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# 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:
```bash
git clone https://git.scratko.xyz/threaded-tcp-counter
gcc -pthread -o tcp_counter_server server.c
```
Run:
```bash
./tcp_counter_server <port>
```
Example:
```bash
./tcp_counter_server 12345
```
Then connect with telnet or netcat:
```bash
telnet localhost 12345
```
Send commands like:
```bash
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.
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