Source code for tornado.ioloop

#!/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.

"""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`
case.

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`.
"""

import errno
import heapq
import os
import logging
import select
import time
import traceback

from tornado import stack_context
from tornado.escape import utf8

try:
    import signal
except ImportError:
    signal = None

try:
    import fcntl
except ImportError:
    if os.name == 'nt':
        from tornado import win32_support
        from tornado import win32_support as fcntl
    else:
        raise

[docs]class IOLoop(object): """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: try: connection, address = sock.accept() except socket.error, e: if e.args[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() if hasattr(self._impl, 'fileno'): self._set_close_exec(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 os.name != 'nt': r, w = os.pipe() self._set_nonblocking(r) self._set_nonblocking(w) self._set_close_exec(r) self._set_close_exec(w) self._waker_reader = os.fdopen(r, "rb", 0) self._waker_writer = os.fdopen(w, "wb", 0) else: self._waker_reader = self._waker_writer = win32_support.Pipe() r = self._waker_writer.reader_fd self.add_handler(r, self._read_waker, self.READ) @classmethod
[docs] 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
@classmethod
[docs] def initialized(cls): """Returns true if the singleton instance has been created.""" return hasattr(cls, "_instance")
[docs] 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)
[docs] def update_handler(self, fd, events): """Changes the events we listen for fd.""" self._impl.modify(fd, events | self.ERROR)
[docs] 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, IOError): logging.debug("Error deleting fd from IOLoop", exc_info=True)
[docs] 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 platform. 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") return self._blocking_signal_threshold = seconds if seconds is not None: signal.signal(signal.SIGALRM, action if action is not None else signal.SIG_DFL)
[docs] 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)
[docs] 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', self._blocking_signal_threshold, ''.join(traceback.format_stack(frame)))
[docs] 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 return 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: self._run_callback(callback) if self._callbacks: poll_timeout = 0.0 if self._timeouts: now = time.time() while self._timeouts: if self._timeouts[0].callback is None: # the timeout was cancelled heapq.heappop(self._timeouts) elif self._timeouts[0].deadline <= now: timeout = heapq.heappop(self._timeouts) self._run_callback(timeout.callback) else: milliseconds = self._timeouts[0].deadline - now poll_timeout = min(milliseconds, poll_timeout) break if not self._running: break 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) try: 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)): continue else: raise if self._blocking_signal_threshold is not None: signal.setitimer(signal.ITIMER_REAL, 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 self._events.update(event_pairs) while self._events: fd, events = self._events.popitem() try: self._handlers[fd](fd, events) except (KeyboardInterrupt, SystemExit): raise except (OSError, IOError), e: if e.args[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) # 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)
[docs] 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() 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 self._wake()
[docs] def running(self): """Returns true if this IOLoop is currently running.""" return self._running
[docs] 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)) heapq.heappush(self._timeouts, timeout) return timeout
[docs] def remove_timeout(self, timeout): """Cancels a pending timeout. The argument is a handle as returned by add_timeout. """ # Removing from a heap is complicated, so just leave the defunct # timeout object in the queue (see discussion in # http://docs.python.org/library/heapq.html). # 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
[docs] 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. """ if not self._callbacks: self._wake() self._callbacks.append(stack_context.wrap(callback))
def _wake(self): try: self._waker_writer.write(utf8("x")) except IOError: pass def _run_callback(self, callback): try: callback() except (KeyboardInterrupt, SystemExit): raise except: self.handle_callback_exception(callback)
[docs] 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): try: while True: result = self._waker_reader.read() if not result: break 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) 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 # 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)))
[docs]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
[docs] def start(self): """Starts the timer.""" self._running = True timeout = time.time() + self.callback_time / 1000.0 self.io_loop.add_timeout(timeout, self._run)
[docs] def stop(self): """Stops the timer.""" self._running = False
def _run(self): if not self._running: return try: self.callback() except (KeyboardInterrupt, SystemExit): raise except: logging.error("Error in periodic callback", exc_info=True) if self._running: self.start()
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 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.unregister(fd) 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: kevents.append(select.kevent( fd, filter=select.KQ_FILTER_WRITE, flags=flags)) if events & IOLoop.READ or not kevents: # Always read when there is not a write kevents.append(select.kevent( 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 if kevent.filter == select.KQ_FILTER_READ: events[fd] = events.get(fd, 0) | IOLoop.READ if kevent.filter == select.KQ_FILTER_WRITE: if kevent.flags & select.KQ_EV_EOF: # If an asynchronous connection is refused, kqueue # returns a write event with the EOF flag set. # Turn this into an error for consistency with the # other IOLoop implementations. # Note that for read events, EOF may be returned before # all data has been consumed from the socket buffer, # so we only check for EOF on write events. events[fd] = IOLoop.ERROR else: 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: self.error_fds.add(fd) # 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. self.read_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 elif hasattr(select, "kqueue"): # Python 2.6+ on BSD or Mac _poll = _KQueue 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