Multi-Elevator Control System Simulation

Project Overview

The project involves writing a POSIX-compliant C program to control a set of elevators efficiently using shared memory and message queues. The goal is to minimize the number of turns and elevator movements required to serve passenger requests.

Features

• Multi-Process Communication: Uses message queues to obtain authorization strings and communicate with helper processes.
• Shared Memory Management: Stores elevator states, passenger requests, and movement commands in shared memory.
• Efficient Scheduling Algorithm: Minimizes turns and elevator movements while handling all passenger requests.
• POSIX Compliance: Implements inter-process communication (IPC) for synchronization.
• Solver Processes: Uses multiple solver processes to determine correct authorization strings for moving elevators.
• Threading for Performance: Utilizes threads to handle multiple elevators concurrently, improving efficiency.

How It Works

1. Initialization:

   • The program reads from input.txt to get the number of elevators, floors, and solver processes.
   • Connects to shared memory and message queues for inter-process communication.

2. Processing Turns:

   • The main helper process provides the current state of elevators and new passenger requests.
   • The program decides which elevators should move and whether passengers should be picked up or dropped off.
   • If an elevator has passengers, the program requests an authorization string from the solver process.

3. Sending Commands:

   • The program updates shared memory with elevator movement commands ('u', 'd', 's').
   • Picks up and drops off passengers as required.
   • Sends a message to the main helper process to verify authorization and process movements.

4. Receiving Updates:

   • The helper responds with the updated state of the elevators.
   • The process repeats until all passenger requests are fulfilled.

5. Termination:

   • Once all requests are completed, the helper sends a termination signal, and the program exits cleanly.

Installation & Execution

Prerequisites

• Ubuntu 22.04 or later
• GCC compiler with POSIX thread support

Compilation

gcc solution.c -lpthread -o solution

gcc helper-program.c -lpthread -o helper

testcase[t].txt & testcaseDetails.txt should be in the same folder as your solution.c & helper-program.c

Running the Program

./helper <test_case_number>

Example:

./helper 3

This will process testcase3.txt.

Possible Errors

Sometimes you might get an error message saying No space left on device. This might be due to your system's message queue limit and/or shared memory limit being reached

Clear Message Queues

Run the following command to list active message queues:

ipcs -q

Run the following command to clear all queues owned by your user:

for id in $(ipcs -q | awk '{print $2}'); do ipcrm -q $id; done

Clear Shared Memory

Run the following command to list active shared memory:

ipcs -m

Run the following command to clear all shared memory owned by your user:

for id in $(ipcs -m | awk 'NR>3 {print $2}'); do ipcrm -m $id; done

Now it should work.