Re: deadlock??

Thomas Hawtin <>
Fri, 15 Dec 2006 14:38:33 +0000
tcl wrote:

class semaphore

It would be a good deal less confusing if you used initial caps for
class names.

There already is a Semaphore class in the Java library. Why not use
that? If you are using a really old version of Java, then there is the
JSR166 backport.

   private long myCount = 0;
   public semaphore() {myCount = 0;}

Why assign myCount twice. In fact, why assign it at all. Without the
assignment, you could get away with unsafe publishing.

   public void acquire()
         while(myCount == 0){ wait(); }
   public synchronized void release()

class myStuff
    private LinkList myList=null;

The Java library already has a linked list class.

    private semaphore mySem = null;
    public myStuff()
       myList = new LinkList();
       mySem = new semaphore()

Again why assign twice? Marking the fields final would be a good idea.

    public void addNotification(xyz a)
    public void run()
           xyz ref=null;

No need to assign ref here. In fact, it could be made final.

              ref = myList.removeFirst();

At no point in this code to acquire either the semaphore or LinkList
intrinsic lock at the same time, so that isn't deadlocking. Does jstack,
ctrl-\ (ctrl-break on Windows) or your debugger give any clues?

There isn't any need to move the acquire into the synchronized block.

I suggest using the much better BlockingQueue implementations supplied
in the Java library (and JSR166 backport).

Tom Hawtin

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