Thread filter optim

[r1viollet]

• Reserve padded slots
• Introduce a register / unregister to retrieve slots
• manage a free list

What does this PR do?:

Motivation:

Additional Notes:

How to test the change?:

For Datadog employees:

• If this PR touches code that signs or publishes builds or packages, or handles
  credentials of any kind, I've requested a review from @DataDog/security-design-and-guidance.
• This PR doesn't touch any of that.
• JIRA: [JIRA-XXXX]

Unsure? Have a question? Request a review!

[github-actions]

🔧 Report generated by pr-comment-cppcheck

CppCheck Report

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 (8)

• The class 'RecordingBuffer' defines member function with name 'flushIfNeeded' also defined in its parent class 'Buffer'.
• Member variable 'CodeCache::_image_base' is not initialized in the copy constructor.
• Member variable 'CodeCache::_image_base' is not assigned a value in 'CodeCache::operator='.
• Member variable 'JitWriteProtection::_restore' is not initialized in the constructor.
• Member variable 'JitWriteProtection::_restore' is not initialized in the constructor.
• Either the condition 'uc!=nullptr' is redundant or there is possible null pointer dereference: uc.
• Obsolete function 'alloca' called.
• Member variable 'ElfParser::_vaddr_diff' is not initialized in the constructor.

Style Violations (306)

• Class 'Arguments' has a constructor with 1 argument that is not explicit.
• struct member 'Multiplier::symbol' is never used.
• struct member 'Multiplier::multiplier' is never used.
• class member 'Error::OK' is never used.
• Class 'AsyncSampleMutex' has a constructor with 1 argument that is not explicit.
• The class 'NativeFunc' does not declare a constructor although it has private member variables which likely require initialization.
• Local variable 'count' shadows outer function
• Local variable 'blob' shadows outer function
• Local variable 'i' shadows outer variable
• Parameter 'prefixes' can be declared as reference to const
• 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.
• struct member 'ContextPage::capacity' is never used.
• struct member 'ContextPage::storage' is never used.
• class member 'Contexts::_max_pages' is never used.
• class member 'Contexts::_pages' is never used.
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• class member 'CTimer::_cstack' is never used.
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• Class 'Dictionary' has a constructor with 1 argument that is not explicit.
• struct member 'DictRow::keys' is never used.
• struct member 'DictRow::next' is never used.
• Operator '|' with one operand equal to zero is redundant.
• Operator '|' with one operand equal to zero is redundant.
• Operator '|' with one operand equal to zero is redundant.
• Local variable 'table' shadows outer function
• Local variable 'pc_off' shadows outer variable
• Variable 'table' can be declared as pointer to const
• struct member 'FrameDesc::fp_off' is never used.
• struct member 'FrameDesc::pc_off' is never used.
• class member 'DwarfParser::_name' is never used.
• class member 'DwarfParser::_image_base' is never used.
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• class member 'ITimer::_cstack' is never used.
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• The function 'enableEvents' overrides a function in a base class but is identical to the overridden function
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• The function 'registerThread' overrides a function in a base class but is not marked with a 'override' specifier.
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• The function 'enableEvents' overrides a function in a base class but is not marked with a 'override' specifier.
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• class member 'PerfEvents::_ring' is never used.
• class member 'PerfEvents::_cstack' is never used.
• class member 'PerfEvents::_use_mmap_page' is never used.
• Class 'ReservoirSampler' has a constructor with 1 argument that is not explicit.
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• class member 'UnloadProtection::_lib_handle' is never used.
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• Local variable 'section' shadows outer function
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• Variable 'plt' can be declared as pointer to const
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• Variable 'sym' can be declared as pointer to const
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• class member 'ElfParser::_root_symbols' is never used.
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• Same expression on both sides of '-'.
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[github-actions]

🔧 Report generated by pr-comment-scanbuild

[r1viollet]

I have reasonable performance on most runs:

Benchmark                                                       (command)  (skipResults)  (workload)  Mode  Cnt    Score   Error  Units
ThreadFilterBenchmark.threadFilterStress01  cpu=100us,wall=100us,filter=1           true           0  avgt         0.039          us/op
ThreadFilterBenchmark.threadFilterStress01  cpu=100us,wall=100us,filter=1           true           7  avgt         0.041          us/op
ThreadFilterBenchmark.threadFilterStress01  cpu=100us,wall=100us,filter=1           true       70000  avgt       111.094          us/op
ThreadFilterBenchmark.threadFilterStress02  cpu=100us,wall=100us,filter=1           true           0  avgt         0.132          us/op
ThreadFilterBenchmark.threadFilterStress02  cpu=100us,wall=100us,filter=1           true           7  avgt         0.139          us/op
ThreadFilterBenchmark.threadFilterStress02  cpu=100us,wall=100us,filter=1           true       70000  avgt       108.666          us/op
ThreadFilterBenchmark.threadFilterStress04  cpu=100us,wall=100us,filter=1           true           0  avgt         0.258          us/op
ThreadFilterBenchmark.threadFilterStress04  cpu=100us,wall=100us,filter=1           true           7  avgt         0.278          us/op
ThreadFilterBenchmark.threadFilterStress04  cpu=100us,wall=100us,filter=1           true       70000  avgt       118.940          us/op
ThreadFilterBenchmark.threadFilterStress08  cpu=100us,wall=100us,filter=1           true           0  avgt         0.624          us/op
ThreadFilterBenchmark.threadFilterStress08  cpu=100us,wall=100us,filter=1           true           7  avgt         0.646          us/op
ThreadFilterBenchmark.threadFilterStress08  cpu=100us,wall=100us,filter=1           true       70000  avgt       160.170          us/op
ThreadFilterBenchmark.threadFilterStress16  cpu=100us,wall=100us,filter=1           true           0  avgt         1.780          us/op
ThreadFilterBenchmark.threadFilterStress16  cpu=100us,wall=100us,filter=1           true           7  avgt         2.288          us/op
ThreadFilterBenchmark.threadFilterStress16  cpu=100us,wall=100us,filter=1           true       70000  avgt       221.987          us/op

I'm not sure why some runs still blow up for higher numbers of threads.

[r1viollet]

this code path should not happen, though I still need to think about whether it is safe if it happens (possible allocs)

[jbachorik]

This is not happening in the signal context - this is a standard JVMTI callback - so allocation is fine here.
Also, I didn't really get the comment this code path should not happen - this is the path where we register newly created Java threads. This will happen quite often in a Java program.

[r1viollet]

interesting!

[r1viollet]

What is missing to merge this:

• Think carefully about some of the error code paths
• Run this in a test environment
• Measure memory overhead

[jbachorik]

I did run some comparison of native memory usage with different thread filter implementations - data is in the notebook

TL;DR there is no observable increase in the native memory usage (the UNDEFINED category). Anyway, it would be useful to have an extra counter for the ThreadIDTable utilization.