Procedure

This experiment demonstrates Lamport’s Algorithm for Mutual Exclusion in a distributed system using an interactive simulation. Follow the steps below to perform the experiment:

1. Launch the Simulation

• Open the simulation page in your browser.
• You will see 4 processes (P1, P2, P3, P4) represented as nodes, connected by communication links.
• Each process can send REQUEST, REPLY, and RELEASE messages to others to coordinate entry into the Critical Section (CS).

2. Interact with the Simulation

You can perform the following actions manually:

• Right-click a process to open a context menu:

  • Request CS: Makes the selected process request access to the Critical Section.
  • Release CS: When a process is in CS, this option becomes available to release the CS.
  • Send Reply: If a process is holding a reply, you can manually send it.

• Click on a link between two processes:

  • Clicking cycles the communication link between Normal speed and Slow speed.
  • Slower links delay message delivery, simulating network latencies or faults.

• Observe:

  • Each process maintains a Request Queue (for pending REQUEST messages).
  • Each process also maintains a Reply Queue (for REPLY messages received).
  • Logs on the left panel display all events: CS requests, message sends/receives, releases, etc.

3. Enable Test Mode (Gamified Mode)

• Enable "Test Mode" by checking the Enable Test Mode checkbox at the top.

• In Test Mode:

  • Processes will randomly request and release the CS.
  • Links will randomly become slow or return to normal.
  • The simulation will pause periodically and ask you: ➔ "Which process will be granted CS next?"

• Answer Prompt:

  • A prompt window will appear listing all process IDs.
  • Type the ID of the process you believe will be next granted the CS.
  • If correct, you score 10 points.
  • Otherwise, the correct process is revealed.

4. Understand Test Mode Levels

• The experiment includes 4 test modes, increasing in difficulty:

  • Test Mode 1: Only one process can request CS at a time.
  • Test Mode 2: Up to two processes can request CS simultaneously.
  • Test Mode 3: Up to three processes can request CS simultaneously.
  • Test Mode 4: All four processes can simultaneously request CS.

• Higher modes create more contention for CS, making prediction and understanding of Lamport’s mutual exclusion behavior more challenging.

5. Complete the Experiment

• Continue playing until a set number of rounds or until you achieve a target score.
• Observe how Lamport’s logical clocks and message passing ensure that only one process enters the Critical Section at a time — even with random delays and failures.

Notes:

• In normal mode, you control everything manually — allowing you to carefully step through the protocol.
• In test mode, the simulation introduces random events to challenge your understanding of the algorithm.
• Mutual exclusion is always maintained, even under high message delays and randomized process behavior — demonstrating the correctness of Lamport’s algorithm.