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bpo-44951: Allow setting EPOLLEXCLUSIVE on selectors.EpollSelector #27819

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bpo-44951: Allow setting EPOLLEXCLUSIVE on selectors.EpollSelector #27819

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15 changes: 15 additions & 0 deletions Doc/library/selectors.rst
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Original file line number Diff line number Diff line change
Expand Up @@ -212,11 +212,26 @@ constants below:

:func:`select.epoll`-based selector.

.. attribute:: exclusive

Check if *EPOLLEXCLUSIVE* will be set on newly registered
files.

.. method:: fileno()

This returns the file descriptor used by the underlying
:func:`select.epoll` object.

.. method:: set_exclusive(value)

Enable or disable setting *EPOLLEXCLUSIVE* on newly
registered files. A file descriptor with *EPOLLEXCLUSIVE* set on it
will raise :exc:`OSError` if you attempt to
:meth:`~BaseSelector.modify` it. You must unregister and
re-register a file descriptor to enable or disable *EPOLLEXCLUSIVE*.

*value* must be a boolean.

.. class:: DevpollSelector()

:func:`select.devpoll`-based selector.
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34 changes: 29 additions & 5 deletions Lib/selectors.py
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Original file line number Diff line number Diff line change
Expand Up @@ -348,15 +348,16 @@ def __init__(self):
super().__init__()
self._selector = self._selector_cls()

def register(self, fileobj, events, data=None):
def register(self, fileobj, events, data=None, register_flags=None):
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Since this is in a method literally called register, I'd name the new argument simply flags.

key = super().register(fileobj, events, data)
poller_events = 0
if register_flags is None:
register_flags = 0
if events & EVENT_READ:
poller_events |= self._EVENT_READ
register_flags |= self._EVENT_READ
if events & EVENT_WRITE:
poller_events |= self._EVENT_WRITE
register_flags |= self._EVENT_WRITE
try:
self._selector.register(key.fd, poller_events)
self._selector.register(key.fd, register_flags)
except:
super().unregister(fileobj)
raise
Expand Down Expand Up @@ -445,6 +446,29 @@ class EpollSelector(_PollLikeSelector):
_EVENT_READ = select.EPOLLIN
_EVENT_WRITE = select.EPOLLOUT

def __init__(self):
super().__init__()
self._exclusive = False

@property
def exclusive(self):
return self._exclusive

def set_exclusive(self, value):
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So far selectors haven't had this but looking at asyncio, ssl, socket, threading, and multiprocessing code, we usually either use properties for both getting and setting a value, or we use both a get_* and a set_* method.

Since we already have get_key and get_map in selectors.py, and there are no public fields nor properties here, I'd change the exclusive getter to an explicit get_exclusive() method.

if not isinstance(value, bool):
raise ValueError("Not a boolean")
if not hasattr(select, "EPOLLEXCLUSIVE"):
raise ValueError("Python was not compiled "
"with EPOLLEXCLUSIVE")
self._exclusive = value

def register(self, fileobj, events, data=None):
register_flags = 0
if self._exclusive:
register_flags |= select.EPOLLEXCLUSIVE
return super().register(fileobj, events,
data=data, register_flags=register_flags)

def fileno(self):
return self._selector.fileno()

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20 changes: 20 additions & 0 deletions Lib/test/test_selectors.py
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Original file line number Diff line number Diff line change
@@ -1,6 +1,7 @@
import errno
import os
import random
import select
import selectors
import signal
import socket
Expand Down Expand Up @@ -533,6 +534,25 @@ def test_register_file(self):
s.get_key(f)


@unittest.skipUnless(hasattr(selectors, 'EpollSelector'),
"Test needs selectors.EpollSelector")
@unittest.skipUnless(hasattr(select, 'EPOLLEXCLUSIVE'),
"Test needs select.EPOLLEXCLUSIVE")
class EpollExclusiveSelectorTestCase(BaseSelectorTestCase,
ScalableSelectorMixIn):

@property
def SELECTOR(self):
sel = getattr(selectors, 'EpollSelector')()
sel.set_exclusive(True)
return lambda: sel

def test_modify(self):
with self.assertRaises(OSError) as ex:
super().test_modify()
self.assertEqual(ex.exception.errno, errno.EINVAL)


@unittest.skipUnless(hasattr(selectors, 'KqueueSelector'),
"Test needs selectors.KqueueSelector)")
class KqueueSelectorTestCase(BaseSelectorTestCase, ScalableSelectorMixIn,
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1 change: 1 addition & 0 deletions Misc/ACKS
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Original file line number Diff line number Diff line change
Expand Up @@ -617,6 +617,7 @@ Subhendu Ghosh
Jonathan Giddy
Johannes Gijsbers
Michael Gilfix
David Gilman
Julian Gindi
Yannick Gingras
Neil Girdhar
Expand Down
1 change: 1 addition & 0 deletions Misc/NEWS.d/next/Library/2021-08-19-02-56-29.bpo-44951.zamheK.rst
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Original file line number Diff line number Diff line change
@@ -0,0 +1 @@
:func:`selectors.EpollSelector.set_exclusive` added to enable setting *EPOLLEXCLUSIVE* automatically on polled file descriptors.