Re: Can we display list of held monitors and their holders in JVM?

From:

Thomas Hawtin <usenet@tackline.plus.com>

Newsgroups:

comp.lang.java.programmer

Date:

Wed, 30 Aug 2006 13:36:01 +0100

Message-ID:

<44f585ee$0$3201$ed2619ec@ptn-nntp-reader01.plus.net>

Babu Kalakrishnan wrote:

ThomasH wrote:

ThomasH wrote on 29-Aug-06 16:25:

Larry Barowski wrote on 29-Aug-06 15:38:

"ThomasH" <henrymot@coco.net> wrote in message
news:3U%Ig.64$yd2.134@news.oracle.com...

I wonder if there is a possibility to access the list of
locks/monitors and display them in Java, kind of similar
to what we do with threads and thread lists. This would
greatly simplify search for contentions and maybe even
for deadlocks.

Most debuggers do this. I don't think there is a way
to do it from within a Java program though.

Actually, on Unix and Linux, if you run jdk 1.4 or later
with hotspot and issue "kill -3" against the Java process,
JVM will dump threads. Its not precisely what I need, but
it contains the information looked after...

I believe a Ctrl-Break on the console does the same on Windows as well.

Or ctrl-\ on Solaris or Linux. I believe from 1.5 jstack (and presumably
jconsole) will do it without requiring access to the process output.

From 1.6 a program can examine its own locks (without connecting to its
own debugging port) through java.lang.management. As an example, I wrote
some code to detect when java.awt.EventQueue.invokeAndWait is called
with a lock held:

http://jroller.com/page/tackline?entry=detecting_invokeandwait_abuse

IIRC in 1.5 you will only get details of intrinsic locks. From 1.6 you
will also get details from java.utiil.concurrency.locks.

Tom Hawtin
--
Unemployed English Java programmer
http://jroller.com/page/tackline/