CustomReentrantLockSuccessExample

package multithreading.lock.reentrant_custom_lock_success;

public class CustomReentrantLock {

    private boolean isLocked = false;
    private Thread lockedBy = null;
    private int lockedCount = 0;

    public void lock() throws InterruptedException {
        synchronized(this) {
            while(isLocked && Thread.currentThread() != lockedBy) wait();
            lockedBy = Thread.currentThread();
            lockedCount++;
            isLocked = true;
        }
    }

    public void unlock() {
        synchronized(this) {
            if(Thread.currentThread() == lockedBy) {
                lockedCount--;
                if(lockedCount == 0) {
                    lockedBy = null;
                    isLocked = false;
                    notify();
                }
            }
        }
    }

}


package multithreading.lock.reentrant_custom_lock_success;

import multithreading.lock.custom_lock.CustomLock;

public class ReentrantCustomLockSuccessExample {

    private final CustomReentrantLock lock = new CustomReentrantLock();
    public synchronized void outer() throws InterruptedException {
        lock.lock();
        System.out.println(Thread.currentThread().getName() + " enters OUTER");
        Thread.sleep(500);
        inner();
        lock.unlock();
    }

    private synchronized void inner() throws InterruptedException {
        lock.lock();
        System.out.println(Thread.currentThread().getName() + " tries to enter INNER");
        System.out.println(Thread.currentThread().getName() + " enters INNER");
        lock.unlock();
    }

}


package multithreading.lock.reentrant_custom_lock_success;

public class ReentrantCustomLockSuccessExampleClient {

    public static void main(String[] args) throws InterruptedException {
        ReentrantCustomLockSuccessExample reentrantCustomLockFailExample = new ReentrantCustomLockSuccessExample();
        for (int i = 0; i < 5; i++) {
            new Thread(() -> {
                try {
                    reentrantCustomLockFailExample.outer();
                } catch (InterruptedException e) {
                    throw new RuntimeException(e);
                }
            }, "Thread " + i).start();
        }

        Thread.sleep(7000); // needed to wait all threads to be completed (I'm lazy to call join on them after starting =) )
    }
}