This module provides functions to efficiently wait for events on multiple
streams (select streams which are ready for operations).
Create an instance of the Poll class.
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
Pollis recommended instead.
streamobj 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.POLLERRare 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.
It is OK to call this function multiple times for the same obj. Successive calls will update obj‘s eventmask to the value of eventmask (i.e. will behave as
Unregister obj from polling.
Modify the eventmask for obj. If obj is not registered,
OSErroris raised with error of ENOENT.
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 (
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
eventelement specifies which events happened with a stream and is a combination of
uselect.POLL*constants described above. Note that flags
uselect.POLLERRcan 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.
Difference to CPython
Tuples returned may contain more than 2 elements as described above.
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.
Difference to CPython
This function is a MicroPython extension.