KVS — Key-Value Store with Pub/Sub

A key-value store (KVS) server with real-time pub/sub notifications, written in C as an Operating Systems course project.

Architecture

The system consists of two executables that communicate via named pipes (FIFOs):

• Server (src/server/kvs) — stores key-value pairs, processes job files using multiple worker threads, and notifies subscribed clients when values are updated or deleted.
• Client (src/client/client) — connects to the server, sends commands interactively, and receives asynchronous notifications on a dedicated thread.

Key technical concepts

• IPC via named pipes (FIFOs)
• POSIX threads with RW-locks and mutexes
• Producer-consumer pattern with semaphores
• Hash table with chaining (26 buckets)
• Signal handling (SIGUSR1 to disconnect all clients)
• Concurrent backups via child processes (fork)

Build

make

Running the Server

./src/server/kvs <jobs_dir> <max_threads> <max_backups> <register_fifo_name>

Argument	Description
jobs_dir	Directory containing .job files to process
max_threads	Maximum number of worker threads
max_backups	Maximum number of concurrent backups
register_fifo_name	Name for the register FIFO (e.g. server1)

Example:

./src/server/kvs ./jobs 4 2 server1

The server creates the FIFO /tmp/server1 and starts processing all .job files in the given directory.

Running the Client

./src/client/client <client_id> <register_fifo_name>

Argument	Description
client_id	Unique client identifier (used to name its FIFOs)
register_fifo_name	Register FIFO name of the server (must match)

Example:

./src/client/client client1 server1

Server Commands (.job files)

Job files contain a sequence of commands, one per line:

WRITE [(key,value)(key2,value2)]
READ [key,key2]
DELETE [key]
SHOW
WAIT <ms>
BACKUP

For each foo.job file, a foo.out file is generated with the output.

Example (jobs/example.job):

WRITE [(name,Alice)(age,30)]
READ [name]
SHOW
DELETE [age]

Client Commands (stdin)

SUBSCRIBE [key]       # subscribe to notifications for a key
UNSUBSCRIBE [key]     # cancel a subscription
DELAY <ms>            # wait N milliseconds
DISCONNECT            # disconnect from the server

When a subscribed key is updated or deleted on the server, the client automatically receives a notification:

(name,Bob)        # key updated
(age,DELETED)     # key deleted

Sending SIGUSR1 to the Server

To disconnect all connected clients without stopping the server:

kill -SIGUSR1 <server_pid>

Project Structure

src/
├── common/       # shared code (protocol, I/O, constants)
├── server/       # KVS server and job processing
├── client/       # interactive client
└── tests/        # client test files