Project: Simulation of the Readers-Writers Problem

Description

The project addresses the thread synchronization problem in a library context, where readers and writers compete for synchronized access to shared resources.
The algorithm ensures that readers can read simultaneously, while writers require exclusive access to the resources.

Main Components:

1. Readers - threads that access the library to read.
2. Writers - threads that require exclusive access to the library to write.
3. Library - manages access to resources, synchronizing access for both readers and writers.

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How to Run

To run the program, use the following command in the terminal:

java -jar .\main\target\main-1.0.jar numberOfReaders numberOfWriters

If numberOfReaders and numberOfWriters are not specified then the program asks user to enter them.

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Communication Protocol

Messages Sent by the Server:

• "Reader X wants to read"
  Triggered in the requestRead(int readerId) method of the Library class when a reader tries to access the library.

• "Writer X wants to write"
  Triggered in the requestWrite(int writerId) method of the Library class when a writer tries to access the library.

• "Reader X has entered and is reading"
  Triggered in the requestRead(int readerId) method of the Library class when a reader starts reading.

• "Writer X has entered and is writing"
  Triggered in the requestWrite(int writerId) method of the Library class when a writer starts writing.

• "Reader X has finished reading"
  Triggered in the finishRead(int readerId) method of the Library class when a reader finishes reading.

• "Writer X has finished writing"
  Triggered in the finishWrite(int writerId) method of the Library class when a writer finishes writing.

Messages Sent by the Client:

• "I want to read"
  Triggered in the run() method of the Reader class when a reader tries to access the library.

• "I want to write"
  Triggered in the run() method of the Writer class when a writer tries to access the library.

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Implementation Details

• Readers can access the library's resources simultaneously.
• Writers require exclusive access to the resources.
• Synchronization relies on blocking mechanisms (wait(), notify()) and FIFO queues.

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Thread Synchronization with wait() and notify()

1. Methods wait() and notify()

• wait()
  Invoked by threads that must wait for certain conditions to be met:

  • The reader is not at the front of the queue.
  • The number of readers exceeds the allowed limit (maxReadersInside).
  • The writer is not at the front of the queue or other users are in the library.

• notifyAll()
  Wakes up threads waiting for library access after a reading or writing session ends.

2. Variable maxPeopleInside

Represents the maximum number of readers allowed in the library simultaneously.

3. Queue waitingPeople

Holds threads waiting for library access. Ensures FIFO processing.

4. Variable peopleCurrentlyInside

Tracks the current number of people in the library. Uses AtomicInteger for safe operations in a multithreaded environment.

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Additional Information

• The program supports concurrent threads for readers and writers.
• Threads perform simulated tasks such as reading and writing with random delays.
• Synchronization uses mechanisms like synchronized, AtomicInteger, and FIFO queues.