Process Scheduler Emulator

A C-based application that emulates the simplified behavior of a process scheduler, allowing users to interactively manage a scheduling table. This project was developed as part of the Systems Architecture course at Carlos III University of Madrid.

Project Status

Implemented up to: Part 3 Step 4 (inclusive)

Overview

This application simulates a process scheduler with the following capabilities:

• Interactive management of a process schedule (add, delete, search, display, sort)
• File I/O operations for saving and loading schedules
• Process execution emulation using fork/exec with round-robin scheduling
• Signal handling for process control (SIGINT, SIGALRM, SIGSTOP, SIGCONT)

Features

Part 1: Core Functionality

• Add Process: Create new processes with owner name, priority, and execution time
• Delete Process: Remove a process by its PID
• Process Information: Display details of a specific process
• Show Schedule: Display all processes in the current schedule
• Delete Schedule: Clear all processes from the schedule
• Sort Schedule: Sort processes by PID, priority (P), execution time (C), or owner name using function pointers

Part 2: File Operations

• Load from File: Import a schedule from a binary file using fread
• Save to File: Export the current schedule to a binary file using fwrite

Part 3: Process Execution

• Execute Schedule: Launch child processes and manage them with round-robin scheduling
• Round-Robin Scheduling: Each process receives a 1-second timeslot before being suspended
• Signal Handling: Graceful termination with CTRL+C, displaying execution summary

Data Structures

Each process contains the following fields:

Field	Description
pid	Process identifier (unique, auto-assigned, never reused)
user	Owner name (dynamically allocated, unlimited length)
p	Priority (integer > 0)
C	Execution time (integer > 0)
state	Process state: READY, RUNNING, or TERMINATED

Project Structure

File	Description
program.c	Main program with menu logic and error handling
menu.c / menu.h	Menu display module
input_usr.c / input_usr.h	Keyboard input handling module
item.c / item.h	Process (item) definition and management
collection.c / collection.h	Process collection management (dynamic array)
errors.c / errors.h	Error handling with custom error codes
execute_schedule.c / execute_schedule.h	Schedule execution with fork/exec
process.c	Child process executable (separate compilation)

Compilation

The project requires two separate compilations:

# Compile main program
gcc -g -Wall collection.c errors.c execute_schedule.c input_usr.c item.c menu.c program.c -o program

# Compile child process executable
gcc -g -Wall process.c -o process

Execution

./program

Usage

Upon execution, the following menu is displayed:

Program that emulates a process scheduler.

Select one of the following options:

1. Add a new process to the schedule
2. Delete a certain process from the schedule
3. Information about a process
4. Show the entire schedule
5. Delete the current schedule
6. Sort the schedule according to a criteria
7. Load from file
8. Save to file
9. Execute schedule
10. Help
0. Exit

If you enter CTRL+D:
- In this menu, the program will terminate in a controlled manner.
- In a submenu, the program will return to this menu.

Please enter an option (help: 10):

Example: Adding a Process

Please enter an option (help: 10): 1
Adding a new process.
Enter the name of the owner: Ada Lovelace
Enter the priority of the process: 1
Enter the execution time (C): 10
Process added to the schedule at position 1

Example: Executing the Schedule

Please enter an option (help: 10): 9
Executing the current schedule
POS   PID     P       C       STAT            OWNER
  1     2     4       5       READY       Annie Easley
  2     5     3      15       READY      Maria Mitchell
  3    12     2      25       READY       Grace Hopper
I launched the child processes.
[9980] Process 2 **** iter 1
[9980] Process 2 **** iter 2
[9981] Process 5 *** iter 1
...
^C
Execution summary:
  PID   real PID        STAT   NUM-EXEC   END-STATUS
    2       9980       READY          2            0
    5       9981     RUNNING          2            0
   12       9982       READY          1            0

Input Validation

The program enforces strict input validation:

Input Type	Expected Format
Name	Characters or integers
PID	Integer
Execution time	Integer
Priority	Integer
Yes/No	YES, Yes, yes, y, Y, NO, No, no, n, N

Invalid inputs will prompt the user to re-enter the value until a valid input is received.

Signal Handling

• CTRL+D in main menu: Terminates the program gracefully
• CTRL+D in submenus: Returns to the main menu
• CTRL+C during schedule execution: Kills all child processes and displays execution summary
• CTRL+C outside execution: Terminates the program

Process Execution Details

The child process (process) receives two command-line arguments:

1. The PID assigned by the application
2. The priority of the process

It prints an infinite loop with the format:

[<real_PID>] Process <app_PID> [<stars>] iter <iteration>

where the number of stars equals the priority value.

Technical Notes

• Dynamic memory allocation is used for both the process collection and owner names
• Error handling uses the errno.h library with custom error codes
• Function pointers are used for sorting operations (required by specification)
• The schedule uses a dynamic array that doubles in capacity when full
• PIDs are never reused, even after process deletion

Limitations

• Steps 5 and 6 of Part 3 are not implemented:
  • Natural process termination based on C parameter
  • Named pipe communication with stats_process

Acknowledgments

Some functions in collection.c, collection.h, errors.c, errors.h, input_usr.c, item.c, and item.h were adapted from course materials provided in lecture slides.

Authors

Noel Andolz Aguado and Daniel Lozano Uceda