🧵 DomainLock – Custom Mutex (Ticket Lock) in C++

A minimal C++ implementation of a fair mutex using a ticket lock mechanism – for educational purposes only.

📌 Overview

This project demonstrates how to implement a basic mutual exclusion (mutex) mechanism in C++ from scratch. (version 0.1--SpinLock) Inspired by the ticket lock algorithm, DomainLock ensures FIFO ordering: the first thread that tries to acquire the lock will be the first to hold it.

The lock uses two atomic counters:

• ticket: tracks the next ticket to assign.
• serving: tracks the currently served ticket.

Each thread receives a unique ticket and waits until its number matches the serving counter.

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🔧 Features

• ✅ Fair lock acquisition (FIFO)
• ✅ try_lock() and lock() support
• ✅ Uses C++20 <atomic> for thread-safe primitives
• ✅ Logs thread activity (acquire/release)
• ✅ Lightweight and dependency-free
• ⚠️ Not suitable for production use – built for educational purposes only

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🚀 Getting Started

✅ Prerequisites

• C++20 compatible compiler (g++, clang++)

🧠 Example Output

[Thread 140184607512320] acquired lock (ticket 0)
[Thread 140184599119616] waiting for turn (ticket 1, serving 0)
[Thread 140184607512320] released the variable
[Thread 140184599119616] acquired lock (ticket 1)
...
Counter: 4

📚 Resources

• SpinLock
• atomic
• memory_order
• C++ Concurrency in Action by Anthony Williams

🛠️ TODO :

• SpinLock simple atomic lock
• Fair lock and ticket logic
• Add try_lock_for(timeout) method with time-based locking
• Implement DomainLockGuard (RAII wrapper like std::lock_guard)
• Implement the use of condition_variables
• Implement unique_lock
• Optional logging toggle to enable/disable thread logs
• Benchmark and compare with std::mutex under various loads
• Add reentrant locking (like recursive_mutex)
• Experiment with condition variable support (wait() / notify() interface)
• Stress test with 100+ threads and measure fairness/starvation

✨ Fancy TODOs ✨

• Add visuals (e.g., ticket lock flow diagram)
• Unit test :/
• Using logging library