实际上Python比java提供了更激进的并发模式 (当然java也可以做到,不过没人愿意启动那么多虚拟机吧)
它使用多进程的方式来处理并发需求
下面是一个简单例子,看起来跟多线程都差不多
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from multiprocessing import Process
import os
# 子进程要执行的代码
def run_proc(name):
print ('Run child process %s (%s)...' % (name, os.getpid()));
if __name__=='__main__':
print ('Parent process %s.' % os.getpid());
p = Process(target=run_proc, args=('test',));
print ('Process will start.');
p.start();
p.join();
print ('Process end.');
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然后我们来尝试一下上一个计算pi的例子,看看多进程模式下python的并发性能
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from multiprocessing import Process
import os
from decimal import *;
import sys;
import math;
import time;
def bellard(n):
pi=Decimal(0)
k=0
while k < n:
pi+=(Decimal(-1)**k/(1024**k))*( Decimal(256)/(10*k+1)+Decimal(1)/(10*k+9)-Decimal(64)/(10*k+3)-Decimal(32)/(4*k+1)-Decimal(4)/(10*k+5)-Decimal(4)/(10*k+7)-Decimal(1)/(4*k+3))
k+=1
pi=pi*1/(2**6)
return pi
def say(name):
start = time.clock();
for i in range(100):
p = bellard(1000);
# print("running..."+str(p));
end = time.clock();
print ("read: %f s" % (end - start));
def run_proc(name):
print ('Run child process %s (%s)...' % (name, os.getpid()));
if __name__=='__main__':
print ('Parent process %s.' % os.getpid());
p = Process(target=say, args=('test',));
print ('Process will start.');
p.start();
p.join();
print ('Process end.');
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单进程下结果
Parent process 8184.
Process will start.
read: 25.787227 s
Process end. |
双进程稍微修改一下程序
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from multiprocessing import Process
import os
from decimal import *;
import sys;
import math;
import time;
def bellard(n):
pi=Decimal(0)
k=0
while k < n:
pi+=(Decimal(-1)**k/(1024**k))*( Decimal(256)/(10*k+1)+Decimal(1)/(10*k+9)-Decimal(64)/(10*k+3)-Decimal(32)/(4*k+1)-Decimal(4)/(10*k+5)-Decimal(4)/(10*k+7)-Decimal(1)/(4*k+3))
k+=1
pi=pi*1/(2**6)
return pi
def say(name):
start = time.clock();
for i in range(100):
p = bellard(1000);
# print("running..."+str(p));
end = time.clock();
print ("read: %f s" % (end - start));
def run_proc(name):
print ('Run child process %s (%s)...' % (name, os.getpid()));
if __name__=='__main__':
print ('Parent process %s.' % os.getpid());
p = Process(target=say, args=('test',));
p2 = Process(target=say, args=('test',));
print ('Process will start.');
p.start();
p2.start();
# p.join();
print ('Process end.');
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Parent process 7020.
Process will start.
Process end.
read: 26.193302 s
read: 26.187929 s
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可以看到并没有消耗两倍的时间,是真实并发
4 进程消耗如下
Parent process 7796.
Process will start.
Process end.
read: 29.337095 s
read: 29.761048 s
read: 29.792244 s
read: 30.208371 s
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最后8进程,在4核cpu上消耗了差不多两倍时间
Parent process 5844.
Process will start.
Process end.
read: 51.267404 s
read: 55.194120 s
read: 58.598105 s
read: 58.615099 s
read: 59.172344 s
read: 59.067506 s
read: 59.797957 s
read: 60.902044 s
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