concurrent.futures 學習筆記

concurrent.futures

先看下官方介紹

The asynchronous execution can be performed with threads, using ThreadPoolExecutor, or separate processes, using ProcessPoolExecutor. Both implement the same interface, which is defined by the abstract Executor class.

重點是 asynchronous

concurrent.futures._base.Executor

submit(fn, *args, **kwargs) -> Future

with ThreadPoolExecutor(max_workers=1) as executor:
    future = executor.submit(pow, 323, 1235)
    print(future.result())

map(func, *iterables, timeout=None, chunksize=1) -> typing.Generator

相似於 map(內置函數)

In [26]: def test(item):
    ...:     print("echo", item)
    ...:     return item
    ...:
In [27]: list(map(test, range(10)))
echo 0
echo 1
echo 2
echo 3
echo 4
echo 5
echo 6
echo 7
echo 8
echo 9
Out[27]: [0, 1, 2, 3, 4, 5, 6, 7, 8, 9]

• demo

def test(item):
    print(f"echo {item}")
    return item
with ThreadPoolExecutor(max_workers=1) as executor:
    future = executor.map(test, range(3))

shutdown

# todo

ThreadPoolExecutor

• 注意避免在一個 Future 裏面獲取另一個 Future 的 result

ProcessPoolExecutor

在 IO 密集型下使用 ThreadPoolExecutor

Future

• cancel()
  • 沒法取消當前正在執行的
• result() -> bool
• running() -> bool
• done() -> bool
• result(timeout=None) -> Any
• exception(timeout=None) -> Exception

exector = ThreadPoolExecutor(max_workers=10)
f: Future = exector.submit(test, 1)
exception: Exception = f.exception(timeout=None)

• add_done_callback(fn) -> None

def callback(*args):
    print(args) # (<Future at 0x102bcb898 state=finished raised KeyError>,) 即 f


exector = ThreadPoolExecutor(max_workers=10)
f: Future = exector.submit(test, 1)
f.add_done_callback(callback)