Context vars are not usable in wrapped function

[cfytrok]

cachetools-async/src/cachetools_async/decorators.py

Line 80 in a9fb6eb

task = loop.create_task(coro)

The function under the decorator is executed in another task. This breaks code that depends on context variables. asyncache avoided creating tasks. Is it possible to do without it here too?

[imnotjames]

Would it be correct to change the title to "maintain context variables"? It sounds like a new task doesn't matter to you but the lack of maintaining the context variables does.

[imnotjames]

The reason why a new task is created is that this implementation doesn't run the async function multiple times if you have multiple calls while the async function is running - they all wait for the same instance of the function to complete.

Without that, multiple calls to the async function will allow for multiple executions of the code until one of them completes - and then future calls will be cached.

I think this could be solved by passing the context vars to the new task -- but that's also assuming the context vars aren't important for the cache key. I am pretty certain you can use context vars in the cache key, though, if you wanted.

Path forward:

• Add tests validating context vars fail
• Pass current context vars to task
• Update docs to clarify how context vars will work

[imnotjames]

Do you have a minimal test case that exhibits the behavior? I just tried to write a test case to validate this and the contextvar values pass through as I'd expect them to.

Here's the test I was adding but it doesn't exhibit any issues:

    async def test_context_var_passed(self):
        var = contextvars.ContextVar("var")
        var.set("example")

        async def example():
            return var.get()

        decorated_fn = cachetools_async.cached({})(example)

        actual = await decorated_fn()
        assert actual == "example"

I can add this as a regression test but I'm struggling to replicate the issue you're having.