asyncio-extending
asyncio
Extending
The main direction for asyncio extending is writing custom event loop classes. Asyncio has helpers that could be used to simplify this task.
[!NOTE] Third-parties should reuse existing asyncio code with caution, a new Python version is free to break backward compatibility in the internal part of the API.
Writing a custom event loop
asyncio.AbstractEventLoop declares very many methods. See asyncio-event-loop-methods for the full list. Implementing them all from scratch is a tedious job.
A loop can get many common methods implementation for free by inheriting from asyncio.BaseEventLoop.
In turn, the successor should implement a bunch of private methods declared but not implemented in asyncio.BaseEventLoop.
For example, loop.create_connection() checks arguments, resolves DNS addresses, and calls loop._make_socket_transport() that should be implemented by inherited class. The _make_socket_transport() method is not documented and is considered as an internal API.
Future and Task private constructors
asyncio.Future and asyncio.Task should be never created directly, please use corresponding loop.create_future and loop.create_task, or asyncio.create_task factories instead.
However, third-party event loops may reuse built-in future and task implementations for the sake of getting a complex and highly optimized code for free.
For this purpose the following, private constructors are listed:
Future.__init__(*, loop=None)
Create a built-in future instance.
loop is an optional event loop instance.
Task.__init__(coro, *, loop=None, name=None, context=None)
Create a built-in task instance.
loop is an optional event loop instance. The rest of arguments are described in loop.create_task description.
3.11
context argument is added.
Task lifetime support
A third party task implementation should call the following functions to keep a task visible by asyncio.all_tasks and asyncio.current_task:
register_task(task)
Register a new task as managed by asyncio.
Call the function from a task constructor.
unregister_task(task)
Unregister a task from asyncio internal structures.
The function should be called when a task is about to finish.
enter_task(loop, task)
Switch the current task to the task argument.
Call the function just before executing a portion of embedded coroutine (coroutine.send or coroutine.throw).
leave_task(loop, task)
Switch the current task back from task to None.
Call the function just after coroutine.send or coroutine.throw execution.
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