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Filename : pollreactor.py
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# Copyright (c) Twisted Matrix Laboratories.
# See LICENSE for details.

"""
A poll() based implementation of the twisted main loop.

To install the event loop (and you should do this before any connections,
listeners or connectors are added)::

    from twisted.internet import pollreactor
    pollreactor.install()
"""


# System imports
import errno
from select import (
    POLLERR,
    POLLHUP,
    POLLIN,
    POLLNVAL,
    POLLOUT,
    error as SelectError,
    poll,
)

from zope.interface import implementer

from twisted.internet import posixbase
from twisted.internet.interfaces import IReactorFDSet

# Twisted imports
from twisted.python import log


@implementer(IReactorFDSet)
class PollReactor(posixbase.PosixReactorBase, posixbase._PollLikeMixin):
    """
    A reactor that uses poll(2).

    @ivar _poller: A L{select.poll} which will be used to check for I/O
        readiness.

    @ivar _selectables: A dictionary mapping integer file descriptors to
        instances of L{FileDescriptor} which have been registered with the
        reactor.  All L{FileDescriptor}s which are currently receiving read or
        write readiness notifications will be present as values in this
        dictionary.

    @ivar _reads: A dictionary mapping integer file descriptors to arbitrary
        values (this is essentially a set).  Keys in this dictionary will be
        registered with C{_poller} for read readiness notifications which will
        be dispatched to the corresponding L{FileDescriptor} instances in
        C{_selectables}.

    @ivar _writes: A dictionary mapping integer file descriptors to arbitrary
        values (this is essentially a set).  Keys in this dictionary will be
        registered with C{_poller} for write readiness notifications which will
        be dispatched to the corresponding L{FileDescriptor} instances in
        C{_selectables}.
    """

    _POLL_DISCONNECTED = POLLHUP | POLLERR | POLLNVAL
    _POLL_IN = POLLIN
    _POLL_OUT = POLLOUT

    def __init__(self):
        """
        Initialize polling object, file descriptor tracking dictionaries, and
        the base class.
        """
        self._poller = poll()
        self._selectables = {}
        self._reads = {}
        self._writes = {}
        posixbase.PosixReactorBase.__init__(self)

    def _updateRegistration(self, fd):
        """Register/unregister an fd with the poller."""
        try:
            self._poller.unregister(fd)
        except KeyError:
            pass

        mask = 0
        if fd in self._reads:
            mask = mask | POLLIN
        if fd in self._writes:
            mask = mask | POLLOUT
        if mask != 0:
            self._poller.register(fd, mask)
        else:
            if fd in self._selectables:
                del self._selectables[fd]

    def _dictRemove(self, selectable, mdict):
        try:
            # the easy way
            fd = selectable.fileno()
            # make sure the fd is actually real.  In some situations we can get
            # -1 here.
            mdict[fd]
        except BaseException:
            # the hard way: necessary because fileno() may disappear at any
            # moment, thanks to python's underlying sockets impl
            for fd, fdes in self._selectables.items():
                if selectable is fdes:
                    break
            else:
                # Hmm, maybe not the right course of action?  This method can't
                # fail, because it happens inside error detection...
                return
        if fd in mdict:
            del mdict[fd]
            self._updateRegistration(fd)

    def addReader(self, reader):
        """Add a FileDescriptor for notification of data available to read."""
        fd = reader.fileno()
        if fd not in self._reads:
            self._selectables[fd] = reader
            self._reads[fd] = 1
            self._updateRegistration(fd)

    def addWriter(self, writer):
        """Add a FileDescriptor for notification of data available to write."""
        fd = writer.fileno()
        if fd not in self._writes:
            self._selectables[fd] = writer
            self._writes[fd] = 1
            self._updateRegistration(fd)

    def removeReader(self, reader):
        """Remove a Selectable for notification of data available to read."""
        return self._dictRemove(reader, self._reads)

    def removeWriter(self, writer):
        """Remove a Selectable for notification of data available to write."""
        return self._dictRemove(writer, self._writes)

    def removeAll(self):
        """
        Remove all selectables, and return a list of them.
        """
        return self._removeAll(
            [self._selectables[fd] for fd in self._reads],
            [self._selectables[fd] for fd in self._writes],
        )

    def doPoll(self, timeout):
        """Poll the poller for new events."""
        if timeout is not None:
            timeout = int(timeout * 1000)  # convert seconds to milliseconds

        try:
            l = self._poller.poll(timeout)
        except SelectError as e:
            if e.args[0] == errno.EINTR:
                return
            else:
                raise
        _drdw = self._doReadOrWrite
        for fd, event in l:
            try:
                selectable = self._selectables[fd]
            except KeyError:
                # Handles the infrequent case where one selectable's
                # handler disconnects another.
                continue
            log.callWithLogger(selectable, _drdw, selectable, fd, event)

    doIteration = doPoll

    def getReaders(self):
        return [self._selectables[fd] for fd in self._reads]

    def getWriters(self):
        return [self._selectables[fd] for fd in self._writes]


def install():
    """Install the poll() reactor."""
    p = PollReactor()
    from twisted.internet.main import installReactor

    installReactor(p)


__all__ = ["PollReactor", "install"]