Thread Scheduler

Table of Contents

1. Project Overview
2. Research and Foundations
3. The Basic Library
4. Synchronization: Mutexes
5. Scheduling Algorithms

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Project Overview

A user-level thread library made to understand POSIX threads. The best way to learn something is the make it!

Research and Foundations

• Read Documentation: Understand the project requirements.
• Master ucontext: Focus on swapcontext for switching between execution flows.

The Basic Library

Implementation Notes

• Scheduler Context: Needed for handling context swaps.
• Main Thread Context: Needed for benchmarks and returning to the entry point.

Data Structures

• TCB (Thread Control Block): Defined in thread_worker_type.h.
• Context: Each TCB holds a ucontext.
• RunQueue: A list of TCBs that are ready to run.

Core Functions

• worker_create(): Mallocs the stack (SIGSTKSZ) and uses makecontext().
• worker_yield(): Voluntarily pauses the current thread.
• worker_exit(): Saves return value and cleans up the TCB.
• worker_join(): Blocks the current thread until the target thread exits.

Synchronization: Mutexes

• worker_mutex_init(): Initialize the lock.
• worker_mutex_lock(): Locks the mutex or blocks the thread if held.
• worker_mutex_unlock(): Unlocks and wakes up waiting threads.
• worker_mutex_destroy(): Cleanup; ensure lock is free before destroying.

Scheduling Algorithms

First Come First Serve (FCFS)

• Baseline implementation.
• No preemption.

Round Robin (RR)

• FCFS with preemption.
• Quantum: Fixed time limit per thread.
• Implementation: Use sigaction() and timers to trigger the scheduler handler.