1 files changed, 511 insertions, 0 deletions
diff --git a/Lib/selectors.py b/Lib/selectors.py
new file mode 100644
index 0000000000..a44d5e96b4
--- /dev/null
+++ b/Lib/selectors.py
@@ -0,0 +1,511 @@
+"""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
+
+    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
+    performant 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:
+            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()
+
+    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):
+            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(_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):
+            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(_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):
+            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