Supermarket Simulation

This project simulates operations of a supermarket with multiple cash registers, where customers interact with cashiers in real-time. Customers select the shortest queue, wait for their turn, and are served by cashiers. The system manages cashier breaks, shift changes, and synchronizes all processes using monitors and locks to ensure smooth operation and avoid conflicts when accessing shared resources.

Key features

• Customer Process: The customer enters the supermarket, selects the shortest queue, and waits for their turn to be served. After being served by a cashier, the customer process completes. Customers are visualized as moving circles, which change colors when being served.
• Cashier Process: Cashiers serve customers from their respective queues. After serving customers for a specified period, cashiers can request breaks or shift changes. When this happens, the register temporarily closes, and the queue is blocked for new customers.
• Animation: Using JavaFX, the simulation provides a dynamic visualization of customers and cashiers interacting in real-time. Cash registers are represented as rectangles, and customers as moving circles, with color changes reflecting different statuses (open, on break, closing, etc.).
• Synchronization and Thread Management: The simulation uses locks to ensure that resources like queues and cashier operations are accessed in a thread-safe manner, preventing race conditions and ensuring smooth operation.

Project Structure

SupermarketSimulation/
│── src/main/                    
│   ├── java/com/supermarketsimulation/  
│   │   ├── Client.java                 # Represents a customer 
│   │   ├── Cashier.java                # Represents a cashier and handles operations (serving, breaks, shifts)
│   │   ├── CashRegistersMonitor.java   # Manages the state of all registers and queues
│   │   ├── SupermarketController.java  # Controls simulation logic
│   │   ├── Main.java                   # Main class to start the simulation 
│── resources/com/supermarketsimulation/  
│   ├── SupermarketLayout.fxml          # JavaFX layout for the simulation interface
│── .gitignore                         # Files and directories to be ignored in version control
│── pom.xml                            # Maven project configuration
│── README.md                          # Project documentation (this file)

Technical Requirements

• Java 21 or higher
• Maven
• JavaFX

Installation & Usage

1. Clone the repository:

git clone https://github.com/alaszmigiel/Supermarket-simulation.git
cd Supermarket-Simulation

2. Build the project:

mvn clean install

3. Run the simulation:

mvn javafx:run

Shared Resources & Synchronization:

The simulation relies on several shared resources that are synchronized:

• Customer Queues: Each register has its own queue, and the system uses locks to manage safe access to these queues and prevent race conditions.
• Cash Registers and Operations: System makes sure that operations like breaks and shifts are synchronized, and register status changes are handled without conflicts.
• Synchronization Objects:
  • Local Locks: Each customer queue is protected by a dedicated lock to have thread-safe access.
  • Global Lock: A global lock is used for operations that affect multiple queues or the overall system.

Simulation Workflow

• Customer Process: Customers enter the store, choose the shortest queue, and wait to be served. As they are served, their circle in the animation turns green. Once served, the customer process ends.

• Cashier Process: Cashiers serve customers from their respective queues. After a set time, the cashier may request a break, which turns the register color to yellow. Cashier must wait in line for their turn to take a break and when he becomes first it will be approved when no other cashier is currently on break and no other cashier is in the process of switching shifts. Once a break request is approved, the register color changes to orange, and the queue is temporarily blocked from accepting new customers. When a cashier returns from their break, the register color turns green, signaling it is open again.

• Shift Change: After returning from their break, the cashier may request a shift change. Register color then turns dark blue. A shift change is only allowed if cashier is the first in line for a shift change and no other cashier is currently changing or on break Once all customers in the queue are served, the register color changes to light blue, meaning that a new cashier will take over the register.

• Store Closing: Once all customers have entered the store, the registers turn light gray, signaling that the store is closing. After all customers have been served, the register turns dark gray, marking the end of the simulation. At this point, no further break or shift requests can be made, and all cashiers finish their work.

Simulation States:

• Register States:
  • Green: Register is open and serving customers.
  • Yellow: Cashier has requested a break.
  • Orange: Register is closing, serving last customers.
  • Red: Cashier is on break.
  • Dark Blue: Cashier has requested a shift change.
  • Light Blue: Register is closed for a shift change, and a new cashier takes over.
  • Light Gray: All customers have entered the store, store is closing.
  • Dark Gray: Register is closed, no more customers to serve.
• Customer States:
  • Black: Customer is choosing a queue or waiting in line.
  • Green: Customer is being served.