Thread filter optim

[r1viollet]

What does this PR do?:

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

Motivation:

Improve throughput of applications that run on many threads with many context updates.

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.
• The function 'check' overrides a function in a base class but is not marked with a 'override' specifier.
• The function 'start' overrides a function in a base class but is not marked with a 'override' specifier.
• The function 'registerThread' overrides a function in a base class but is not marked with a 'override' specifier.
• The function 'unregisterThread' overrides a function in a base class but is not marked with a 'override' specifier.
• The function 'name' overrides a function in a base class but is not marked with a 'override' specifier.
• The function 'interval' overrides a function in a base class but is not marked with a 'override' specifier.
• The function 'check' overrides a function in a base class but is not marked with a 'override' specifier.
• The function 'start' overrides a function in a base class but is not marked with a 'override' specifier.
• The function 'stop' overrides a function in a base class but is not marked with a 'override' specifier.
• The function 'enableEvents' overrides a function in a base class but is not marked with a 'override' specifier.
• class member 'CTimer::_cstack' is never used.
• class member 'CTimer::_signal' is never used.
• class member 'CTimer::_max_timers' is never used.
• class member 'CTimer::_timers' is never used.
• class member 'Shims::_tid_setter_ref' is never used.
• 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.
• class member 'DwarfParser::_capacity' is never used.
• class member 'DwarfParser::_prev' is never used.
• class member 'DwarfParser::_data_align' is never used.
• Class 'WallClockEpochEvent' has a constructor with 1 argument that is not explicit.
• class member 'LockEvent::_address' is never used.
• class member 'LockEvent::_timeout' is never used.
• The function 'name' overrides a function in a base class but is not marked with a 'override' specifier.
• The function 'interval' overrides a function in a base class but is not marked with a 'override' specifier.
• The function 'check' overrides a function in a base class but is not marked with a 'override' specifier.
• The function 'start' overrides a function in a base class but is not marked with a 'override' specifier.
• The function 'stop' overrides a function in a base class but is not marked with a 'override' specifier.
• The function 'enableEvents' overrides a function in a base class but is not marked with a 'override' specifier.
• class member 'ITimer::_cstack' is never used.
• The class 'J9WallClock' does not declare a constructor although it has private member variables which likely require initialization.
• The function 'name' overrides a function in a base class but is not marked with a 'override' specifier.
• The function 'interval' overrides a function in a base class but is not marked with a 'override' specifier.
• The function 'start' overrides a function in a base class but is not marked with a 'override' specifier.
• The function 'stop' overrides a function in a base class but is not marked with a 'override' specifier.
• The function 'enableEvents' overrides a function in a base class but is not marked with a 'override' specifier.
• class member 'J9WallClock::_max_stack_depth' is never used.
• class member 'J9WallClock::_running' is never used.
• Class 'Element' has a constructor with 1 argument that is not explicit.
• Class 'NoField' has a constructor with 1 argument that is not explicit.
• The function 'is_nofield' overrides a function in a base class but is not marked with a 'override' specifier.
• class member 'JfrMetadata::_initialized' is never used.
• class member 'JVM::_is_readable_pointer_resolved' is never used.
• class member 'JVM::_is_readable_pointer' is never used.
• The class 'VirtualSpaceSummary' does not declare a constructor although it has private member variables which likely require initialization.
• The class 'GCHeapSummary' does not declare a constructor although it has private member variables which likely require initialization.
• The class 'CollectedHeapWrapper' does not declare a constructor although it has private member variables which likely require initialization.
• class member 'VirtualSpaceSummary::_committed_end' is never used.
• class member 'GCHeapSummary::vptr' is never used.
• class member 'CollectedHeapWrapper::vptr' is never used.
• class member 'CollectedHeapWrapper::_gc_heap_log' is never used.
• class member 'CollectedHeapWrapper::_capacity_at_last_gc' is never used.
• class member 'CollectedHeapWrapper::_used_at_last_gc' is never used.
• struct member 'Chunk::prev' is never used.
• struct member 'Chunk::offs' is never used.
• struct member 'Chunk::_padding' is never used.
• class member 'LinearAllocator::_chunk_size' is never used.
• class member 'LinearAllocator::_tail' is never used.
• class member 'LinearAllocator::_reserve' is never used.
• Class 'SpinLock' has a constructor with 1 argument that is not explicit.
• struct member 'TrackingEntry::skipped' is never used.
• class member 'LivenessTracker::MAX_TRACKING_TABLE_SIZE' is never used.
• class member 'LivenessTracker::MIN_SAMPLING_INTERVAL' is never used.
• class member 'LivenessTracker::_table_lock' is never used.
• class member 'Log::_file' is never used.
• class member 'Log::LEVEL_NAME' is never used.
• The function 'check' overrides a function in a base class but is not marked with a 'override' specifier.
• The function 'start' overrides a function in a base class but is not marked with a 'override' specifier.
• The function 'stop' overrides a function in a base class but is not marked with a 'override' specifier.
• The function 'interval' overrides a function in a base class but is not marked with a 'override' specifier.
• class member 'ObjectSampler::CONFIG_UPDATE_CHECK_PERIOD_SECS' is never used.
• class member 'JitWriteProtection::_restore' is never used.
• class member 'OS::page_size' is never used.
• class member 'OS::page_mask' is never used.
• The function 'rewind' overrides a function in a base class but is not marked with a 'override' specifier.
• The function 'next' overrides a function in a base class but is not marked with a 'override' specifier.
• The function 'size' overrides a function in a base class but is not marked with a 'override' specifier.
• Variable 'entry' can be declared as pointer to const
• The function 'rewind' overrides a function in a base class but is not marked with a 'override' specifier.
• The function 'next' overrides a function in a base class but is not marked with a 'override' specifier.
• The function 'size' overrides a function in a base class but is not marked with a 'override' specifier.
• The function 'check' overrides a function in a base class but is not marked with a 'override' specifier.
• The function 'start' overrides a function in a base class but is not marked with a 'override' specifier.
• The function 'enableEvents' overrides a function in a base class but is not marked with a 'override' specifier.
• The function 'registerThread' overrides a function in a base class but is not marked with a 'override' specifier.
• The function 'unregisterThread' overrides a function in a base class but is not marked with a 'override' specifier.
• The function 'interval' overrides a function in a base class but is not marked with a 'override' specifier.
• The function 'enableEvents' overrides a function in a base class but is identical to the overridden function
• The function 'registerThread' overrides a function in a base class but is identical to the overridden function
• The function 'unregisterThread' overrides a function in a base class but is identical to the overridden function
• The function 'check' overrides a function in a base class but is not marked with a 'override' specifier.
• The function 'start' overrides a function in a base class but is not marked with a 'override' specifier.
• The function 'stop' overrides a function in a base class but is not marked with a 'override' specifier.
• The function 'registerThread' overrides a function in a base class but is not marked with a 'override' specifier.
• The function 'unregisterThread' overrides a function in a base class but is not marked with a 'override' specifier.
• The function 'interval' overrides a function in a base class but is not marked with a 'override' specifier.
• The function 'name' overrides a function in a base class but is not marked with a 'override' specifier.
• The function 'enableEvents' overrides a function in a base class but is not marked with a 'override' specifier.
• class member 'PerfEvents::_max_events' is never used.
• class member 'PerfEvents::_events' is never used.
• class member 'PerfEvents::_event_type' is never used.
• 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.
• Class 'UnloadProtection' has a constructor with 1 argument that is not explicit.
• class member 'Symbols::_libs_limit_reported' is never used.
• class member 'UnloadProtection::_lib_handle' is never used.
• Class 'SymbolDesc' has a constructor with 1 argument that is not explicit.
• Class 'MemoryMapDesc' has a constructor with 1 argument that is not explicit.
• Local variable 'section' shadows outer function
• Local variable 'section' shadows outer function
• Local variable 'section' shadows outer function
• Variable 'ident' can be declared as pointer to const
• Parameter 'section' can be declared as pointer to const
• Variable 'checked' can be declared as pointer to const
• Variable 'pheader' can be declared as pointer to const
• Variable 'sym' can be declared as pointer to const
• Variable 'sym' can be declared as pointer to const
• Variable 'chain' can be declared as pointer to const
• Variable 'plt' can be declared as pointer to const
• Variable 'note' can be declared as pointer to const
• Variable 'sym' can be declared as pointer to const
• Parameter 'info' can be declared as pointer to const
• struct member 'RootSymbolEntry::name' is never used.
• struct member 'RootSymbolEntry::kind' is never used.
• class member 'ElfParser::_root_symbols' is never used.
• Class 'ExclusiveLock' has a constructor with 1 argument that is not explicit.
• Class 'SharedLock' has a constructor with 1 argument that is not explicit.
• Same expression on both sides of '-'.
• Local variable 'count' shadows outer function
• Parameter 'failures' can be declared as reference to const
• class member 'ProfiledThread::_buffer_size' is never used.
• class member 'ProfiledThread::_buffer' is never used.
• Variable 'existing' can be declared as pointer to const
• Variable 'chunk' can be declared as pointer to const
• class member 'ThreadFilter::kChunkShift' is never used.
• class member 'ThreadFilter::kChunkMask' is never used.
• class member 'ThreadFilter::kFreeListSize' is never used.
• struct member 'Slot::padding' is never used.
• struct member 'ChunkStorage::slots' is never used.
• class member 'ThreadInfo::_thread_names' is never used.
• class member 'ThreadInfo::_thread_ids' is never used.
• Condition 'enabled()' is always false
• The function 'loadAcquire' is never used.
• The function 'message' is never used.
• The function 'hasOption' is never used.
• The function 'cpuSamplerInterval' is never used.
• The function 'acquired' is never used.
• The function 'offset' is never used.
• The function 'skip' is never used.
• The function 'put16' is never used.
• The function 'put64' is never used.
• The function 'putFloat' is never used.
• The function 'putVar64' is never used.
• The function 'findBlobByAddress' is never used.
• The function 'binarySearch' is never used.
• The function 'dump' is never used.
• The function 'findSymbolsByPrefix' is never used.
• The function 'findImport' is never used.
• The function 'patchImport' is never used.
• The function 'findFrameDesc' is never used.
• The function 'libIndex' is never used.
• The function 'isMarked' is never used.
• The function 'minAddress' is never used.
• The function 'contains' is never used.
• The function 'get' is never used.
• The function 'getPage' is never used.
• The function 'get_tag' is never used.
• The function 'getCounters' is never used.
• The function 'getCounter' is never used.
• The function 'describeCounters' is never used.
• The function 'units' is never used.
• The function 'check' is never used.
• The function 'start' is never used.
• The function 'supported' is never used.
• The function 'setSighandlerTid' is never used.
• The function 'bounded_lookup' is never used.
• The function 'stop' is never used.
• The function 'interval' is never used.
• The function 'registerThread' is never used.
• The function 'unregisterThread' is never used.
• The function 'enableEvents' is never used.
• The function 'updateCounter' is never used.
• The function 'hasChanged' is never used.
• The function 'updateNumSamplableThreads' is never used.
• The function 'updateNumSuccessfulSamples' is never used.
• The function 'updateNumFailedSamples' is never used.
• The function 'updateNumExitedThreads' is never used.
• The function 'updateNumPermissionDenied' is never used.
• The function 'endEpoch' is never used.
• The function 'clean' is never used.
• The function 'newEpoch' is never used.
• The function 'encode' is never used.
• The function 'decode' is never used.
• The function 'threadEntry' is never used.
• The function 'sampleIdleThreads' is never used.
• The function 'field' is never used.
• The function 'category' is never used.
• The function 'root' is never used.
• The function 'strings' is never used.
• The function 'jniExceptionCheck' is never used.
• The function 'is_readable_pointer' is never used.
• The function 'used' is never used.
• The function 'alloc' is never used.
• The function 'level' is never used.
• The function 'next' is never used.
• The function 'cputime' is never used.
• The function 'micros' is never used.
• The function 'processStartTime' is never used.
• The function 'sleep' is never used.
• The function 'ntoh64' is never used.
• The function 'threadId' is never used.
• The function 'schedPolicy' is never used.
• The function 'threadName' is never used.
• The function 'listThreads' is never used.
• The function 'isLinux' is never used.
• The function 'installSignalHandler' is never used.
• The function 'replaceSigsegvHandler' is never used.
• The function 'replaceSigbusHandler' is never used.
• The function 'sendSignalToThread' is never used.
• The function 'getCpuDescription' is never used.
• The function 'getProcessCpuTime' is never used.
• The function 'getTotalCpuTime' is never used.
• The function 'copyFile' is never used.
• The function 'truncateFile' is never used.
• The function 'fileSize' is never used.
• The function 'freePageCache' is never used.
• The function 'mallocArenaMax' is never used.
• The function 'walkKernel' is never used.
• The function 'resetBuffer' is never used.
• The function 'getEventName' is never used.
• The function 'compute' is never used.
• The function 'sample' is never used.
• The function 'reverse16' is never used.
• The function 'is_probably_rust_legacy' is never used.
• The function 'demangle' is never used.
• The function 'handle_safefetch' is never used.
• The function 'safeFetch32' is never used.
• The function 'safeFetch64' is never used.
• The function 'load32' is never used.
• The function 'tryLockShared' is never used.
• The function 'withinCurrentStack' is never used.
• The function 'restore' is never used.
• The function 'stackAt' is never used.
• The function 'clearParsingCaches' is never used.
• The function 'parseLibraries' is never used.
• The function 'isRootSymbol' is never used.
• The function 'forTid' is never used.
• The function 'inBuffer' is never used.
• The function 'tid' is never used.
• The function 'noteCPUSample' is never used.
• The function 'lookupWallclockCallTraceId' is never used.
• The function 'recordCallTraceId' is never used.
• The function 'enterCrashHandler' is never used.
• The function 'exitCrashHandler' is never used.
• The function 'resetCrashHandler' is never used.
• The function 'isDeepCrashHandler' is never used.
• The function 'unwindFailures' is never used.
• The function 'filterSlotId' is never used.
• The function 'setFilterSlotId' is never used.
• The function 'accept' is never used.
• The function 'getThreadId' is never used.
• The function 'clearAll' is never used.
• The function 'updateThreadName' is never used.
• The function 'reportCounters' is never used.
• The function 'convertJvmExecutionState' is never used.
• The function 'initialized' is never used.
• The function 'ticks' is never used.
• The function 'frequency' is never used.
• The function 'ticks_to_millis' is never used.
• The function 'record' is never used.
• The function 'forEach' is never used.
• The function 'countFailures' is never used.
• The function 'collectAndReset' is never used.

[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]

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 (305)

• 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.
• The function 'check' overrides a function in a base class but is not marked with a 'override' specifier.
• The function 'start' overrides a function in a base class but is not marked with a 'override' specifier.
• The function 'registerThread' overrides a function in a base class but is not marked with a 'override' specifier.
• The function 'unregisterThread' overrides a function in a base class but is not marked with a 'override' specifier.
• The function 'name' overrides a function in a base class but is not marked with a 'override' specifier.
• The function 'interval' overrides a function in a base class but is not marked with a 'override' specifier.
• The function 'check' overrides a function in a base class but is not marked with a 'override' specifier.
• The function 'start' overrides a function in a base class but is not marked with a 'override' specifier.
• The function 'stop' overrides a function in a base class but is not marked with a 'override' specifier.
• The function 'enableEvents' overrides a function in a base class but is not marked with a 'override' specifier.
• class member 'CTimer::_cstack' is never used.
• class member 'CTimer::_signal' is never used.
• class member 'CTimer::_max_timers' is never used.
• class member 'CTimer::_timers' is never used.
• class member 'Shims::_tid_setter_ref' is never used.
• 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.
• class member 'DwarfParser::_capacity' is never used.
• class member 'DwarfParser::_prev' is never used.
• class member 'DwarfParser::_data_align' is never used.
• Class 'WallClockEpochEvent' has a constructor with 1 argument that is not explicit.
• class member 'LockEvent::_address' is never used.
• class member 'LockEvent::_timeout' is never used.
• The function 'name' overrides a function in a base class but is not marked with a 'override' specifier.
• The function 'interval' overrides a function in a base class but is not marked with a 'override' specifier.
• The function 'check' overrides a function in a base class but is not marked with a 'override' specifier.
• The function 'start' overrides a function in a base class but is not marked with a 'override' specifier.
• The function 'stop' overrides a function in a base class but is not marked with a 'override' specifier.
• The function 'enableEvents' overrides a function in a base class but is not marked with a 'override' specifier.
• class member 'ITimer::_cstack' is never used.
• The class 'J9WallClock' does not declare a constructor although it has private member variables which likely require initialization.
• The function 'name' overrides a function in a base class but is not marked with a 'override' specifier.
• The function 'interval' overrides a function in a base class but is not marked with a 'override' specifier.
• The function 'start' overrides a function in a base class but is not marked with a 'override' specifier.
• The function 'stop' overrides a function in a base class but is not marked with a 'override' specifier.
• The function 'enableEvents' overrides a function in a base class but is not marked with a 'override' specifier.
• class member 'J9WallClock::_max_stack_depth' is never used.
• class member 'J9WallClock::_running' is never used.
• Class 'Element' has a constructor with 1 argument that is not explicit.
• Class 'NoField' has a constructor with 1 argument that is not explicit.
• The function 'is_nofield' overrides a function in a base class but is not marked with a 'override' specifier.
• class member 'JfrMetadata::_initialized' is never used.
• class member 'JVM::_is_readable_pointer_resolved' is never used.
• class member 'JVM::_is_readable_pointer' is never used.
• The class 'VirtualSpaceSummary' does not declare a constructor although it has private member variables which likely require initialization.
• The class 'GCHeapSummary' does not declare a constructor although it has private member variables which likely require initialization.
• The class 'CollectedHeapWrapper' does not declare a constructor although it has private member variables which likely require initialization.
• class member 'VirtualSpaceSummary::_committed_end' is never used.
• class member 'GCHeapSummary::vptr' is never used.
• class member 'CollectedHeapWrapper::vptr' is never used.
• class member 'CollectedHeapWrapper::_gc_heap_log' is never used.
• class member 'CollectedHeapWrapper::_capacity_at_last_gc' is never used.
• class member 'CollectedHeapWrapper::_used_at_last_gc' is never used.
• struct member 'Chunk::prev' is never used.
• struct member 'Chunk::offs' is never used.
• struct member 'Chunk::_padding' is never used.
• class member 'LinearAllocator::_chunk_size' is never used.
• class member 'LinearAllocator::_tail' is never used.
• class member 'LinearAllocator::_reserve' is never used.
• Class 'SpinLock' has a constructor with 1 argument that is not explicit.
• struct member 'TrackingEntry::skipped' is never used.
• class member 'LivenessTracker::MAX_TRACKING_TABLE_SIZE' is never used.
• class member 'LivenessTracker::MIN_SAMPLING_INTERVAL' is never used.
• class member 'Log::_file' is never used.
• class member 'Log::LEVEL_NAME' is never used.
• The function 'check' overrides a function in a base class but is not marked with a 'override' specifier.
• The function 'start' overrides a function in a base class but is not marked with a 'override' specifier.
• The function 'stop' overrides a function in a base class but is not marked with a 'override' specifier.
• The function 'interval' overrides a function in a base class but is not marked with a 'override' specifier.
• class member 'ObjectSampler::CONFIG_UPDATE_CHECK_PERIOD_SECS' is never used.
• class member 'JitWriteProtection::_restore' is never used.
• class member 'OS::page_size' is never used.
• class member 'OS::page_mask' is never used.
• The function 'rewind' overrides a function in a base class but is not marked with a 'override' specifier.
• The function 'next' overrides a function in a base class but is not marked with a 'override' specifier.
• The function 'size' overrides a function in a base class but is not marked with a 'override' specifier.
• Variable 'entry' can be declared as pointer to const
• The function 'rewind' overrides a function in a base class but is not marked with a 'override' specifier.
• The function 'next' overrides a function in a base class but is not marked with a 'override' specifier.
• The function 'size' overrides a function in a base class but is not marked with a 'override' specifier.
• The function 'check' overrides a function in a base class but is not marked with a 'override' specifier.
• The function 'start' overrides a function in a base class but is not marked with a 'override' specifier.
• The function 'enableEvents' overrides a function in a base class but is not marked with a 'override' specifier.
• The function 'registerThread' overrides a function in a base class but is not marked with a 'override' specifier.
• The function 'unregisterThread' overrides a function in a base class but is not marked with a 'override' specifier.
• The function 'interval' overrides a function in a base class but is not marked with a 'override' specifier.
• The function 'enableEvents' overrides a function in a base class but is identical to the overridden function
• The function 'registerThread' overrides a function in a base class but is identical to the overridden function
• The function 'unregisterThread' overrides a function in a base class but is identical to the overridden function
• The function 'check' overrides a function in a base class but is not marked with a 'override' specifier.
• The function 'start' overrides a function in a base class but is not marked with a 'override' specifier.
• The function 'stop' overrides a function in a base class but is not marked with a 'override' specifier.
• The function 'registerThread' overrides a function in a base class but is not marked with a 'override' specifier.
• The function 'unregisterThread' overrides a function in a base class but is not marked with a 'override' specifier.
• The function 'interval' overrides a function in a base class but is not marked with a 'override' specifier.
• The function 'name' overrides a function in a base class but is not marked with a 'override' specifier.
• The function 'enableEvents' overrides a function in a base class but is not marked with a 'override' specifier.
• class member 'PerfEvents::_max_events' is never used.
• class member 'PerfEvents::_events' is never used.
• class member 'PerfEvents::_event_type' is never used.
• 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.
• Class 'UnloadProtection' has a constructor with 1 argument that is not explicit.
• class member 'Symbols::_libs_limit_reported' is never used.
• class member 'UnloadProtection::_lib_handle' is never used.
• Class 'SymbolDesc' has a constructor with 1 argument that is not explicit.
• Class 'MemoryMapDesc' has a constructor with 1 argument that is not explicit.
• Local variable 'section' shadows outer function
• Local variable 'section' shadows outer function
• Local variable 'section' shadows outer function
• Variable 'ident' can be declared as pointer to const
• Parameter 'section' can be declared as pointer to const
• Variable 'checked' can be declared as pointer to const
• Variable 'pheader' can be declared as pointer to const
• Variable 'sym' can be declared as pointer to const
• Variable 'sym' can be declared as pointer to const
• Variable 'chain' can be declared as pointer to const
• Variable 'plt' can be declared as pointer to const
• Variable 'note' can be declared as pointer to const
• Variable 'sym' can be declared as pointer to const
• Parameter 'info' can be declared as pointer to const
• struct member 'RootSymbolEntry::name' is never used.
• struct member 'RootSymbolEntry::kind' is never used.
• class member 'ElfParser::_root_symbols' is never used.
• Class 'ExclusiveLock' has a constructor with 1 argument that is not explicit.
• Class 'SharedLock' has a constructor with 1 argument that is not explicit.
• Same expression on both sides of '-'.
• Local variable 'count' shadows outer function
• Parameter 'failures' can be declared as reference to const
• class member 'ProfiledThread::_buffer_size' is never used.
• class member 'ProfiledThread::_buffer' is never used.
• Variable 'existing' can be declared as pointer to const
• Variable 'chunk' can be declared as pointer to const
• class member 'ThreadFilter::kChunkShift' is never used.
• class member 'ThreadFilter::kChunkMask' is never used.
• class member 'ThreadFilter::kFreeListSize' is never used.
• struct member 'Slot::padding' is never used.
• struct member 'ChunkStorage::slots' is never used.
• class member 'ThreadInfo::_thread_names' is never used.
• class member 'ThreadInfo::_thread_ids' is never used.
• Condition 'enabled()' is always false
• The function 'loadAcquire' is never used.
• The function 'message' is never used.
• The function 'hasOption' is never used.
• The function 'cpuSamplerInterval' is never used.
• The function 'acquired' is never used.
• The function 'offset' is never used.
• The function 'skip' is never used.
• The function 'put16' is never used.
• The function 'put64' is never used.
• The function 'putFloat' is never used.
• The function 'putVar64' is never used.
• The function 'findBlobByAddress' is never used.
• The function 'binarySearch' is never used.
• The function 'dump' is never used.
• The function 'findSymbolsByPrefix' is never used.
• The function 'findImport' is never used.
• The function 'patchImport' is never used.
• The function 'findFrameDesc' is never used.
• The function 'libIndex' is never used.
• The function 'isMarked' is never used.
• The function 'minAddress' is never used.
• The function 'contains' is never used.
• The function 'get' is never used.
• The function 'getPage' is never used.
• The function 'get_tag' is never used.
• The function 'getCounters' is never used.
• The function 'getCounter' is never used.
• The function 'describeCounters' is never used.
• The function 'units' is never used.
• The function 'check' is never used.
• The function 'start' is never used.
• The function 'supported' is never used.
• The function 'setSighandlerTid' is never used.
• The function 'bounded_lookup' is never used.
• The function 'stop' is never used.
• The function 'interval' is never used.
• The function 'registerThread' is never used.
• The function 'unregisterThread' is never used.
• The function 'enableEvents' is never used.
• The function 'updateCounter' is never used.
• The function 'hasChanged' is never used.
• The function 'updateNumSamplableThreads' is never used.
• The function 'updateNumSuccessfulSamples' is never used.
• The function 'updateNumFailedSamples' is never used.
• The function 'updateNumExitedThreads' is never used.
• The function 'updateNumPermissionDenied' is never used.
• The function 'endEpoch' is never used.
• The function 'clean' is never used.
• The function 'newEpoch' is never used.
• The function 'encode' is never used.
• The function 'decode' is never used.
• The function 'threadEntry' is never used.
• The function 'sampleIdleThreads' is never used.
• The function 'field' is never used.
• The function 'category' is never used.
• The function 'root' is never used.
• The function 'strings' is never used.
• The function 'jniExceptionCheck' is never used.
• The function 'is_readable_pointer' is never used.
• The function 'used' is never used.
• The function 'alloc' is never used.
• The function 'level' is never used.
• The function 'next' is never used.
• The function 'cputime' is never used.
• The function 'micros' is never used.
• The function 'processStartTime' is never used.
• The function 'sleep' is never used.
• The function 'ntoh64' is never used.
• The function 'threadId' is never used.
• The function 'schedPolicy' is never used.
• The function 'threadName' is never used.
• The function 'listThreads' is never used.
• The function 'isLinux' is never used.
• The function 'installSignalHandler' is never used.
• The function 'replaceSigsegvHandler' is never used.
• The function 'replaceSigbusHandler' is never used.
• The function 'sendSignalToThread' is never used.
• The function 'getCpuDescription' is never used.
• The function 'getProcessCpuTime' is never used.
• The function 'getTotalCpuTime' is never used.
• The function 'copyFile' is never used.
• The function 'truncateFile' is never used.
• The function 'fileSize' is never used.
• The function 'freePageCache' is never used.
• The function 'mallocArenaMax' is never used.
• The function 'walkKernel' is never used.
• The function 'resetBuffer' is never used.
• The function 'getEventName' is never used.
• The function 'compute' is never used.
• The function 'sample' is never used.
• The function 'reverse16' is never used.
• The function 'is_probably_rust_legacy' is never used.
• The function 'demangle' is never used.
• The function 'handle_safefetch' is never used.
• The function 'safeFetch32' is never used.
• The function 'safeFetch64' is never used.
• The function 'load32' is never used.
• The function 'tryLockShared' is never used.
• The function 'withinCurrentStack' is never used.
• The function 'restore' is never used.
• The function 'stackAt' is never used.
• The function 'clearParsingCaches' is never used.
• The function 'parseLibraries' is never used.
• The function 'isRootSymbol' is never used.
• The function 'forTid' is never used.
• The function 'inBuffer' is never used.
• The function 'tid' is never used.
• The function 'noteCPUSample' is never used.
• The function 'lookupWallclockCallTraceId' is never used.
• The function 'recordCallTraceId' is never used.
• The function 'enterCrashHandler' is never used.
• The function 'exitCrashHandler' is never used.
• The function 'resetCrashHandler' is never used.
• The function 'isDeepCrashHandler' is never used.
• The function 'unwindFailures' is never used.
• The function 'filterSlotId' is never used.
• The function 'setFilterSlotId' is never used.
• The function 'accept' is never used.
• The function 'getThreadId' is never used.
• The function 'clearAll' is never used.
• The function 'updateThreadName' is never used.
• The function 'reportCounters' is never used.
• The function 'convertJvmExecutionState' is never used.
• The function 'initialized' is never used.
• The function 'ticks' is never used.
• The function 'frequency' is never used.
• The function 'ticks_to_millis' is never used.
• The function 'record' is never used.
• The function 'forEach' is never used.
• The function 'countFailures' is never used.
• The function 'collectAndReset' is never used.

[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.

[r1viollet]

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 (305)

• 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.
• The function 'check' overrides a function in a base class but is not marked with a 'override' specifier.
• The function 'start' overrides a function in a base class but is not marked with a 'override' specifier.
• The function 'registerThread' overrides a function in a base class but is not marked with a 'override' specifier.
• The function 'unregisterThread' overrides a function in a base class but is not marked with a 'override' specifier.
• The function 'name' overrides a function in a base class but is not marked with a 'override' specifier.
• The function 'interval' overrides a function in a base class but is not marked with a 'override' specifier.
• The function 'check' overrides a function in a base class but is not marked with a 'override' specifier.
• The function 'start' overrides a function in a base class but is not marked with a 'override' specifier.
• The function 'stop' overrides a function in a base class but is not marked with a 'override' specifier.
• The function 'enableEvents' overrides a function in a base class but is not marked with a 'override' specifier.
• class member 'CTimer::_cstack' is never used.
• class member 'CTimer::_signal' is never used.
• class member 'CTimer::_max_timers' is never used.
• class member 'CTimer::_timers' is never used.
• class member 'Shims::_tid_setter_ref' is never used.
• 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.
• class member 'DwarfParser::_capacity' is never used.
• class member 'DwarfParser::_prev' is never used.
• class member 'DwarfParser::_data_align' is never used.
• Class 'WallClockEpochEvent' has a constructor with 1 argument that is not explicit.
• class member 'LockEvent::_address' is never used.
• class member 'LockEvent::_timeout' is never used.
• The function 'name' overrides a function in a base class but is not marked with a 'override' specifier.
• The function 'interval' overrides a function in a base class but is not marked with a 'override' specifier.
• The function 'check' overrides a function in a base class but is not marked with a 'override' specifier.
• The function 'start' overrides a function in a base class but is not marked with a 'override' specifier.
• The function 'stop' overrides a function in a base class but is not marked with a 'override' specifier.
• The function 'enableEvents' overrides a function in a base class but is not marked with a 'override' specifier.
• class member 'ITimer::_cstack' is never used.
• The class 'J9WallClock' does not declare a constructor although it has private member variables which likely require initialization.
• The function 'name' overrides a function in a base class but is not marked with a 'override' specifier.
• The function 'interval' overrides a function in a base class but is not marked with a 'override' specifier.
• The function 'start' overrides a function in a base class but is not marked with a 'override' specifier.
• The function 'stop' overrides a function in a base class but is not marked with a 'override' specifier.
• The function 'enableEvents' overrides a function in a base class but is not marked with a 'override' specifier.
• class member 'J9WallClock::_max_stack_depth' is never used.
• class member 'J9WallClock::_running' is never used.
• Class 'Element' has a constructor with 1 argument that is not explicit.
• Class 'NoField' has a constructor with 1 argument that is not explicit.
• The function 'is_nofield' overrides a function in a base class but is not marked with a 'override' specifier.
• class member 'JfrMetadata::_initialized' is never used.
• class member 'JVM::_is_readable_pointer_resolved' is never used.
• class member 'JVM::_is_readable_pointer' is never used.
• The class 'VirtualSpaceSummary' does not declare a constructor although it has private member variables which likely require initialization.
• The class 'GCHeapSummary' does not declare a constructor although it has private member variables which likely require initialization.
• The class 'CollectedHeapWrapper' does not declare a constructor although it has private member variables which likely require initialization.
• class member 'VirtualSpaceSummary::_committed_end' is never used.
• class member 'GCHeapSummary::vptr' is never used.
• class member 'CollectedHeapWrapper::vptr' is never used.
• class member 'CollectedHeapWrapper::_gc_heap_log' is never used.
• class member 'CollectedHeapWrapper::_capacity_at_last_gc' is never used.
• class member 'CollectedHeapWrapper::_used_at_last_gc' is never used.
• struct member 'Chunk::prev' is never used.
• struct member 'Chunk::offs' is never used.
• struct member 'Chunk::_padding' is never used.
• class member 'LinearAllocator::_chunk_size' is never used.
• class member 'LinearAllocator::_tail' is never used.
• class member 'LinearAllocator::_reserve' is never used.
• Class 'SpinLock' has a constructor with 1 argument that is not explicit.
• struct member 'TrackingEntry::skipped' is never used.
• class member 'LivenessTracker::MAX_TRACKING_TABLE_SIZE' is never used.
• class member 'LivenessTracker::MIN_SAMPLING_INTERVAL' is never used.
• class member 'Log::_file' is never used.
• class member 'Log::LEVEL_NAME' is never used.
• The function 'check' overrides a function in a base class but is not marked with a 'override' specifier.
• The function 'start' overrides a function in a base class but is not marked with a 'override' specifier.
• The function 'stop' overrides a function in a base class but is not marked with a 'override' specifier.
• The function 'interval' overrides a function in a base class but is not marked with a 'override' specifier.
• class member 'ObjectSampler::CONFIG_UPDATE_CHECK_PERIOD_SECS' is never used.
• class member 'JitWriteProtection::_restore' is never used.
• class member 'OS::page_size' is never used.
• class member 'OS::page_mask' is never used.
• The function 'rewind' overrides a function in a base class but is not marked with a 'override' specifier.
• The function 'next' overrides a function in a base class but is not marked with a 'override' specifier.
• The function 'size' overrides a function in a base class but is not marked with a 'override' specifier.
• Variable 'entry' can be declared as pointer to const
• The function 'rewind' overrides a function in a base class but is not marked with a 'override' specifier.
• The function 'next' overrides a function in a base class but is not marked with a 'override' specifier.
• The function 'size' overrides a function in a base class but is not marked with a 'override' specifier.
• The function 'check' overrides a function in a base class but is not marked with a 'override' specifier.
• The function 'start' overrides a function in a base class but is not marked with a 'override' specifier.
• The function 'enableEvents' overrides a function in a base class but is not marked with a 'override' specifier.
• The function 'registerThread' overrides a function in a base class but is not marked with a 'override' specifier.
• The function 'unregisterThread' overrides a function in a base class but is not marked with a 'override' specifier.
• The function 'interval' overrides a function in a base class but is not marked with a 'override' specifier.
• The function 'enableEvents' overrides a function in a base class but is identical to the overridden function
• The function 'registerThread' overrides a function in a base class but is identical to the overridden function
• The function 'unregisterThread' overrides a function in a base class but is identical to the overridden function
• The function 'check' overrides a function in a base class but is not marked with a 'override' specifier.
• The function 'start' overrides a function in a base class but is not marked with a 'override' specifier.
• The function 'stop' overrides a function in a base class but is not marked with a 'override' specifier.
• The function 'registerThread' overrides a function in a base class but is not marked with a 'override' specifier.
• The function 'unregisterThread' overrides a function in a base class but is not marked with a 'override' specifier.
• The function 'interval' overrides a function in a base class but is not marked with a 'override' specifier.
• The function 'name' overrides a function in a base class but is not marked with a 'override' specifier.
• The function 'enableEvents' overrides a function in a base class but is not marked with a 'override' specifier.
• class member 'PerfEvents::_max_events' is never used.
• class member 'PerfEvents::_events' is never used.
• class member 'PerfEvents::_event_type' is never used.
• 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.
• Class 'UnloadProtection' has a constructor with 1 argument that is not explicit.
• class member 'Symbols::_libs_limit_reported' is never used.
• class member 'UnloadProtection::_lib_handle' is never used.
• Class 'SymbolDesc' has a constructor with 1 argument that is not explicit.
• Class 'MemoryMapDesc' has a constructor with 1 argument that is not explicit.
• Local variable 'section' shadows outer function
• Local variable 'section' shadows outer function
• Local variable 'section' shadows outer function
• Variable 'ident' can be declared as pointer to const
• Parameter 'section' can be declared as pointer to const
• Variable 'checked' can be declared as pointer to const
• Variable 'pheader' can be declared as pointer to const
• Variable 'sym' can be declared as pointer to const
• Variable 'sym' can be declared as pointer to const
• Variable 'chain' can be declared as pointer to const
• Variable 'plt' can be declared as pointer to const
• Variable 'note' can be declared as pointer to const
• Variable 'sym' can be declared as pointer to const
• Parameter 'info' can be declared as pointer to const
• struct member 'RootSymbolEntry::name' is never used.
• struct member 'RootSymbolEntry::kind' is never used.
• class member 'ElfParser::_root_symbols' is never used.
• Class 'ExclusiveLock' has a constructor with 1 argument that is not explicit.
• Class 'SharedLock' has a constructor with 1 argument that is not explicit.
• Same expression on both sides of '-'.
• Local variable 'count' shadows outer function
• Parameter 'failures' can be declared as reference to const
• class member 'ProfiledThread::_buffer_size' is never used.
• class member 'ProfiledThread::_buffer' is never used.
• Variable 'existing' can be declared as pointer to const
• Variable 'chunk' can be declared as pointer to const
• class member 'ThreadFilter::kChunkShift' is never used.
• class member 'ThreadFilter::kChunkMask' is never used.
• class member 'ThreadFilter::kFreeListSize' is never used.
• struct member 'Slot::padding' is never used.
• struct member 'ChunkStorage::slots' is never used.
• class member 'ThreadInfo::_thread_names' is never used.
• class member 'ThreadInfo::_thread_ids' is never used.
• Condition 'enabled()' is always false
• The function 'loadAcquire' is never used.
• The function 'message' is never used.
• The function 'hasOption' is never used.
• The function 'cpuSamplerInterval' is never used.
• The function 'acquired' is never used.
• The function 'offset' is never used.
• The function 'skip' is never used.
• The function 'put16' is never used.
• The function 'put64' is never used.
• The function 'putFloat' is never used.
• The function 'putVar64' is never used.
• The function 'findBlobByAddress' is never used.
• The function 'binarySearch' is never used.
• The function 'dump' is never used.
• The function 'findSymbolsByPrefix' is never used.
• The function 'findImport' is never used.
• The function 'patchImport' is never used.
• The function 'findFrameDesc' is never used.
• The function 'libIndex' is never used.
• The function 'isMarked' is never used.
• The function 'minAddress' is never used.
• The function 'contains' is never used.
• The function 'get' is never used.
• The function 'getPage' is never used.
• The function 'get_tag' is never used.
• The function 'getCounters' is never used.
• The function 'getCounter' is never used.
• The function 'describeCounters' is never used.
• The function 'units' is never used.
• The function 'check' is never used.
• The function 'start' is never used.
• The function 'supported' is never used.
• The function 'setSighandlerTid' is never used.
• The function 'bounded_lookup' is never used.
• The function 'stop' is never used.
• The function 'interval' is never used.
• The function 'registerThread' is never used.
• The function 'unregisterThread' is never used.
• The function 'enableEvents' is never used.
• The function 'updateCounter' is never used.
• The function 'hasChanged' is never used.
• The function 'updateNumSamplableThreads' is never used.
• The function 'updateNumSuccessfulSamples' is never used.
• The function 'updateNumFailedSamples' is never used.
• The function 'updateNumExitedThreads' is never used.
• The function 'updateNumPermissionDenied' is never used.
• The function 'endEpoch' is never used.
• The function 'clean' is never used.
• The function 'newEpoch' is never used.
• The function 'encode' is never used.
• The function 'decode' is never used.
• The function 'threadEntry' is never used.
• The function 'sampleIdleThreads' is never used.
• The function 'field' is never used.
• The function 'category' is never used.
• The function 'root' is never used.
• The function 'strings' is never used.
• The function 'jniExceptionCheck' is never used.
• The function 'is_readable_pointer' is never used.
• The function 'used' is never used.
• The function 'alloc' is never used.
• The function 'level' is never used.
• The function 'next' is never used.
• The function 'cputime' is never used.
• The function 'micros' is never used.
• The function 'processStartTime' is never used.
• The function 'sleep' is never used.
• The function 'ntoh64' is never used.
• The function 'threadId' is never used.
• The function 'schedPolicy' is never used.
• The function 'threadName' is never used.
• The function 'listThreads' is never used.
• The function 'isLinux' is never used.
• The function 'installSignalHandler' is never used.
• The function 'replaceSigsegvHandler' is never used.
• The function 'replaceSigbusHandler' is never used.
• The function 'sendSignalToThread' is never used.
• The function 'getCpuDescription' is never used.
• The function 'getProcessCpuTime' is never used.
• The function 'getTotalCpuTime' is never used.
• The function 'copyFile' is never used.
• The function 'truncateFile' is never used.
• The function 'fileSize' is never used.
• The function 'freePageCache' is never used.
• The function 'mallocArenaMax' is never used.
• The function 'walkKernel' is never used.
• The function 'resetBuffer' is never used.
• The function 'getEventName' is never used.
• The function 'compute' is never used.
• The function 'sample' is never used.
• The function 'reverse16' is never used.
• The function 'is_probably_rust_legacy' is never used.
• The function 'demangle' is never used.
• The function 'handle_safefetch' is never used.
• The function 'safeFetch32' is never used.
• The function 'safeFetch64' is never used.
• The function 'load32' is never used.
• The function 'tryLockShared' is never used.
• The function 'withinCurrentStack' is never used.
• The function 'restore' is never used.
• The function 'stackAt' is never used.
• The function 'clearParsingCaches' is never used.
• The function 'parseLibraries' is never used.
• The function 'isRootSymbol' is never used.
• The function 'forTid' is never used.
• The function 'inBuffer' is never used.
• The function 'tid' is never used.
• The function 'noteCPUSample' is never used.
• The function 'lookupWallclockCallTraceId' is never used.
• The function 'recordCallTraceId' is never used.
• The function 'enterCrashHandler' is never used.
• The function 'exitCrashHandler' is never used.
• The function 'resetCrashHandler' is never used.
• The function 'isDeepCrashHandler' is never used.
• The function 'unwindFailures' is never used.
• The function 'filterSlotId' is never used.
• The function 'setFilterSlotId' is never used.
• The function 'accept' is never used.
• The function 'getThreadId' is never used.
• The function 'clearAll' is never used.
• The function 'updateThreadName' is never used.
• The function 'reportCounters' is never used.
• The function 'convertJvmExecutionState' is never used.
• The function 'initialized' is never used.
• The function 'ticks' is never used.
• The function 'frequency' is never used.
• The function 'ticks_to_millis' is never used.
• The function 'record' is never used.
• The function 'forEach' is never used.
• The function 'countFailures' is never used.
• The function 'collectAndReset' is never used.

[zhengyu123]

I think assert(current != nllptr) should be sufficient, otherwise, we have a bigger problem.

[r1viollet]

I think this happens on unloading. JVMTI cleanup can be removed before all threads are finished ?

[r1viollet]

We have the assert for debug builds, though we can keep avoiding crashes for release builds. Feel free to answer if you do not agree.

[zhengyu123]

Is it possible? or we should just assert

[r1viollet]

Good question
I think we are missing the instrumentation of some threads. Could non-java threads call back into java?
It could be nice to have asserts to debug this, though I think I'd prefer the safer path for a prod release.

[zhengyu123]

Same as above

[zhengyu123]

It looks like that filterThreadAdd0 == filterThread0(true) and filterThreadRemove0 == filterThread0(false). Please remove duplications.

[zhengyu123]

We have definition of DEFAULT_CACHE_LINE_SIZE in dd_arch.h. I would suggest following code for readability and portability.

  struct alignas(DEFAULT_CACHE_LINE_SIZE) Slot {
      std::atomic<int> value{-1};
      char padding[DEFAULT_CACHE_LINE_SIZE - sizeof(value)];
  };

[zhengyu123]

Use DEFAULT_CACHE_LINE_SIZE for readability and portability.

[r1viollet]

thanks

[zhengyu123]

memory_order_release should be sufficient.

[r1viollet]

agreed

[zhengyu123]

I don't see any memory ordering _enabled providing. Could you explain what it releases

[r1viollet]

We want the init to be called (so that constructor is finished)
This means other threads might not have the init finished
Though we can always lazily register them later (even if the on thread start path is better)
So this acts as a load barrier. I think it makes sense. Feel free to challenge.

[zhengyu123]

I think you need memory_order_acquire ordering here to match the release store.

[r1viollet]

same as the add, I think we can keep relaxed. Feel free to challenge.

[zhengyu123]

I think you do need std::memory_order_acquire, just as you did in ThreadFilter::accept()

[zhengyu123]

I did partial second round reviewing, I think there are many inconsistencies in memory ordering.

[zhengyu123]

memory_order_acquire instead of memory_order_acq_rel

[r1viollet]

adjusting

[zhengyu123]

Need memory_order_acquire ordering

[r1viollet]

This was intentional, the idea is that we either have null, or a valid chunk. The impact of missing one trace is acceptable if we don't see the chunk in the current thread (which is pretty unlikely). wdyt ?

[zhengyu123]

memory_order_relaxed should be sufficient.

[r1viollet]

I think this is a tradeoff. I hope this is a path where acquire is acceptable. If you think otherwise I can adjust.

[r1viollet]

Thanks @zhengyu123 I really appreciate the thorough review. Apologies if I only have a little time to spend on this every week.

[zhengyu123]

I think you do need std::memory_order_acquire, just as you did in ThreadFilter::accept() and match the release from ChunkStorage* expected = nullptr; if (_chunks[chunk_idx].compare_exchange_strong(expected, new_chunk, std::memory_order_release))

[r1viollet]

I'm not sure we do, but let's measure before we debate. I'll run the test to see if this changes anything on perf.

[zhengyu123]

I think you do need std::memory_order_acquire, just as you did in ThreadFilter::accept()

[r1viollet]

@zhengyu123 are we OK with this version ?

[zhengyu123]

Release here?

[r1viollet]

I think memory_order_acq_rel is good here for the old_index. Though we might be talking about something else.

[zhengyu123]

Can current == nullptr?

[r1viollet]

I remember seeing a crash around this..
Basically JVMTI could unload and delete the profiled thread from under our feet.

[r1viollet]

Notes for future: if we care about the ~100KB, we can reduce the padding. This becomes a tradeoff between memory and risk of false sharing.