Lamport Distributed Mutual Exclusion

Overview

This repository implements a distributed mutual exclusion system using Lamport’s Distributed Mutual Exclusion Algorithm, where multiple clients maintain a blockchain-based transaction ledger and ensure safe money transfers via mutual exclusion. Each client holds a local copy of the blockchain and a balance table, ensuring consistent updates across the distributed system. The project simulates a banking system where clients transfer funds securely while maintaining a globally ordered transaction history.

Setup & Execution

Prerequisites

• Python 3.10

Running the Project

1. Start multiple client instances (either on different machines or using multiple processes on a single machine).

python client1.py -port <portno> -client <clientid> -balance <balance amount>

Initialize all the clients in the following order:

python client1.py -port 8001 -client 1 -balance 10.0

python client1.py -port 8002 -client 2 -balance 10.0

python client1.py -client 3 -balance 10.0

Execute the client commands in order, because each client connects to all the other clients on startup.

1. Each client initializes with $10 in balance, and a client id which acts as the process id.
2. Use the interface to:
   • Perform money transfers between clients.
   • Query balances.
   • Print blockchain history.
3. Observe logs for message passing, clock updates, and mutual exclusion handling.

Features

• Blockchain-based transaction history: Each block contains a single financial transaction with cryptographic hash pointers ensuring data integrity.
• Lamport’s Mutual Exclusion Algorithm: Clients coordinate access to the blockchain using Lamport timestamps.
• Concurrency Control: Transactions execute sequentially across distributed clients to prevent race conditions.
• TCP/UDP Communication: Clients communicate over a network using message-passing techniques.
• Balance Verification: Transactions are validated before execution, ensuring sufficient funds exist.
• Logging & Debugging: Console logs track message exchanges, logical clock updates, and transactions.

Implementation Details

Clients

Each client maintains:

• A blockchain storing transactions.
• A balance table tracking all client balances.
• A Lamport logical clock for ordering transactions.
• A Priority Request Queue for ordering requests based on lamport logical clock time.
• A Banking Server instance for performing transactions and balance requests.
• A Communication Factory for message passing abstraction.

Transactions

• Transfer Transaction: Moves money between clients and updates the blockchain.
• Balance Query: Returns the current balance of a client (does not modify the blockchain).

Mutual Exclusion

• Clients use Lamport’s algorithm to request exclusive access before modifying the blockchain.
• If a client lacks sufficient funds, the transaction is aborted.

Communication

• Clients connect via TCP sockets.
• Messages include transaction requests, acknowledgments, and blockchain updates.

Example Transaction Flow

1. Client A requests to send $4 to Client B.
2. Lamport’s mutual exclusion protocol ensures ordered execution.
3. If A has sufficient funds, the transaction is added to the blockchain.
4. The transaction block is sent to other clients.
5. All clients update their local copies of the blockchain and balance tables.
6. The system logs messages, timestamps, and transaction details.

Notes

• Transactions are totally ordered using Lamport timestamps.
• The project can run on multiple machines or simulate distribution using multiple processes.
• Future improvements can include Byzantine Fault Tolerance, leader election, or enhanced consensus mechanisms.

Authors

• Sai Vamsi Alisetti