Re: Locking objects in an array

Daniel Pitts wrote:
Important code correction:
notice the "synchronized (next)" section has changed. There was a
possible race condition that would cause the "lock" method to block
indefinitely.

Replace the "lock" method in the previous post with the following version:

     /**
      * Locks a region. Blocks until existing locks that intersect the
region are released.
      * @param region the region to lock
      * @return a Lock handle.
      * @throws InterruptedException if the thread is interrupted
      */
     public Lock lock(Region region) throws InterruptedException {
         Lock release = null;
         try {
             while (true) {
                 final Lock h = head.get();
                 release = new Lock(region, h);
                 if (!head.compareAndSet(h, release)) {
                     continue;
                 }
                 Lock cur = release;
                 Lock next = cur.next;
                 while (next != null) {
                     if (next.region.intersects(region)) {
                         if (!next.complete) {
                             synchronized (next) {
                                 while (!next.complete) {
                                     next.wait();
                                 }
                             }
                         }
                         Lock nn = next.next;
                         cur.compareAndSetNext(next, nn);
                     }
                     cur = next;
                     next = cur.next;
                 }
                 Lock ret = release;
                 release = null;
                 return ret;
             }
         } finally {
             if (release != null) {
                 release.release();
             }
         }
     }

--
Daniel Pitts' Tech Blog: <http://virtualinfinity.net/wordpress/>