Hi Gunter,
The output you are adding is all useful. I think the question is (and
I'd like to see a few people chime in on this for this review) is
whether or not all of it is the appropriate for a thread's stack dump.
For example, defined_classes is on the fringe of what I would call
generally useful info in a stack dump. Sure, there might be that rare
case when you need it, but how often compared to other useful info
maintained on a per thread basis. How many other bits of useful info are
not being printed in favor of defined_classes? It seems you have more in
the queue. How many? I'm worried about how cluttered the stack dumps
will get. Maybe we should add some sort of verbose thread dumping
option. Just a thought.
As for the implementation, overall it looks good, but I can't speak to
whether or not you are doing proper accounting of defined_classes and
bytes allocated. You'll need input from someone with more knowledge of
those areas. We'll also need to do some testing to make sure tool tests
are not impacted.
thanks,
Chris
On 4/30/18 2:51 AM, Haug, Gunter wrote:
Hi,
this is an update to an RFR I posted on hotspot-dev, but it is probably more
suitable to post it here. Can I please have a review and a sponsor for the
following enhancement:
http://cr.openjdk.java.net/~ghaug/webrevs/8200720.v1
https://bugs.openjdk.java.net/browse/JDK-8200720
We at SAP have extended the thread dumps (obtained by jstack or jcmd) by
several fields providing thread specific information. These extensions are
quite popular with our support team. With some knowledge of the architecture of
the application, they often allow for quick and simple diagnosis of a running
system. Therefore we would like to contribute these enhancements.
I took a few simple examples here, namely cpu time, elapsed time since thread
creation, bytes allocated and classes defined by the thread and the pthread-id
or equivalent on platforms where it makes sense. Provided it is known how the
application should behave, a misbehaving thread can identified easily.
There is no measurable overhead for this enhancement. However, it may be a
problem that the format of the output is changed. Tools parsing the output may
have to be changed.
Here is an example of the output generated:
------------------------------------------------------
"main" #1 prio=5 os_prio=31 cpu=6300.65ms elapsed=123.28s allocated=242236760B defined_classes=1725 tid=0x00007fa13a806000 nid=0x1c03 pthread-id=0x109708000 waiting on condition [0x0000000109707000]
java.lang.Thread.State: TIMED_WAITING (sleeping)
JavaThread state: _thread_blocked
Thread: 0x00007fa13a806000 [0x1c03] State: _at_safepoint _has_called_back 0
_at_poll_safepoint 0
JavaThread state: _thread_blocked
at java.lang.Thread.sleep(java.base/Native Method)
...
------------------------------------------------------
As mentioned above, we have a whole bunch of other enhancements to the thread
dump similar to this one and would be willing to contribute them if there is
any interest.
Thanks and best regards,
Gunter
