Lock组件
当我们用多进程来读写文件的时候，如果一个进程是写文件，一个进程是读文件，
如果两个文件同时进行，肯定是不行的，必须是文件写结束后，才可以进行读操作。
或者是多个进程在共享一些资源的时候，同时只能有一个进程进行访问，那就需要锁机制进行控制。
需求：
一个进程写入一个文件，一个进程追加文件，一个进程读文件，同时启动起来
我们可以通过进程的join()方法来实现，这是一种方法，本节用Lock（进程锁）来实现。
函数说明：
# lock = multiprocessing.Lock()
# lock.acquire() #获得锁
# lock.release() #释放锁
先写不加锁的程序：
#不加锁
# number +1
# number +3
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import multiprocessing
import time
def add(number,value,lock):
print ("init add{0} number = {1}".format(value, number))
for i in xrange(1, 6):
number += value
time.sleep(1)
print ("add{0} number = {1}".format(value, number))
if __name__ == "__main__":
lock = multiprocessing.Lock()
number = 0
p1 = multiprocessing.Process(target=add,args=(number, 1, lock))
p2 = multiprocessing.Process(target=add,args=(number, 3, lock))
p1.start()
p2.start()
print ("main end")
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结果：
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main endinit add1 number = 0init add3 number = 0add1 number = 1add3 number = 3add1 number = 2add3 number = 6add1 number = 3add3 number = 9add1 number = 4add3 number = 12add1 number = 5add3 number = 15 |
再写加锁的程序：
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import multiprocessing
import time
def add(number,value,lock):
with lock:
print ("init add{0} number = {1}".format(value, number))
for i in xrange(1, 6):
number += value
time.sleep(1)
print ("add{0} number = {1}".format(value, number))
if __name__ == "__main__":
lock = multiprocessing.Lock()
number = 0
p1 = multiprocessing.Process(target=add,args=(number, 1, lock))
p2 = multiprocessing.Process(target=add,args=(number, 3, lock))
p1.start()
p2.start()
print ("main end")
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结果：
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main endinit add1 number = 0 #add1优先抢到锁，优先执行
add1 number = 1add1 number = 2add1 number = 3add1 number = 4add1 number = 5init add3 number = 0 #add3被阻塞，等待add1执行完成，释放锁后执行add3
add3 number = 3add3 number = 6add3 number = 9add3 number = 12add3 number = 15 |
使用 lock.acquire() 和 lock.release()
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import multiprocessing
import time
def add(number,value,lock):
lock.acquire()
try:
print ("init add{0} number = {1}".format(value, number))
for i in xrange(1, 6):
number += value
time.sleep(1)
print ("add{0} number = {1}".format(value, number))
except Exception as e:
raise e
finally:
lock.release()
if __name__ == "__main__":
lock = multiprocessing.Lock()
number = 0
p1 = multiprocessing.Process(target=add,args=(number, 1, lock))
p2 = multiprocessing.Process(target=add,args=(number, 3, lock))
p1.start()
p2.start()
print ("main end")
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结果：
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main endinit add1 number = 0
add1 number = 1
add1 number = 2
add1 number = 3
add1 number = 4
add1 number = 5
init add3 number = 0
add3 number = 3
add3 number = 6
add3 number = 9
add3 number = 12
add3 number = 15
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共享内存
python的multiprocessing模块也给我们提供了共享内存的操作
一般的变量在进程之间是没法进行通讯的，multiprocessing 给我们提供了 Value 和 Array 模块，他们可以在不通的进程*同使用
例子：不加锁，让number加完1后再继续加3，再继续加一，再继续加3...
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import multiprocessing
import time
def add(number,add_value):
try:
print ("init add{0} number = {1}".format(add_value, number.value))
for i in xrange(1, 6):
number.value += add_value
print ("***************add{0} has added***********".format(add_value))
time.sleep(1)
print ("add{0} number = {1}".format(add_value, number.value))
except Exception as e:
raise e
if __name__ == "__main__":
number = multiprocessing.Value('i', 0)
p1 = multiprocessing.Process(target=add,args=(number, 1))
p2 = multiprocessing.Process(target=add,args=(number, 3))
p1.start()
p2.start()
print ("main end")
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打印结果：
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main endinit add1 number = 0
***************add1 has added***********
init add3 number = 1
***************add3 has added***********
add1 number = 4
***************add1 has added***********
add3 number = 5
***************add3 has added***********
add1 number = 8
***************add1 has added***********
add3 number = 9
***************add3 has added***********
add1 number = 12
***************add1 has added***********
add3 number = 13
***************add3 has added***********
add1 number = 16
***************add1 has added***********
add3 number = 17
***************add3 has added***********
add1 number = 20
add3 number = 20
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再给加上锁：
加1的进程加完后，再执行加上3的进程
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import multiprocessing
import time
def add(number,add_value,lock):
lock.acquire()
try:
print ("init add{0} number = {1}".format(add_value, number.value))
for i in xrange(1, 6):
number.value += add_value
print ("***************add{0} has added***********".format(add_value))
time.sleep(1)
print ("add{0} number = {1}".format(add_value, number.value))
except Exception as e:
raise e
finally:
lock.release()
if __name__ == "__main__":
lock = multiprocessing.Lock()
number = multiprocessing.Value('i', 0)
p1 = multiprocessing.Process(target=add,args=(number, 1, lock))
p2 = multiprocessing.Process(target=add,args=(number, 3, lock))
p1.start()
p2.start()
print ("main end")
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执行结果（对比上面）：
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main endinit add1 number = 0***************add1 has added***********add1 number = 1***************add1 has added***********add1 number = 2***************add1 has added***********add1 number = 3***************add1 has added***********add1 number = 4***************add1 has added***********add1 number = 5init add3 number = 5***************add3 has added***********add3 number = 8***************add3 has added***********add3 number = 11***************add3 has added***********add3 number = 14***************add3 has added***********add3 number = 17***************add3 has added***********add3 number = 20 |
多进程共享内存实现：
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import multiprocessing
import time
def add(number,add_value,lock):
lock.acquire()
try:
print ("init add{0} number = {1}".format(add_value, number.value))
for i in xrange(1, 6):
number.value += add_value
print ("***************add{0} has added***********".format(add_value))
time.sleep(1)
print ("add{0} number = {1}".format(add_value, number.value))
except Exception as e:
raise e
finally:
lock.release()
def change(arr):
for i in range(len(arr)):
arr[i] = -arr[i]
if __name__ == "__main__":
lock = multiprocessing.Lock()
number = multiprocessing.Value('i', 0)
arr = multiprocessing.Array('i', range(10))
print (arr[:])
p1 = multiprocessing.Process(target=add,args=(number, 1, lock))
p2 = multiprocessing.Process(target=add,args=(number, 3, lock))
p3 = multiprocessing.Process(target=change,args=(arr,))
p1.start()
p2.start()
p3.start()
p3.join()
print (arr[:])
print ("main end")
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结果：
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[0, 1, 2, 3, 4, 5, 6, 7, 8, 9]init add3 number = 0***************add3 has added***********[0, -1, -2, -3, -4, -5, -6, -7, -8, -9]main endadd3 number = 3***************add3 has added***********add3 number = 6***************add3 has added***********add3 number = 9***************add3 has added***********add3 number = 12***************add3 has added***********add3 number = 15init add1 number = 15***************add1 has added***********add1 number = 16***************add1 has added***********add1 number = 17***************add1 has added***********add1 number = 18***************add1 has added***********add1 number = 19***************add1 has added***********add1 number = 20 |
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本文转自 听丶飞鸟说 51CTO博客，原文链接:http://blog.51cto.com/286577399/2049535