User-Level Threads Library (uthreads)

A C++ user-level threading library supporting both preemptive and cooperative multithreading, with quantum-based scheduling and a clear API for thread management in user space.

Easily create, schedule, and manage multiple user-level threads in your application, with robust context switching and safe signal handling.

Technical Highlights

• Implements user-level context switching using setjmp/longjmp and manual stack manipulation
• Uses Linux signals and virtual timers (setitimer, SIGVTALRM) for preemptive scheduling
• Thread management and scheduling logic is decoupled from application logic
• Emphasis on reliability, maintainability, and clear error handling

Features

• User-level threads (uthreads) with context switching
• Thread creation, termination, blocking, resuming, and sleeping
• Quantum-based round-robin scheduling
• Signal-safe API using sigprocmask for thread safety

Example Usage

#include "uthreads.h"
#include <iostream>

void thread_func() {
    std::cout << "Hello from thread " << uthread_get_tid() << std::endl;
    uthread_terminate(uthread_get_tid());
}

int main() {
    uthread_init(1000);
    int tid = uthread_spawn(thread_func);
    std::cout << "Main thread, spawned thread id: " << tid << std::endl;
    while (true) {} // Let threads run
}

Project Structure

• uthreads.h / uthreads.cpp — Main API and implementation
• Thread.h / Thread.cpp — Thread class and context management
• examples/ — Usage examples and tests
• tests/ — Expected outputs for validation

Quick Start

cd src
make
g++ -std=c++11 -Wall -Wextra -g -o test0_sanity ../examples/test0_sanity.cpp uthreads.cpp Thread.cpp
./test0_sanity

Design Notes

• Context switching is implemented with setjmp/longjmp for portability and control.
• Preemptive scheduling is achieved using Linux virtual timers and signals.
• All thread management is signal-safe to prevent race conditions and ensure robustness.

Example Output

test0_sanity

Thread:m Number:(0) 0
Init Quantum num is: 1
m0 Quanta:1
...

test2_two_thread

test2:
--------------
***0***
***1***
...

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For questions or feedback, feel free to open an issue or contact me via GitHub.