====== 第二十九章：多进程 ======

===== 本章目标 =====

完成本章学习后，你将能够：
  * 创建和管理进程
  * 进程间通信
  * 使用进程池
  * 理解进程vs线程

===== 创建进程 =====

<code python>
import multiprocessing
import time

def worker(name):
    print(f"Process {name} started")
    time.sleep(2)
    print(f"Process {name} finished")

if __name__ == '__main__':
    # 创建进程
    p1 = multiprocessing.Process(target=worker, args=("P1",))
    p2 = multiprocessing.Process(target=worker, args=("P2",))
    
    p1.start()
    p2.start()
    
    p1.join()
    p2.join()
</code>

===== 进程间通信 =====

<code python>
import multiprocessing

# Queue
queue = multiprocessing.Queue()

def producer(queue):
    for i in range(5):
        queue.put(i)

def consumer(queue):
    while True:
        item = queue.get()
        if item is None:
            break
        print(f"Got {item}")

# Pipe
parent_conn, child_conn = multiprocessing.Pipe()
parent_conn.send('hello')
print(child_conn.recv())

# Shared memory
from multiprocessing import Value, Array
num = Value('d', 0.0)      # 共享双精度浮点数
arr = Array('i', range(10))  # 共享整数数组
</code>

===== 进程池 ======

<code python>
from multiprocessing import Pool
import os

def square(n):
    return n * n

if __name__ == '__main__':
    with Pool(processes=4) as pool:
        # map
        results = pool.map(square, range(10))
        
        # apply_async
        result = pool.apply_async(square, (5,))
        print(result.get())
        
        # 多个任务
        multiple_results = [pool.apply_async(square, (i,)) for i in range(10)]
        print([r.get() for r in multiple_results])
</code>

===== 本章练习 =====

1. 实现多进程并行计算
2. 实现进程池下载器
3. 比较进程vs线程性能

下一章：[[python_course:chapter30|第三十章：异步编程]]