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ERROR_GRAPHICS_UNASSIGNED_MODESET_ALREADY_EXISTS
Why this is not a generic GPU failure: graphics unassigned modeset already exists
ERROR_GRAPHICS_UNASSIGNED_MODESET_ALREADY_EXISTS, value 0xC0262350, is produced by vidpn when a second unassigned mode set was created for an endpoint that already has one pending. The investigation should stay attached to unassigned source or target mode set and to the exact generation in which it was obtained.
This result: VidPN handles and subobjects are generation-bound. A monitor hot-plug, docking action, session switch or mode commit can invalidate an otherwise well-formed cached object. The built-in one-line message identifies the immediate result; diagnosis also needs the producing API, object ownership and the display generation current at the time.
The smallest evidence set
| Capture item | Why it matters for it |
|---|---|
| Rejected boundary | a second unassigned mode set was created for an endpoint that already has one pending |
| Decisive capture | endpoint ID, existing unassigned handle, transaction state and assignment attempt order |
| Current graph state | VidPN, topology, source and target mode sets, and the present path connecting them |
| Supporting trace | source and target IDs, topology generation, path descriptors, pinned modes, mode-set handles and monitor timing data |
| Object identity | unassigned source or target mode set |
Preserve the unsigned HRESULT, symbolic name, first failing API and timestamp in one record. If cleanup later fails too, keep that secondary result separately from this result.
A/B test for the exact condition
- Freeze the result generation. Record endpoint ID, existing unassigned handle, transaction state and assignment attempt order. Before diagnosing this result, do not resize, hot-plug, recreate or release the object under examination.
- Run the narrow this result comparison. assign or release the first mode set before creating another. During the result comparison, keep every driver, monitor, resource format and unrelated policy unchanged.
- Observe the layer after it. for it, if the exact check passes, record the next HRESULT or visible outcome. A different downstream result shows that the boundary was crossed.
- Repeat it through a lifecycle transition. for it, exercise one relevant resize, mode switch, device recreation, hot-plug or session change and confirm that it does not reuse stale handles.
The comparison with ERROR_GRAPHICS_MODE_ALREADY_IN_MODESET is especially useful: ERROR_GRAPHICS_MODE_ALREADY_IN_MODESET concerns duplicate mode membership inside a set. Recording both names prevents a broad “graphics error” label from merging distinct ownership, capability and lifetime problems.
Safe remediation
Enforce one in-flight unassigned set per source or target. Repair of it is complete only when the original call succeeds or returns its documented nonfatal status and the same lifetime test remains correct after a second display transition.
- The result trace identifies one producing API and one current graphics object, rather than only the final UI symptom.
- The passing run changes exactly the condition described for it; unrelated adapter, monitor and application state remains unchanged.
- debug-layer, ETW or driver diagnostics no longer report the rejected unassigned source or target mode set contract during the same scenario.
- The application handles recurrence of it without an unbounded retry loop, leaked resource, duplicate composition target or stale topology handle.
Implementation notes
Log source and target IDs, topology generation, path descriptors, pinned modes, mode-set handles and monitor timing data. When the path returns a count, size, status flag or replacement object, retain it even on a nonfatal result because it can direct the next call.
A production fallback for it should be explicit: pause rendering, re-enumerate, rebuild one cache entry, recreate a device, or decline a protected path only when this layer calls for that action. Reinstalling every display component, deleting all caches or forcing a resolution change is not an evidence-based fix for it.
Technical references
- Microsoft: Introduction to Video Present Networks — background for the unassigned source or target mode set boundary involved in it.
- Microsoft: VidPN objects and interfaces
- Microsoft: Enumerating cofunctional VidPN modes
- Microsoft: Determining VidPN support
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