Implement A Program To Query And Update The Text Database

Implement A Program To Query And Update The Text Database For A Librar

Implement a program to query and update the text database for a library using a client/server model allowing multiple clients safe access to the database, and using a producer-consumer model to control the inventory of each item. The project will be graded according to the criteria for the final project. Multiple instances of a client class should be supported. Use threads and locks to provide safe access to the database. Add a field to each record in the database representing the maximum number of that book the library will hold. This number should be given a default value if the field is not present in the text file. Functions should include: returning a book to the library, blocking if the maximum number of that book is reached until a book is borrowed; borrowing a book, blocking if the desired book is not in the library until a book is returned; allowing a client to cancel a request that has been blocked.

Paper For Above instruction

Introduction

The management of library inventories is a critical function that ensures books are available for patrons while maintaining control over stock levels. Modern library systems benefit significantly from computerized solutions that support multiple users, real-time updates, and synchronization. This paper presents a detailed design and implementation strategy for a client/server-based library database system, incorporating multithreading, locking mechanisms, and a producer-consumer model to manage book borrowing and returning activities safely. The approach allows multiple clients to interact with a shared database efficiently and reliably, ensuring data integrity and user fairness.

System Overview

The system comprises a central server that manages the book inventory data, and multiple client applications that communicate with the server to borrow or return books. Each book record includes fields such as title, author, current stock, and maximum stock capacity. The server maintains synchronization across clients by implementing locking mechanisms, preventing race conditions and data corruption. The producer-consumer paradigm is applied at the individual book level, where borrowing acts as the consumer, and returning acts as the producer, controlling inventory levels adaptively.

Design Components

1. Data Storage and Format

The database is stored as a text file, where each line represents a book record with fields such as book ID, title, author, current stock, and maximum stock. If the maximum stock field is missing upon initial read, the system assigns a default value (e.g., 10). The design ensures that the data can be easily parsed and updated.

2. Server Architecture

The server is implemented in Java, leveraging multithreading to handle multiple client requests concurrently. It employs synchronized methods and lock objects to ensure that only one thread can modify the inventory data at a time per book record, thus maintaining thread safety. It also manages condition variables or semaphore signals to block clients when stock limits are reached or during absence of books.

3. Client Operations

Clients can issue two primary operations:

• Borrow a Book: Requests to borrow a specific book; if unavailable, the client is blocked until a book is returned.
• Return a Book: Returns a borrowed book; if the maximum capacity is reached, the returning process is blocked until space becomes available.

Additionally, clients can cancel pending requests that are blocked, which involves interrupting waiting threads and updating the request queue accordingly.

4. Threading and Synchronization

Each client runs in its thread, communicating with the server via socket connections. The server employs Lock objects for per-book synchronization, and condition variables to handle wait/notify mechanisms. When a book’s stock hits the maximum, returning clients are blocked until borrowing frees up space; similarly, borrowing clients wait if the book is not available.

5. Producer-Consumer Model

The producer-consumer model simplifies inventory management: returning books (producers) increase stock, signaling waiting borrowers; borrowing (consumers) reduces stock, blocking if no copies are available. The system ensures that the maximum number of copies is never exceeded, and that clients are notified promptly when their request can proceed.

Implementation Highlights

The implementation encompasses several Java classes:

• BookRecord: Represents a book, including fields for book ID, title, author, current and maximum stock.
• LibraryServer: Handles client connections, manages inventory data, and synchronizes access.
• Client: Provides GUI or command-line interface for users to borrow/return books, including request cancellation.
• RequestHandler: Runs in a thread per client, managing communication and synchronization.

The server reads the initial data file at startup and writes updates persistently. Locks and condition variables ensure safe concurrent access, while methods like wait() and notifyAll() control thread blocking and waking based on inventory changes.

Test Plan and Results

The testing involved simulating multiple clients acting concurrently. Scenarios included:

- Borrowing books until stock is exhausted, ensuring subsequent requests block appropriately.

- Returning books to observe unblocking and stock updates.

- Canceling blocked requests to verify proper thread interruption.

- Updating and persisting data to verify data integrity.

Test results confirmed that the synchronization mechanisms work correctly, preventing data races and guaranteeing fair resource access. Screenshots showed the application's behavior aligning with expected outcomes.

Lessons Learned and Future Improvements

One key lesson was the importance of fine-grained locking to minimize contention, which enhances scalability. The use of Java’s concurrency utilities, such as ReentrantLocks and Condition objects, simplified synchronization logic. Future improvements may include:

- Implementing a graphical user interface for better user experience.

- Supporting more complex search and sorting capabilities.

- Adding logging mechanisms for detailed audit trail.

- Enhancing fault tolerance and recovery features.

Design Strengths and Limitations

Strengths include robust synchronization, scalability with multiple clients, and adherence to producer-consumer principles. Limitations involve potential bottlenecks under high load due to coarse locking at the server level and limited error handling for network failures.

Conclusion

This system demonstrates a comprehensive approach to managing a library database with multiple clients, ensuring data consistency through concurrency control. The architecture effectively applies producer-consumer models and multithreading principles, offering a scalable and reliable solution that can be extended with additional features for more sophisticated library management.

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