RE: Is enq(Node node) safe?

My original posting does not assume that both threads need to successfully
compareAndSetHead at the same time, they do have orders, one at a time, the
point is, the first succeeded thread was forced to sleep after it
successfully compareAndSetHead, since the first thread already finished
this, the second thread should not fail on compareAndSetHead.
 

-----Original Message-----
From: Doug Lea [mailto:dl@xxxxxxxxxxxxx] 
Sent: Wednesday, February 09, 2005 3:17 PM
To: Luke Blanshard
Cc: jhu@xxxxxxxx; concurrency-interest@xxxxxxxxxxxxxxxxxxxx
Subject: Re: [concurrency-interest] Is enq(Node node) safe?

Luke Blanshard wrote:
> I think the premise that both threads can succeed in setting the head is 
> false.  One will succeed, the other will fail.  The compareAndSetHead 
> call uses an atomic compare-and-set instruction to set the head only if 
> it is currently null.  (Actually, I'm just guessing here -- if I'm wrong 
> I'm sure someone will correct me.

Thanks! Yes, this is true. I should have said this in my last mail,
to make clear that the compensation code elsewhere only needs to
cover apparently-null vs non-null cases.

-Doug