RFR: 8351594: JFR: Rate-limited sampling of Java events [v8]

[Alan Bateman]

On Thu, 5 Jun 2025 09:37:45 GMT, Erik Gahlin <egahlin at openjdk.org> wrote:

>> Could I have review of an enhancement that adds rate-limited sampling to Java events, including five events in the JDK (SocketRead, SocketWrite, FileRead, FileWrite, and JavaExceptionThrow).
>> 
>> Testing: test/jdk/jdk/jfr
>> 
>> Thanks
>> Erik
>
> Erik Gahlin has updated the pull request incrementally with two additional commits since the last revision:
> 
>  - Remove the mistakenly added file.
>  - Fix whitespace

src/java.base/share/classes/java/io/FileInputStream.java line 219:

> 217:             }
> 218:         } finally {
> 219:             FileReadEvent.offer(start, path, bytesRead);

Thanks for this update, this looks much better. It think would be better again if `start = FileReadEvent.timestamp()` is moved to before the try.

src/java.base/share/classes/sun/nio/ch/FileChannelImpl.java line 328:

> 326:         } finally {
> 327:             long end = FileReadEvent.timestamp();
> 328:             FileReadEvent.offer(start, path, bytesRead);

I don't think "end" is needed now.

src/java.base/share/classes/sun/nio/ch/FileChannelImpl.java line 382:

> 380:             FileWriteEvent.offer(start, path, bytes);
> 381:         }
> 382:         return bytes;

The method returns the number of bytes written and traceImplRead uses bytesRead for the number of bytes read. So I think better to leave it as bytesWritten.

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PR Review Comment: https://git.openjdk.org/jdk/pull/25559#discussion_r2128400058
PR Review Comment: https://git.openjdk.org/jdk/pull/25559#discussion_r2128401565
PR Review Comment: https://git.openjdk.org/jdk/pull/25559#discussion_r2128406420