CODEWITHSUNDEEP
javamultithreading
user1919035
user1919035

Reputation: 227

How to lock a function access from threads

Hi I've a code as below.

class main{
    main()
    {
        myThread1 mt1 = new myThread1();
        myThread2 mt2 = new myThread2();

        mt1.start();
        mt2.start();

        mt1.join();
        mt2.join()

        System.out.println(access.sb.toString());
    }
}

class myThread1{
    run(){
        access.grow(" IJKLMNOP ");
    }
}

class myThread2{
    run(){
        access.grow(" ABCDEFGH ");
    }
}

class access{
StringBuilder sb = new StringBuilder();
    void grow(str)
    {
        sb.append(str);
    }

}

**Ignore errors

Output: 

 ABCDE IJKLMFGHFGH

Expected Output should be one after the other, or vice. I figured it out that, it is due to random access to function grow by both the threads. Is there any process so that I can allow access to function grow only one thread at an instance.

Upvotes: 1

Views: 43

Answers (2)

varsha
varsha

Reputation: 1

For better performance use synchronize block

       void grow(str)

      {
          synchronize(sb){
            sb.append(str);
       }
       }

also u can use concurrency pkg lock class

      Lock lock = new ReentrantLock();
        void grow(str)

      {
          try{ lock.lock();
            sb.append(str);
        finally(){
           lock.unlock();
        }

       }

Upvotes: 0

Mark Elliot
Mark Elliot

Reputation: 77044

Marking grow as synchronized will cause a particular instance of access to serialize calls to grow amongst threads:

synchronized void grow() {
    ...
}

Another approach would be to enqueue work onto some flavor of a thread-safe Queue (typically some kind of BlockingQueue) and then to read work from the queue on a different thread, but that might not be necessary given the context you've provided.

Upvotes: 4

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