Simple Examples of Concurrent Server Design in Python

This repository contains minimal, educational examples of different concurrent server design patterns in Python. Each server demonstrates a classic approach used in Unix/Linux systems programming: forking, multiplexing, preforking, and more.

The goal: keep the code small and focused so you can learn the concepts without distractions.

Client

The test client works with all servers:

client.py

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Server Examples

| Example | Technique | Notes | |---------|-----------|-------| | server01.py | One child per client (fork) | Simple, but resource-heavy with many clients | | server02.py | I/O multiplexing (select) | Efficient single-process model | | server03.py | Preforked, children call accept | Demonstrates the Thundering Herd problem — multiple children wake on the same listening socket, but only one accepts. Details | | server03a.py | Preforked, connection distribution demo | Shows how Linux distributes connections | | server04.py | Parent accepts, passes socket to child | Avoids the Thundering Herd problem by handling accept in the parent and passing the connected socket to a child. |

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Quickstart

Run a server in one terminal:

python server01.py

Run the client in another:

python client.py -i localhost -p 2000 -c 5 -t 10 -b 1024

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Miscellaneous Examples

Extra socket programming tricks and demos are available in the misc/ folder:

• RST Packet Generation
  Demonstrates how to send TCP RST packets using SO_LINGER.

• SIGPIPE Demo
  Shows what happens when writing to a reset socket.

• Self-Pipe Trick
  Classic technique to avoid race conditions with select.

• Sendfile Optimization
  Efficient file transfers using the sendfile(2) system call.

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Roadmap

• [x] TCP Concurrent Server, One Child per Client
• [x] TCP Concurrent Server, I/O Multiplexing (select)
• [x] TCP Preforked Server, Children Call accept
• [x] TCP Preforked Server, Descriptor Passing
• [ ] TCP Concurrent Server, One Thread per Client
• [ ] TCP Concurrent Server, I/O Multiplexing (poll)
• [ ] TCP Concurrent Server, I/O Multiplexing (epoll)
• [ ] TCP Prethreaded Server
• [ ] TCP_CORK socket option examples
• [ ] Documentation for every example

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Acknowledgments

• Unix Network Programming, Volume 1: The Sockets Networking API (3rd Edition) by W. Richard Stevens, Bill Fenner, Andrew M. Rudoff
  The classic. Many techniques here are drawn from this book.

• The Linux Programming Interface by Michael Kerrisk
  Another excellent reference.