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ERROR_INVALID_EVENT_COUNT
What ERROR_INVALID_EVENT_COUNT means
The number of semaphore events supplied to a multiple-wait operation is invalid. This legacy result is tied to multiplexed semaphore waits such as DosMuxSemWait. It means the caller supplied a count outside the supported range or inconsistent with the provided list.
Common causes
- The count is zero when at least one event is required
- The count exceeds the implementation limit
- The array length and declared count differ
- Integer truncation or structure-layout mismatch corrupts the count
How to investigate
- Log the declared event count and the actual allocated array length
- Validate every entry before crossing a module or ABI boundary
- Check 32-bit versus 64-bit packing in compatibility structures
- Reduce the wait set to the smallest failing example
Developer guidance
Represent the list and its length together rather than passing unrelated values. Validate the range before calling the legacy interface and split very large wait sets into a scalable dispatcher.
Administrator and support guidance
Configuration that controls worker or endpoint counts can trigger the limit, but confirm the exact count before changing capacity settings.
How this code differs from related results
ERROR_INVALID_LIST_FORMAT concerns the structure or contents of the list; this result specifically concerns its event count.
Evidence worth collecting
For ERROR_INVALID_EVENT_COUNT, begin the trace at the operation where the count is zero when at least one event is required. For ERROR_INVALID_EVENT_COUNT, preserve the exact API boundary, numeric result, process and thread identifiers, relevant object state, and the component version. The first verification point should be to log the declared event count and the actual allocated array length. This evidence distinguishes the specific ERROR_INVALID_EVENT_COUNT contract from a later secondary failure.
Recovery and verification
Recovery for ERROR_INVALID_EVENT_COUNT should address the observed condition rather than merely retrying the same call. After the change, reproduce the scenario in which the count is zero when at least one event is required, then confirm that the intended operation completes and that cleanup returns all associated resources. For ERROR_INVALID_EVENT_COUNT, also verify that the next repeated operation follows the same successful path without increasing the resource class implicated by this result.
When to escalate
Escalate ERROR_INVALID_EVENT_COUNT with a minimal reproduction focused on the failing pipe or compatibility boundary. Include the operating-system build, binary architecture, runtime or compatibility-layer version, the exact input values, and a timestamped trace showing the count is zero when at least one event is required. For the ERROR_INVALID_EVENT_COUNT escalation record, note whether changing concurrency, object lifetime, target process, module set, or endpoint location alters the result.
References
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