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poller.py
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# Copyright (c) 2010, 2015 Nicira, Inc. # # 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. import errno import os import select import socket import sys import ovs.timeval import ovs.vlog if sys.platform == "win32": import ovs.winutils as winutils try: import ssl except ImportError: ssl = None try: from eventlet import patcher as eventlet_patcher def _using_eventlet_green_select(): return eventlet_patcher.is_monkey_patched(select) except: eventlet_patcher = None def _using_eventlet_green_select(): return False try: from gevent import monkey as gevent_monkey except: gevent_monkey = None vlog = ovs.vlog.Vlog("poller") POLLIN = 0x001 POLLOUT = 0x004 POLLERR = 0x008 POLLHUP = 0x010 POLLNVAL = 0x020 # eventlet/gevent doesn't support select.poll. If select.poll is used, # python interpreter is blocked as a whole instead of switching from the # current thread that is about to block to other runnable thread. # So emulate select.poll by select.select because using python means that # performance isn't so important. class _SelectSelect(object): """ select.poll emulation by using select.select. Only register and poll are needed at the moment. """ def __init__(self): self.rlist = [] self.wlist = [] self.xlist = [] def register(self, fd, events): if isinstance(fd, socket.socket): fd = fd.fileno() if ssl and isinstance(fd, ssl.SSLSocket): fd = fd.fileno() if sys.platform != 'win32': # Skip this on Windows, it also register events assert isinstance(fd, int) if events & POLLIN: self.rlist.append(fd) events &= ~POLLIN if events & POLLOUT: self.wlist.append(fd) events &= ~POLLOUT if events: self.xlist.append(fd) def poll(self, timeout): # XXX workaround a bug in eventlet # see https://github.com/eventlet/eventlet/pull/25 if timeout == 0 and _using_eventlet_green_select(): timeout = 0.1 if sys.platform == 'win32': events = self.rlist + self.wlist + self.xlist if not events: return [] if len(events) > winutils.win32event.MAXIMUM_WAIT_OBJECTS: raise WindowsError("Cannot handle more than maximum wait" "objects\n") # win32event.INFINITE timeout is -1 # timeout must be an int number, expressed in ms if timeout == 0.1: timeout = 100 else: timeout = int(timeout) # Wait until any of the events is set to signaled try: retval = winutils.win32event.WaitForMultipleObjects( events, False, # Wait all timeout) except winutils.pywintypes.error: return [(0, POLLERR)] if retval == winutils.winerror.WAIT_TIMEOUT: return [] if events[retval] in self.rlist: revent = POLLIN elif events[retval] in self.wlist: revent = POLLOUT else: revent = POLLERR return [(events[retval], revent)] else: if timeout == -1: # epoll uses -1 for infinite timeout, select uses None. timeout = None else: timeout = float(timeout) / 1000 rlist, wlist, xlist = select.select(self.rlist, self.wlist, self.xlist, timeout) events_dict = {} for fd in rlist: events_dict[fd] = events_dict.get(fd, 0) | POLLIN for fd in wlist: events_dict[fd] = events_dict.get(fd, 0) | POLLOUT for fd in xlist: events_dict[fd] = events_dict.get(fd, 0) | (POLLERR | POLLHUP | POLLNVAL) return list(events_dict.items()) SelectPoll = _SelectSelect # If eventlet/gevent isn't used, we can use select.poll by replacing # _SelectPoll with select.poll class # _SelectPoll = select.poll class Poller(object): """High-level wrapper around the "poll" system call. Intended usage is for the program's main loop to go about its business servicing whatever events it needs to. Then, when it runs out of immediate tasks, it calls each subordinate module or object's "wait" function, which in turn calls one (or more) of the functions Poller.fd_wait(), Poller.immediate_wake(), and Poller.timer_wait() to register to be awakened when the appropriate event occurs. Then the main loop calls Poller.block(), which blocks until one of the registered events happens.""" def __init__(self): self.__reset() def fd_wait(self, fd, events): """Registers 'fd' as waiting for the specified 'events' (which should be select.POLLIN or select.POLLOUT or their bitwise-OR). The following call to self.block() will wake up when 'fd' becomes ready for one or more of the requested events. The event registration is one-shot: only the following call to self.block() is affected. The event will need to be re-registered after self.block() is called if it is to persist. 'fd' may be an integer file descriptor or an object with a fileno() method that returns an integer file descriptor.""" self.poll.register(fd, events) def __timer_wait(self, msec): if self.timeout < 0 or msec < self.timeout: self.timeout = msec def timer_wait(self, msec): """Causes the following call to self.block() to block for no more than 'msec' milliseconds. If 'msec' is nonpositive, the following call to self.block() will not block at all. The timer registration is one-shot: only the following call to self.block() is affected. The timer will need to be re-registered after self.block() is called if it is to persist.""" if msec <= 0: self.immediate_wake() else: self.__timer_wait(msec) def timer_wait_until(self, msec): """Causes the following call to self.block() to wake up when the current time, as returned by ovs.timeval.msec(), reaches 'msec' or later. If 'msec' is earlier than the current time, the following call to self.block() will not block at all. The timer registration is one-shot: only the following call to self.block() is affected. The timer will need to be re-registered after self.block() is called if it is to persist.""" now = ovs.timeval.msec() if msec <= now: self.immediate_wake() else: self.__timer_wait(msec - now) def immediate_wake(self): """Causes the following call to self.block() to wake up immediately, without blocking.""" self.timeout = 0 def block(self): """Blocks until one or more of the events registered with self.fd_wait() occurs, or until the minimum duration registered with self.timer_wait() elapses, or not at all if self.immediate_wake() has been called.""" try: try: events = self.poll.poll(self.timeout) self.__log_wakeup(events) except OSError as e: """ On Windows, the select function from poll raises OSError exception if the polled array is empty.""" if e.errno != errno.EINTR: vlog.err("poll: %s" % os.strerror(e.errno)) except select.error as e: # XXX rate-limit error, msg = e if error != errno.EINTR: vlog.err("poll: %s" % e[1]) finally: self.__reset() def __log_wakeup(self, events): if not events: vlog.dbg("%d-ms timeout" % self.timeout) else: for fd, revents in events: if revents != 0: s = "" if revents & POLLIN: s += "[POLLIN]" if revents & POLLOUT: s += "[POLLOUT]" if revents & POLLERR: s += "[POLLERR]" if revents & POLLHUP: s += "[POLLHUP]" if revents & POLLNVAL: s += "[POLLNVAL]" vlog.dbg("%s on fd %d" % (s, fd)) def __reset(self): self.poll = SelectPoll() self.timeout = -1 def get_system_poll(): """Returns the original select.poll() object. If select.poll is monkey patched by eventlet or gevent library, it gets the original select.poll and returns an object of it using the eventlet.patcher.original/gevent.monkey.get_original functions. As a last resort, if there is any exception it returns the SelectPoll() object. """ try: if _using_eventlet_green_select(): _system_poll = eventlet_patcher.original("select").poll elif gevent_monkey and gevent_monkey.is_object_patched( 'select', 'poll'): _system_poll = gevent_monkey.get_original('select', 'poll') else: _system_poll = select.poll except: _system_poll = SelectPoll return _system_poll()