linux keepalive探测对应用层socket api的影响

问题

大部分人都知道tcp的keepalive. 假设读者知道keepalive会如何触发. 这篇文章想讨论keepalive触发后, 对socket使用者的影响.

keepalive设置

修改/etc/sysctl.conf

ubuntu# vim /etc/sysctl.conf 
ubuntu# sysctl -p
fs.file-max = 131072
net.ipv4.tcp_keepalive_time = 10
net.ipv4.tcp_keepalive_intvl = 5
net.ipv4.tcp_keepalive_probes = 3

验证

ubuntu# sysctl -a | grep keepalive
net.ipv4.tcp_keepalive_intvl = 5
net.ipv4.tcp_keepalive_probes = 3
net.ipv4.tcp_keepalive_time = 10

tcp_server.py

import socket
import sys

sock = socket.socket(socket.AF_INET, socket.SOCK_STREAM)
sock.setsockopt(socket.SOL_SOCKET, socket.SO_REUSEADDR, 1)
server_address = ('localhost', 22345)
sock.bind(server_address)
sock.listen(1)
connection, client_address = sock.accept()
while True:
    data = connection.recv(1024)
    print("data", data)

tcp_client.py

import socket
import sys
import time

sock = socket.socket(socket.AF_INET, socket.SOCK_STREAM)
sock.setsockopt(socket.SOL_SOCKET, socket.SO_KEEPALIVE, 1)
server_address = ('localhost', 22345)
sock.connect(server_address)

time.sleep(999999999)

可以看到, 因为tcp_client开启了SO_KEEPALIVE, 所以tcp_client主动往tcp_server发起KEEPALIVE探测.

若tcp_server开启SO_KEEPALIVE, 则是tcp_server往tcp_client发送KEEPALIVE探测.

如果tcp_server/tcp_client都开启KEEPALIVE, 则会双向探测.

对应用层socket api的影响

为了模拟keepalive生效的情况, 用 docker 模拟断网线的情况.

docker commit -a "enjolras" -m "ubuntu python" 92edf5cfb2e0 ubuntu_with_python

对send/recv的影响

对select的影响

对epoll的影响