python中socket在bind之后listen，比如listen(5)这个5，是对什么的限制

Question

服务端

# coding:utf-8   
# server.py                                                               
import socket

sock_server = socket.socket()
sock_server.setsockopt(socket.SOL_SOCKET, socket.SO_REUSEADDR, 1)
sock_server.bind(("127.0.0.1",1234))
sock_server.listen(3)
print("server start ...")
while True:
    tmp = sock_server.accept()
    print(tmp,"\n\n") 

客户端

# coding:utf-8                                                                  
import socket


def make_socks(sock_num):
    socks = []
    for i in range(sock_num):
        tmp_sock = socket.socket()
        tmp_sock.connect(("127.0.0.1",1234))
        socks.append(tmp_sock)
    

    return socks

if __name__ == "__main__":
    make_socks(5)

如上例代码中，有listen(3)，这个3是指什么，是指，这个socket只能与3个socket建立链接吗，为什么我用上面的代码可以创建大于3个的tcp连接却没报错，理论上大于3个连接应该报错的

Answer 1

The size of the tcp connection queue, that is, the number of connections

TCP handshake and socket communication details

Answer 2

Python has not been studied, but in C, it refers to the queue length of the client that can establish a connection on the server side, indicating that the server has experienced two handshakes waiting for the accept system call, which is mentioned in the book Linux High-Performance Server Programming , now this backlog is just a suggested value for the kernel, in fact it can be slightly larger. If I remember correctly, this is how it was described

Answer 3

sock_server.listen(5)  # 开始监听TCP传入连接

The value passed in specifies the maximum number of connections the operating system can suspend before rejecting the connection. This value should be at least 1, and 5 will be fine for most applications.