socket_dup

Reference

• The evolution of reuseport in the Linux kernel
• 跨进程复制socket
• Linux网络编程“惊群”问题总结
• accept 与 epoll 惊群
• Advanced Programming in the UNIX Environment. 3rd Edition, Page 642, 17.4 Passing File Descriptors
• UNIX Network Programming - The Sockets Networking API. Volume 1, 3rd Edition, Page 420, 15.7 Passing Descriptors
• UNIX Network Programming - The Sockets Networking API. Volume 1, 3rd Edition, Page 829, 4.4 BSD Implementation

Demo steps

Run the following command to build the binaraies.

• go build -o demo main.go

Run the following command to start the first server.

• ./demo

You should get the following output:

$ ./demo 
listen on:  [::]:7000
Listening on /tmp/unix_socket_tcp
[49451] 2021-11-06 21:43:55.0125327 +0800 CST m=+4.472036001 recv msg is: hello
[49451] 2021-11-06 21:43:55.1211736 +0800 CST m=+4.580667201 recv msg is: hello

Run the following command to start the client. The client will keep sending hello message to localhost:7000

• while true; do nc localhost 7000 -e echo hello; sleep 0.1; done

Run the following command to start the second server.

• ./demo 2

You should get the following output:

$ ./demo 2
recv fd 7
listen on:  [::]:7000
[49591] 2021-11-06 21:44:02.6632161 +0800 CST m=+1.219149001 recv msg is: hello
[49591] 2021-11-06 21:44:02.8883711 +0800 CST m=+1.444308201 recv msg is: hello
[49591] 2021-11-06 21:44:03.0006343 +0800 CST m=+1.556868001 recv msg is: hello

You can run more servers, if you like it.

$ ./demo 3
recv fd 7
listen on:  [::]:7000
[49778] 2021-11-06 21:44:13.1593171 +0800 CST m=+1.555800001 recv msg is: hello
[49778] 2021-11-06 21:44:13.6133832 +0800 CST m=+2.009869001 recv msg is: hello
[49778] 2021-11-06 21:44:13.717499 +0800 CST m=+2.113980301 recv msg is: hello

Now, watch the output from the client and 3 servers. The same socket is shared by 3 processes.