A process in the process pool was terminated abruptly while the future was running or pending

解决方法：

把代码加到main中执行，有时能加速6倍左右

改之前：

p = ProcessPoolExecutor(max_workers=3)
results = p.map(task, URLS,range(3))
p.shutdown(wait=True)
for ret,url in results:
    print(ret,url)

改之后：

if __name__ == "__main__": 
    p = ProcessPoolExecutor(max_workers=3)
    results = p.map(task, URLS,range(3))
    p.shutdown(wait=True)
    for ret,url in results:
        print(ret,url)

二.使用ProcessPoolExecutor
在concurrent.futures 库中有ThreadPoolExecutor(多线程)，ProcessPoolExecutor(多进程)
ThreadPoolExecutor，ProcessPoolExecutor的区别:
ThreadPoolExecutor:
ThreadPoolExecutor多线程并行执行任务，可以共享当前进程变量，但缺点也很致命，由于python GIL(Global Interpreter Lock 全局解释器锁)
的原因，及时多线程，但其实仍然最多只能占用CPU一个核，准确只能说是并发了，如果指定的任务和线程数不恰当(比如一个任务很