Other methods of the process

P = Process(target=f,)

P.Pid view process No. view process name p.name

P.is_alive(), return a true or False

P.terminate() sends a signal to the operating system to end the process

Verify that processes are spatially isolated

 

from multiprocessing import Process

num = 100

def f1():
    global num
    num = 3
    print(num)  # Result 3

if __name__ == '__main__':
    p = Process(target=f1,)
    p.start()
    p.join()
    print(num)  # Result 100

 

 

 

 

Daemon

When the code of the main process finishes running, the subprocesses set as daemons will end

P.daemon = True

import time
from multiprocessing import Process

def f1():
    time.sleep(3)
    print('xxxx')

def f2():
    time.sleep(5)
    print('Code for normal subprocesses')

if __name__ == '__main__':

    p = Process(target=f1,)
    p.daemon = True  
    p.start()
    p2 = Process(target=f2,)
    p2.start()
    print('End of main process')  #  The daemons will end with the code that follows the parent,End

Process lock

Data sharing manager

When data (file content) is shared by multiple processes, it will cause data insecurity

To ensure data security, but at the expense of efficiency, the code with lock becomes the state of (synchronous) serial execution, also known as synchronous lock / mutually exclusive lock

Two ways to lock

l = Lock()

1).with l:

Content in lock

2).

l.acquire()

Lock contents

l.release()

import time
from multiprocessing import Process,Manager,Lock

def f1(m_d,l2):
    with l2:
        # l2.acquire()
        tmp = m_d['num']
        tmp -= 1
        time.sleep(0.1)
        m_d['num'] = tmp
        # l2.release()

if __name__ == '__main__':
    m = Manager()
    l2 = Lock()
    m_d = m.dict({'num':100})
    p_list = []
    for i in range(10):
        p = Process(target=f1,args=(m_d,l2))
        p.start()
        p_list.append(p)

    [pp.join() for pp in p_list]

    print(m_d['num'])

queue

Queue()

Q = Queue(10)

Q.put() put data

Q.get() fetching data

Q.qsize() returns the length of content in the current queue

Q.put_nowait(), do not wait, but report an error

Q.get ﹣ nowait(), not waiting, is also an error

Q.full()  q.empty() 

Using queue to implement consumer producer model: buffering, decoupling,

import time
from multiprocessing import Process,Queue,JoinableQueue
#Producer
def producer(q):
    for i in range(10):
        time.sleep(0.2)
        s = 'Big stuffed bun%s Number'%i
        print(s+'Fresh baked')
        q.put(s)
    q.join() #Just wait. task_done()Number of signals,And I put When the number of entries is the same,To continue
    print('All the tasks have been dealt with')
#Consumer
def consumer(q):
    while 1:
        time.sleep(0.5)
        baozi = q.get()

        print(baozi+'Be eaten')
        q.task_done()  #Send a signal to the queue that the task has been processed

if __name__ == '__main__':
    # q = Queue(30)
    q = JoinableQueue(30) #It's also a queue with a length of 30

    pro_p = Process(target=producer,args=(q,))
    con_p = Process(target=consumer,args=(q,))
    pro_p.start()
    con_p.daemon = True
    con_p.start()

    pro_p.join()
    print('End of main process')