The given code implements a simple example of synchronization in Java using semaphores. The main goal of this code is to demonstrate the concept of read-write locks, where multiple readers can access the shared resource simultaneously, but only one writer can access the resource at a time.
This class serves as the entry point for the program. It creates an instance of the ExecutorService class and a ReadWriteLock object. After that, it creates four instances of the Writer class and four instances of the Reader class, passing them the ReadWriteLock object as a parameter. Finally, it submits all the tasks to the executor service, which runs them concurrently.
This class implements the read-write lock mechanism. It has three methods for acquiring and releasing the lock for reading and writing. It uses two semaphores: mutex and S. mutex ensures that only one thread can access the readerCount variable at a time, and S ensures that only one writer can access the shared resource at a time.
The readLock method acquires the mutex semaphore and increments the readerCount variable. If it is the first reader, it acquires the S semaphore, allowing other readers to read but blocking any writers from accessing the resource. It then releases the mutex semaphore.
The writeLock method acquires the S semaphore, blocking any readers or writers from accessing the resource. It then prints a message indicating that the writer is writing.
The readUnLock method acquires the mutex semaphore and decrements the readerCount variable. If it is the last reader, it releases the S semaphore, allowing writers to access the resource. It then releases the mutex semaphore.
The writeUnLock method prints a message indicating that the writer is done writing and releases the S semaphore, allowing other writers to access the resource.
This class contains a utility method nap that causes the current thread to sleep for a random amount of time between 0 and 5 seconds.
This class implements the Runnable interface and represents a writer thread. It has a ReadWriteLock object and a writerNum variable as instance variables.
The run method is an infinite loop that sleeps for a random amount of time, attempts to acquire the write lock, sleeps again, and releases the write lock.
This class implements the Runnable interface and represents a reader thread. It has a ReadWriteLock object and a readerNum variable as instance variables.
The run method is an infinite loop that sleeps for a random amount of time, attempts to acquire the read lock, sleeps again, and releases the read lock.
In conclusion, this code implements a simple example of synchronization in Java using semaphores. It demonstrates the concept of read-write locks and how multiple readers can access the shared resource simultaneously, but only one writer can access the resource at a time.