Currently, There is two types of Executor in `concurrent.futures`. They are `ThreadPoolExecutor` and `ProcessPoolExecutor`, there is GIL limitation of `ThreadPoolExecutor` and `ProcessPoolExecutor` need to use `pickle` which have limitation on decorated function. It would be nice to add new Executor `UnixForkExecutor` which is based on `os.fork` and shared memory (to return future). The drawback of UnixForkExecutor can only be used on Unix platform. This is not a problem, because the majority people use python for parallel computing on Unix platform. Anyone have any opinion about it?