# 多进程
# 创建子进程
'''
import os

print('Process (%s) start...' % os.getpid())
pid = os.fork()
if pid == 0:
    print('%s %s' % (os.getpid(), os.getppid()))
else:
    print('%s %s' % (os.getpid(), pid))
'''

# 启动一个子进程并等待结束
'''
import os
from multiprocessing import Process

def run_proc(name):
    print('Run child process %s (%s)...' % (name, os.getpid()))

if __name__=='__main__':
    print('Parent process %s.' % os.getpid())
    p = Process(target=run_proc, args=('test',))
    print('Child process will start')
    p.start()
    p.join() # 可以等待子进程结束后再继续往下运行，通常用于进程间的同步
    print('Child process end.')
'''

# Pool进程池，批量创建子进程
'''
from multiprocessing import Pool
import os, time, random

def long_time_task(name):
    print('Run task %s (%s)...' % (name, os.getpid()))
    start = time.time()
    time.sleep(random.random() * 3)
    end = time.time()
    print('Task %s runs %0.2f seconds.' % (name, (end - start)))

if __name__=='__main__':
    print('Parent process %s.' % os.getpid())
    p = Pool(4) # 默认大小是CPU的核数
    for i in range(5):
        p.apply_async(long_time_task, args=(i,))
    print('Waiting for all subprocesses done...')
    p.close()
    p.join()
    print('All subprocesses done.')
'''

# 子进程
# import subprocess

'''
print('$ nslookup www.python.org')
r = subprocess.call(['nslookup', 'www.liaoxuefeng.com'])
print('Exit code:', r)
'''

'''
print('$ nslookup')
p = subprocess.Popen(['nslookup'], stdin=subprocess.PIPE, stdout=subprocess.PIPE, stderr=subprocess.PIPE)
output, err = p.communicate(b'set q=mx\npython.org\nexit\n')
print(output.decode('utf-8'))
print('Exit code:', p.returncode)
'''

# 进程间通信 Queue,Pipes
from multiprocessing import Process, Queue
import os, time, random

# 写数据进程执行的代码
def write(q):
    print('Process to write: %s' % os.getpid())
    for value in ['A', 'B', 'C']:
        print('Put %s to queue...' % value)
        q.put(value)
        time.sleep(random.random())

# 读数据进程执行的代码
def read(q):
    print('Process to read: %s' % os.getpid())
    while True:
        value = q.get(True)
        print('Get %s from queue.' % value)

if __name__=='__main__':
    # 父进程创建queue，并传给各个子进程
    q = Queue() 
    pw = Process(target=write, args=(q,))
    pr = Process(target=read, args=(q,))
    # 启动子进程pw，写入
    pw.start()
    # 启动子进程pr，读取
    pr.start()
    # 等待pw结束
    pw.join()
    # pr进程里是死循环，无法等待结束，只能强行终止
    pr.terminate()