🚢 Ferry Tour Simulation (Multithreading & Synchronization)

This project is a concurrent simulation of a ferry transportation system operating between two sides of a city. It demonstrates key Operating Systems concepts such as multithreading, mutual exclusion, thread coordination, and shared resource management in Java.

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📌 Project Overview

The simulation involves a total of 30 distinct vehicle threads interacting with a shared single ferry instance:

• 🚗 12 Cars (Weight: 1 unit)
• 🚐 10 Minibuses (Weight: 2 units)
• 🚛 8 Trucks (Weight: 3 units)

Each vehicle is implemented as an independent thread that must pass through a toll booth, wait in a local square, cross to the opposite side via the ferry, spend some time there, and then complete a full return journey back to its starting side.

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🛠️ System Architecture & Workflow

1. Toll Gate Processing: Vehicles randomly select one of two toll booths on their current side and experience a simulated processing delay.
2. Waiting Square: Vehicles enter a synchronized waiting queue corresponding to their side.
3. Ferry Loading: The ferry loads vehicles one-by-one under strict constraints:
   • The vehicle must be on the same side as the ferry.
   • The ferry's maximum capacity ($20$ units) must not be exceeded.
4. Transit & Return: Once the ferry is full or no more matching vehicles are waiting, it departs, crosses the river, unloads, and the vehicles execute their return trip.

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💻 Technical Implementation Details

🔑 Synchronization Strategy

• synchronized(lock) Blocks: Used within the core loading logic to ensure mutual exclusion and prevent race conditions during capacity updates.
• Conditional Waiting (wait() & notifyAll()): Vehicle threads gracefully yield CPU execution and wait if the ferry is on the opposite side or if their vehicle weight would overload the ferry's current capacity.
• Thread Safety: Separate thread-safe queues are used to manage waiting structures on both Side 0 and Side 1 independently to reduce lock contention.

Core Simulation Snippet (Ferry Loading)

public void loadOntoFerry(Vehicle v) throws InterruptedException {
    synchronized (lock) {
        while (v.startSide != side || currentCapacity + v.getLoadValue() > MAX_CAPACITY) {
            lock.wait();
        }
        synchronized (waitingVehicles[side]) {
            if (waitingVehicles[side].remove(v)) {
                currentCapacity += v.getLoadValue();
                System.out.println(v + " loaded onto ferry on side " + side);
            }
        }
        Thread.sleep(100); 
        if (currentCapacity >= MAX_CAPACITY || waitingVehicles[side].isEmpty()) {
            depart();
        }
    }
}