loop.call_soon_threadsafe¹ is a thread safe API to schedule callbacks from other threads however the handle returned by it i.e.asyncio.Handle² isn't thread safe like itscancel³ method. This is an issue even with the GIL because thread switching is preemptive and is a bigger issue for free-threading builds.

Proposal

Add a new_ThreadSafeHandle which inherits fromasyncio.Handle but internally uses a mutex to avoid multiple threads cancelling and running the callback at the same time for callbacks scheduled byloop.call_soon_threadsafe API, other APIs such asloop.call_soon will continue to use the oldasyncio.Handle.

Linked PRs

• gh-128340: make asyncio.events.Handle.cancel() atomic #128347
• gh-128340: thread safe handle forloop.call_soon_threadsafe #128369