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# Backport of selectors.py from Python 3.5+ to support Python < 3.4 # Also has the behavior specified in PEP 475 which is to retry syscalls # in the case of an EINTR error. This module is required because selectors34 # does not follow this behavior and instead returns that no dile descriptor # events have occurred rather than retry the syscall. The decision to drop # support for select.devpoll is made to maintain 100% test coverage. import errno import math import select import socket import sys import time from collections import namedtuple, Mapping try: monotonic = time.monotonic except (AttributeError, ImportError): # Python 3.3< monotonic = time.time EVENT_READ = (1 << 0) EVENT_WRITE = (1 << 1) HAS_SELECT = True # Variable that shows whether the platform has a selector. _SYSCALL_SENTINEL = object() # Sentinel in case a system call returns None. _DEFAULT_SELECTOR = None class SelectorError(Exception): def __init__(self, errcode): super(SelectorError, self).__init__() self.errno = errcode def __repr__(self): return "<SelectorError errno={0}>".format(self.errno) def __str__(self): return self.__repr__() def _fileobj_to_fd(fileobj): """ Return a file descriptor from a file object. If given an integer will simply return that integer back. """ if isinstance(fileobj, int): fd = fileobj else: try: fd = int(fileobj.fileno()) except (AttributeError, TypeError, ValueError): raise ValueError("Invalid file object: {0!r}".format(fileobj)) if fd < 0: raise ValueError("Invalid file descriptor: {0}".format(fd)) return fd # Determine which function to use to wrap system calls because Python 3.5+ # already handles the case when system calls are interrupted. if sys.version_info >= (3, 5): def _syscall_wrapper(func, _, args, kwargs): """ This is the short-circuit version of the below logic because in Python 3.5+ all system calls automatically restart and recalculate their timeouts. """ try: return func(args, *kwargs) except (OSError, IOError, select.error) as e: errcode = None if hasattr(e, "errno"): errcode = e.errno raise SelectorError(errcode) else: def _syscall_wrapper(func, recalc_timeout, args, *kwargs): """ Wrapper function for syscalls that could fail due to EINTR. All functions should be retried if there is time left in the timeout in accordance with PEP 475. """ timeout = kwargs.get("timeout", None) if timeout is None: expires = None recalc_timeout = False else: timeout = float(timeout) if timeout < 0.0: # Timeout less than 0 treated as no timeout. expires = None else: expires = monotonic() + timeout args = list(args) if recalc_timeout and "timeout" not in kwargs: raise ValueError( "Timeout must be in args or kwargs to be recalculated") result = _SYSCALL_SENTINEL while result is _SYSCALL_SENTINEL: try: result = func(args, *kwargs) # OSError is thrown by select.select # IOError is thrown by select.epoll.poll # select.error is thrown by select.poll.poll # Aren't we thankful for Python 3.x rework for exceptions? except (OSError, IOError, select.error) as e: # select.error wasn't a subclass of OSError in the past. errcode = None if hasattr(e, "errno"): errcode = e.errno elif hasattr(e, "args"): errcode = e.args[0] # Also test for the Windows equivalent of EINTR. is_interrupt = (errcode == errno.EINTR or (hasattr(errno, "WSAEINTR") and errcode == errno.WSAEINTR)) if is_interrupt: if expires is not None: current_time = monotonic() if current_time > expires: raise OSError(errno=errno.ETIMEDOUT) if recalc_timeout: if "timeout" in kwargs: kwargs["timeout"] = expires - current_time continue if errcode: raise SelectorError(errcode) else: raise return result SelectorKey = namedtuple('SelectorKey', ['fileobj', 'fd', 'events', '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("{0!r} is not registered.".format(fileobj)) def __iter__(self): return iter(self._selector._fd_to_key) class BaseSelector(object): """ Abstract 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 info, a callback, etc. A selector can use various implementations (select(), poll(), epoll(), and kqueue()) depending on the platform. The 'DefaultSelector' class uses the most efficient implementation for the current platform. """ def __init__(self): # 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. 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: # Search through all our mapped keys. 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): """ Register a file object for a set of events to monitor. """ if (not events) or (events & ~(EVENT_READ \| EVENT_WRITE)): raise ValueError("Invalid events: {0!r}".format(events)) key = SelectorKey(fileobj, self._fileobj_lookup(fileobj), events, data) if key.fd in self._fd_to_key: raise KeyError("{0!r} (FD {1}) is already registered" .format(fileobj, key.fd)) self._fd_to_key[key.fd] = key return key def unregister(self, fileobj): """ Unregister a file object from being monitored. """ try: key = self._fd_to_key.pop(self._fileobj_lookup(fileobj)) except KeyError: raise KeyError("{0!r} is not registered".format(fileobj)) # Getting the fileno of a closed socket on Windows errors with EBADF. except socket.error as e: # Platform-specific: Windows. if e.errno != errno.EBADF: raise else: for key in self._fd_to_key.values(): if key.fileobj is fileobj: self._fd_to_key.pop(key.fd) break else: raise KeyError("{0!r} is not registered".format(fileobj)) return key def modify(self, fileobj, events, data=None): """ Change a registered file object monitored events and data. """ # NOTE: Some subclasses optimize this operation even further. try: key = self._fd_to_key[self._fileobj_lookup(fileobj)] except KeyError: raise KeyError("{0!r} is not registered".format(fileobj)) 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 select(self, timeout=None): """ Perform the actual selection until some monitored file objects are ready or the timeout expires. """ raise NotImplementedError() def close(self): """ Close the selector. This must be called to ensure that all underlying resources are freed. """ self._fd_to_key.clear() self._map = None def get_key(self, fileobj): """ Return the key associated with a registered file object. """ mapping = self.get_map() if mapping is None: raise RuntimeError("Selector is closed") try: return mapping[fileobj] except KeyError: raise KeyError("{0!r} is not registered".format(fileobj)) def get_map(self): """ Return a mapping of file objects to selector keys """ return self._map def _key_from_fd(self, fd): """ Return the key associated to a given file descriptor Return None if it is not found. """ try: return self._fd_to_key[fd] except KeyError: return None def __enter__(self): return self def __exit__(self, args): self.close() # Almost all platforms have select.select() if hasattr(select, "select"): class SelectSelector(BaseSelector): """ Select-based selector. """ def __init__(self): super(SelectSelector, self).__init__() self._readers = set() self._writers = set() def register(self, fileobj, events, data=None): key = super(SelectSelector, self).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(SelectSelector, self).unregister(fileobj) self._readers.discard(key.fd) self._writers.discard(key.fd) return key def _select(self, r, w, timeout=None): """ Wrapper for select.select because timeout is a positional arg """ return select.select(r, w, [], timeout) def select(self, timeout=None): # Selecting on empty lists on Windows errors out. if not len(self._readers) and not len(self._writers): return [] timeout = None if timeout is None else max(timeout, 0.0) ready = [] r, w, _ = _syscall_wrapper(self._select, True, self._readers, self._writers, timeout) 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(PollSelector, self).__init__() self._poll = select.poll() def register(self, fileobj, events, data=None): key = super(PollSelector, self).register(fileobj, events, data) event_mask = 0 if events & EVENT_READ: event_mask \|= select.POLLIN if events & EVENT_WRITE: event_mask \|= select.POLLOUT self._poll.register(key.fd, event_mask) return key def unregister(self, fileobj): key = super(PollSelector, self).unregister(fileobj) self._poll.unregister(key.fd) return key def _wrap_poll(self, timeout=None): """ Wrapper function for select.poll.poll() so that _syscall_wrapper can work with only seconds. """ if timeout is not None: if timeout <= 0: timeout = 0 else: # select.poll.poll() has a resolution of 1 millisecond, # round away from zero to wait at least timeout seconds. timeout = math.ceil(timeout * 1e3) result = self._poll.poll(timeout) return result def select(self, timeout=None): ready = [] fd_events = _syscall_wrapper(self._wrap_poll, True, timeout=timeout) for fd, event_mask in fd_events: events = 0 if event_mask & ~select.POLLIN: events \|= EVENT_WRITE if event_mask & ~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(EpollSelector, self).__init__() self._epoll = select.epoll() def fileno(self): return self._epoll.fileno() def register(self, fileobj, events, data=None): key = super(EpollSelector, self).register(fileobj, events, data) events_mask = 0 if events & EVENT_READ: events_mask \|= select.EPOLLIN if events & EVENT_WRITE: events_mask \|= select.EPOLLOUT _syscall_wrapper(self._epoll.register, False, key.fd, events_mask) return key def unregister(self, fileobj): key = super(EpollSelector, self).unregister(fileobj) try: _syscall_wrapper(self._epoll.unregister, False, key.fd) except SelectorError: # This can occur when the fd was closed since registry. pass return key def select(self, timeout=None): if timeout is not None: if timeout <= 0: timeout = 0.0 else: # select.epoll.poll() has a resolution of 1 millisecond # but luckily takes seconds so we don't need a wrapper # like PollSelector. Just for better rounding. timeout = math.ceil(timeout * 1e3) * 1e-3 timeout = float(timeout) else: timeout = -1.0 # epoll.poll() must have a float. # We always want at least 1 to ensure that select can be called # with no file descriptors registered. Otherwise will fail. max_events = max(len(self._fd_to_key), 1) ready = [] fd_events = _syscall_wrapper(self._epoll.poll, True, timeout=timeout, maxevents=max_events) for fd, event_mask in fd_events: events = 0 if event_mask & ~select.EPOLLIN: events \|= EVENT_WRITE if event_mask & ~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(EpollSelector, self).close() if hasattr(select, "kqueue"): class KqueueSelector(BaseSelector): """ Kqueue / Kevent-based selector """ def __init__(self): super(KqueueSelector, self).__init__() self._kqueue = select.kqueue() def fileno(self): return self._kqueue.fileno() def register(self, fileobj, events, data=None): key = super(KqueueSelector, self).register(fileobj, events, data) if events & EVENT_READ: kevent = select.kevent(key.fd, select.KQ_FILTER_READ, select.KQ_EV_ADD) _syscall_wrapper(self._kqueue.control, False, [kevent], 0, 0) if events & EVENT_WRITE: kevent = select.kevent(key.fd, select.KQ_FILTER_WRITE, select.KQ_EV_ADD) _syscall_wrapper(self._kqueue.control, False, [kevent], 0, 0) return key def unregister(self, fileobj): key = super(KqueueSelector, self).unregister(fileobj) if key.events & EVENT_READ: kevent = select.kevent(key.fd, select.KQ_FILTER_READ, select.KQ_EV_DELETE) try: _syscall_wrapper(self._kqueue.control, False, [kevent], 0, 0) except SelectorError: pass if key.events & EVENT_WRITE: kevent = select.kevent(key.fd, select.KQ_FILTER_WRITE, select.KQ_EV_DELETE) try: _syscall_wrapper(self._kqueue.control, False, [kevent], 0, 0) except SelectorError: pass return key def select(self, timeout=None): if timeout is not None: timeout = max(timeout, 0) max_events = len(self._fd_to_key) * 2 ready_fds = {} kevent_list = _syscall_wrapper(self._kqueue.control, True, None, max_events, timeout) for kevent in kevent_list: fd = kevent.ident event_mask = kevent.filter events = 0 if event_mask == select.KQ_FILTER_READ: events \|= EVENT_READ if event_mask == select.KQ_FILTER_WRITE: events \|= EVENT_WRITE key = self._key_from_fd(fd) if key: if key.fd not in ready_fds: ready_fds[key.fd] = (key, events & key.events) else: old_events = ready_fds[key.fd][1] ready_fds[key.fd] = (key, (events \| old_events) & key.events) return list(ready_fds.values()) def close(self): self._kqueue.close() super(KqueueSelector, self).close() if not hasattr(select, 'select'): # Platform-specific: AppEngine HAS_SELECT = False def _can_allocate(struct): """ Checks that select structs can be allocated by the underlying operating system, not just advertised by the select module. We don't check select() because we'll be hopeful that most platforms that don't have it available will not advertise it. (ie: GAE) """ try: # select.poll() objects won't fail until used. if struct == 'poll': p = select.poll() p.poll(0) # All others will fail on allocation. else: getattr(select, struct)().close() return True except (OSError, AttributeError) as e: return False # Choose the best implementation, roughly: # kqueue == epoll > poll > select. Devpoll not supported. (See above) # select() also can't accept a FD > FD_SETSIZE (usually around 1024) def DefaultSelector(): """ This function serves as a first call for DefaultSelector to detect if the select module is being monkey-patched incorrectly by eventlet, greenlet, and preserve proper behavior. """ global _DEFAULT_SELECTOR if _DEFAULT_SELECTOR is None: if _can_allocate('kqueue'): _DEFAULT_SELECTOR = KqueueSelector elif _can_allocate('epoll'): _DEFAULT_SELECTOR = EpollSelector elif _can_allocate('poll'): _DEFAULT_SELECTOR = PollSelector elif hasattr(select, 'select'): _DEFAULT_SELECTOR = SelectSelector else: # Platform-specific: AppEngine raise ValueError('Platform does not have a selector') return _DEFAULT_SELECTOR()

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