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Update analysis with x64 vs ARM confirmation from @tig

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Co-authored-by: tig <585482+tig@users.noreply.github.com>
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copilot-swe-agent[bot]
2025-10-21 16:58:10 +00:00
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InvokeLeakTest_Analysis.md
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@@ -211,15 +211,19 @@ Time T2: Next iteration, UtcNow = 1100 ticks
But if the test's 100ms polling window expires before T2, it throws TimeoutException.
```
#### 5. **Why @BDisp's Machine Specifically?**
#### 5. **Why x64 Machines Specifically?**
Possible factors:
- **CPU/Chipset**: Intel vs ARM have different timer implementations
**UPDATE**: @tig confirmed he can reproduce on his x64 Windows machine but NOT on his ARM Windows machine, validating this hypothesis.
Architecture-specific factors:
- **CPU/Chipset**: Intel/AMD x64 vs ARM have fundamentally different timer implementations
- x64: Uses legacy TSC (Time Stamp Counter) or HPET (High Precision Event Timer)
- ARM: Uses different timer architecture with potentially better resolution
- **VM/Virtualization**: MacOS VM on Intel laptop may have timer virtualization quirks
- **OS Configuration**: Windows timer resolution settings (can be 1ms to 15.6ms)
- **Debugger Version**: Specific VS2022 build with different debugging hooks
- **System Load**: Background processes affecting timer accuracy
- **Hardware**: Specific timer hardware behavior on his x64 machine
- **Hardware**: Specific timer hardware behavior on x64 architecture
### Secondary Hypothesis: Thread Scheduling Under Debugger
@@ -229,13 +233,16 @@ The test spawns tasks with `Task.Run()` and small random delays (2-4ms). Under a
- More tasks could complete within same timer resolution window
- Creates "burst" of invocations that all get same timestamp
### Why It Doesn't Fail in CI/CD
### Why It Doesn't Fail on ARM
CI/CD environments:
- Run without debugger (no debugging overhead)
- Different timer characteristics
**CONFIRMED**: @tig cannot reproduce on ARM Windows machine, only on x64 Windows.
ARM environments:
- Run without debugger (no debugging overhead) in CI/CD
- Different timer characteristics - ARM timer architecture has better resolution
- Faster iterations (less time for race conditions)
- Different CPU architectures (ARM runners have different timer behavior)
- ARM CPU architecture uses different timer implementation than x64
- ARM timer subsystem may have higher base resolution or better behavior under load
## Evidence Supporting the Hypothesis
@@ -250,8 +257,10 @@ CI/CD environments:
3. **Only fails under debugger**: Strong indicator of timing-related issue
- Debugger affects iteration speed and timer behavior
4. **Platform-specific**: Fails on specific hardware/VM configurations
- Suggests timer resolution/behavior differences
4. **Architecture-specific (CONFIRMED)**: @tig reproduced on x64 Windows but NOT on ARM Windows
- This strongly supports the timer resolution hypothesis
- x64 timer implementation is more susceptible to this race condition
- ARM timer architecture handles the scenario more gracefully
## Recommended Solutions