Python并发变成之concurrent.futures

    concurrent.futures模块提供了一个异步执行callables的高级接口。 可以使用ThreadPoolExecutor和ProcessPoolExecutor。 两者都继承了相同的接口，该接口由抽象的Executor类定义。

    一个抽象类，提供异步执行调用的方法。 它不应该直接使用，而是通过其具体的子类。

    submit (fn, *args, **kwargs)：提交执行的函数并获取一个Future对象，例如：

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

    ThreadPoolExecutor：是Executor子类，它使用一个线程池来异步执行调用。concurrent.futures.ThreadPoolExecutor(max_workers=None, thread_name_prefix='', initializer=None, initargs=())。例如：

import concurrent.futures
import urllib.request

URLS = ['http://www.foxnews.com/',
        'http://www.cnn.com/',
        'http://europe.wsj.com/',
        'http://www.bbc.co.uk/',
        'http://some-made-up-domain.com/']

# Retrieve a single page and report the URL and contents
def load_url(url, timeout):
    with urllib.request.urlopen(url, timeout=timeout) as conn:
        return conn.read()

# We can use a with statement to ensure threads are cleaned up promptly
with concurrent.futures.ThreadPoolExecutor(max_workers=5) as executor:
    # Start the load operations and mark each future with its URL
    future_to_url = {executor.submit(load_url, url, 60): url for url in URLS}
    for future in concurrent.futures.as_completed(future_to_url):
        url = future_to_url[future]
        try:
            data = future.result()
        except Exception as exc:
            print('%r generated an exception: %s' % (url, exc))
        else:
            print('%r page is %d bytes' % (url, len(data)))

    ProcessPoolExecutor：concurrent.futures.ProcessPoolExecutor(max_workers=None, mp_context=None, initializer=None, initargs=())：使用如下：

import concurrent.futures
import math

executor = ProcessPoolExecutor(max_workers=5)

def is_prime(n):
    if n % 2 == 0:
        return False

    sqrt_n = int(math.floor(math.sqrt(n)))
    for i in range(3, sqrt_n + 1, 2):
        if n % i == 0:
            return False
    return True

def main():
    for i in range(10):

        future = executor.submit(is_prime, n)

if __name__ == '__main__':
    main()

    Future: Future类封装了可调用的异步执行。 该实例由Executor.submit（）创建。