What does Windows error code 812 (ERROR_CALLBACK_INVOKE_INLINE) mean?

ERROR_CALLBACK_INVOKE_INLINE

The callback function must be invoked inline.

ERROR_CALLBACK_INVOKE_INLINE is Win32 error 812 (0x32C) and belongs to callback dispatch and completion.

Where the result appears

• An API that can queue or synchronously invoke a completion callback.
• A framework deciding that deferred dispatch cannot preserve ordering.
• A callback tied to a short-lived stack or request context.
• A completion path that must run before the initiating call returns.

Likely causes

• the callback contract requires execution on the current call path.
• the operation completed before asynchronous dispatch was established.
• the callback owns data whose lifetime ends at return.
• ordering constraints prohibit handing the callback to another thread.

Troubleshooting steps

• Record API name and documented callback contract.
• Record whether the callback ran before the initiating function returned.
• Record thread identifier, reentrancy depth, and held locks.
• Record lifetime of callback context and captured buffers.
• Record the completion status delivered to the callback.

What to verify

Verify whether the callback contract requires execution on the current call path. Check API name and documented callback contract together with whether the callback ran before the initiating function returned.

Handling, retry, and recovery

Invoke or accept the callback inline as the API requires, while making the handler reentrancy-safe. Do not blindly enqueue it later because that can outlive supplied storage or reverse completion order.

Difference from nearby codes

This status communicates a dispatch requirement rather than failure of the callback itself.

Practical example

A wrapper assumes every completion is posted to a worker thread.

References

• Microsoft: System Error Codes (500–999) — reference for error 812.
• Microsoft: File management functions — reference for error 812.