Add the micro-benchmark for thread filtering

[jbachorik]

What does this PR do?:
It adds the very limited micro-benchmark for ThreadFilter.addThread/removeThread combination

Motivation:
Reduce the noise in the more 'macro-benchmarky' benchmarks. Allow to focus on the sole performance of adding and removing a thread to the filter with specific parallelism and synthetic workload and see how the performance scales.

Additional Notes:
Running this benchmark on MacBook M1 the difference between the JNI access and Unsafe access is almost non-existent.

We see a huge cliff when going from single thread to more threads when the workload is very low (10-100ns) which seems to be caused by:

1. Single contended _size variable which is mutated in atomic fashion by all benchmark threads. I tried sharding that variable and collect the actual size only when needed but that improves the situation only marginally and makes it quite difficult to maintain the unsafe implementation.
2. I tried a more 'random' thread id mapping using golden ration fibonacci hash - but that also provides almost no improvement and makes the unsafe implementation unhappy, as it assumes the original mapping.
3. There is the only remaining thing

JNI access

Benchmark	Workload	Mode	Score	Units
ThreadFilterBenchmark.threadFilterStress01	0	avgt	0.021	us/op
ThreadFilterBenchmark.threadFilterStress01	7	avgt	0.023	us/op
ThreadFilterBenchmark.threadFilterStress01	70000	avgt	147.206	us/op
ThreadFilterBenchmark.threadFilterStress02	0	avgt	0.143	us/op
ThreadFilterBenchmark.threadFilterStress02	7	avgt	0.151	us/op
ThreadFilterBenchmark.threadFilterStress02	70000	avgt	149.653	us/op
ThreadFilterBenchmark.threadFilterStress04	0	avgt	0.402	us/op
ThreadFilterBenchmark.threadFilterStress04	7	avgt	0.449	us/op
ThreadFilterBenchmark.threadFilterStress04	70000	avgt	166.627	us/op
ThreadFilterBenchmark.threadFilterStress08	0	avgt	1.315	us/op
ThreadFilterBenchmark.threadFilterStress08	7	avgt	1.302	us/op
ThreadFilterBenchmark.threadFilterStress08	70000	avgt	167.421	us/op
ThreadFilterBenchmark.threadFilterStress16	0	avgt	2.783	us/op
ThreadFilterBenchmark.threadFilterStress16	7	avgt	2.772	us/op
ThreadFilterBenchmark.threadFilterStress16	70000	avgt	304.041	us/op
ThreadFilterBenchmark.threadFilterStress99	0	avgt	15.222	us/op
ThreadFilterBenchmark.threadFilterStress99	7	avgt	15.599	us/op
ThreadFilterBenchmark.threadFilterStress99	70000	avgt	1797.784	us/op

Unsafe access

Benchmark	Workload	Mode	Score	Units
ThreadFilterBenchmark.threadFilterStress01	0	avgt	0.029	us/op
ThreadFilterBenchmark.threadFilterStress01	7	avgt	0.032	us/op
ThreadFilterBenchmark.threadFilterStress01	70000	avgt	145.954	us/op
ThreadFilterBenchmark.threadFilterStress02	0	avgt	0.165	us/op
ThreadFilterBenchmark.threadFilterStress02	7	avgt	0.171	us/op
ThreadFilterBenchmark.threadFilterStress02	70000	avgt	150.606	us/op
ThreadFilterBenchmark.threadFilterStress04	0	avgt	0.497	us/op
ThreadFilterBenchmark.threadFilterStress04	7	avgt	0.574	us/op
ThreadFilterBenchmark.threadFilterStress04	70000	avgt	163.668	us/op
ThreadFilterBenchmark.threadFilterStress08	0	avgt	1.713	us/op
ThreadFilterBenchmark.threadFilterStress08	7	avgt	1.690	us/op
ThreadFilterBenchmark.threadFilterStress08	70000	avgt	165.619	us/op
ThreadFilterBenchmark.threadFilterStress16	0	avgt	3.817	us/op
ThreadFilterBenchmark.threadFilterStress16	7	avgt	3.953	us/op
ThreadFilterBenchmark.threadFilterStress16	70000	avgt	303.807	us/op
ThreadFilterBenchmark.threadFilterStress99	0	avgt	15.862	us/op
ThreadFilterBenchmark.threadFilterStress99	7	avgt	16.451	us/op
ThreadFilterBenchmark.threadFilterStress99	70000	avgt	1788.177	us/op

Unsure? Have a question? Request a review!

[datadog-datadog-staging-us1-all]

🟠 Code Quality Violation

Suggested change

	privatelongworkloadNum = 0;
	privatelongworkloadNum;

Remove initialization, this is already the default value. (...read more)

When initializing fields, prevent initializing fields to the default value. Any additional initialization means more bytecode instructions, and allocating many of these objects may impact your application performance.

If you initialize to a default value, remove the initialization.

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Errors (2)

• There is an unknown macro here somewhere. Configuration is required. If LP64_ONLY is a macro then please configure it.
• syntax error

Warnings (4)

• The class 'RecordingBuffer' defines member function with name 'flushIfNeeded' also defined in its parent class 'Buffer'.
• Member variable 'JitWriteProtection::_restore' is not initialized in the constructor.
• Member variable 'JitWriteProtection::_restore' is not initialized in the constructor.
• Member variable 'ElfParser::_vaddr_diff' is not initialized in the constructor.

Style Violations (297)

• Class 'Arguments' has a constructor with 1 argument that is not explicit.
• struct member 'Multiplier::symbol' is never used.
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• Variable 'cb1' can be declared as pointer to const
• Variable 'cb2' can be declared as pointer to const
• Variable 'fd1' can be declared as pointer to const
• Variable 'fd2' can be declared as pointer to const
• Parameter 'name' can be declared as pointer to const
• Consider using std::transform algorithm instead of a raw loop.
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