| """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 math |
| 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 |
| |
| Raises: |
| ValueError if the object is invalid |
| """ |
| 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: |
| fd = self._selector._fileobj_lookup(fileobj) |
| return self._selector._fd_to_key[fd] |
| 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): |
| """Selector abstract base 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 |
| efficient implementation on the current platform. |
| """ |
| |
| @abstractmethod |
| 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 |
| |
| Raises: |
| ValueError if events is invalid |
| KeyError if fileobj is already registered |
| OSError if fileobj is closed or otherwise is unacceptable to |
| the underlying system call (if a system call is made) |
| |
| Note: |
| OSError may or may not be raised |
| """ |
| raise NotImplementedError |
| |
| @abstractmethod |
| def unregister(self, fileobj): |
| """Unregister a file object. |
| |
| Parameters: |
| fileobj -- file object or file descriptor |
| |
| Returns: |
| SelectorKey instance |
| |
| Raises: |
| KeyError if fileobj is not registered |
| |
| Note: |
| If fileobj is registered but has since been closed this does |
| *not* raise OSError (even if the wrapped syscall does) |
| """ |
| raise NotImplementedError |
| |
| 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 |
| |
| Raises: |
| Anything that unregister() or register() raises |
| """ |
| self.unregister(fileobj) |
| return self.register(fileobj, events, data) |
| |
| @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. |
| """ |
| pass |
| |
| def get_key(self, fileobj): |
| """Return the key associated to a registered file object. |
| |
| Returns: |
| SelectorKey for this file object |
| """ |
| mapping = self.get_map() |
| try: |
| if mapping is None: |
| raise KeyError |
| return mapping[fileobj] |
| except KeyError: |
| raise KeyError("{!r} is not registered".format(fileobj)) from None |
| |
| @abstractmethod |
| def get_map(self): |
| """Return a mapping of file objects to selector keys.""" |
| raise NotImplementedError |
| |
| def __enter__(self): |
| return self |
| |
| def __exit__(self, *args): |
| self.close() |
| |
| |
| class _BaseSelectorImpl(BaseSelector): |
| """Base selector implementation.""" |
| |
| 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 _fileobj_lookup(self, fileobj): |
| """Return a file descriptor from a file object. |
| |
| This wraps _fileobj_to_fd() to do an exhaustive search in case |
| the object is invalid but we still have it in our map. This |
| is used by unregister() so we can unregister an object that |
| was previously registered even if it is closed. It is also |
| used by _SelectorMapping. |
| """ |
| try: |
| return _fileobj_to_fd(fileobj) |
| except ValueError: |
| # Do an exhaustive search. |
| for key in self._fd_to_key.values(): |
| if key.fileobj is fileobj: |
| return key.fd |
| # Raise ValueError after all. |
| raise |
| |
| def register(self, fileobj, events, data=None): |
| if (not events) or (events & ~(EVENT_READ | EVENT_WRITE)): |
| raise ValueError("Invalid events: {!r}".format(events)) |
| |
| key = SelectorKey(fileobj, self._fileobj_lookup(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): |
| try: |
| key = self._fd_to_key.pop(self._fileobj_lookup(fileobj)) |
| except KeyError: |
| raise KeyError("{!r} is not registered".format(fileobj)) from None |
| return key |
| |
| def modify(self, fileobj, events, data=None): |
| # TODO: Subclasses can probably optimize this even further. |
| try: |
| key = self._fd_to_key[self._fileobj_lookup(fileobj)] |
| except KeyError: |
| raise KeyError("{!r} is not registered".format(fileobj)) from None |
| if events != key.events: |
| self.unregister(fileobj) |
| 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 |
| return key |
| |
| def close(self): |
| self._fd_to_key.clear() |
| self._map = None |
| |
| def get_map(self): |
| return self._map |
| |
| 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(_BaseSelectorImpl): |
| """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(_BaseSelectorImpl): |
| """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): |
| if timeout is None: |
| timeout = None |
| elif timeout <= 0: |
| timeout = 0 |
| else: |
| # poll() has a resolution of 1 millisecond, round away from |
| # zero to wait *at least* timeout seconds. |
| timeout = math.ceil(timeout * 1e3) |
| 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(_BaseSelectorImpl): |
| """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) |
| try: |
| self._epoll.unregister(key.fd) |
| except OSError: |
| # This can happen if the FD was closed since it |
| # was registered. |
| pass |
| return key |
| |
| def select(self, timeout=None): |
| if timeout is None: |
| timeout = -1 |
| elif timeout <= 0: |
| timeout = 0 |
| else: |
| # epoll_wait() has a resolution of 1 millisecond, round away |
| # from zero to wait *at least* timeout seconds. |
| timeout = math.ceil(timeout * 1e3) * 1e-3 |
| |
| # epoll_wait() expects `maxevents` to be greater than zero; |
| # we want to make sure that `select()` can be called when no |
| # FD is registered. |
| max_ev = max(len(self._fd_to_key), 1) |
| |
| 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): |
| try: |
| self._epoll.close() |
| finally: |
| super().close() |
| |
| |
| if hasattr(select, 'kqueue'): |
| |
| class KqueueSelector(_BaseSelectorImpl): |
| """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) |
| try: |
| self._kqueue.control([kev], 0, 0) |
| except OSError: |
| # This can happen if the FD was closed since it |
| # was registered. |
| pass |
| if key.events & EVENT_WRITE: |
| kev = select.kevent(key.fd, select.KQ_FILTER_WRITE, |
| select.KQ_EV_DELETE) |
| try: |
| self._kqueue.control([kev], 0, 0) |
| except OSError: |
| # See comment above. |
| pass |
| 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): |
| try: |
| self._kqueue.close() |
| finally: |
| 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 |