Edit File: poll.py
# -*- coding: utf-8 -*- # Copyright (C) 2013 Sebastian Wiesner <lunaryorn@gmail.com> # This library is free software; you can redistribute it and/or modify it # under the terms of the GNU Lesser General Public License as published by the # Free Software Foundation; either version 2.1 of the License, or (at your # option) any later version. # This library is distributed in the hope that it will be useful, but WITHOUT # ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or # FITNESS FOR A PARTICULAR PURPOSE. See the GNU Lesser General Public License # for more details. # You should have received a copy of the GNU Lesser General Public License # along with this library; if not, write to the Free Software Foundation, # Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA """ pyudev._os.poll =============== Operating system interface for pyudev. .. moduleauthor:: Sebastian Wiesner <lunaryorn@gmail.com> """ from __future__ import absolute_import from __future__ import division from __future__ import print_function from __future__ import unicode_literals import select from pyudev._util import eintr_retry_call class Poll(object): """A poll object. This object essentially provides a more convenient interface around :class:`select.poll`. """ _EVENT_TO_MASK = {'r': select.POLLIN, 'w': select.POLLOUT} @staticmethod def _has_event(events, event): return events & event != 0 @classmethod def for_events(cls, *events): """Listen for ``events``. ``events`` is a list of ``(fd, event)`` pairs, where ``fd`` is a file descriptor or file object and ``event`` either ``'r'`` or ``'w'``. If ``r``, listen for whether that is ready to be read. If ``w``, listen for whether the channel is ready to be written to. """ notifier = eintr_retry_call(select.poll) for fd, event in events: mask = cls._EVENT_TO_MASK.get(event) if not mask: raise ValueError('Unknown event type: {0!r}'.format(event)) notifier.register(fd, mask) return cls(notifier) def __init__(self, notifier): """Create a poll object for the given ``notifier``. ``notifier`` is the :class:`select.poll` object wrapped by the new poll object. """ self._notifier = notifier def poll(self, timeout=None): """Poll for events. ``timeout`` is an integer specifying how long to wait for events (in milliseconds). If omitted, ``None`` or negative, wait until an event occurs. Return a list of all events that occurred before ``timeout``, where each event is a pair ``(fd, event)``. ``fd`` is the integral file descriptor, and ``event`` a string indicating the event type. If ``'r'``, there is data to read from ``fd``. If ``'w'``, ``fd`` is writable without blocking now. If ``'h'``, the file descriptor was hung up (i.e. the remote side of a pipe was closed). """ # Return a list to allow clients to determine whether there are any # events at all with a simple truthiness test. return list(self._parse_events(eintr_retry_call(self._notifier.poll, timeout))) def _parse_events(self, events): """Parse ``events``. ``events`` is a list of events as returned by :meth:`select.poll.poll()`. Yield all parsed events. """ for fd, event_mask in events: if self._has_event(event_mask, select.POLLNVAL): raise IOError('File descriptor not open: {0!r}'.format(fd)) elif self._has_event(event_mask, select.POLLERR): raise IOError('Error while polling fd: {0!r}'.format(fd)) if self._has_event(event_mask, select.POLLIN): yield fd, 'r' if self._has_event(event_mask, select.POLLOUT): yield fd, 'w' if self._has_event(event_mask, select.POLLHUP): yield fd, 'h'