplementedError()
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.
raise NotImplementedError()
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.
gen_log.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.
raise NotImplementedError()
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.
Note that even after `stop` has been called, the IOLoop is not
completely stopped until `IOLoop.start` has also returned.
raise NotImplementedError()
def time(self):
"""Returns the current time according to the IOLoop's clock.
The return value is a floating-point number relative to an
unspecified time in the past.
By default, the IOLoop's time function is `time.time`. However,
it may be configured to use e.g. `time.monotonic` instead.
Calls to `add_timeout` that pass a number instead of a
`datetime.timedelta` should use this function to compute the
appropriate time, so they can work no matter what time function
is chosen.
return time.time()
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.
``deadline`` may be a number denoting a time relative to
`IOLoop.time`, or a ``datetime.timedelta`` object for a
deadline relative to the current time.
Note that it is not safe to call `add_timeout` from other threads.
Instead, you must use `add_callback` to transfer control to the
IOLoop's thread, and then call `add_timeout` from there.
raise NotImplementedError()
def remove_timeout(self, timeout):
"""Cancels a pending timeout.
The argument is a handle as returned by add_timeout.
raise NotImplementedError()
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,
except from a signal handler. Note that this is the *only*
method in IOLoop that makes this thread-safety 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.
To add a callback from a signal handler, see
raise NotImplementedError()
def add_callback_from_signal(self, callback):
"""Calls the given callback on the next I/O loop iteration.
Safe for use from a Python signal handler; should not be used
Callbacks added with this method will be run without any
stack_context, to avoid picking up the context of the function
that was interrupted by the signal.
raise NotImplementedError()
if futures is not None:
_FUTURE_TYPES = (futures.Future, DummyFuture)
_FUTURE_TYPES = DummyFuture
def add_future(self, future, callback):
"""Schedules a callback on the IOLoop when the given future is finished.
The callback is invoked with one argument, the future.
assert isinstance(future, IOLoop._FUTURE_TYPES)
callback = stack_context.wrap(callback)
lambda future: self.add_callback(
functools.partial(callback, future)))
def _run_callback(self, callback):
"""Runs a callback with error handling.
For use in subclasses.
except Exception:
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.
app_log.error("Exception in callback %r", callback, exc_info=True)
class PollIOLoop(IOLoop):
"""Base class for IOLoops built around a select-like function.
For concrete implementations, see `tornado.platform.epoll.EPollIOLoop`
(Linux), `tornado.platform.kqueue.KQueueIOLoop` (BSD and Mac), or
`` (all platforms).
def initialize(self, impl, time_func=None):
super(PollIOLoop, self).initialize()
self._impl = impl
if hasattr(self._impl, 'fileno'):
self.time_func = time_func or time.time
self._handlers = {}
self._events = {}
self._callbacks = []
self._callback_lock = threading.Lock()
self._timeouts = []
self._running = False
self._stopped = False
self._thread_ident = None
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
self._waker = Waker()
lambda fd, events: self._waker.consume(),
def close(self, all_fds=False):
if all_fds:
for fd in self._handlers.keys()[:]:
except Exception:
gen_log.debug("error closing fd %s", fd, exc_info=True)
def add_handler(self, fd, handler, events):
self._handlers[fd] = stack_context.wrap(handler)
self._impl.register(fd, events | self.ERROR)
def update_handler(self, fd, events):
self._impl.modify(fd, events | self.ERROR)
def remove_handler(self, fd):
self._handlers.pop(fd, None)
self._events.pop(fd, None)
except (OSError, IOError):
gen_log.debug("Error deleting fd from IOLoop", exc_info=True)
def set_blocking_signal_threshold(self, seconds, action):
if not hasattr(signal, "setitimer"):
gen_log.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 start(self):
if not logging.getLogger().handlers:
# The IOLoop catches and logs exceptions, so it's
# important that log output be visible. However, python's
# default behavior for non-root loggers (prior to python
# 3.2) is to print an unhelpful "no handlers could be
# found" message rather than the actual log entry, so we
# must explicitly configure logging if we've made it this
# far without anything.
if self._stopped:
self._stopped = False
old_current = getattr(IOLoop._current, "instance", None)
IOLoop._current.instance = self
self._thread_ident = thread.get_ident()
self._running = True
# signal.set_wakeup_fd closes a race condition in event loops:
# a signal may arrive at the beginning of select/poll/etc
# before it goes into its interruptible sleep, so the signal
# will be consumed without waking the select. The solution is
# for the (C, synchronous) signal handler to write to a pipe,
# which will then be seen by select.
# In python's signal handling semantics, this only matters on the
# main thread (fortunately, set_wakeup_fd only works on the main
# thread and will raise a ValueError otherwise).
# If someone has already set a wakeup fd, we don't want to
# disturb it. This is an issue for twisted, which does its
# SIGCHILD processing in response to its own wakeup fd being
# written to. As long as the wakeup fd is registered on the IOLoop,
# the loop will still wake up and everything should work.
old_wakeup_fd = None
if hasattr(signal, 'set_wakeup_fd') and == 'posix':
# requires python 2.6+, unix. set_wakeup_fd exists but crashes
# the python process on windows.
old_wakeup_fd = signal.set_wakeup_fd(self._waker.write_fileno())
if old_wakeup_fd != -1:
# Already set, restore previous value. This is a little racy,
# but there's no clean get_wakeup_fd and in real use the
# IOLoop is just started once at the beginning.
old_wakeup_fd = None
except ValueError: # non-main thread
while True:
poll_timeout = 3600.0
# Prevent IO event starvation by delaying new callbacks
# to the next iteration of the event loop.
with self._callback_lock:
callbacks = self._callbacks
self._callbacks = []
for callback in callbacks:
if self._timeouts:
now = self.time()
while self._timeouts:
if self._timeouts[0].callback is None:
# the timeout was cancelled
elif self._timeouts[0].deadline <= now:
timeout = heapq.heappop(self._timeouts)
seconds = self._timeouts[0].deadline - now
poll_timeout = min(seconds, poll_timeout)
if self._callbacks:
# If any callbacks or timeouts called add_callback,
# we don't want to wait in poll() before we run them.
poll_timeout = 0.0
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 (OSError, IOError), e:
if e.args[0] == errno.EPIPE:
# Happens when the client closes the connection
app_log.error("Exception in I/O handler for fd %s",
fd, exc_info=True)
except Exception:
app_log.error("Exception in I/O handler for fd %s",
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)
IOLoop._current.instance = old_current
if old_wakeup_fd is not None:
def stop(self):
self._running = False
self._stopped = True
def time(self):
return self.time_func()
def add_timeout(self, deadline, callback):
timeout = _Timeout(deadline, stack_context.wrap(callback), self)
heapq.heappush(self._timeouts, timeout)
return timeout
def remove_timeout(self, timeout):
# Removing from a heap is complicated, so just leave the defunct
# timeout object in the queue (see discussion in
# If this turns out to be a problem, we could add a garbage
# collection pass whenever there are too many dead timeouts.
timeout.callback = None
def add_callback(self, callback):
with self._callback_lock:
list_empty = not self._callbacks
if list_empty and thread.get_ident() != self._thread_ident:
# If we're in the IOLoop's thread, we know it's not currently
# polling. If we're not, and we added the first callback to an
# empty list, we may need to wake it up (it may wake up on its
# own, but an occasional extra wake is harmless). Waking
# up a polling IOLoop is relatively expensive, so we try to
# avoid it when we can.
def add_callback_from_signal(self, callback):
with stack_context.NullContext():
if thread.get_ident() != self._thread_ident:
# if the signal is handled on another thread, we can add
# it normally (modulo the NullContext)
# If we're on the IOLoop's thread, we cannot use
# the regular add_callback because it may deadlock on
# _callback_lock. Blindly insert into self._callbacks.
# This is safe because the GIL makes list.append atomic.
# One subtlety is that if the signal interrupted the
# _callback_lock block in IOLoop.start, we may modify
# either the old or new version of self._callbacks,
# but either way will work.
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, io_loop):
if isinstance(deadline, (int, long, float)):
self.deadline = deadline
elif isinstance(deadline, datetime.timedelta):
self.deadline = io_loop.time() + _Timeout.timedelta_to_seconds(deadline)
raise TypeError("Unsupported deadline %r" % deadline)
self.callback = callback
def timedelta_to_seconds(td):
"""Equivalent to td.total_seconds() (introduced in python 2.7)."""
return (td.microseconds + (td.seconds + td.days * 24 * 3600) * 10 ** 6) / float(10 ** 6)
# Comparison methods to sort by deadline, with object id as a tiebreaker
# to guarantee a consistent ordering. The heapq module uses __le__
# in python2.5, and __lt__ in 2.6+ (sort() and most other comparisons
# use __lt__).
def __lt__(self, other):
return ((self.deadline, id(self)) <
(other.deadline, id(other)))
def __le__(self, other):
return ((self.deadline, id(self)) <=
(other.deadline, id(other)))
class PeriodicCallback(object):
"""Schedules the given callback to be called periodically.
The callback is called every callback_time milliseconds.
`start` must be called after the PeriodicCallback is created.
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
self._timeout = None
def start(self):
"""Starts the timer."""
self._running = True
self._next_timeout = self.io_loop.time()
def stop(self):
"""Stops the timer."""
self._running = False
if self._timeout is not None:
self._timeout = None
def _run(self):
if not self._running:
except Exception:
app_log.error("Error in periodic callback", exc_info=True)
def _schedule_next(self):
if self._running:
current_time = self.io_loop.time()
while self._next_timeout <= current_time:
self._next_timeout += self.callback_time / 1000.0
self._timeout = self.io_loop.add_timeout(self._next_timeout, self._run)
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