Round Robin Scheduling Algorithm

Explanation

1. Purpose

This program simulates the Round Robin (RR) CPU scheduling algorithm, which shares CPU time fairly among processes by giving each a fixed time slice (quantum). It tracks the execution of each process over time and calculates key performance metrics: Completion Time (CT), Turnaround Time (TAT), and Waiting Time (WT).

2. Key Concepts

• Queue Data Structure (FIFO): Uses queue.pop(0) and queue.append() to handle processes in First-In, First-Out order.
• Nested Lists (2D Array): Manages process metadata in the format: [PID, Arrival Time, Burst Time, Remaining Time, Completion Time].
• State Simulation (while loop): Advances virtual system time step-by-step until all processes are marked complete.
• Search / Generator Expressions: Uses next(...) to locate specific process records by their ID.

3. Code Walkthrough

1. Input & Setup (Lines 1–5): Gathers process details (Arrival Time, Burst Time) and the Time Quantum (q). Initializes Remaining Time equal to Burst Time.

2. Scheduling Loop (Lines 6–25):

   • Arrival Check: At the current time, any process that has arrived and is unfinished is pushed into the queue.
   • Idle Handling: If the queue is empty, time advances by 1 (time += 1).
   • Execution: Pops the front process and runs it for min(q, remaining_time). Advances virtual time and reduces the job's remaining time.
   • Re-queuing: Adds newly arrived processes first, then re-queues the current process if it still needs more time. If finished, it records the current time as its Completion Time.

3. Metric Calculation & Output (Lines 26–36): Iterates through completed jobs to compute:

   • $\text{Turnaround Time (TAT)} = \text{Completion Time (CT)} - \text{Arrival Time (AT)}$
   • $\text{Waiting Time (WT)} = \text{TAT} - \text{Burst Time (BT)}$ Computes and displays the averages of both.

4. Output

The program prints:

1. A tab-separated table displaying each process with its PID, AT, BT, CT, TAT, and WT.
2. The Average Waiting Time and Average Turnaround Time formatted to 2 decimal places.