RFR (L): 8046148: JEP 158 Unified JVM Logging

Coleen Phillimore coleen.phillimore at oracle.com
Wed Sep 23 18:14:04 UTC 2015

Looks good!

On 9/23/15 7:10 AM, Marcus Larsson wrote:
> Hi again,
> Here is the third and hopefully final version of the patch.
> Incremental webrev:
> http://cr.openjdk.java.net/~mlarsson/8046148/webrev.01-02/
> Full webrev:
> http://cr.openjdk.java.net/~mlarsson/8046148/webrev.02/
> Changes:
> * Use update_position() in logStream::write so that indent() works 
> properly
> * Add units (ms, ns) to all time decorations
> * Additional comments
> Thanks,
> Marcus
> On 2015-09-15 11:36, Marcus Larsson wrote:
>> Hi,
>> Here is the updated version of the patch, including the feedback and 
>> suggestions from Coleen, David and Ioi.
>> Incremental webrev:
>> http://cr.openjdk.java.net/~mlarsson/8046148/webrev.00-01/
>> Full webrev:
>> http://cr.openjdk.java.net/~mlarsson/8046148/webrev.01/
>> Changes include:
>> * New NMT tag 'mtLogging' used by UL
>> * Added storage allocation classes for all new classes
>> * Added Log::puts<Level>(const char*) for plain string messages of 
>> any length
>> * Fixed broken printf-attribute on Log::write functions
>> * Moved VM startup timestamp to after os::init
>> * Formatting and code style changes
>> Thanks,
>> Marcus
>> On 2015-09-07 15:33, Marcus Larsson wrote:
>>> Hi,
>>> Please review the following patch adding the unified logging 
>>> framework to hotspot.
>>> JEP:
>>> https://bugs.openjdk.java.net/browse/JDK-8046148
>>> Webrev:
>>> http://cr.openjdk.java.net/~mlarsson/8046148/webrev.00/
>>> See the JEP description for a general overview of the new feature. 
>>> Below are some notes on the implementation.
>>> The patch adds the new 'share/vm/logging' subdirectory containing 
>>> the unified logging framework. The main entry point is log.hpp, 
>>> which contains the necessary macros and definitions to use the 
>>> framework.
>>> Log tags are defined/listed in logTag.hpp, and are passed as 
>>> template arguments to the Log class. Every combination of tags used 
>>> in a log call has a corresponding LogTagSet instance, which keeps a 
>>> track of all the outputs it should write the log message to (and 
>>> their levels). Having tags as template arguments allows mapping 
>>> directly from a set of tags to the LogTagSet instance, which means 
>>> that the overhead for disabled logging should be low. Currently each 
>>> log message can be tagged with up to 5 tags, but this can be 
>>> increased if ever required (and with C++11's variadic templates the 
>>> limit can be removed completely).
>>> The LogConfiguration class keeps track of configured outputs 
>>> (stdout, stderr, and possible file outputs). Configuration is done 
>>> either by command line arguments (-Xlog) or by DCMD. Both methods 
>>> will in turn use the LogConfiguration class to perform the parsing & 
>>> configuration. This configuration includes iterating over all 
>>> LogTagSet instances and updating them accordingly. The 
>>> LogTagLevelExpression class is used to represent the selection of 
>>> tags and levels for a given configuration request (the 
>>> "what"-expression).
>>> The LogDecorators class contains a selection of decorators. 
>>> Instances of this class is kept in LogTagSet to track what 
>>> decorators to use (this is the union of all decorators used by its 
>>> outputs). Each log call will create a LogDecorations instance (note: 
>>> different classes), which will contain the actual decoration strings 
>>> for the log message. These decorations are used for each output the 
>>> tagset is set to log on, and are then discarded.
>>> The LogPrefix class allows messages of specific sets of tags to be 
>>> prefixed. The prefix should supply a printf-style format with 
>>> argument. (This allows GC logging to prefix messages of certain 
>>> tagsets with GCId.) Prefixes are implemented using template 
>>> specializations based on the specified tags, with the 
>>> general/unspecialized case giving an empty prefix.
>>> The LogOutput class defines the interface for all types of log 
>>> outputs. LogFileStreamOutput corresponds to FILE* stream based log 
>>> outputs. LogFileOutput builds on this and adds the file management 
>>> and log rotation support.
>>> A simple jtreg test is included in this patch. Additional tests will 
>>> be added at a later stage.
>>> Thanks,
>>> Marcus

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