RFR: JDK-8266503: [UL] Make Decorations safely copy-able and reduce their size [v2]

[Xin Liu]

On Thu, 6 May 2021 12:00:21 GMT, Thomas Stuefe <stuefe at openjdk.org> wrote:

>> This patch reduces the size of UL `LogDecorations` by about 85% (from 368 -> 56 bytes on Linux x64). This matters in the context of asynchronous logging in UL where we plan to keep a buffer containing log messages, including decorations, for asynchronous printing.
>> 
>> As a side effect, it makes the LogDecorations object safe to copy with trivial assignment constructors and operators (which it had not been before).
>> 
>> As another side effect, the 256-char-for-all-decorators limit has been removed with this patch.
>> 
>> What the patch does:
>> 
>> In LogDecorations, we resolve the values of the given decorators ("uptime", "tid" etc) and print them in human-readable format. Before this patch, the class LogDecorations stored the printed decorators in an internal (limited, fixed-sized) buffer. This is inefficient since this takes much more memory than storing the binary data before printing them.
>> 
>> So this patch separates the decorator value resolving from the printing. It stores the resolved values in binary form and only prints them when needed. Since a decorations object is only printed once this is fine. No need to cache the formatted text.
>> 
>> *Please Note that this patch includes the fix for JDK-8266536: "Provide a variant of os::iso8601_time which works with arbitrary timestamps" which is in a separate PR (https://github.com/openjdk/jdk/pull/3869) - so please ignore all the iso6801 stuff. It also contains a fix for the broken harfbuzz build.*
>> 
>> Testing:
>> - gtests, manually
>> - jtreg runtime/logging, manually
>> - SAP nightlies ran fine, but since then the tests changed, will run them again tonight
>
> Thomas Stuefe has updated the pull request with a new target base due to a merge or a rebase. The incremental webrev excludes the unrelated changes brought in by the merge/rebase. The pull request contains six additional commits since the last revision:
> 
>  - Merge
>  - Remove harfbuzz build fix
>  - Volker feedback
>  - start
>  - cherry-picked JDK-8266536
>  - harfbuzz-buildfix

src/hotspot/share/logging/logDecorations.cpp line 39:

> 37:     if (os::get_host_name(buffer, sizeof(buffer))) {
> 38:       // Use raw malloc here
> 39:       return ::strdup(buffer);

I don't think `strdup` is necessary. If you decide to use static variable, you can use `static char buffer[1024]` in the function.

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PR: https://git.openjdk.java.net/jdk/pull/3874