RFR: 8286180: Enable construction of LogStreamImpl from LogMessageImpl [v4]

[David Holmes]

On Tue, 17 May 2022 13:35:53 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 one additional commit since the last revision:
> 
>   Don't use get_ prefix and fix indentation

src/hotspot/share/logging/logStream.hpp line 72:

> 70: 
> 71:   virtual ~LogStreamImpl() {
> 72:     if (_current_line.is_empty() == false) {

Nit: boolean functions can be used directly in expressions - so `if (!_current_line.is_empty()) {`

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