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circuitpython/docs/library/uselect.rst

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:mod:`uselect` -- wait for events on a set of streams
========================================================================
.. include:: ../templates/unsupported_in_circuitpython.inc
.. module:: uselect
:synopsis: wait for events on a set of streams
|see_cpython_module| :mod:`cpython:select`.
This module provides functions to efficiently wait for events on multiple
`streams <stream>` (select streams which are ready for operations).
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 by some MicroPython ports for compatibility
and is not efficient. Usage of :class:`Poll` is recommended instead.
.. _class: Poll
class ``Poll``
--------------
Methods
~~~~~~~
.. method:: poll.register(obj[, eventmask])
Register `stream` *obj* for polling. *eventmask* is logical OR of:
* ``uselect.POLLIN`` - data available for reading
* ``uselect.POLLOUT`` - more data can be written
Note that flags like ``uselect.POLLHUP`` and ``uselect.POLLERR`` are
*not* valid as input eventmask (these are unsolicited events which
will be returned from `poll()` regardless of whether they are asked
for). This semantics is per POSIX.
*eventmask* defaults to ``uselect.POLLIN | uselect.POLLOUT``.
.. method:: poll.unregister(obj)
Unregister *obj* from polling.
.. method:: poll.modify(obj, eventmask)
Modify the *eventmask* for *obj*.
.. method:: poll.poll(timeout=-1)
Wait for at least one of the registered objects to become ready or have an
exceptional condition, with optional timeout in milliseconds (if *timeout*
arg is not specified or -1, there is no timeout).
Returns list of (``obj``, ``event``, ...) tuples. There may be other elements in
tuple, depending on a platform and version, so don't assume that its size is 2.
The ``event`` element specifies which events happened with a stream and
is a combination of ``uselect.POLL*`` constants described above. Note that
flags ``uselect.POLLHUP`` and ``uselect.POLLERR`` can be returned at any time
(even if were not asked for), and must be acted on accordingly (the
corresponding stream unregistered from poll and likely closed), because
otherwise all further invocations of `poll()` may return immediately with
these flags set for this stream again.
In case of timeout, an empty list is returned.
.. admonition:: Difference to CPython
:class: attention
Tuples returned may contain more than 2 elements as described above.
.. method:: poll.ipoll(timeout=-1, flags=0)
Like :meth:`poll.poll`, but instead returns an iterator which yields a
``callee-owned tuples``. This function provides efficient, allocation-free
way to poll on streams.
If *flags* is 1, one-shot behavior for events is employed: streams for
which events happened will have their event masks automatically reset
(equivalent to ``poll.modify(obj, 0)``), so new events for such a stream
won't be processed until new mask is set with `poll.modify()`. This
behavior is useful for asynchronous I/O schedulers.
.. admonition:: Difference to CPython
:class: attention
This function is a MicroPython extension.