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Subj : Re: Synchronization constructs in Java and their implications
To   : comp.programming.threads
From : Minkoo Seo
Date : Mon Sep 26 2005 06:23 am

Firstly, I'd like to thank you for your reply. Please, let me leave
'Spinlock' case out. I made a mistake regarding the spin lock
construct. Anyway, I still have questions about the other constructs.
Following is the code to get a lock using synchronized/Semaphore/Re-
entrantLock:

  // old synchornized keyword
  public void synchornized_method(int n) {

    try { startSignal.await(); } catch(InterruptedException ie) {
ie.printStackTrace(); }
    synchronized(this) {

      System.out.println(dummy + "+" + n + "=" + (dummy+n));
      dummy++;
    }
  }

  // lock approach
  private ReentrantLock lock = new ReentrantLock();
  public void lock_method(int n) {

    try { startSignal.await(); } catch(InterruptedException ie) {
ie.printStackTrace(); }
    lock.lock();
    try {
      System.out.println(dummy + "+" + n + "=" + (dummy+n));
      dummy++;
    }
    finally {
      lock.unlock();
    }
  }

  // semaphore approach
  private Semaphore s = new Semaphore(1);
  public void semaphore_method(int n) {

    try { startSignal.await(); } catch(InterruptedException ie) {
ie.printStackTrace(); }

    try {
      s.acquire();
      System.out.println(dummy + "+" + n + "=" + (dummy+n));
      dummy++;
    }
    catch(InterruptedException ie) {
      ie.printStackTrace();
    }
    finally {
      s.release();
    }
  }

To me, all three seem to try to get a lock in a quite similar
fashion. But, their performance are different. What's the reason?
Could you elaborate?

Sincerely,
Minkoo Seo.

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