Python 多线程示例

Process Class

from multiprocessing import Process

def print_func(continent='Asia'):
    print('The name of continent is : ', continent)

if __name__ == "__main__":  # confirms that the code is under main function
    names = ['America', 'Europe', 'Africa']
    procs = []
    proc = Process(target=print_func)  # instantiating without any argument
    procs.append(proc)
    proc.start()

    # instantiating process with arguments
    for name in names:
        # print(name)
        proc = Process(target=print_func, args=(name,))
        procs.append(proc)
        proc.start()

    # complete the processes
    for proc in procs:
        proc.join()

• Process对象

• 带参数
  需要通过关键字args传递

• 启动
  虽然定义了Process obj， 但是启动该Process需要调用start( )， 否则什么也不做。 当调用start之后，process开始run,并且返回结果

• 结束

上述代码的输出：

The name of continent is :  Asia
The name of continent is :  America
The name of continent is :  Europe
The name of continent is :  Africa

Process Queue Class

• First-in-First-out
• 将queue传递给进程的目标函数
• put(): 向queue插入数据
• get()：从queue获取数据

from multiprocessing import Queue

colors = ['red', 'green', 'blue', 'black']
cnt = 1
# instantiating a queue object
queue = Queue()
print('pushing items to queue:')
for color in colors:
    print('item no: ', cnt, ' ', color)
    queue.put(color)
    cnt += 1

print('\npopping items from queue:')
cnt = 0
while not queue.empty():
    print('item no: ', cnt, ' ', queue.get())
    cnt += 1

输出如下：

pushing items to queue:
item no:  1   red
item no:  2   green
item no:  3   blue
item no:  4   black

popping items from queue:
item no:  0   red
item no:  1   green
item no:  2   blue
item no:  3   black

Process Lock Class

• Lock object
• acquire()
• release()

import multiprocessing
import time
 

def task1(lock):
    with lock:  # with  context using lock, release lock automatically
        n = 5
        while n > 1:
            print(f"{time.strftime('%H:%M:%S')} task1 output")
            time.sleep(1)
            n -= 1
 
 
def task2(lock):
    lock.acquire()
    n = 5
    while n > 1:
        print(f"{time.strftime('%H:%M:%S')} task2 output")
        time.sleep(1)
        n -= 1
    lock.release()
 
 
def task3(lock):
    lock.acquire()
    n = 5
    while n > 1:
        print(f"{time.strftime('%H:%M:%S')} task3 output")
        time.sleep(1)
        n -= 1
    lock.release()
 
 
if __name__ == "__main__":
    lock = multiprocessing.Lock()
    p1 = multiprocessing.Process(target=task1, args=(lock,))
    p2 = multiprocessing.Process(target=task2, args=(lock,))
    p3 = multiprocessing.Process(target=task3, args=(lock,))
    p1.start()
    p2.start()

Multiprocess Example

from multiprocessing import Lock, Process, Queue, current_process
import time
import queue # imported for using queue.Empty exception


def do_job(tasks_to_accomplish, tasks_that_are_done):
    while True:
        try:
            '''
                try to get task from the queue. get_nowait() function will 
                raise queue.Empty exception if the queue is empty. 
                queue(False) function would do the same task also.
            '''
            print('get task')
            task = tasks_to_accomplish.get_nowait()
        except queue.Empty:
			print('queue empty')
            break
        else:
            '''
                if no exception has been raised, add the task completion 
                message to task_that_are_done queue
            '''
            print(task)
            tasks_that_are_done.put(task + ' is done by ' + current_process().name)
            time.sleep(.5)
    return True


def main():
    number_of_task = 10
    number_of_processes = 4
    tasks_to_accomplish = Queue()
    tasks_that_are_done = Queue()
    processes = []

    for i in range(number_of_task):
        tasks_to_accomplish.put("Task no " + str(i))

    # creating processes
    for w in range(number_of_processes):
        p = Process(target=do_job, args=(tasks_to_accomplish, tasks_that_are_done))
        processes.append(p)
        p.start()

    # completing process
    for p in processes:
        p.join()

    # print the output
    while not tasks_that_are_done.empty():
        print(tasks_that_are_done.get())

    return True


if __name__ == '__main__':
    main()

输出：

Task no 0
Task no 1
Task no 2
Task no 3
Task no 4
Task no 5
Task no 6
Task no 7
Task no 8
Task no 9
Task no 0 is done by Process-1
Task no 2 is done by Process-3
Task no 1 is done by Process-2
Task no 3 is done by Process-4
Task no 4 is done by Process-2
Task no 6 is done by Process-1
Task no 5 is done by Process-3
Task no 7 is done by Process-4
Task no 8 is done by Process-2
Task no 9 is done by Process-3

参考：
Python多进程之Process、Pool、Lock、Queue、Event、Semaphore、Pipe
Python多线程详解
Python之多进程与多线程
Python Multiprocessing Example