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

Fri Oct 30 14:39:33 UTC 2015

Hi Marcus,

Thank you for your comment.

> Still missing the renaming of rotate_all_logfile to rotate_all_outputs.

Sorry, I will fix.

> 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.

> 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.

However, we might have to rotate at safepoint.
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.

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

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
>>>>>>>
>>>>>
>>>
>