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Mitigating the Blitter duplicate-initialization error

Traced a Blitter duplicate-initialization error firing 137,080 times/day on Android down to its root cause via two-stage hypothesis verification.

Problem

Overview

A large volume of URP-related error logs was collected on Android, prompting root-cause estimation and a defensive code change.

Exception: Blitter is already initialized. Please only initialize the blitter once or you will leak engine resources. If you need to re-initialize the blitter with different shaders destroy & recreate it.

From the stack, this surfaces as Blitter.Initialize() being called repeatedly during UniversalRenderPipeline construction.

Reports collected: AOS 137,080
Environment: mostly Android
Note: a similar issue under GLES is listed on the Unity Issue Tracker

Approach

Two hypothesis-verification cycles — log reduction measured at each step.

Step	Hypothesis	Verification
1st	Applying graphic options re-assigns URP Asset properties, triggering pipeline regeneration	Guard against re-assigning the same value → monitor Kibana
2nd	A URP Asset setter is called on a per-frame code path	Audit every setter call site in the codebase

Rather than nailing down the root cause in one shot, the approach was add a guard per hypothesis and measure log change — narrowing down incrementally. The most realistic strategy when reproduction isn't possible.

Implementation

01
1st fix — GraphicOptionAssets.ApplyURPSettings() guard
Blocks URP Asset properties from being re-assigned to the same value when options are applied.

Result: 137,080 → 2,978 (−98%) — effective, but residual errors remained.
02
2nd fix — tracing setters on per-frame call paths
To find the cause of the remaining 2,978, all URP Asset setter call sites in the codebase were audited. The culprit: MaterialGlobalPropertiesFeature.AddRenderPasses() was calling the shadowDistance setter every frame.

Android likely shows a higher frequency because GraphicsDevice resets frequently (device resume / focus changes, etc.).

Validation

Side-effect verification matrix

Item	Verification
Where `shadowDistance` is used	`MaterialGlobalPropertiesFeature.cs` is the only place modified → no conflicts
ShadowVolume on/off equivalence	Applies on the first frame, then skips → behavior identical
When ShadowVolume value changes	Applies only on the frame the value changed → behavior identical
Volume on→off transition	Applies 100 on the next frame → behavior identical
External writes overwritten	Overwritten on the next frame → behavior identical
`Mathf.Approximately` precision	At 100f the epsilon is 0.0001 → ample for shadow distance
NaN input	`Approximately(NaN, NaN) == false` → setter called (safe fallback)
Effect on deterministic simulation	Visual-only code → unrelated
Cost	1 getter + 1 compare; negligible vs. setter cost

Monitoring metric: tracked Kibana globalManagerException messages converging to 0/hour.

Device validation: Vivo Y11, Galaxy A12, S9, S21 — including graphic option changes → no side effects.

Note — 향후 가이드라인

Cautions when changing URPAsset properties at runtime: 1. Do NOT change URPAsset properties directly inside methods called per frame (AddRenderPasses / Update / LateUpdate, etc.). 2. If unavoidable, only call the setter after detecting an actual change. 3. More fundamentally, per-frame values should be handled through Shader Properties / GlobalConstantBuffers, not URPAsset properties. URPAsset setters touch the RenderPipeline dirty flag and trigger regeneration, so they must be used only as a "configuration channel", not a "data channel".

Conclusion

A case study of tracing a production-only issue that couldn't be reproduced locally — using hypothesis-based incremental fixes plus log monitoring. The first fix quickly validated a visible hypothesis and yielded a 98% drop; the residual logs became the clue for the second-stage root-cause trace. The behavior "URP internal property setters trigger the dirty flag" became clear through this investigation. Because the same pattern can hide in other RendererFeatures / runtime code, a guideline was left behind to prevent recurrence.