Fix: Unity AssetDatabase.Refresh Blocking the Main Thread

An editor tool generates 200 ScriptableObject assets. After each CreateAsset, you call AssetDatabase.Refresh. The tool takes 90 seconds and the editor is frozen the whole time. Single batched refresh would do it in 2 seconds.

Batch with Start/Stop

AssetDatabase.StartAssetEditing();
try {
    for (int i = 0; i < 200; i++) {
        var obj = ScriptableObject.CreateInstance<MyAsset>();
        AssetDatabase.CreateAsset(obj, $"Assets/Generated/Asset_{i}.asset");
    }
} finally {
    AssetDatabase.StopAssetEditing();
    AssetDatabase.SaveAssets();
}

Start/Stop pauses asset import processing. Inside the block, CreateAsset queues but doesn’t trigger import. StopAssetEditing flushes the queue, importing everything once. 50× faster than per-asset refresh.

Use ImportAsset for Targeted Updates

// When you know exactly which file changed
AssetDatabase.ImportAsset("Assets/Levels/level1.asset");

Reimports just one asset. Faster than Refresh which scans everything. Use whenever you know the modified path.

Avoid Per-Frame Refresh

Some editor tools call Refresh from EditorApplication.update. Don’t. Refresh is heavy; calling it 60 times a second freezes Unity. Trigger Refresh only on user actions or external file change events.

External File Watcher

For tools that watch external folders (e.g., a Tiled file outside Assets/), use System.IO.FileSystemWatcher and call ImportAsset only when a target file changes — not on every Refresh cycle.

SaveAssets for Persistence

StopAssetEditing imports but doesn’t necessarily save the .asset to disk. Call AssetDatabase.SaveAssets() after — ensures changes survive editor crash.

Verifying

Profile the editor tool. Before fix: 200 individual Refresh calls dominate the timeline. After: a single import burst at StopAssetEditing. Total runtime drops dramatically.

Understanding the issue

AI bugs are emergent. The code is correct in isolation; the behavior emerges from interaction with other systems. Reproducing means controlling the interaction; fixing means deciding which interaction was wrong.

The specific bug described above is the kind that surfaces during integration rather than unit testing. It depends on a combination of factors: the asset configuration, the runtime state, the platform's specific behavior. In isolation, each piece looks correct; in combination, the bug emerges. This is why thorough integration testing - playing the actual game in realistic conditions - catches things that automated tests miss.

Why this happens

This bug class disproportionately affects late-stage development. The work to surface it is interactive testing in realistic conditions, which only really happens after the gameplay is in place and assets are populated. Catching it early requires deliberate testing of conditions that look unimportant.

At the engine level, the behavior comes from a deliberate design decision in Unity. The engine team chose a particular trade-off - usually performance versus convenience, or generality versus specificity - and that trade-off has consequences when you push against it. Understanding the trade-off is what turns 'this bug is mysterious' into 'this bug is the expected consequence of this design'.

Verifying the fix

After applying the fix, the verification step has three parts: confirm the original repro is resolved, confirm no obvious regressions in adjacent functionality, and (for shipping titles) deploy to a small player cohort first and watch the crash and report rates. Each step catches something the others miss.

Reproducibility is the prerequisite for verification. If you can't reliably reproduce the bug pre-fix, you can't reliably verify it post-fix. Spend time getting a clean reproduction before you write any fix code. The fix is fast once you understand the reproduction; the reproduction is the slow part.

Variations to watch for

There's almost always a less obvious case where the same problem applies. The reported case is the one a player hit; the related cases hide because they're rarer or affect fewer players. After fixing the reported case, search the codebase for the pattern - one fix often unlocks several.

Adjacent bugs often share a root cause. After fixing the case you've found, spend an hour searching the codebase for similar patterns. What's the same call with different arguments? The same data flow with a different entity type? The same lifecycle issue in a sibling system? Each match is a candidate for the same fix, or a related fix that prevents future bugs of the same class.

In production

In shipping builds, this issue may interact with other production-only behavior. Stripping, encryption, asset bundling, and platform-specific code paths can each modify the symptoms. When players report a related issue, capture build SHA, platform, and any feature flags - those three fields cover most of the production-only variations.

When triaging a similar issue in production, prioritize gathering data over hypothesizing causes. A player report describes a symptom; what you need is a build SHA, a session timestamp, and ideally a screen recording or session replay. With those, the bug becomes tractable. Without them, you're guessing at hypothetical reproductions that may not match what the player actually hit.

Performance considerations

Performance implications matter when this bug class scales with player count or asset count. A bug that fires once per session is annoying; a bug that fires once per frame compounds. After fixing, profile the affected code path under realistic load. The fix that's correct for one entity may be too slow for ten thousand.

Diagnostic approach

Diagnosing this class of bug benefits from a structured approach: confirm the symptom, isolate the variables, hypothesize the cause, and verify the hypothesis before writing fix code. Skipping the isolation step is the most common mistake; without it, fixes often address symptoms while the underlying cause continues to produce other variations.

For Unity-specific diagnostics, the editor's profiler is the canonical starting point. Capture a representative frame with the symptom present; compare against a frame without the symptom; the diff often points directly at the cause. If the symptom is non-deterministic, capture multiple frames and look for the pattern - the cause is usually a state transition or a specific input value rather than a continuous effect.

Tooling and ecosystem

Third-party plugins often provide better diagnostics for their own behavior than the engine does. If the affected code is in a plugin, check the plugin's documentation for debug modes, verbose logging, or inspector tools - these can save hours of investigation when they exist.

Within Unity, the relevant diagnostic surfaces include the standard frame debugger, memory profiler, and engine-specific debug overlays. Each one shows a different facet of what's happening. The frame debugger reveals draw call ordering and state transitions; the memory profiler shows allocation patterns; the debug overlay reveals per-system state. Bugs that resist one tool usually surrender to another - the trick is knowing which tool to reach for first.

Edge cases and pitfalls

Platform-specific edge cases are worth enumerating explicitly. iOS handles backgrounding differently than Android; Windows handles focus changes differently than macOS. A fix that works on the development platform may not work on every target. Test on each shipping platform deliberately.

When writing a regression test for this fix, focus on the boundary conditions that surfaced the original bug. Tests that exercise the happy path catch obvious regressions; tests that exercise the boundary catch the subtler regressions that look like new bugs but are really the original returning. The latter are the tests that earn their keep over the long life of the project.

Team communication

Document the fix and its rationale in the commit message or attached engineering doc. Future engineers will encounter related issues; the rationale tells them whether your fix is reusable or specific to the case at hand. Without rationale, the fix gets reverted or copied incorrectly.

If this fix touches a system several engineers work in, a short writeup in the team's engineering channel helps. Not a full design doc - a paragraph explaining what was wrong, what's fixed, and what to watch for. Future engineers encountering similar symptoms will search for the fix; making it findable is a small investment that pays back later.

“Refresh is a hammer; ImportAsset is a scalpel. Batch with Start/Stop and only Refresh when truly needed.”

For editor tools generating many assets, batching is the single biggest perf win — minutes become seconds.