Expose a dictionary of javaThreads from JfrReader

[lbloder]

Describe the feature

We would like to expose a Dictionary javaThreadIds that maps eventIds to javaThreadIds in JfrReader.

Use Case

In order to implement profiling for the sentry-java sdk we had to vendor-in the JfrReader.java in order to get the JavaThread Ids, which we need to map them to running transactions.

If this feature would be implemented we could depend on the jfr-converter as-is without vendoring and customizing.

We can also supply a PR for this, if you'd like.

Proposed Solution

As part of the readThread method in JfrReader (

async-profiler/src/converter/one/jfr/JfrReader.java

Lines 453 to 464 in ea09546

	private void readThreads(int fieldCount) {
	int count = threads.preallocate(getVarint());
	for (int i = 0; i < count; i++) {
	long id = getVarlong();
	String osName = getString();
	int osThreadId = getVarint();
	String javaName = getString();
	long javaThreadId = getVarlong();
	readFields(fieldCount - 4);
	threads.put(id, javaName != null ? javaName : osName);
	}
	}

).

We would propose to track the javaThreads in a Dictionary just like the threads are tracked by their name, so we can map them from the event id.

Here's our version of the JfrReader for reference: https://github.com/getsentry/sentry-java/blob/main/sentry-async-profiler/src/main/java/io/sentry/asyncprofiler/vendor/asyncprofiler/jfr/JfrReader.java

Acknowledgements

• I may be able to implement this feature request
• This feature might incur a breaking change

[apangin]

Sounds good. Please go ahead and submit a PR. Thanks.