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# Copyright (c) 2010 Nicira Networks
#
# 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 logging
import select
import ovs.timeval
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 select.error, e:
# XXX rate-limit
error, msg = e
if error != errno.EINTR:
logging.error("poll: %s" % e[1])
finally:
self.__reset()
def __log_wakeup(self, events):
if not events:
logging.debug("%d-ms timeout" % self.timeout)
else:
for fd, revents in events:
if revents != 0:
s = ""
if revents & select.POLLIN:
s += "[POLLIN]"
if revents & select.POLLOUT:
s += "[POLLOUT]"
if revents & select.POLLERR:
s += "[POLLERR]"
if revents & select.POLLHUP:
s += "[POLLHUP]"
if revents & select.POLLNVAL:
s += "[POLLNVAL]"
logging.debug("%s on fd %d" % (s, fd))
def __reset(self):
self.poll = select.poll()
self.timeout = -1
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