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

[Ioi Lam]

Hi Marcus,

I am eagerly waiting for this to implement a new logging feature in the 
VM. How much testing has been done on this patch? I can see only two 
locations where any logs are bring generated:

+    log_error(logging)("%s", errbuf);
+    log_error(logging)("Could not open log file '%s' (%s).\n", _file_name, strerror(errno));

Do you have a follow-on patch that's already in work to test the various 
functionalists of the Unified JVM Logging framework? I am asking so that 
I can know how much surprise to expect when I start using it.

Thanks
- Ioi


On 9/7/15 6:33 AM, 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