What does Windows error code 1280 (ERROR_ALREADY_FIBER) mean?

ERROR_ALREADY_FIBER

ERROR_ALREADY_FIBER meaning

ERROR_ALREADY_FIBER has value 1280. The current thread has already been converted to a fiber, so another ConvertThreadToFiber or ConvertThreadToFiberEx call is invalid for that thread.

Evidence to collect for ERROR_ALREADY_FIBER

Record the thread id, initialization path, library or runtime that performed conversion, fiber pointer stored by the application, and whether multiple modules independently manage fibers. Keep conversion and cleanup ownership in one layer.

• Preserve the exact API or command that returned ERROR_ALREADY_FIBER, the caller identity, target object, complete numeric status, and the first component log that records the failure.
• Compare the failing request with a working request for ERROR_ALREADY_FIBER at the same subsystem boundary before applying destructive configuration changes.

Recovery and retry for ERROR_ALREADY_FIBER

Reuse the existing fiber context or redesign initialization so conversion occurs exactly once. ConvertFiberToThread is appropriate only when the current fiber was created by thread conversion and no remaining fiber scheduling depends on it.

Official references for ERROR_ALREADY_FIBER

• Microsoft: ConvertThreadToFiberEx
• Microsoft: ConvertFiberToThread
• Microsoft: Fibers

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