Store current task on the loop

kumaraditya303 · January 2, 2025, 11:48am

Currently the current task of a loop in stored in a global dict mapping loops to their corresponding current tasks.

python/cpython/blob/8d16919a06a55a50756bf083221a6f6cab43de50/Modules/_asynciomodule.c#L102


      
          PyTypeObject *FutureIterType;
          PyTypeObject *TaskStepMethWrapper_Type;
          PyTypeObject *FutureType;
          PyTypeObject *TaskType;
          
          PyObject *asyncio_mod;
          PyObject *context_kwname;
          
          /* Dictionary containing tasks that are currently active in
             all running event loops.  {EventLoop: Task} */
          PyObject *current_tasks;
          
          /* WeakSet containing scheduled 3rd party tasks which don't
             inherit from native asyncio.Task */
          PyObject *non_asyncio_tasks;
          
          /* Set containing all eagerly executing tasks. */
          PyObject *eager_tasks;
          
          /* An isinstance type cache for the 'is_coroutine()' function. */
          PyObject *iscoroutine_typecache;

However this will perform poorly in free threading build as such I propose to store it in on the loop itself.

asyncio._enter_task will set the task on the loop as _current_task
asyncio._leave_task will set it to None if the task matches otherwise it’ll raise error
asyncio.current_task will just lookup the attribute on loop._current_task and return it

Note that there isn’t any compatibility issue here because third party tasks already need to call _enter_task/_leave_task so it is just a change of where the data is stored.

achimnol · May 21, 2025, 5:42pm

I also believe that making loop-specific things private to loops will improve the performance a lot in free threading, considering cache-line sharing, avoiding locks, etc.

guido · May 21, 2025, 11:22pm

Yes please.

TobiasHT · June 18, 2025, 12:26pm

On an unrelated note… I don’t seem to see your coredev badge sir.