Problem

The absence of a Drop call for non-terminal futures can lead to memory leaks or infinite waiting for mutexes and other synchronization primitives in case of an exception.

Solution

Call Future cancellation in the object finalizer and suppress the finalization when completed correctly

Alternatives

Do nothing.
The low-level implementation of Future is responsible for the correct Drop call, and the user should not be able to cause these errors by any of his actions.
Exceptions are the explicit acquisition of resources similar to locks, as in Mutex.