Issue #16853: Add new selectors module.

3 files changed, 236 insertions, 3 deletions

diff --git a/Doc/library/concurrency.rst b/Doc/library/concurrency.rst
index f2a512f..2d69107 100644
--- a/Doc/library/concurrency.rst
+++ b/Doc/library/concurrency.rst
@@ -21,6 +21,7 @@ multitasking). Here's an overview:
    sched.rst
    queue.rst
    select.rst
+   selectors.rst
 
 
 The following are support modules for some of the above services:
diff --git a/Doc/library/selectors.rst b/Doc/library/selectors.rst
new file mode 100644
index 0000000..ece5e7d
--- /dev/null
+++ b/Doc/library/selectors.rst
@@ -0,0 +1,231 @@
+:mod:`selectors` -- High-level I/O multiplexing
+===============================================
+
+.. module:: selectors
+   :synopsis: High-level I/O multiplexing.
+
+.. versionadded:: 3.4
+
+
+Introduction
+------------
+
+This module allows high-level and efficient I/O multiplexing, built upon the
+:mod:`select` module primitives. Users are encouraged to use this module
+instead, unless they want precise control over the OS-level primitives used.
+
+It defines a :class:`BaseSelector` abstract base class, along with several
+concrete implementations (:class:`KqueueSelector`, :class:`EpollSelector`...),
+that can be used to wait for I/O readiness notification on multiple file
+objects. In the following, "file object" refers to any object with a
+:meth:`fileno()` method, or a raw file descriptor. See :term:`file object`.
+
+:class:`DefaultSelector` is an alias to the most efficient implementation
+available on the current platform: this should be the default choice for most
+users.
+
+.. note::
+   The type of file objects supported depends on the platform: on Windows,
+   sockets are supported, but not pipes, whereas on Unix, both are supported
+   (some other types may be supported as well, such as fifos or special file
+   devices).
+
+.. seealso::
+
+   :mod:`select`
+      Low-level I/O multiplexing module.
+
+
+Classes
+-------
+
+Classes hierarchy::
+
+   BaseSelector
+   +-- SelectSelector
+   +-- PollSelector
+   +-- EpollSelector
+   +-- KqueueSelector
+
+
+In the following, *events* is a bitwise mask indicating which I/O events should
+be waited for on a given file object. It can be a combination of the constants
+below:
+
+   +-----------------------+-----------------------------------------------+
+   | Constant              | Meaning                                       |
+   +=======================+===============================================+
+   | :const:`EVENT_READ`   | Available for read                            |
+   +-----------------------+-----------------------------------------------+
+   | :const:`EVENT_WRITE`  | Available for write                           |
+   +-----------------------+-----------------------------------------------+
+
+
+.. class:: SelectorKey
+
+   A :class:`SelectorKey` is a :class:`~collections.namedtuple` used to
+   associate a file object to its underlying file decriptor, selected event
+   mask and attached data. It is returned by several :class:`BaseSelector`
+   methods.
+
+   .. attribute:: fileobj
+
+      File object registered.
+
+   .. attribute:: fd
+
+      Underlying file descriptor.
+
+   .. attribute:: events
+
+      Events that must be waited for this file object.
+
+   .. attribute:: data
+
+      Optional opaque data associated to this file object: for example, this
+      could be used to store per-client session.
+
+
+.. class:: BaseSelector
+
+   A :class:`BaseSelector` is used to wait for I/O event readiness on multiple
+   file objects. It supports file stream registration, unregistration, and a
+   method to wait for I/O events on those streams, with an optional timeout.
+   It's an abstract base class, so cannot be instantiated. Use
+   :class:`DefaultSelector` instead, or one of :class:`SelectSelector`,
+   :class:`KqueueSelector` etc. if you want to specifically use an
+   implementation, and your platform supports it.
+   :class:`BaseSelector` and its concrete implementations support the
+   :term:`context manager` protocol.
+
+   .. method:: register(fileobj, events, data=None)
+
+      Register a file object for selection, monitoring it for I/O events.
+
+      *fileobj* is the file object to monitor.
+      *events* is a bitwise mask of events to monitor.
+      *data* is an opaque object.
+
+      This returns a new :class:`SelectorKey` instance, or raises a
+      :exc:`ValueError` in case of invalid event mask or file descriptor, or
+      :exc:`KeyError` if the file object is already registered.
+
+   .. method:: unregister(fileobj)
+
+      Unregister a file object from selection, removing it from monitoring. A
+      file object shall be unregistered prior to being closed.
+
+      *fileobj* must be a file object previously registered.
+
+      This returns the associated :class:`SelectorKey` instance, or raises a
+      :exc:`KeyError` if the file object is not registered.
+
+   .. method:: modify(fileobj, events, data=None)
+
+      Change a registered file object monitored events or attached data.
+
+      This is equivalent to :meth:`BaseSelector.unregister(fileobj)` followed
+      by :meth:`BaseSelector.register(fileobj, events, data)`, except that it
+      can be implemented more efficiently.
+
+      This returns a new :class:`SelectorKey` instance, or raises a
+      :exc:`ValueError` in case of invalid event mask or file descriptor, or
+      :exc:`KeyError` if the file object is not registered.
+
+   .. method:: select(timeout=None)
+
+      Wait until some registered file objects become ready, or the timeout
+      expires.
+
+      If ``timeout > 0``, this specifies the maximum wait time, in seconds.
+      If ``timeout <= 0``, the call won't block, and will report the currently
+      ready file objects.
+      If *timeout* is ``None``, the call will block until a monitored file object
+      becomes ready.
+
+      This returns a list of ``(key, events)`` tuple, one for each ready file
+      object.
+
+      *key* is the :class:`SelectorKey` instance corresponding to a ready file
+      object.
+      *events* is a bitmask of events ready on this file object.
+
+   .. method:: close()
+
+      Close the selector.
+
+      This must be called to make sure that any underlying resource is freed.
+      The selector shall not be used once it has been closed.
+
+   .. method:: get_key(fileobj)
+
+      Return the key associated to a registered file object.
+
+      This returns the :class:`SelectorKey` instance associated to this file
+      object, or raises :exc:`KeyError` if the file object is not registered.
+
+
+.. class:: DefaultSelector()
+
+   The default selector class, using the most efficient implementation
+   available on the current platform. This should be the default choice for
+   most users.
+
+
+.. class:: SelectSelector()
+
+   :func:`select.select`-based selector.
+
+
+.. class:: PollSelector()
+
+   :func:`select.poll`-based selector.
+
+
+.. class:: EpollSelector()
+
+   :func:`select.epoll`-based selector.
+
+   .. method:: fileno()
+
+      This returns the file descriptor used by the underlying
+      :func:`select.epoll` object.
+
+
+.. class:: KqueueSelector()
+
+   :func:`select.kqueue`-based selector.
+
+   .. method:: fileno()
+
+      This returns the file descriptor used by the underlying
+      :func:`select.kqueue` object.
+
+
+Examples of selector usage::
+
+   >>> import selectors
+   >>> import socket
+   >>>
+   >>> s = selectors.DefaultSelector()
+   >>> r, w = socket.socketpair()
+   >>>
+   >>> s.register(r, selectors.EVENT_READ)
+   SelectorKey(fileobj=<socket.socket fd=4, family=1, type=1, proto=0>, fd=4, events=1, data=None)
+   >>> s.register(w, selectors.EVENT_WRITE)
+   SelectorKey(fileobj=<socket.socket fd=5, family=1, type=1, proto=0>, fd=5, events=2, data=None)
+   >>>
+   >>> print(s.select())
+   [(SelectorKey(fileobj=<socket.socket fd=5, family=1, type=1, proto=0>, fd=5, events=2, data=None), 2)]
+   >>>
+   >>> for key, events in s.select():
+   ...     if events & selectors.EVENT_WRITE:
+   ...         key.fileobj.send(b'spam')
+   ...
+   4
+   >>> for key, events in s.select():
+   ...     if events & selectors.EVENT_READ:
+   ...         print(key.fileobj.recv(1024))
+   ...
+   b'spam'
+   >>> s.close()
diff --git a/Doc/whatsnew/3.4.rst b/Doc/whatsnew/3.4.rst
index 427083a..e15e534 100644
--- a/Doc/whatsnew/3.4.rst
+++ b/Doc/whatsnew/3.4.rst
@@ -174,10 +174,11 @@ Some smaller changes made to the core Python language are:
 New Modules
 ===========
 
-.. module name
-.. -----------
+selectors
+---------
 
-* None yet.
+The new :mod:`selectors` module allows high-level and efficient I/O
+multiplexing, built upon the :mod:`select` module primitives.
 
 
 Improved Modules