What does HRESULT 0x80040238 (TPC_E_QUEUE_FULL) mean?

TPC_E_QUEUE_FULL

Meaning

Windows documents TPC_E_QUEUE_FULL as “TabletPC inking error code. Queue is full”. In practical terms, it is returned when a Tablet PC stylus-data queue has reached capacity and cannot accept more input or plug-in output.

Evidence to collect

• Capture 1: input and output queue depth over time.
• Capture 2: per-plug-in processing latency and packet rate.
• Capture 3: UI-thread stalls, callback backlog and dropped-data policy.

Where the failure belongs

This result belongs to Tablet PC ink, stylus and recognition. Tablet PC APIs span device enumeration, RealTimeStylus packet queues, ink-object lifetime and recognizer-specific capabilities. The numerical facility does not identify which Tablet PC layer produced the result. The relevant condition is that a Tablet PC stylus-data queue has reached capacity and cannot accept more input or plug-in output.

Likely causes

• Possible cause 1: an asynchronous plug-in processes packets slower than they arrive.
• Possible cause 2: the UI thread blocks and stops draining the output queue.
• Possible cause 3: a plug-in expands data or recursively enqueues work.

Diagnostic sequence

1. Confirm that the observed path matches this condition: a Tablet PC stylus-data queue has reached capacity and cannot accept more input or plug-in output.

Correct handling and retry

• Corrective action 1: remove blocking work from the real-time path.
• Corrective action 2: bound plug-in processing and move expensive analysis to a worker.
• Corrective action 3: define overload behavior that preserves responsiveness and data integrity.

Retry guidance. Retrying the same packet is safe only if queue semantics and ordering are preserved; first restore consumption capacity and avoid unbounded producer loops. When retrying, avoid replay stale strokes, reorder stylus packets or reuse an invalid recognizer context.

Difference from nearby HRESULTs

TPC_E_OUT_OF_ORDER_CALL is a lifecycle sequencing error; it is a throughput and backpressure failure.

Developer and operational guidance

Operational repair should use supported device, Tablet PC component, recognizer and application lifecycle paths. Avoid unsupported configuration edits or component replacement unless evidence identifies that layer. Retain the original trace and a post-fix trace so the result can be attributed and the change reversed.

Practical scenario

A synchronous stylus plug-in performs network I/O on every packet and fills the queue; moving that work off the real-time path prevents it.

Official Microsoft references

• Microsoft: generic COM error codes
• Microsoft: StylusInput architecture
• Microsoft: StylusInput threading