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ERROR_EVENT_PENDING
What ERROR_EVENT_PENDING means
A Transport Driver Interface event indication entered a pending state. In practical terms, this status belongs to legacy asynchronous TDI events: the client will finish processing later and must eventually complete the operation.
Typical causes
- The indication requires asynchronous I/O
- The client retained buffers or context for deferred processing
- Backpressure delayed immediate completion
How to investigate
- Record the pending context and ownership of every retained buffer
- Ensure a completion or cancellation path always runs
- Check unload and disconnect handling for outstanding indications
Developer guidance
Pending transfers ownership and lifetime responsibilities. Drivers must not free request state until the later completion path has executed.
Operational interpretation
When ERROR_EVENT_PENDING appears, first determine whether the operation actually failed, completed with an informational condition, or transferred work to another component. Record the API name, returned value, affected process or object, and the immediately preceding event. For this code, the most useful boundary is the legacy asynchronous TDI events boundary; broad machine-wide remediation before that boundary is identified can hide the original evidence.
Example scenario
An incident begins when the indication requires asynchronous I/O. A responder investigating this result should not begin with a generic reboot that destroys the original context. A better first step is to record the pending context and ownership of every retained buffer. That evidence connects it to its producing operation and reveals whether this particular result is repeatable, expected, or merely secondary.
Logging and telemetry
Telemetry for this Win32 error should preserve its numeric value, component version, process and thread identifiers, operation name, affected object or endpoint, elapsed time, and the first earlier failure in the same activity. Keep the result correlation identifier stable across callbacks so the status can be joined to the request that initiated this exact operation.
Recovery and validation
Apply recovery only after the responsible state has demonstrably changed. After changing that state, repeat one controlled this result scenario and verify both the returned status and the resulting system state. Absence of another log line is not sufficient: confirm that the intended legacy asynchronous TDI events action completed, that no resource remains pending, and that later cleanup does not produce a different secondary error.
Escalation notes
Escalate this result with a minimal reproduction, the exact binary architecture, operating-system build, and a timestamped trace covering initialization through cleanup. Include whether the result changes after the affected object is recreated. These details allow the owner of the legacy asynchronous TDI events component to distinguish a contract violation from environmental state.
References
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