UNIVERSITY OF WEST ATTICA
SCHOOL OF ENGINEERING
DEPARTMENT OF COMPUTER ENGINEERING AND INFORMATICS

University of West Attica · Department of Computer Engineering and Informatics

---

Operating Systems II

POSIX Threads Synchronization - Semaphores, Condition Variables

Vasileios Evangelos Athanasiou
Student ID: 19390005

GitHub · LinkedIn

---

Supervision

Supervisor: Vasileios Mamalis, Professor

UNIWA Profile

Co-supervisor: Nikolaos Psarras, Applications Lecturer

UNIWA Profile · LinkedIn

---

Athens, June 2022

---

---

README

POSIX Threads Synchronization - Semaphores, Condition Variables

This repository contains an assignment for Operating Systems II, focusing on thread synchronization using POSIX threads to repeatedly print the phrase:

What A Wonderful World!

---

Table of Contents

Section	Folder/File	Description
1	assign/	Assignment material
1.1	assign/ASK-2B-OS-II-LAB-2021-22.png	Assignment description in English
1.2	assign/ΑΣΚ-2Β-ΛΣ-ΙΙ-ΕΡΓ-2021-22.png	Assignment description in Greek
2	src/	Source code implementations
2.1	src/semaphores.c	Semaphore-based synchronization
2.2	src/condition_vars.c	Condition variable synchronization
3	README.md	Project documentation
4	INSTALL.md	Usage instructions

---

1. Project Overview

The project demonstrates synchronization techniques using POSIX threads to ensure correct printing order among multiple threads.

Three threads cooperate:

• Thread 1 prints "What A "
• Thread 2 prints "Wonderful "
• Thread 3 prints "World!"

The program continuously prints the phrase in correct sequence.

Two synchronization approaches are implemented:

• Semaphore-based synchronization
• Condition variable synchronization

---

2. Objectives

• Implement multi-threaded execution using POSIX threads.
• Synchronize thread execution order correctly.
• Prevent race conditions using mutex protection.
• Demonstrate synchronization techniques in practice.

---

3. Key Features

• Thread Cooperation
  Multiple threads cooperate to print a single output sequence.

• Synchronization Control
  Ensures proper execution order.

• Mutex Protection
  Prevents race conditions in shared resources.

• Continuous Execution
  Program runs until manually terminated.

---

4. Program Structure

1. Initialize synchronization mechanisms.
2. Create three worker threads.
3. Each thread prints its assigned word.
4. Synchronization ensures proper printing order.
5. Execution repeats indefinitely.