Python 多线程及进程

threading使用 （工业风案例）

import threading
from time import sleep, ctime


loop = [4, 2]


class ThreadFunc:

    def __init__(self, name):
        self.name = name

    def loop(self, nloop, nsec):
        '''
        :param nloop: loop函数的名称
        :param nsec: 系统休眠时间
        :return:
        '''
        print('Start loop ', nloop, 'at ', ctime())
        sleep(nsec)
        print('Done loop ', nloop, ' at ', ctime())


def main():
    print("Starting at: ", ctime())

    # ThreadFunc("loop").loop 跟一下两个式子相等：
    # t = ThreadFunc("loop")
    # t.loop
    # 以下t1 和  t2的定义方式相等
    t = ThreadFunc("loop")
    t1 = threading.Thread( target = t.loop, args=("LOOP1", 4))
    # 下面这种写法更西方人，工业化一点
    t2 = threading.Thread( target = ThreadFunc('loop').loop, args=("LOOP2", 2))

    # 常见错误写法
    #t1 = threading.Thread(target=ThreadFunc('loop').loop(100,4))
    #t2 = threading.Thread(target=ThreadFunc('loop').loop(100,2))

    t1.start()
    t2.start()

    t1.join( )
    t2.join()

    print("ALL done at: ", ctime())


if __name__ == '__main__':
    main()

输出>>>

Starting at: Sun Sep 2 10:04:47 2018
Start loop LOOP1 at Sun Sep 2 10:04:47 2018
Start loop LOOP2 at Sun Sep 2 10:04:47 2018
Done loop LOOP2 at Sun Sep 2 10:04:49 2018
Done loop LOOP1 at Sun Sep 2 10:04:51 2018
ALL done at: Sun Sep 2 10:04:51 2018

分析：注意：实例化时threading.Thread(target=xxx, args=(xxx,))格式完整，工业风写法为init了的类的函数，args为其余param，一行搞定喵

1. 可以通过设置守护线程，使不重要线程同主线程一同结束

   t1 = threading.Thread(target=fun, args=() )
   # 社会守护线程的方法，必须在start之前设置，否则无效
   t1.setDaemon(True)
   #t1.daemon = True
   t1.start()
   

2. threading.Lock()的两个线程，竞争资源都acquire()，造成无法release()，最后无法继续程序。

3. threading.Semaphore(n)n=允许同时运行线程数

4. threading.Timer(t, func)指定时间开始线程

多进程

1. 用multiprocessing.Process()直接生成进程

2. 创建子类生成：

   import multiprocessing
   from time import sleep, ctime
   
   
   class ClockProcess(multiprocessing.Process):
       '''
       两个函数比较重要
       1. init构造函数
       2. run
       '''
   
       def __init__(self, interval):
           super().__init__()
           self.interval = interval
   
       def run(self):
           while True:
               print("The time is %s" % ctime())
               sleep(self.interval)
   
   
   if __name__ == '__main__':
       p = ClockProcess(3)
       p.start()
   
       while True:
           print('sleeping.......')
           sleep(1)
   
   

   注意：

   1. __init__里用super().__init__

   2. 重写run()

   3. 可以用os.getppid()得到父进程id，用os.getpid()得到本进程id

   4. 建立进程：

      q = multiprocessing.JoinableQueue()
      # 运行消费者进程
      cons_p = multiprocessing.Process (target = consumer, args = (q,))
      cons_p.daemon = True
      cons_p.start()
      

example：

import multiprocessing
from time import ctime


def consumer(input_q):
    print("Into consumer:", ctime())
    while True:
        item = input_q.get()
        if item is None:
            break
        print("pull", item, "out of q")
    print("Out of consumer:", ctime())


def producer(sequence, output_q):
    for item in sequence:
        print("Into procuder:", ctime())
        output_q.put(item)
        print("Out of procuder:", ctime())


if __name__ == '__main__':
    q = multiprocessing.Queue()
    cons_p1 = multiprocessing.Process(target=consumer, args=(q,))
    cons_p1.start()

    cons_p2 = multiprocessing.Process (target=consumer, args=(q,))
    cons_p2.start()

    sequence = [1, 2, 3, 4]
    producer(sequence, q)

    q.put(None)
    q.put(None)

    cons_p1.join()
    cons_p2.join()

Into procuder: Tue Sep 4 15:57:37 2018
Out of procuder: Tue Sep 4 15:57:37 2018
Into procuder: Tue Sep 4 15:57:37 2018
Out of procuder: Tue Sep 4 15:57:37 2018
Into procuder: Tue Sep 4 15:57:37 2018
Out of procuder: Tue Sep 4 15:57:37 2018
Into procuder: Tue Sep 4 15:57:37 2018
Out of procuder: Tue Sep 4 15:57:37 2018
Into consumer: Tue Sep 4 15:57:37 2018
pull 1 out of q
pull 2 out of q
pull 3 out of q
pull 4 out of q
Out of consumer: Tue Sep 4 15:57:37 2018
Into consumer: Tue Sep 4 15:57:37 2018
Out of consumer: Tue Sep 4 15:57:37 2018

分析：

1. multiprocessing.Queue()建立一个进程间队列
2. Queue.put()以及Queue.get()为队列操作，先进先出