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

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ThomasH - 29 Aug 2006 19:21 GMT

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.

Thomas

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Larry Barowski - 29 Aug 2006 23:38 GMT

>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.

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ThomasH - 30 Aug 2006 00:25 GMT

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

>> I wonder if there is a possibility to access the list of
>> locks/monitors and display them in Java, kind of similar
[quoted text clipped - 4 lines]
> Most debuggers do this. I don't think there is a way
> to do it from within a Java program though.

Thanks.
This occurred to me too, I wanted verify if I miss something.

The reason for this omission is not obvious to me,
finally we have a full knowledge of all granted Java
lacks and of all pending classes and threads in the JVM.

Thomas

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ThomasH - 30 Aug 2006 03:09 GMT

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

> Larry Barowski wrote on 29-Aug-06 15:38:
>>> I wonder if there is a possibility to access the list of
[quoted text clipped - 5 lines]
>> 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...

> Thanks.
> This occurred to me too, I wanted verify if I miss something.
[quoted text clipped - 4 lines]
>
> Thomas

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Babu Kalakrishnan - 30 Aug 2006 04:25 GMT

> ThomasH wrote on 29-Aug-06 16:25:
> > Larry Barowski wrote on 29-Aug-06 15:38:
[quoted text clipped - 11 lines]
> 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.

BK

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Thomas Hawtin - 30 Aug 2006 13:35 GMT

>> ThomasH wrote on 29-Aug-06 16:25:
>>> Larry Barowski wrote on 29-Aug-06 15:38:
[quoted text clipped - 11 lines]
>
> 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

Signature

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

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ThomasH - 30 Aug 2006 21:42 GMT

Thomas Hawtin wrote on 30-Aug-06 05:36:

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

[...]

>>> Actually, on Unix and Linux, if you run jdk 1.4 or later
>>> with hotspot and issue "kill -3" against the Java process,
[quoted text clipped - 12 lines]
>
> http://jroller.com/page/tackline?entry=detecting_invokeandwait_abuse

Very nice idea, thanks!

> 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

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Piotr Kobzda - 30 Aug 2006 13:51 GMT

> 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.

Take a look at a ThreadInfo and ThreadMXBean classes from
java.lang.management package.
Note this API is extended in Mustang with additional support for
java.util.concurrent locks.

piotr

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

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