from concurrent.futures import ThreadPoolExecutor data = [ list(range(0, 5)), list(range(5, 10)), ] def _f(x): print(f"Processing {x}") return True print("=== 1 - No consumption from the iterator ===") executor = ThreadPoolExecutor(max_workers=1) for ints in data: executor.map(_f, ints) executor.shutdown(wait=True) print("=== 2 - Consume all values from the iterator ===") executor = ThreadPoolExecutor(max_workers=1) for ints in data: futures = executor.map(_f, ints) results = list(futures) executor.shutdown(wait=True) print("=== 3 - Consume one value from the iterator ===") executor = ThreadPoolExecutor(max_workers=1) for ints in data: futures = executor.map(_f, ints) first = next(futures) executor.shutdown(wait=True) print("=== 4 - Dropping iterator cancels remaining futures ===") executor = ThreadPoolExecutor(max_workers=1) futures = executor.map(_f, range(0, 5)) first = next(futures) del futures executor.shutdown(wait=True)