Simple Multithreaded TCP Counter Server

This project implements a basic multithreaded TCP server in C that maintains a shared integer counter. Clients can connect to the server and send commands to modify or query the counter value concurrently.

Features

Handles multiple clients concurrently using POSIX threads (pthread).
Synchronizes access to a shared counter variable with a mutex to avoid race conditions.
Supports three commands from clients:
- up — increments the counter by 1.
- down — decrements the counter by 1.
- show — returns the current value of the counter.
Responds with "Ok\n" to confirm up and down commands.
Responds with the counter value followed by newline for show command.
Handles unknown commands gracefully with an error message.
Uses semaphores for thread synchronization on startup.
Detaches threads after creation to clean up resources automatically.

How It Works

The server listens on a TCP port specified as a command-line argument.
For each incoming client connection, it spawns a detached worker thread.
The worker thread reads commands line-by-line from the client socket.
Commands are parsed and processed with proper mutex locking on the shared counter.
The connection closes when the client disconnects.

Usage

Build with:

git clone https://git.scratko.xyz/threaded-tcp-counter
gcc -pthread -o tcp_counter_server server.c

Run:

./tcp_counter_server <port>

Example:

./tcp_counter_server 12345

Then connect with telnet or netcat:

telnet localhost 12345

Send commands like:

up
show
down
show

Limitations and Notes

The server currently uses a single shared thread_data struct, which may cause race conditions if multiple clients connect simultaneously. Improvements could include per-thread data allocation.
The server supports only simple line-based commands.
No security or authentication.
Minimal error handling for simplicity.