RFR: 8151526: Print -Xlog configuration in the hs_err_pid file
Marcus Larsson
marcus.larsson at oracle.com
Thu Apr 14 08:30:12 UTC 2016
Hi,
On 04/13/2016 09:33 PM, Max Ockner wrote:
> Hello,
> I have made these changes.
> - refactored describe into a portion which uses locking and one that
> does not.
> - in the print_vm_info function in vmError.cpp, describe() is used,
> since this function is called while the program is running.
> - in the report function, the describe_no_lock and describe_with_lock
> functions are both used without taking a lock. If it doesnt crash,
> then fantastic. If it does crash, the error handler will skip this
> step anyway.
>
> webrev: http://cr.openjdk.java.net/~mockner/8151526.04
I suggest making the new two functions private in LogConfiguration, and
friending VMError, instead of keeping them public. That should reduce
confusion about which describe-method to use, and prevent misuse of the
describe_with_lock in other places.
Otherwise this looks good.
Thanks,
Marcus
>
> Thanks,
> Max
>
> On 4/12/2016 1:30 PM, Marcus Larsson wrote:
>> Hey,
>>
>> On 2016-04-12 17:01, Max Ockner wrote:
>>> Marcus,
>>>
>>> I just spoke with Coleen about this. If I attempt to print
>>> configuration during a crash without lock and it crashes, the error
>>> handler will eat it up and start at the next step. It would be fun
>>> to write a locking mechanism, but this seems better to me.
>>>
>>> I will continue to call describe() from VM.info, but I will refactor
>>> the code in describe so that all of the information can be printed
>>> easily without taking a lock. For a crash, I'll use the refactored
>>> print functions to print all the necessary information without
>>> taking a lock. Even if the vm crashes during this step it is not
>>> such a bad thing because of the robust error handler.
>>
>> Alright, that sounds good!
>>
>> Thanks,
>> Marcus
>>
>>>
>>>
>>> Thanks,
>>> Max
>>>
>>> On 4/12/2016 8:46 AM, Marcus Larsson wrote:
>>>> Hi Max,
>>>>
>>>> On 04/11/2016 07:36 PM, Max Ockner wrote:
>>>>> Hello again,
>>>>>
>>>>> I have looked into this and I see a possible workaround to the
>>>>> issue raised by Marcus:
>>>>>
>>>>> 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.
>>>>>
>>>>>
>>>>> My proposed solution is this:
>>>>>
>>>>> If the ConfigurationLock is held by another thread during the
>>>>> crash, then I think we could print "Log configuration can not be
>>>>> accessed because ConfigurationLock is currently held by another
>>>>> thread" or something similar. If the ConfigurationLock can be
>>>>> taken by the current thread, then print the configuration.
>>>>>
>>>>> We can accomplish this as follows:
>>>>>
>>>>> In *logConfiguration.cpp*: Create a ConfigurationLockMaybe class
>>>>> extending ConfigurationLock.
>>>>>
>>>>> class ConfigurationLockMaybe : ConfigurationLock {
>>>>> private:
>>>>> bool _success;
>>>>> public:
>>>>> ConfigurationLockMaybe() {
>>>>> if (_semaphore.trywait()){_success = true;}
>>>>> }
>>>>> ~ConfigurationLock() {
>>>>> if(_success){_semaphore.signal();}
>>>>> }
>>>>> bool has_lock(){return _success;}
>>>>> };
>>>>>
>>>>> _semaphore is a static var in ConfigurationLock, so the same copy
>>>>> is accessed in child classes.
>>>>>
>>>>> Another method LogConfiguration::describe_on_crash(outputStream*
>>>>> out) can use ConfigurationLockMaybe to attempt to print the
>>>>> configuration.
>>>>>
>>>>> In *vmError.cpp*: Replace LogConfiguration::describe with
>>>>> LogConfiguration::describe_on_crash.
>>>>
>>>> Sounds good to me.
>>>>
>>>> ConfigurationLockMaybe sounds a bit weird but I don't have a better
>>>> suggestion.
>>>>
>>>> Thanks,
>>>> Marcus
>>>>
>>>>>
>>>>> Max
>>>>>
>>>>> On 4/11/2016 10:23 AM, Max Ockner wrote:
>>>>>> I missed this before. I'm going to investigate.
>>>>>> Max
>>>>>>
>>>>>> On 4/11/2016 4:19 AM, Marcus Larsson wrote:
>>>>>>>
>>>>>>>
>>>>>>> On 04/11/2016 09:00 AM, Thomas Stüfe wrote:
>>>>>>>> Hi Max,
>>>>>>>>
>>>>>>>> On Fri, Apr 8, 2016 at 9:56 PM, Max Ockner
>>>>>>>> <max.ockner at oracle.com <mailto:max.ockner at oracle.com>> wrote:
>>>>>>>>
>>>>>>>> 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.
>>>>>>>>
>>>>>>>>
>>>>>>>>
>>>>>>>> This is a good example. A small easy solution, as I mentioned
>>>>>>>> before, could be just to distinguish between "logging
>>>>>>>> parameters stable since startup" and "logging parameters
>>>>>>>> changed at some time". That way you would at least know whether
>>>>>>>> to trust the logging output.
>>>>>>>>
>>>>>>>> But you are right, this can be added later.
>>>>>>>
>>>>>>> I've filed https://bugs.openjdk.java.net/browse/JDK-8153945 for
>>>>>>> this.
>>>>>>>
>>>>>>> Max: Did you see my comments about the ConfigurationLock? It was
>>>>>>> an inline reply to your first mail.
>>>>>>>
>>>>>>> Thanks,
>>>>>>> Marcus
>>>>>>>
>>>>>>>>
>>>>>>>> Kind Regards, Thomas
>>>>>>>>
>>>>>>>>
>>>>>>>>>
>>>>>>>>>>
>>>>>>>>>> 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
>>>>>>>>>>>
>>>>>>>>>>>
>>>>>>>>>>
>>>>>>>>>
>>>>>>>>
>>>>>>>>
>>>>>>>
>>>>>>
>>>>>
>>>>
>>>
>>
>
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