path: root/python/gevent/select.py

# Copyright (c) 2009-2011 Denis Bilenko. See LICENSE for details.
"""
Waiting for I/O completion.
"""
from __future__ import absolute_import, division, print_function

import sys

from gevent.event import Event
from gevent.hub import _get_hub_noargs as get_hub
from gevent.hub import sleep as _g_sleep
from gevent._compat import integer_types
from gevent._compat import iteritems
from gevent._util import copy_globals
from gevent._util import _NONE

from errno import EINTR
from select import select as _real_original_select
if sys.platform.startswith('win32'):
    def _original_select(r, w, x, t):
        # windows cant handle three empty lists, but we've always
        # accepted that
        if not r and not w and not x:
            return ((), (), ())
        return _real_original_select(r, w, x, t)
else:
    _original_select = _real_original_select


try:
    from select import poll as original_poll
    from select import POLLIN, POLLOUT, POLLNVAL
    __implements__ = ['select', 'poll']
except ImportError:
    original_poll = None
    __implements__ = ['select']

__all__ = ['error'] + __implements__

import select as __select__

error = __select__.error

__imports__ = copy_globals(__select__, globals(),
                           names_to_ignore=__all__,
                           dunder_names_to_keep=())

_EV_READ = 1
_EV_WRITE = 2

def get_fileno(obj):
    try:
        fileno_f = obj.fileno
    except AttributeError:
        if not isinstance(obj, integer_types):
            raise TypeError('argument must be an int, or have a fileno() method: %r' % (obj,))
        return obj
    else:
        return fileno_f()


class SelectResult(object):
    __slots__ = ('read', 'write', 'event')

    def __init__(self):
        self.read = []
        self.write = []
        self.event = Event()

    def add_read(self, socket):
        self.read.append(socket)
        self.event.set()

    add_read.event = _EV_READ

    def add_write(self, socket):
        self.write.append(socket)
        self.event.set()

    add_write.event = _EV_WRITE

    def __add_watchers(self, watchers, fdlist, callback, io, pri):
        for fd in fdlist:
            watcher = io(get_fileno(fd), callback.event)
            watcher.priority = pri
            watchers.append(watcher)
            watcher.start(callback, fd)

    def _make_watchers(self, watchers, rlist, wlist):
        loop = get_hub().loop
        io = loop.io
        MAXPRI = loop.MAXPRI

        try:
            self.__add_watchers(watchers, rlist, self.add_read, io, MAXPRI)
            self.__add_watchers(watchers, wlist, self.add_write, io, MAXPRI)
        except IOError as ex:
            raise error(*ex.args)

    def _closeall(self, watchers):
        for watcher in watchers:
            watcher.stop()
            watcher.close()
        del watchers[:]

    def select(self, rlist, wlist, timeout):
        watchers = []
        try:
            self._make_watchers(watchers, rlist, wlist)
            self.event.wait(timeout=timeout)
            return self.read, self.write, []
        finally:
            self._closeall(watchers)


def select(rlist, wlist, xlist, timeout=None): # pylint:disable=unused-argument
    """An implementation of :meth:`select.select` that blocks only the current greenlet.

    .. caution:: *xlist* is ignored.

    .. versionchanged:: 1.2a1
       Raise a :exc:`ValueError` if timeout is negative. This matches Python 3's
       behaviour (Python 2 would raise a ``select.error``). Previously gevent had
       undefined behaviour.
    .. versionchanged:: 1.2a1
       Raise an exception if any of the file descriptors are invalid.
    """
    if timeout is not None and timeout < 0:
        # Raise an error like the real implementation; which error
        # depends on the version. Python 3, where select.error is OSError,
        # raises a ValueError (which makes sense). Older pythons raise
        # the error from the select syscall...but we don't actually get there.
        # We choose to just raise the ValueError as it makes more sense and is
        # forward compatible
        raise ValueError("timeout must be non-negative")

    # First, do a poll with the original select system call. This
    # is the most efficient way to check to see if any of the file descriptors
    # have previously been closed and raise the correct corresponding exception.
    # (Because libev tends to just return them as ready...)
    # We accept the *xlist* here even though we can't below because this is all about
    # error handling.
    sel_results = ((), (), ())
    try:
        sel_results = _original_select(rlist, wlist, xlist, 0)
    except error as e:
        enumber = getattr(e, 'errno', None) or e.args[0]
        if enumber != EINTR:
            # Ignore interrupted syscalls
            raise

    if sel_results[0] or sel_results[1] or sel_results[2] or (timeout is not None and timeout == 0):
        # If we actually had stuff ready, go ahead and return it. No need
        # to go through the trouble of doing our own stuff.

        # Likewise, if the timeout is 0, we already did a 0 timeout
        # select and we don't need to do it again. Note that in libuv,
        # zero duration timers may be called immediately, without
        # cycling the event loop at all. 2.7/test_telnetlib.py "hangs"
        # calling zero-duration timers if we go to the loop here.

        # However, because this is typically a place where scheduling switches
        # can occur, we need to make sure that's still the case; otherwise a single
        # consumer could monopolize the thread. (shows up in test_ftplib.)
        _g_sleep()
        return sel_results

    result = SelectResult()
    return result.select(rlist, wlist, timeout)


if original_poll is not None:
    class PollResult(object):
        __slots__ = ('events', 'event')

        def __init__(self):
            self.events = set()
            self.event = Event()

        def add_event(self, events, fd):
            if events < 0:
                result_flags = POLLNVAL
            else:
                result_flags = 0
                if events & _EV_READ:
                    result_flags = POLLIN
                if events & _EV_WRITE:
                    result_flags |= POLLOUT

            self.events.add((fd, result_flags))
            self.event.set()

    class poll(object):
        """
        An implementation of :class:`select.poll` that blocks only the current greenlet.

        .. caution:: ``POLLPRI`` data is not supported.

        .. versionadded:: 1.1b1
        """
        def __init__(self):
            # {int -> flags}
            # We can't keep watcher objects in here because people commonly
            # just drop the poll object when they're done, without calling
            # unregister(). dnspython does this.
            self.fds = {}
            self.loop = get_hub().loop

        def register(self, fd, eventmask=_NONE):
            if eventmask is _NONE:
                flags = _EV_READ | _EV_WRITE
            else:
                flags = 0
                if eventmask & POLLIN:
                    flags = _EV_READ
                if eventmask & POLLOUT:
                    flags |= _EV_WRITE
                # If they ask for POLLPRI, we can't support
                # that. Should we raise an error?

            fileno = get_fileno(fd)
            self.fds[fileno] = flags

        def modify(self, fd, eventmask):
            self.register(fd, eventmask)

        def poll(self, timeout=None):
            """
            poll the registered fds.

            .. versionchanged:: 1.2a1
               File descriptors that are closed are reported with POLLNVAL.

            .. versionchanged:: 1.3a2
               Under libuv, interpret *timeout* values less than 0 the same as *None*,
               i.e., block. This was always the case with libev.
            """
            result = PollResult()
            watchers = []
            io = self.loop.io
            MAXPRI = self.loop.MAXPRI
            try:
                for fd, flags in iteritems(self.fds):
                    watcher = io(fd, flags)
                    watchers.append(watcher)
                    watcher.priority = MAXPRI
                    watcher.start(result.add_event, fd, pass_events=True)
                if timeout is not None:
                    if timeout < 0:
                        # The docs for python say that an omitted timeout,
                        # a negative timeout and a timeout of None are all
                        # supposed to block forever. Many, but not all
                        # OS's accept any negative number to mean that. Some
                        # OS's raise errors for anything negative but not -1.
                        # Python 3.7 changes to always pass exactly -1 in that
                        # case from selectors.

                        # Our Timeout class currently does not have a defined behaviour
                        # for negative values. On libuv, it uses a check watcher and effectively
                        # doesn't block. On libev, it seems to block. In either case, we
                        # *want* to block, so turn this into the sure fire block request.
                        timeout = None
                    elif timeout:
                        # The docs for poll.poll say timeout is in
                        # milliseconds. Our result objects work in
                        # seconds, so this should be *=, shouldn't it?
                        timeout /= 1000.0
                result.event.wait(timeout=timeout)
                return list(result.events)
            finally:
                for awatcher in watchers:
                    awatcher.stop()
                    awatcher.close()

        def unregister(self, fd):
            """
            Unregister the *fd*.

            .. versionchanged:: 1.2a1
               Raise a `KeyError` if *fd* was not registered, like the standard
               library. Previously gevent did nothing.
            """
            fileno = get_fileno(fd)
            del self.fds[fileno]

del original_poll