🧵 Smart Traffic Signal Simulation with Multithreading (OS Project)

📌 Project Description

This project implements a multithreaded traffic signal simulation system using POSIX threads in C.

Each traffic light is modeled as a thread, and the system calculates traffic flow using matrix multiplication under strict energy constraints.

Unlike standard matrix multiplication, computations are performed step-by-step due to:

• Limited shared resources (energy pool)
• Synchronization requirements
• Controlled execution order

This project is designed to demonstrate Operating Systems concepts, particularly thread synchronization and resource management.

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🧠 Scenario

In a smart city:

• Each traffic signal operates as an independent thread
• Signals consume energy from a shared global pool
• Energy is limited and must be managed carefully
• Threads must wait when energy is exhausted

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⚙️ System Design

🔋 Global Energy Model

• globalEnergy is a shared global resource
• Initial value: 23 units
• Each multiplication step consumes 1 energy
• If energy reaches 0, threads are blocked
• A dedicated Power Thread replenishes energy every 200 ms

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🔁 Thread Model

• One thread is created for each matrix cell C[i][j]

• Each thread:

  • Computes only its assigned cell
  • Cannot interfere with others

• Due to shared tempSum, only one thread computes at a time

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🔐 Synchronization

• mutex is used for:

  • globalEnergy
  • tempSum
  • log file access

• condition variables are used for:

  • Waiting when energy is exhausted
  • Ensuring ordered execution (single active thread)

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📊 Computation Model

Matrix multiplication is performed as:

C[i][j] = Σ ( A[i][k] × B[k][j] )

However, each step:

1. Locks mutex
2. Checks energy
3. Waits if energy = 0
4. Decrements energy
5. Unlocks mutex
6. Performs multiplication
7. Locks mutex
8. Updates tempSum
9. Logs operation
10. Unlocks mutex
11. Applies delay

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📁 Project Structure

threaded-matrix-sim/
├── src/main.c
├── input/inputA.txt
├── input/inputB.txt
├── output/simulation_log.txt
├── README.md
├── Makefile
└── .gitignore

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▶️ Compilation & Execution

Compile

make

Run

make run

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📝 Logging System

All operations are logged into:

output/simulation_log.txt

Example log entry:

[Thread 140735 | Hucre (1,2)]: Enerji Harcandi | K-Adimi: 2 | tempSum: 45

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⚠️ Important Design Constraints

• tempSum and globalEnergy are global and shared
• Threads cannot run computations simultaneously
• Busy-waiting is NOT allowed
• All shared variables are protected by mutex
• Condition variables are used for proper blocking

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🚀 Learning Outcomes

This project demonstrates:

• Thread creation and management (pthreads)
• Mutex and condition variable usage
• Race condition prevention
• Resource allocation and blocking
• Producer-consumer pattern (Power Thread)
• Controlled execution under constraints

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📞 Support & Contact

• 📧 Email: ozdogrumerve57@gmail.com
• 🐛 Issues: Feel free to report bugs or suggest features on GitHub Issues
• 👤 Author: Merve Özdoğru

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⭐ Star this repo if you find it helpful!

Made with ❤️ by Merve Özdoğru

Operating Systems Assignment