Python：同时执行多个函数
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Python: Executing multiple functions simultaneously
提问by user2739601
I'm trying to run two functions simultaneously in Python. I have tried the below code which uses multiprocessingbut when I execute the code, the second function starts only after the first is done.
我正在尝试在 Python 中同时运行两个函数。我尝试了下面使用multiprocessing的代码，但是当我执行代码时，第二个函数仅在第一个函数完成后才启动。
from multiprocessing import Process
def func1:
#does something
def func2:
#does something
if __name__=='__main__':
p1 = Process(target = func1)
p1.start()
p2 = Process(target = func2)
p2.start()
采纳答案by Shashank
You are doing it correctly. :)
你做得对。:)
Try running this silly piece of code:
尝试运行这段愚蠢的代码：
from multiprocessing import Process
import sys
rocket = 0
def func1():
global rocket
print 'start func1'
while rocket < sys.maxint:
rocket += 1
print 'end func1'
def func2():
global rocket
print 'start func2'
while rocket < sys.maxint:
rocket += 1
print 'end func2'
if __name__=='__main__':
p1 = Process(target = func1)
p1.start()
p2 = Process(target = func2)
p2.start()
You will see it print 'start func1' and then 'start func2' and then after a (very) long time you will finally see the functions end. But they will indeed execute simultaneously.
您将看到它打印“start func1”，然后打印“start func2”，然后在（非常）很长时间后，您将最终看到函数结束。但它们确实会同时执行。
Because processes take a while to start up, you may even see 'start func2' before'start func1'.
由于进程需要一段时间才能启动，您甚至可能会在“start func1”之前看到“start func2 ”。
回答by Alistair Bendall
This is just what i needed. I know it wasn't asked but i modified shashank's code to suit Python 3 for anyone else looking :)
这正是我所需要的。我知道它没有被问到，但我修改了 shashank 的代码以适合 Python 3 以供其他人查找:)
from multiprocessing import Process
import sys
rocket = 0
def func1():
global rocket
print ('start func1')
while rocket < sys.maxsize:
rocket += 1
print ('end func1')
def func2():
global rocket
print ('start func2')
while rocket < sys.maxsize:
rocket += 1
print ('end func2')
if __name__=='__main__':
p1 = Process(target=func1)
p1.start()
p2 = Process(target=func2)
p2.start()
Substitute sys.maxsize for an number then print(rocket)and you can see it count up one at a time. Get to a number and stop
将 sys.maxsize 替换为一个数字，然后打印（火箭），您可以看到它一次计数一个。到达一个数字并停止
回答by TheWalkingData
This is a very good example by @Shashank. I just want to say that I had to add joinat the end, or else the two processes were not running simultaneously:
这是@Shashank 的一个很好的例子。我只想说join最后必须加上，不然两个进程不是同时运行的：
from multiprocessing import Process
import sys
rocket = 0
def func1():
global rocket
print 'start func1'
while rocket < sys.maxint:
rocket += 1
print 'end func1'
def func2():
global rocket
print 'start func2'
while rocket < sys.maxint:
rocket += 1
print 'end func2'
if __name__=='__main__':
p1 = Process(target = func1)
p1.start()
p2 = Process(target = func2)
p2.start()
# This is where I had to add the join() function.
p1.join()
p2.join()
Furthermore, Check this thread out: When to call .join() on a process?
此外，请查看此线程： 何时在进程上调用 .join()？
回答by Ahmed Benhida
Here is another version, if a dynamic list of processes need to be run. I am including the two shell scripts, if you want to try it:
这是另一个版本，如果需要运行进程的动态列表。如果您想尝试一下，我将包含两个 shell 脚本：
t1.sh
t1.sh
for i in {1..10}
do
echo "1... t.sh i:"$i
sleep 1
done
t2.sh
t2.sh
for i in {1..3}
do
echo "2.. t2.sh i:"$i
sleep 1
done
np.py
压缩包
import os
from multiprocessing import Process, Lock
def f(l, cmd):
os.system(cmd)
if __name__ == '__main__':
lock = Lock()
for cmd in ['sh t1.sh', 'sh t2.sh']:
Process(target=f, args=(lock, cmd)).start()
output
输出
1... t.sh i:1
2.. t2.sh i:1
1... t.sh i:2
2.. t2.sh i:2
1... t.sh i:3
2.. t2.sh i:3
1... t.sh i:4
1... t.sh i:5
1... t.sh i:6
1... t.sh i:7
1... t.sh i:8
1... t.sh i:9
1... t.sh i:10
"lock" left there can be acquired before task "l.acquire()" and released after "l.release()"
留在那里的“锁”可以在任务“ l.acquire()”之前获取并在“ l.release()”之后释放
回答by Ion Stoica
This can be done elegantly with Ray, a system that allows you to easily parallelize and distribute your Python code.
这可以通过Ray优雅地完成，这是一个允许您轻松并行化和分发 Python 代码的系统。
To parallelize your example, you'd need to define your functions with the @ray.remote decorator, and then invoke them with .remote.
要并行化您的示例，您需要使用 定义函数@ray.remote decorator，然后使用 调用它们.remote。
import ray
ray.init()
# Define functions you want to execute in parallel using
# the ray.remote decorator.
@ray.remote
def func1():
#does something
@ray.remote
def func2():
#does something
# Execute func1 and func2 in parallel.
ray.get([func1.remote(), func2.remote()])
If func1()and func2()return results, you need to rewrite the code as follows:
如果func1()和func2()返回结果，则需要将代码改写如下：
ret_id1 = func1.remote()
ret_id2 = func1.remote()
ret1, ret2 = ray.get([ret_id1, ret_id2])
There are a number of advantages of using Ray over the multiprocessingmodule. In particular, the same codewill run on a single machine as well as on a cluster of machines. For more advantages of Ray see this related post.
与多处理模块相比，使用 Ray 有许多优点。特别是，相同的代码将在单台机器和机器集群上运行。有关 Ray 的更多优势，请参阅此相关帖子。
