RFR: 8151526: Print -Xlog configuration in the hs_err_pid file

[Max Ockner]

I forgot to respond to this:
On 4/1/2016 4:45 AM, Marcus Larsson wrote:
> Hi,
>
> On 03/31/2016 08:08 PM, Max Ockner wrote:
>> (Replies in line)
>>
>> On 3/30/2016 9:31 AM, Thomas Stüfe wrote:
>>> Hi Max,
>>>
>>> Disclaimer: not a (R)eviewer.
>>>
>>> Do we really need a list of all tags and all decorators?
>>>
>> Just going by what we currently put in the hs_err file, I think this 
>> may be the first "Do we really need" we've ever asked for this type 
>> of change.
>>
>> All joking aside, I think it is a good idea to direct users toward 
>> proper UL usage whenever we have a chance.
>>
>>> Also: I assume what you print is the Log state as it is at the time 
>>> the hs-err file is printed. If logging was enabled/changed during 
>>> lifetime of the VM, e.g. with jcmd, would it be possible to see 
>>> that? At least a warning if logging was not enabled from the start on.
>>>
>> Would it be possible? Yes, but I think this would require a framework 
>> change. It does not look like any marks are made when the 
>> LogConfiguration changes during runtime, and we would need to record 
>> that in order to know what to print when we dump into hs_err.
>
> Yes, this would required the framework to keep some sort of log of 
> configuration changes. Is there value in knowing that the log 
> configuration changed since startup?

I think it is useful along with other information. An example case:

Let's say we are logging a message whenever a lock is acquired or 
released. In a subsystem like this, the action which dooms the vm may 
not cause an immediate crash. This leaves time for logging to turn on or 
off in between the bad action and the crash. If you don't know when 
logging was active and when it was not, then the absence of a particular 
message does not give you much information. You may not see the message 
that has the answer for you because it was not logged, though the action 
may have occurred.

However, if we don't have the framework support for this then I believe 
it should be added later.


>
>>
>> Thanks,
>> Max
>>> Kind Regards, Thomas
>>>
>>>
>>>
>>>
>>> On Tue, Mar 29, 2016 at 9:00 PM, Max Ockner <max.ockner at oracle.com 
>>> <mailto:max.ockner at oracle.com>> wrote:
>>>
>>>     Hello,
>>>     Please review another Unified Logging change. They are almost
>>>     done, and we are serious this time.
>>>
>>>     bug: https://bugs.openjdk.java.net/browse/JDK-8151526
>>>     webrev: http://cr.openjdk.java.net/~mockner/8151526.01/
>>>     <http://cr.openjdk.java.net/%7Emockner/8151526.01/>
>>>
>
> LogConfiguration::describe() takes the ConfigurationLock, which might 
> be problematic for the error handler. I suppose the error handler 
> could potentially deadlock if its thread already holds the lock. 
> Unsure how to resolve this, because skipping to take the lock means 
> that we might crash due to another thread changing the configuration 
> as we read it.
>
> Thanks,
> Marcus
>
>>>
>>>     The logging configuration is now printed in each hs_err file.
>>>     The output is the same as you would see from -Xlog:logging=trace
>>>     and it is obtained from LogConfiguration::describe().
>>>
>>>     Below is a sample of the hs_err contents. The Logging info is
>>>     printed after VM Arguments and Whitebox, and before Environment
>>>     Variables.
>>>
>>>     VM Arguments:
>>>     java_command: Kaboom
>>>     java_class_path (initial): .
>>>     Launcher Type: SUN_STANDARD
>>>
>>>     Logging:
>>>     Available log levels: off, trace, debug, info, warning, error
>>>     Available log decorators: time (t), uptime (u), timemillis (tm),
>>>     uptimemillis (um), timenanos (tn), uptimenanos (un), hostname
>>>     (hn), pid (p), tid (ti), level (l), tags (tg)
>>>     Available log tags: alloc, age, barrier, biasedlocking, bot,
>>>     census, classhisto, classresolve, classinit, classload,
>>>     classloaderdata, classunload, classpath, compaction, cpu, cset,
>>>     defaultmethods, ergo, exceptions, exit, freelist, gc, heap,
>>>     humongous, ihop, itables, jni, liveness, logging, marking,
>>>     metaspace, modules, monitorinflation, os, phases, plab,
>>>     promotion, preorder, protectiondomain, ref, refine, region,
>>>     remset, safepoint, safepointcleanup, scavenge, scrub,
>>>     stacktrace, start, startuptime, state, stats, stringdedup,
>>>     stringtable, survivor, sweep, task, thread, tlab, time,
>>>     verboseverification, verify, vmoperation, vtables
>>>     Log output configuration:
>>>     #0: stdout all=off uptime,level,tags,
>>>     #1: stderr all=warning uptime,level,tags,
>>>
>>>     Environment Variables:
>>>     JAVA_HOME=/scratch/mockner/UL/8151526/build/linux-x86_64-normal-server-fastdebug/images/jdk
>>>     PATH=/home/mockner/tools/webrev:/bin:/usr/bin:/usr/local/bin:/usr/sbin:/home/mockner/bin:/home/mockner/linux/bin
>>>     SHELL=/bin/bash
>>>     OS=Linux
>>>
>>>
>>
>