Concurrency Problems | DBMS

https://www.gatevidyalay.com/concurrency-problems-in-transaction/

Implement ThreadPool in java

public class Test {
    public static void main(String[] args) {
        ThreadPool threadPool = new ThreadPool(2);
        for(int i=0;i<2;i++) {
            Task task = new Task(i);
            threadPool.execute(task);
        }
        System.out.println("done");
    }
}


public class Task implements Runnable{

    int i;
   
    public Task(int i) {
        this.i = i;
    }
   
    @Override
    public void run() {
   
         System.out.println("executing i::"+i);
       
    }

}


public class ThreadPool {
    int nThread;
    private LinkedBlockingQueue<Runnable> queue;
    PoolWorker[] arr ;
   
    public ThreadPool(int nThread) {
        this.nThread = nThread;
        this.queue = new LinkedBlockingQueue<>();
        arr = new PoolWorker[nThread];
        for(int i=0;i<nThread;i++) {
            PoolWorker poolWorker = new PoolWorker();
            arr[i] = poolWorker;
            arr[i].start();
        }
    }
   
    public void execute(Task task) {
        synchronized (queue) {
            queue.add(task);
            queue.notify();
        }
       
    }
   
    class PoolWorker extends Thread{

        @Override
        public void run() {
             Runnable task;
             while(true) {
                synchronized (queue) {
                    while(queue.isEmpty()) {
                         try {
                            queue.wait();
                        } catch (InterruptedException e) {
                            // TODO Auto-generated catch block
                            e.printStackTrace();
                        }
                     }
                     task = queue.poll();
                }
               
                task.run();
             }
           
           
           
        }
       
    }
   
}

Ref: https://www.javacodegeeks.com/2016/12/implement-thread-pool-java.html

What does start() function do in multithreading in Java?

The purpose of start() is to create a separate call stack for the thread. A separate call stack is created by it, and then run() is called by JVM.

Ref: https://www.geeksforgeeks.org/start-function-multithreading-java/