3.基于fork模式的进程 案例分析

案例1：子进程会将主进程的数据拷贝一份，造成两次打印

import multiprocessing
def task():
    print(name)
    file_object.write("alex\n")
    file_object.flush()
if __name__ == '__main__':
    multiprocessing.set_start_method("fork")
    name = []
    file_object = open('x1.txt', mode='a+', encoding='utf-8')
    file_object.write("武沛齐\n")
    p1 = multiprocessing.Process(target=task)
    p1.start()
# 输出:
武沛齐  # 这个是子进程
alex    # 这个是子进程        
武沛齐   # 这个是主进程

案例2：flush以后，进程中内存的数据会清空释放

import multiprocessing
def task():
    print(name)
    file_object.write("alex\n")
    file_object.flush()
if __name__ == '__main__':
    multiprocessing.set_start_method("fork")
    name = []
    file_object = open('x1.txt', mode='a+', encoding='utf-8')
    file_object.write("武沛齐\n")
    file_object.flush()
    p1 = multiprocessing.Process(target=task)
    p1.start()

案例3：子进程中的主线程锁释放了，其他子线程才能进入

import multiprocessing
import threading
import time
def func():
    print("来了")
    with lock:
        print(666)
        time.sleep(1)
def task():
    # 拷贝的锁也是被申请走的状态
    # 被谁申请走了? 被子进程中的主线程申请走了
    for i in range(10):
        t = threading.Thread(target=func)
        t.start()
    time.sleep(2)
    lock.release()
if __name__ == '__main__':
    multiprocessing.set_start_method("fork")
    name = []
    lock = threading.RLock()
    lock.acquire()
    # print(lock)
    # lock.acquire() # 申请锁
    # print(lock)
    # lock.release()
    # print(lock)
    # lock.acquire()  # 申请锁
    # print(lock)
    p1 = multiprocessing.Process(target=task)
    p1.start()