RFR: JDK-8140556: Add force rotation option to VM.log jcmd

Marcus Larsson marcus.larsson at oracle.com
Fri Oct 30 15:31:36 UTC 2015 

Hey,

On 2015-10-30 15:39, Yasumasa Suenaga wrote:
> Hi Marcus,
>
> Thank you for your comment.
>
>
>> Still missing the renaming of rotate_all_logfile to rotate_all_outputs.
>
> Sorry, I will fix.
>

Thanks!

>
>> This rotate function works I guess, but it will probably need some 
>> rework once there are other types of log outputs (rotate doesn't make 
>> sense on all types of log outputs).
>
> I will add is_rotetable() to LogOutput as virtual function.
> This function return false (can not rotate) by default, return true if 
> _file_count is
> greater than 0 in LogFileOutput.
>
> LogConfiguration::rotate_all_outputs() will rotate if this function 
> returns true.
>

Small typo, please make that is_rotatable().

>
>> If we configure a rotated file output and then log something on that 
>> output before thread local storage initialization is complete, we 
>> will crash/hit an assert. The previous implementation avoided this as 
>> long as no rotation was needed before this initialization was 
>> complete. (This can be triggered using the following arguments 
>> "-Xlog:all=trace:file.txt::filesize=10,filecount=2 -Xlog:invalid", 
>> for example.)
>
> I do not think so.
> Each -Xlog option creates unique instance of LogOutput (and subclass).
> So they are isolated.

My example includes a second (and intentionally incorrect) -Xlog option 
only to trigger logging on the newly configured rotating LogFileOutput. 
This will cause some logging about the invalid -Xlog argument, and this 
logging happens during the argument parsing. This in turn means that we 
are logging before the thread local storage has been initialized, and 
the JVM will crash/hit the assert because we are trying to take the 
rotation lock. This has nothing to do with concurrent fprintfs or 
freopens, even if that is a problem.

>
> However, we might have to rotate at safepoint.

Doing stuff at a safepoint will not give us much in this case. There are 
threads that continue execution through a safepoint, which means we will 
see log calls being made even during this time.

> Currently, LogOutput might be used by multiple threads concurrently.
> If we rotate log when another thread is writing string to output, we 
> encounter unexpected behavior.
>
> LogFileOutput::rotate() uses freopen().
> LogFileStreamOutput::write() uses vfprintf() through jio_fprintf().
> freopen() and vfprintf() are not atomic.

You're right. There seems to be an overlooked concurrency issue with 
vfprintfs during freopen. I don't think we should resolve this as part 
of this particular fix, so instead I'll create a separate issue for it.

>
> I think that cause of crash/assertion which you say is it.
> (GC log will be rotated at safepoint.)
>

See my comment above for what crash/assert I'm talking about.

Thanks,
Marcus

>
> Thanks,
>
> Yasumasa
>
>
> On 2015/10/29 23:58, Marcus Larsson wrote:
>> Hi,
>>
>> On 2015-10-29 15:01, Yasumasa Suenaga wrote:
>>> Hi Marcus,
>>>
>>> Thank you for your comment.
>>>
>>>> I'll sponsor it.
>>>
>>> Thank you so much!
>>> I've uploaded new webrev:
>>>
>>> http://cr.openjdk.java.net/~ysuenaga/JDK-8140556/webrev.01/
>>>
>>>
>>
>> Still missing the renaming of rotate_all_logfile to rotate_all_outputs.
>>
>>>> logConfiguration.cpp/hpp:
>>>>
>>>> * I don't think we should rely on the archive_name or the output's 
>>>> name to decide whether or not an output should be rotated. It would 
>>>> be better to introduce an is_rotated() test function in LogOutput 
>>>> that could be used here.
>>>>
>>>> * rotate_all_logfile() should be renamed to rotate_all_outputs(). 
>>>> Currently there are only LogFileOutputs (other than stdout/stderr), 
>>>> but in the future there might be other types of outputs so I prefer 
>>>> having a more general name.
>>>> Also, please use static_cast<LogFileOutput*> instead of the C-style 
>>>> cast. (Additional logic will be required here once more types of 
>>>> log outputs are added, but I don't think we need to worry about 
>>>> this right now.)
>>>>
>>>> * Don't print an error if an output is not rotatable, since it's 
>>>> not an error to have some log outputs rotated while others are not. 
>>>> If you really want some traceability here I suggest adding log 
>>>> messages on trace level, tagged with 'logging'.
>>>
>>> I added  LogOutput::rotate(bool) as virtual function.
>>> This function works nothing by default, but will rotate all logs at 
>>> LogFileOutput.
>>
>> This rotate function works I guess, but it will probably need some 
>> rework once there are other types of log outputs (rotate doesn't make 
>> sense on all types of log outputs).
>>
>>>
>>> If true is passed to this function, all files will be rotated.
>>>
>>>
>>>> logDiagnosticCommand.cpp/hpp:
>>>>
>>>> * I think the description could be improved to something like 
>>>> "Lists current log configuration, enables/disables/configures a log 
>>>> output, or disables/rotates all logs."
>>>>
>>>> * The rotate option description should clarify that all logs will 
>>>> be rotated ("current log" is too ambiguous).
>>>
>>> I've fixed.
>>
>> Great, thanks!
>>
>>>
>>>
>>>> logFileOutput.cpp/hpp:
>>>>
>>>> * Moving the MutexLocker like this introduces a race condition 
>>>> where a log might be rotated multiple times by different threads, 
>>>> instead of just once.
>>>> Instead of making the rotate() function public and moving the 
>>>> mutexlocker, I suggest adding something like a public 
>>>> force_rotation() function that grabs the lock and calls the private 
>>>> rotate().
>>>>
>>>> * Given the addition of is_rotated() in LogOutput, then 
>>>> get_archive_name() should be removed.
>>>
>>> I moved MutexLocker and should_rotate() to rotate().
>>> I think this change can avoid race condition.
>>>
>>
>> There is a subtle problem with taking the lock to check if we should 
>> rotate. If we configure a rotated file output and then log something 
>> on that output before thread local storage initialization is 
>> complete, we will crash/hit an assert. The previous implementation 
>> avoided this as long as no rotation was needed before this 
>> initialization was complete. (This can be triggered using the 
>> following arguments 
>> "-Xlog:all=trace:file.txt::filesize=10,filecount=2 -Xlog:invalid", 
>> for example.)
>>
>> Thanks,
>> Marcus
>>
>>>
>>> Thanks,
>>>
>>> Yasumasa
>>>
>>>
>>> On 2015/10/27 21:17, Marcus Larsson wrote:
>>>> Hi,
>>>>
>>>> On 2015-10-27 01:03, Yasumasa Suenaga wrote:
>>>>> Hi Marcus,
>>>>>
>>>>> Thank you for replying.
>>>>>
>>>>> I filed this feature to JBS and change subject of this email.
>>>>> Could you be a sponsor and review it?
>>>>
>>>> I'll sponsor it.
>>>>
>>>>>
>>>>> http://cr.openjdk.java.net/~ysuenaga/JDK-8140556/webrev.00/
>>>>
>>>> logConfiguration.cpp/hpp:
>>>>
>>>> * I don't think we should rely on the archive_name or the output's 
>>>> name to decide whether or not an output should be rotated. It would 
>>>> be better to introduce an is_rotated() test function in LogOutput 
>>>> that could be used here.
>>>>
>>>> * rotate_all_logfile() should be renamed to rotate_all_outputs(). 
>>>> Currently there are only LogFileOutputs (other than stdout/stderr), 
>>>> but in the future there might be other types of outputs so I prefer 
>>>> having a more general name.
>>>> Also, please use static_cast<LogFileOutput*> instead of the C-style 
>>>> cast. (Additional logic will be required here once more types of 
>>>> log outputs are added, but I don't think we need to worry about 
>>>> this right now.)
>>>>
>>>> * Don't print an error if an output is not rotatable, since it's 
>>>> not an error to have some log outputs rotated while others are not. 
>>>> If you really want some traceability here I suggest adding log 
>>>> messages on trace level, tagged with 'logging'.
>>>>
>>>>
>>>> logDiagnosticCommand.cpp/hpp:
>>>>
>>>> * I think the description could be improved to something like 
>>>> "Lists current log configuration, enables/disables/configures a log 
>>>> output, or disables/rotates all logs."
>>>>
>>>> * The rotate option description should clarify that all logs will 
>>>> be rotated ("current log" is too ambiguous).
>>>>
>>>>
>>>> logFileOutput.cpp/hpp:
>>>>
>>>> * Moving the MutexLocker like this introduces a race condition 
>>>> where a log might be rotated multiple times by different threads, 
>>>> instead of just once.
>>>> Instead of making the rotate() function public and moving the 
>>>> mutexlocker, I suggest adding something like a public 
>>>> force_rotation() function that grabs the lock and calls the private 
>>>> rotate().
>>>>
>>>> * Given the addition of is_rotated() in LogOutput, then 
>>>> get_archive_name() should be removed.
>>>>
>>>> Thanks,
>>>> Marcus
>>>>
>>>>>
>>>>>
>>>>> Thanks,
>>>>>
>>>>> Yasumasa
>>>>>
>>>>>
>>>>> On 2015/10/26 18:56, Marcus Larsson wrote:
>>>>>> Hi,
>>>>>>
>>>>>> Sorry for my late reply.
>>>>>>
>>>>>> I think being able to force rotation via jcmd seems like a good 
>>>>>> feature. Files are currently opened in append mode so it should 
>>>>>> already be possible to use external log rotation tools by copying 
>>>>>> and truncating the files. Still I think it would be nice to 
>>>>>> provide the jcmd for rotation as well.
>>>>>>
>>>>>> I can see some small issues with the implementation, but we can 
>>>>>> deal with that during the review.
>>>>>>
>>>>>> Thanks,
>>>>>> Marcus
>>>>>>
>>>>>>
>>>>>> On 2015-10-26 00:26, Yasumasa Suenaga wrote:
>>>>>>> Hi all,
>>>>>>>
>>>>>>> Have you ever seen my change?
>>>>>>> I (and my customers) need log rotation function via external tool.
>>>>>>>
>>>>>>> I want to merge it by Feature Complete.
>>>>>>>
>>>>>>> Thanks,
>>>>>>>
>>>>>>> Yasumasa
>>>>>>> 2015/10/16 22:55 "Yasumasa Suenaga" <yasuenag at gmail.com>:
>>>>>>>
>>>>>>>> Hi all,
>>>>>>>>
>>>>>>>> I contributed JDK-7090324: gclog rotation via external tool to be
>>>>>>>> synchronized with
>>>>>>>> logrotated tool on Linux.
>>>>>>>>
>>>>>>>> I think JEP 158 is in progress.
>>>>>>>> However, this JEP does not contain log rotation via external 
>>>>>>>> tool in the
>>>>>>>> spec.
>>>>>>>> I want to rotate logs via jcmd in this JEP.
>>>>>>>>
>>>>>>>> I've updated a patch for it:
>>>>>>>>
>>>>>>>> http://cr.openjdk.java.net/~ysuenaga/jvmlogging-logrotate/
>>>>>>>>
>>>>>>>> This patch provides new option "rotate" in VM.log command.
>>>>>>>> If this change can be accepted, I will file it to JBS and send 
>>>>>>>> RFR.
>>>>>>>>
>>>>>>>>
>>>>>>>> Thanks,
>>>>>>>>
>>>>>>>> Yasumasa
>>>>>>>>
>>>>>>
>>>>
>>

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