Ex02

Ex02: User-Level Threads Library

👥 Authors

• Amit Joseph
• Maya Heilbrun

📋 Overview

Implementation of a complete user-level threading library providing cooperative multitasking functionality.

🎯 Objectives

• Implement user-level threading system
• Learn thread scheduling and context switching
• Understand cooperative multitasking

📁 Key Files

• uthreads.cpp - Main threading library
• uthreads.h - Public API
• thread.cpp/.h - Thread class implementation

🔧 API

int uthread_init(int quantum_usecs);        // Initialize library
int uthread_spawn(thread_entry_point entry); // Create thread
int uthread_terminate(int tid);             // Terminate thread
int uthread_block(int tid);                 // Block thread
int uthread_resume(int tid);                // Resume thread
int uthread_yield();                        // Yield CPU

🏗️ Architecture

Thread States

• RUNNING: Currently executing
• READY: Waiting to be scheduled
• BLOCKED: Suspended

Key Features

• Round-robin scheduling
• Signal-based preemption (SIGVTALRM)
• Context switching with sigsetjmp/siglongjmp
• Stack management (4096 bytes per thread)

🚀 Usage Example

void worker() {
    for (int i = 0; i < 1000; i++) {
        // Do work
        if (i % 100 == 0) uthread_yield();
    }
}

int main() {
    uthread_init(1000);  // 1ms quantum
    uthread_spawn(worker);
    return 0;
}

💡 Key Concepts

• User-level vs kernel-level threads
• Context switching mechanisms
• Signal handling for preemption
• Thread lifecycle management