cpython/Lib/selectors.py

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"""Selectors module.
This module allows high-level and efficient I/O multiplexing, built upon the
`select` module primitives.
"""
from abc import ABCMeta, abstractmethod
from collections import namedtuple, Mapping
import functools
import select
import sys
# generic events, that must be mapped to implementation-specific ones
EVENT_READ = (1 << 0)
EVENT_WRITE = (1 << 1)
def _fileobj_to_fd(fileobj):
"""Return a file descriptor from a file object.
Parameters:
fileobj -- file object or file descriptor
Returns:
corresponding file descriptor
"""
if isinstance(fileobj, int):
fd = fileobj
else:
try:
fd = int(fileobj.fileno())
except (AttributeError, TypeError, ValueError):
raise ValueError("Invalid file object: "
"{!r}".format(fileobj)) from None
if fd < 0:
raise ValueError("Invalid file descriptor: {}".format(fd))
return fd
SelectorKey = namedtuple('SelectorKey', ['fileobj', 'fd', 'events', 'data'])
"""Object used to associate a file object to its backing file descriptor,
selected event mask and attached data."""
class _SelectorMapping(Mapping):
"""Mapping of file objects to selector keys."""
def __init__(self, selector):
self._selector = selector
def __len__(self):
return len(self._selector._fd_to_key)
def __getitem__(self, fileobj):
try:
return self._selector._fd_to_key[_fileobj_to_fd(fileobj)]
except KeyError:
raise KeyError("{!r} is not registered".format(fileobj)) from None
def __iter__(self):
return iter(self._selector._fd_to_key)
class BaseSelector(metaclass=ABCMeta):
"""Base selector class.
A selector supports registering file objects to be monitored for specific
I/O events.
A file object is a file descriptor or any object with a `fileno()` method.
An arbitrary object can be attached to the file object, which can be used
for example to store context information, a callback, etc.
A selector can use various implementations (select(), poll(), epoll()...)
depending on the platform. The default `Selector` class uses the most
performant implementation on the current platform.
"""
def __init__(self):
# this maps file descriptors to keys
self._fd_to_key = {}
# read-only mapping returned by get_map()
self._map = _SelectorMapping(self)
def register(self, fileobj, events, data=None):
"""Register a file object.
Parameters:
fileobj -- file object or file descriptor
events -- events to monitor (bitwise mask of EVENT_READ|EVENT_WRITE)
data -- attached data
Returns:
SelectorKey instance
"""
if (not events) or (events & ~(EVENT_READ | EVENT_WRITE)):
raise ValueError("Invalid events: {!r}".format(events))
key = SelectorKey(fileobj, _fileobj_to_fd(fileobj), events, data)
if key.fd in self._fd_to_key:
raise KeyError("{!r} (FD {}) is already "
"registered".format(fileobj, key.fd))
self._fd_to_key[key.fd] = key
return key
def unregister(self, fileobj):
"""Unregister a file object.
Parameters:
fileobj -- file object or file descriptor
Returns:
SelectorKey instance
"""
try:
key = self._fd_to_key.pop(_fileobj_to_fd(fileobj))
except KeyError:
raise KeyError("{!r} is not registered".format(fileobj)) from None
return key
def modify(self, fileobj, events, data=None):
"""Change a registered file object monitored events or attached data.
Parameters:
fileobj -- file object or file descriptor
events -- events to monitor (bitwise mask of EVENT_READ|EVENT_WRITE)
data -- attached data
Returns:
SelectorKey instance
"""
# TODO: Subclasses can probably optimize this even further.
try:
key = self._fd_to_key[_fileobj_to_fd(fileobj)]
except KeyError:
raise KeyError("{!r} is not registered".format(fileobj)) from None
if events != key.events:
self.unregister(fileobj)
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key = self.register(fileobj, events, data)
elif data != key.data:
# Use a shortcut to update the data.
key = key._replace(data=data)
self._fd_to_key[key.fd] = key
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return key
@abstractmethod
def select(self, timeout=None):
"""Perform the actual selection, until some monitored file objects are
ready or a timeout expires.
Parameters:
timeout -- if timeout > 0, this specifies the maximum wait time, in
seconds
if timeout <= 0, the select() call won't block, and will
report the currently ready file objects
if timeout is None, select() will block until a monitored
file object becomes ready
Returns:
list of (key, events) for ready file objects
`events` is a bitwise mask of EVENT_READ|EVENT_WRITE
"""
raise NotImplementedError()
def close(self):
"""Close the selector.
This must be called to make sure that any underlying resource is freed.
"""
self._fd_to_key.clear()
def get_key(self, fileobj):
"""Return the key associated to a registered file object.
Returns:
SelectorKey for this file object
"""
try:
return self._fd_to_key[_fileobj_to_fd(fileobj)]
except KeyError:
raise KeyError("{!r} is not registered".format(fileobj)) from None
def get_map(self):
"""Return a mapping of file objects to selector keys."""
return self._map
def __enter__(self):
return self
def __exit__(self, *args):
self.close()
def _key_from_fd(self, fd):
"""Return the key associated to a given file descriptor.
Parameters:
fd -- file descriptor
Returns:
corresponding key, or None if not found
"""
try:
return self._fd_to_key[fd]
except KeyError:
return None
class SelectSelector(BaseSelector):
"""Select-based selector."""
def __init__(self):
super().__init__()
self._readers = set()
self._writers = set()
def register(self, fileobj, events, data=None):
key = super().register(fileobj, events, data)
if events & EVENT_READ:
self._readers.add(key.fd)
if events & EVENT_WRITE:
self._writers.add(key.fd)
return key
def unregister(self, fileobj):
key = super().unregister(fileobj)
self._readers.discard(key.fd)
self._writers.discard(key.fd)
return key
if sys.platform == 'win32':
def _select(self, r, w, _, timeout=None):
r, w, x = select.select(r, w, w, timeout)
return r, w + x, []
else:
_select = select.select
def select(self, timeout=None):
timeout = None if timeout is None else max(timeout, 0)
ready = []
try:
r, w, _ = self._select(self._readers, self._writers, [], timeout)
except InterruptedError:
return ready
r = set(r)
w = set(w)
for fd in r | w:
events = 0
if fd in r:
events |= EVENT_READ
if fd in w:
events |= EVENT_WRITE
key = self._key_from_fd(fd)
if key:
ready.append((key, events & key.events))
return ready
if hasattr(select, 'poll'):
class PollSelector(BaseSelector):
"""Poll-based selector."""
def __init__(self):
super().__init__()
self._poll = select.poll()
def register(self, fileobj, events, data=None):
key = super().register(fileobj, events, data)
poll_events = 0
if events & EVENT_READ:
poll_events |= select.POLLIN
if events & EVENT_WRITE:
poll_events |= select.POLLOUT
self._poll.register(key.fd, poll_events)
return key
def unregister(self, fileobj):
key = super().unregister(fileobj)
self._poll.unregister(key.fd)
return key
def select(self, timeout=None):
timeout = None if timeout is None else max(int(1000 * timeout), 0)
ready = []
try:
fd_event_list = self._poll.poll(timeout)
except InterruptedError:
return ready
for fd, event in fd_event_list:
events = 0
if event & ~select.POLLIN:
events |= EVENT_WRITE
if event & ~select.POLLOUT:
events |= EVENT_READ
key = self._key_from_fd(fd)
if key:
ready.append((key, events & key.events))
return ready
if hasattr(select, 'epoll'):
class EpollSelector(BaseSelector):
"""Epoll-based selector."""
def __init__(self):
super().__init__()
self._epoll = select.epoll()
def fileno(self):
return self._epoll.fileno()
def register(self, fileobj, events, data=None):
key = super().register(fileobj, events, data)
epoll_events = 0
if events & EVENT_READ:
epoll_events |= select.EPOLLIN
if events & EVENT_WRITE:
epoll_events |= select.EPOLLOUT
self._epoll.register(key.fd, epoll_events)
return key
def unregister(self, fileobj):
key = super().unregister(fileobj)
self._epoll.unregister(key.fd)
return key
def select(self, timeout=None):
timeout = -1 if timeout is None else max(timeout, 0)
max_ev = len(self._fd_to_key)
ready = []
try:
fd_event_list = self._epoll.poll(timeout, max_ev)
except InterruptedError:
return ready
for fd, event in fd_event_list:
events = 0
if event & ~select.EPOLLIN:
events |= EVENT_WRITE
if event & ~select.EPOLLOUT:
events |= EVENT_READ
key = self._key_from_fd(fd)
if key:
ready.append((key, events & key.events))
return ready
def close(self):
self._epoll.close()
super().close()
if hasattr(select, 'kqueue'):
class KqueueSelector(BaseSelector):
"""Kqueue-based selector."""
def __init__(self):
super().__init__()
self._kqueue = select.kqueue()
def fileno(self):
return self._kqueue.fileno()
def register(self, fileobj, events, data=None):
key = super().register(fileobj, events, data)
if events & EVENT_READ:
kev = select.kevent(key.fd, select.KQ_FILTER_READ,
select.KQ_EV_ADD)
self._kqueue.control([kev], 0, 0)
if events & EVENT_WRITE:
kev = select.kevent(key.fd, select.KQ_FILTER_WRITE,
select.KQ_EV_ADD)
self._kqueue.control([kev], 0, 0)
return key
def unregister(self, fileobj):
key = super().unregister(fileobj)
if key.events & EVENT_READ:
kev = select.kevent(key.fd, select.KQ_FILTER_READ,
select.KQ_EV_DELETE)
self._kqueue.control([kev], 0, 0)
if key.events & EVENT_WRITE:
kev = select.kevent(key.fd, select.KQ_FILTER_WRITE,
select.KQ_EV_DELETE)
self._kqueue.control([kev], 0, 0)
return key
def select(self, timeout=None):
timeout = None if timeout is None else max(timeout, 0)
max_ev = len(self._fd_to_key)
ready = []
try:
kev_list = self._kqueue.control(None, max_ev, timeout)
except InterruptedError:
return ready
for kev in kev_list:
fd = kev.ident
flag = kev.filter
events = 0
if flag == select.KQ_FILTER_READ:
events |= EVENT_READ
if flag == select.KQ_FILTER_WRITE:
events |= EVENT_WRITE
key = self._key_from_fd(fd)
if key:
ready.append((key, events & key.events))
return ready
def close(self):
self._kqueue.close()
super().close()
# Choose the best implementation: roughly, epoll|kqueue > poll > select.
# select() also can't accept a FD > FD_SETSIZE (usually around 1024)
if 'KqueueSelector' in globals():
DefaultSelector = KqueueSelector
elif 'EpollSelector' in globals():
DefaultSelector = EpollSelector
elif 'PollSelector' in globals():
DefaultSelector = PollSelector
else:
DefaultSelector = SelectSelector