What does this PR do?:

This PR implements a liveness-aware double-buffered call trace storage system with several key improvements:

1. Liveness-aware trace management with selective preservation across JFR dumps
2. Contention handling with dropped trace visibility in JFR output
3. Double-buffered storage with active/standby hash table instances
4. 64-bit trace ID system with instance-based collision avoidance
5. Modular hash table architecture with dedicated CallTraceHashTable class

Motivation:

The changes address critical issues in call trace management:

• Random CI test failures due to lock contention causing dropped samples without visibility
• Liveness tracking requirements for preserving traces of live objects across garbage collection
• Trace ID stability needed for consistent liveness tracking across storage swaps
• Performance and modularity improvements through specialized hash table implementation

Additional Notes:

Key Features:

Liveness-Aware Storage:

• Callback-based liveness checker registration system
• Selective trace preservation during storage transitions
• Coordinated trace collection through processTraces() method
• Support for multiple concurrent liveness checkers

Contention Handling:

• Special dropped trace with reserved ID (1ULL) for contention visibility
• <dropped due to contention> shown in JFR stack traces instead of null entries
• Platform-specific ASGCT_CallFrame alignment using LP64_ONLY macro
• BCI_ERROR routing for proper native method resolution

Double-Buffered Architecture:

• Active/standby hash table pattern for lock-free JFR operations
• Instance-based trace IDs: (instance_id << 32) | slot preventing collisions
• Atomic storage swapping with minimal profiling overhead
• Thread-safe instance ID generation across storage transitions

Hash Table Improvements:

• Extracted dedicated CallTraceHashTable class (441 lines)
• Concurrent table expansion with proper synchronization
• Overflow trace handling for hash table limits
• Lock-free put operations with retry-based contention handling

Implementation Details:

Core Storage Refactoring:

• CallTraceStorage reduced from 265→142 lines through hash table extraction
• Dual active/standby storage instances with atomic swapping
• Liveness preservation system integrated with JFR dump cycles

64-bit Trace ID Migration:

• Updated all profiling interfaces: recordJVMTISample(), recordSample(), recordDeferredSample()
• Modified LivenessTracker for 64-bit trace ID handling
• JFR integration updated for 64-bit trace ID constant pool support
• Instance-based ID generation preventing cross-storage collisions

Platform Compatibility:

• COMMA macro factored to arch_dd.h for consistent designated initializer syntax
• LP64_ONLY macro usage for proper 64-bit platform struct alignment
• Cross-platform ASGCT_CallFrame structure handling

New Files:

• callTraceHashTable.{h,cpp} - Dedicated hash table implementation (441 lines)
• test_callTraceStorage.cpp - Comprehensive unit tests with liveness scenarios (387 lines)
• LivenessTrackingTest.java - Java integration test for end-to-end validation (246 lines)
• ContendedCallTraceStorageTest.java - Contention measurement and validation test (249 lines)

Modified Files:

• Core profiler: profiler.{h,cpp}, objectSampler.cpp, wallClock.{h,cpp} - 64-bit trace ID adoption
• Storage: callTraceStorage.{h,cpp} - major refactoring with liveness integration
• JFR: flightRecorder.{h,cpp} - 64-bit trace ID support and dropped trace handling
• Liveness: livenessTracker.{h,cpp} - 64-bit trace ID migration
• Architecture: arch_dd.h - COMMA macro consolidation

How to test the change?:

# Run comprehensive test suite
./gradlew testDebug

# C++ unit tests for storage and liveness
./gradlew gtestDebug  

# Build verification across configurations
./gradlew buildDebug buildRelease

# Code formatting
./gradlew spotlessApply

The implementation includes extensive test coverage:

• 9 C++ unit tests for CallTraceStorage liveness scenarios
• Java integration tests for end-to-end liveness tracking
• Contention measurement and validation tests
• Platform-specific compatibility tests

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: PROF-12316

Summary: +1689 lines, -447 lines (net +1239 lines)

This implementation provides a robust foundation for liveness-aware profiling with clear visibility into contention issues while maintaining high performance through lock-free operations and efficient storage management.