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This approach leverages JavaScript's built-in setTimeout and clearTimeout functions. We schedule a timeout to execute the function fn after t milliseconds, and we return a cancelFn that, when called, cancels this scheduled timeout.
In C, without a standard set of functions for asynchronous timeouts, it's less about algorithmic complexity and more about the overhead of managing threads, which varies based on the implementation details.
  
The JavaScript solution directly uses setTimeout to schedule the function call and clearTimeout for cancelation. A timeout ID returned by setTimeout allows us to reference and clear the timeout when the cancel function is invoked.
This alternative approach involves using Promises to manage asynchronous execution and potential cancelation. By wrapping the setTimeout within a Promise, we can have more control over its execution and cancelation by managing the Promise lifecycle.
Time Complexity and space complexity would depend on the specific threading mechanism and the use of synchronization primitives.
1import asyncio
2
3async def cancellable(fn, args, t):
4    task = asyncio.ensure_future(asyncio.sleep(t / 1000))
5
6    async def cancel_task():
7        if not task.done():
8            task.cancel()
9            print("Cancelled")
10
11    try:
12        await task
13        fn(*args)
14    except asyncio.CancelledError:
15        pass
16    return cancel_task
17
18async def main():
19    async def myFunction(x):
20        print(x * 5)
21
22    cancel_fn = await cancellable(myFunction, [2], 20)
23
24    # Simulate cancel call
25    await asyncio.sleep(0.01)  # Less than 20ms, hence should cancel the execution
26    await cancel_fn()
27
28asyncio.run(main())Python's asyncio library is employed to establish async tasks similar to Promises. We define an asynchronous cancellable function to handle the timeout and a separate task for cancelation, leveraging the async/await syntax.