40-TCP 多进程共享 socket

tornado 源码多进程(process.py)那段，发现他的多进程模型和一般常见的模型有点不一样，

常见的是主进程 bind -> listen -> accept, 将 accept 返回的 socket 用子进程处理，
tornado 则是 bind -> listen -> fork, 在 listen 之后 fork，多个子进程共享 listen socket，每个子进程都 accept。

感觉会有错误或 “惊群” 现象，自己写了个程序测试一下

import socket
import select
import os
import time
import errno
 
def child_epoll():
    epoll = select.epoll()
    epoll.register(sock.fileno(), select.EPOLLIN)
    try:
        while True:
            events = epoll.poll(1)
            for fileno, event in events:
                if fileno == sock.fileno():
                    connection, address = sock.accept()
                    print(os.getpid(), address)
                    time.sleep(1)
                    connection.close()
    finally:
        epoll.unregister(sock.fileno())
        epoll.close()
 
 
def start_child(i):
    pid = os.fork()
    if pid == 0:
        child_epoll()
    else:
        children[pid] = i
 
sock = socket.socket(socket.AF_INET, socket.SOCK_STREAM, 0)
sock.setsockopt(socket.SOL_SOCKET, socket.SO_REUSEADDR, 1)
sock.setblocking(0)
sock.bind(("0.0.0.0", 9700))
sock.listen(128)
 
 
children = {}
 
for i in range(4):
    start_child(i)
 
time.sleep(2)
print(children)
while children:
    try:
        pid = status = os.wait()
    except Exception as e:
        if e.errno ==  errno.EINTR:
            continue
        raise
    if pid not in children:
        continue
    children.pop(pid)