Classical Process Synchronization Problems

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Arjit Sharma
02 Mins

Process synchronization plays a crucial role in multi-process systems, ensuring data integrity and preventing conflicts. Several classic problems illustrate real-world challenges where synchronization techniques are necessary.

1. Producer-Consumer Problem

Scenario:

A producer generates data and places it into a buffer, while a consumer retrieves and processes it. The challenge is ensuring that:

  • The producer does not overwrite an already filled buffer.
  • The consumer does not read empty data.

Solution Using Semaphores

This problem is solved using two semaphores:

  • Full → Tracks the number of items in the buffer.
  • Empty → Tracks available slots for new items.
semaphore empty = buffer_size;
semaphore full = 0;
mutex lock;

Producer() {
    while (true) {
        wait(empty);  // Ensure buffer has space
        wait(lock);   // Lock access
        buffer.push(item);  // Add item
        signal(lock);
        signal(full);  // Notify consumer
    }
}

Consumer() {
    while (true) {
        wait(full);  // Ensure data is available
        wait(lock);  // Lock access
        item = buffer.pop();  // Retrieve item
        signal(lock);
        signal(empty);  // Notify producer
    }
}

🔹 Used in: Multi-threaded applications, data streaming, request handling in web servers.

2. Reader-Writer Problem

Scenario:

  • Multiple readers can access shared data simultaneously.
  • Only one writer can modify data, ensuring consistency.

Solution Using Read-Write Locks

This is solved by prioritizing either readers or writers using read-write locks.

mutex write_lock;
int read_count = 0;
mutex read_lock;

Reader() {
    while (true) {
        wait(read_lock);
        read_count++;
        if (read_count == 1) wait(write_lock);
        signal(read_lock);

        // Read data...

        wait(read_lock);
        read_count--;
        if (read_count == 0) signal(write_lock);
        signal(read_lock);
    }
}

Writer() {
    while (true) {
        wait(write_lock);
        // Modify data...
        signal(write_lock);
    }
}

🔹 Used in: Databases, logging systems, filesystem read-write access.

3. Dining Philosophers Problem

Scenario:

Five philosophers sit around a table, each needing two forks to eat. The challenge is ensuring that:

  • Philosophers don’t hold one fork indefinitely, causing deadlocks.
  • They alternate eating and thinking to avoid starvation.

Solution Using Mutexes

A deadlock-free approach is ensuring only four philosophers can pick up forks at the same time.

mutex fork[5];

Philosopher(int i) {
    while (true) {
        think();
        wait(fork[i]);  
        wait(fork[(i + 1) % 5]);  
        eat();
        signal(fork[i]);  
        signal(fork[(i + 1) % 5]);  
    }
}

🔹 Used in: Multithreading resource allocation, cloud-based task scheduling.

Conclusion

Synchronization problems like Producer-Consumer, Reader-Writer, and Dining Philosophers illustrate real-world concurrency challenges. Using mechanisms like semaphores, mutexes, and read-write locks, developers can prevent deadlocks, optimize resource allocation, and enhance multi-process efficiency in databases, operating systems, and cloud services.

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