ECE321 — Concurrent Programming

Coursework repository for ECE321 — Concurrent Programming at the University of Thessaly. The projects are implemented primarily in C and cover pthread-based synchronization, custom semaphore abstractions, monitor-style coordination, coroutines, and user-level threads.

The repository includes root-level build and validation scripts so the assignments can be compiled and exercised from a clean checkout.

Quick overview

Area	What is included
Pthreads and synchronization	FIFO pipes, primality workers, external mergesort, and pthread-based coordination workloads.
Semaphores and monitors	Custom binary semaphore APIs, monitor-style synchronization, narrow bridge coordination, and train/passenger simulations.
Coroutine runtime	ucontext-based coroutine primitives used to run earlier workloads without relying on OS threads.
User-level threads	Round-robin scheduling, timer/signal preemption, yield, sleep, join, runtime semaphores, and assignment ports.

Standout work: user-level threading runtime

The strongest part of the repository is Project 4, where the earlier synchronization workloads are ported onto a custom coroutine and user-level threading runtime. Instead of only using pthreads or OS-provided blocking primitives, the project builds the scheduling layer itself and then runs real assignment workloads on top of it.

• Coroutine foundation: getcontext, makecontext, setcontext, and swapcontext are wrapped into reusable coroutine primitives with explicit context switching.
• User-level thread runtime: Project 4 adds round-robin scheduling, timer/signal-based preemption, yield, sleep, join, and runtime-level binary semaphores.
• Workload ports: FIFO file transfer, primality workers, narrow bridge, train/passenger synchronization, and readers/writers are adapted to run on the custom runtime.
• Runtime validation: the final assignments exercise the scheduler through realistic coordination patterns rather than isolated toy calls.

Assignment overview

Project handouts are collected under docs/handouts/. The available project presentation PDFs are collected under docs/presentations/. Project 1 does not currently have a recovered presentation artifact.

Path	Assignment	Implementation summary
Project1/assignment1	1.1 FIFO pipes	One-direction FIFO pipe library backed by a bounded ring buffer. The test program transfers a file through two pipes and validates .copy and .copy2 outputs.
Project1/assignment2	1.2 Primality tester	Master/worker pthread program that dispatches input integers to worker threads for primality testing.
Project1/assignment3	1.3 External mergesort	Parallel external mergesort for a binary file of integers. Recursive work is split across dynamically created pthreads.
Project2/assignment1	2.1 Binary semaphores	Custom binary semaphore API implemented over System V semaphores.
Project2/assignment2	2.2 Primality tester with semaphores	Semaphore-based version of the primality worker scheduler from Assignment 1.2.
Project2/assignment3	2.3 Narrow bridge	Semaphore-based simulation that coordinates cars crossing a one-lane bridge with direction, capacity, and starvation constraints.
Project2/assignment4	2.4 Train ride	Semaphore-based train/passenger synchronization simulation with fixed train capacity and batched boarding/unboarding.
Project3/assignment1	3.1 Binary semaphores with monitor-style synchronization	Revised binary semaphore implementation using monitor-style synchronization.
Project3/assignment2	3.2 Primality tester with monitor-style synchronization	Monitor-style version of the primality worker scheduler.
Project3/assignment2_java	3.2 Java implementation	Java implementation of the master/worker primality-testing assignment.
Project3/assignment3	3.3 Narrow bridge with monitor-style synchronization	Monitor-style solution for the narrow bridge simulation.
Project3/assignment4	3.4 Train ride with monitor-style synchronization	Monitor-style solution for the train/passenger simulation.
Project4/list	Shared list utility	Intrusive list helper used by the coroutine and user-level-thread runtimes.
Project4/assignment1	4.1 Coroutines	Coroutine library built on getcontext, makecontext, setcontext, and swapcontext, validated with the FIFO file-transfer workload.
Project4/assignment2	4.2 User-level threads	User-level thread runtime with round-robin scheduling, timer/signal-based preemption, yield, sleep, join, and binary semaphores.
Project4/assignment3	4.3 Readers/writers	Readers/writers simulation implemented on top of the custom user-level thread and semaphore runtime.
Project4/project1_assignment1	Assignment 1.1 port	FIFO file-transfer workload adapted to the user-level thread runtime.
Project4/project2_assignment2	Assignment 2.2 port	Primality worker scheduler adapted to the user-level thread runtime.
Project4/project2_assignment3	Assignment 2.3 port	Narrow bridge simulation adapted to the user-level thread runtime.
Project4/project2_assignment4	Assignment 2.4 port	Train/passenger simulation adapted to the user-level thread runtime.

Requirements

• Linux environment
• gcc
• make
• POSIX threads (pthread)
• System V semaphore support
• GNU timeout from coreutils, used by the validation script
• Java JDK (javac, java, jar) for the Java implementation in Project3/assignment2_java
• Optional: valgrind for coroutine/user-level-thread debugging

On Debian-based systems:

sudo apt update
sudo apt install build-essential default-jdk coreutils valgrind

Build and test

Build all supported C targets and the Java assignment:

make build

Run the repository validation checks:

make test

Clean generated build/test files:

make clean

Print the assignment inventory:

make list

The root commands are implemented in:

scripts/build_all.sh
scripts/test_all.sh
scripts/clean_all.sh
scripts/list_assignments.sh

Running individual assignments

Each assignment directory keeps its own Makefile. Most assignments also include a run_test.sh script with predefined inputs.

Example:

cd Project2/assignment3
make
./run_test.sh -5

Another example:

cd Project4/assignment3
make
./run_test.sh -1

Some assignments depend on libraries built by earlier directories. Running the root build first is the simplest way to prepare all dependencies:

make build

Dependency examples:

• Project2/assignment2, Project2/assignment3, and Project2/assignment4 link against Project2/assignment1/target/libmysem.a.
• Project3/project2_assignment3 and Project3/project2_assignment4 link against Project3/assignment1/target/libmysem.a.
• Project4/assignment2 depends on Project4/assignment1 and Project4/list.
• Project4/project1_assignment1 and Project4/project2_assignment* link against Project4/assignment2/target/libmythreads.a.