同步调用和异步调用是两种提交任务的方式
同步调用：提交完任务后，就在原地等待任务执行完毕，拿到运行结果/返回值后再执行下一步，同步调用下任务是串行执行。
异步调用：提交完任务后，不会再原地等待任务执行完毕，直接执行下一行代码，异步调用时并发执行。
异步调用，几乎同时下达任务
from concurrent.futures import ProcessPoolExecutor
import os, time,random
def task(x):
print("%s is running" % os.getpid())
time.sleep(random.randint(1,3))
return x**2
if __name__=="__main__":
p = ProcessPoolExecutor()
futures = []
for i in range(10):
future = p.submit(task,i)#返回计算结果
futures.append(future)
p.shutdown(wait=True)#默认waiti为True 等待十个进程任务执行完，关闭进程池的入口。
for future in futures:
print(future.result())
print("主")结果为：
10760 is running
10564 is running
12848 is running
3928 is running
10564 is running
12848 is running
10760 is running
3928 is running
10760 is running
10564 is running
0
1
4
9
16
25
36
49
64
81
主如果把p.shutdown(wait=True)去掉，则会出现结果穿插在进程中
2908 is running
8092 is running
10376 is running
13136 is running
8092 is running
2908 is running
0
1
8092 is running
10376 is running
4
2908 is running
10376 is running
9
16
25
36
49
64
81
主同步调用：
def task(x):
print("%s is running" % os.getpid())
time.sleep(random.randint(1,3))
return x**2
if __name__=="__main__":
p = ProcessPoolExecutor()
for i in range(10):
res = p.submit(task,i).result()#返回计算结果
print(res)
print("主")
结果为：
8360 is running
0
472 is running
1
4888 is running
4
12980 is running
9
8360 is running
16
472 is running
25
4888 is running
36
12980 is running
49
8360 is running
64
472 is running
81
主串行执行，效率低下。