初步解析Python下的多进程编程

# multiprocessing.py
import os

print 'Process (%s) start...' % os.getpid()
pid = os.fork()
if pid==0:
  print 'I am child process (%s) and my parent is %s.' % (os.getpid(), os.getppid())
else:
  print 'I (%s) just created a child process (%s).' % (os.getpid(), pid)

Process (876) start...
I (876) just created a child process (877).
I am child process (877) and my parent is 876.

from multiprocessing import Process
import os

# 子进程要执行的代码
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 'Process will start.'
  p.start()
  p.join()
  print 'Process end.'

Parent process 928.
Process will start.
Run child process test (929)...
Process end.

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()
  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.'

Parent process 669.
Waiting for all subprocesses done...
Run task 0 (671)...
Run task 1 (672)...
Run task 2 (673)...
Run task 3 (674)...
Task 2 runs 0.14 seconds.
Run task 4 (673)...
Task 1 runs 0.27 seconds.
Task 3 runs 0.86 seconds.
Task 0 runs 1.41 seconds.
Task 4 runs 1.91 seconds.
All subprocesses done.

p = Pool(5)

from multiprocessing import Process, Queue
import os, time, random

# 写数据进程执行的代码:
def write(q):
  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):
  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，无法等待其结束，只能强行终止:
  pr.terminate()

Put A to queue...
Get A from queue.
Put B to queue...
Get B from queue.
Put C to queue...
Get C from queue.