RFR: 8286180: Enable construction of LogStreamImpl from LogMessageImpl [v5]

[David Holmes]

On Wed, 18 May 2022 15:10:07 GMT, Johan Sjölén <duke at openjdk.java.net> wrote:

>> May I please have a review of this PR which adds non-interleaving log streams to UL?
>> 
>> In `LogMessageImpl` I remove templates and instead directly store a reference to `LogTagSet` and change `LogTagHandle` to be consistent (from pointer to reference) with `LogMessageImpl`.
>> 
>> Adding a non-interleaving log stream enables UL to replace two patterns found in HotSpot:
>> 
>> 1. `ttyLocker` + `(x)tty`
>> Instead of taking the global tty lock in order to ensure non-interleaving logs we can now make a `NonInterleavingLogstream` and pass that around to various `print_on(outputStream*)` functions.
>> 
>> 2. `stringStream` + `outputStream*`
>> In order to avoid taking the lock and being able to take arbitrary output streams a `stringStream` is created and finally printed through `print_raw(ss.as_string())`. This however requires a `ResourceMark`, which `NonInterleavingLogStream` does not require.
>> 
>> Passes tier 1.
>
> Johan Sjölén has updated the pull request incrementally with three additional commits since the last revision:
> 
>  - Use unary not instead of comparing to false
>  - Sort includes
>  - Style changes

The code looks reasonable just reading through the changes, but I'm missing something fundamental here. We have:

`class NonInterleavingLogStream : public LogStreamImpl<LogMessageHandle>`

and 

`class LogStream : public LogStreamImpl<LogTargetHandle>`

but I can't tell what makes the former "non-inter-leaving" while the latter is "inter-leaving" , nor do I understand the test cases for these.

Thanks.

test/hotspot/gtest/logging/test_logStream.cpp line 101:

> 99:   {
> 100:     LogStream foo(Log(gc)::info());
> 101:     if(foo.is_enabled()) {

Style nit: space after "if" please - here and below.

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PR: https://git.openjdk.java.net/jdk/pull/8748