:mod:`select` -- wait for events on a set of streams
========================================================================

.. module:: select
   :synopsis: wait for events on a set of streams

This module provides functions to wait for events on streams (select streams
which are ready for operations).

Pyboard specifics
-----------------

Polling is an efficient way of waiting for read/write activity on multiple
objects.  Current objects that support polling are: :class:`pyb.UART`,
:class:`pyb.USB_VCP`.

Functions
---------

.. function:: poll()

   Create an instance of the Poll class.

.. function:: select(rlist, wlist, xlist[, timeout])

   Wait for activity on a set of objects.

   This function is provided for compatibility and is not efficient. Usage
   of :class:`Poll` is recommended instead.

.. _class: Poll

class ``Poll``
--------------

Methods
~~~~~~~

.. method:: poll.register(obj[, eventmask])

   Register ``obj`` for polling.  ``eventmask`` is 1 for read, 2 for
   write, 3 for read-write.

.. method:: poll.unregister(obj)

   Unregister ``obj`` from polling.

.. method:: poll.modify(obj, eventmask)

   Modify the ``eventmask`` for ``obj``.

.. method:: poll.poll([timeout])

   Wait for at least one of the registered objects to become ready. Returns
   list of (``obj``, ``event``, ...) tuples, ``event`` element specifying
   whether ``obj`` is ready for reading, writing, or both (see ``register``
   method above). There may be other elements in tuple, depending on platform
   and version, so don't assume that its size is 2. In case of timeout, an
   empty list is returned.

   Timeout is in milliseconds.