First Readers-Writers Problem

Overview

This C program implements the first readers-writers problem using POSIX semaphores and threads. It demonstrates how multiple readers can read simultaneously from a shared resource, while writers gain exclusive access to write to the resource. This ensures no reader reads the resource while a writer writes to it.

Features

• Concurrency Handling: Uses POSIX semaphores to manage concurrent access between readers and writers.
• Thread Management: Employs POSIX threads to simulate multiple readers and writers accessing a shared resource.

How It Works

The program uses two semaphores (x and y) and arrays of pthreads (readerthreads and writerthreads) to manage access between readers and writers. The x semaphore controls access to modify the readercount, which tracks the number of readers currently reading. The y semaphore ensures that either any number of readers or a single writer can access the shared resource, but not both.

Reader Function

• Waits for semaphore x to modify the readercount.
• If it is the first reader, it also waits on semaphore y to block writers.
• After reading, it decrements readercount and, if it's the last reader, signals semaphore y to allow writers to proceed.

Writer Function

• Waits for semaphore y to ensure exclusive access to the shared resource.
• After writing, it signals y to allow other operations (read or write) to proceed.

Compilation and Execution

Ensure you have a C compiler installed (e.g., GCC) and your system supports POSIX threads and semaphores.

Compiling the Code

Run the following command to compile the program:

gcc -o readers_writers readers_writers.c -lpthread