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uselect – Wait for events

This module provides functions to efficiently wait for events on multiple streams.

Poll instance and class

poll() → Poll

Creates an instance of the Poll class.

Returns

The Poll instance.

class Poll
register(object, eventmask=POLLOUT | POLLOUT)

Register a stream object for polling. The stream object will now be monitored for events. If an event happens, it becomes part of the return value of poll().

If this method is called again for the same stream object, the object will not be registered again, but the eventmask flags will be updated, as if calling modify().

Parameters

  • object (FileIO) – Stream to be registered for polling.

  • eventmask (int) – Which events to use. Should be POLLIN, POLLOUT, or their logical disjunction: POLLIN | POLLOUT.

unregister(poll)

Unregister an object from polling.

Parameters

object (FileIO) – Stream to be unregistered from polling.

modify(object, eventmask)

Modifies the event mask for the stream object.

Parameters

  • object (FileIO) – Stream to be registered for polling.

  • eventmask (int) – Which events to use.

Raises

OSError – If the object is not registered. The error is ENOENT.

poll(timeout=- 1) → List[Tuple[FileIO, int]]

Wait until at least one of the registered objects has a new event or exceptional condition ready to be handled.

Parameters

timeout (int) – Timeout in milliseconds. Choose 0 to return immediately or choose -1 to wait indefinitely.

Returns

A list of tuples. There is one (object, eventmask, …) tuple for each object with an event, or no tuples if there are no events to be handled. The eventmask value is a combination of poll flags to indicate what happened. This may include POLLERR and POLLHUP even if they were not registered.

ipoll(timeout=- 1, flags=1) → Iterator[Tuple[FileIO, int]]

First, just like poll(), wait until at least one of the registered objects has a new event or exceptional condition ready to be handled.

But instead of a list, this method returns an iterator for improved efficiency. The iterator yields one (object, eventmask, …) tuple at a time, and overwrites it when yielding the next value. If you need the values later, make sure to copy them explicitly.

Parameters

  • timeout (int) – Timeout in milliseconds. Choose 0 to return immediately or choose -1 to wait indefinitely.

  • flags (int) – If set to 1, one-shot behavior for events is employed. This means that streams for which events happened will have their event masks automatically reset using poll.modify(obj, 0). This way, new events for such a stream won’t be processed until a new mask is set with modify(), which is useful for asynchronous I/O schedulers.

Event mask flags

POLLIN: int

Data is available for reading.

POLLOUT: int

More data can be written.

POLLERR: int

Error condition happened on the associated stream. Should be handled explicitly or else further invocations of poll() may return right away.

POLLHUP: int

Hang up happened on the associated stream. Should be handled explicitly or else further invocations of poll() may return right away.

Examples

See the projects website for a demo that uses this module.