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VFW_E_PIN_ALREADY_BLOCKED_ON_THIS_THREAD
Meaning
Windows documents VFW_E_PIN_ALREADY_BLOCKED_ON_THIS_THREAD as “This thread has already blocked this output pin. There is no need to call IPinFlowControl::Block() again”. Here, the calling thread invokes IPinFlowControl::Block on an output pin that it has already blocked.
Relevant contract
Start with the filter graph, device or persisted configuration that first returned the result.
Conditions that can produce it
- Cause 1: reconfiguration code loses track of its own block state.
- Cause 2: nested operations both attempt to acquire the same logical block.
- Cause 3: an earlier failure path omitted the matching unblock.
Evidence worth preserving
- Evidence 1: pin identity, thread ID and block flags.
- Evidence 2: block/unblock call stack and timestamps.
- Evidence 3: dynamic-reconnection operation owning the block.
Correction strategy
- Action 1: make block ownership explicit and balanced.
- Action 2: avoid nested blocking by the same control path.
- Action 3: use scoped cleanup so exceptions and failures always unblock.
Retry and recovery
Retry rule: Do not retry Block on the same thread until the existing block has been released.
Example incident
A dynamic reconnect helper calls Block and then invokes another helper that calls Block again on the same pin; consolidating ownership removes it.
How it differs from nearby results
VFW_E_PIN_ALREADY_BLOCKED means another thread owns the block, while it identifies redundant blocking by the current thread.
Official Microsoft references
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