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RPC_E_CANTCALLOUT_ININPUTSYNCCALL
Outgoing COM call is forbidden during an input-synchronous call
RPC_E_CANTCALLOUT_ININPUTSYNCCALL is HRESULT 2147549453 (0x8001010D) from winerror.h. AllStat describes it as “An outgoing call cannot be made since the application is dispatching an input-synchronous call.” In the COM/RPC call control, message filtering, apartment routing, marshaling, security negotiation, or remote object lifetime, the code identifies a specific failure boundary and should not be replaced by a generic COM exception.
The caller should keep this result intact through logging, exception translation, and RPC or language projection boundaries.
Where it is encountered
- Cross-apartment or cross-process COM method invocation and activation. Record the interface, method, component version, thread, apartment, process, and correlation ID.
- STA message filtering, reentrancy, call cancellation, timeout, or retry handling.
- DCOM security initialization, proxy/stub marshaling, OBJREF processing, and server object lifetime.
The immediate focus for it is reentrant call control while the current thread dispatches an input-synchronous message that must complete before outbound COM work. Keep it attached to that operation; the same numeric severity outside the owning API does not supply enough context.
Decisive interpretation boundary
Before choosing recovery, verify that the incoming call category and callback stack prove that the thread is inside input-synchronous dispatch. If this condition cannot be proven for it, stop before consuming outputs or repeating side effects.
Also confirm that all observed objects, tokens, buffers, proxies, metadata files, or ACLs belong to the current operation generation and were not retained from an earlier attempt.
Difference from nearby HRESULTs
It is tied to input-synchronous dispatch; RO_E_BLOCKED_CROSS_ASTA_CALL blocks a broader deadlock-prone apartment chain.
A support tool discussing it should name the neighboring result only after the originating API and decisive state are known.
Correct handling and recovery
Post or queue the outbound work until the current call returns. Do not block or make a synchronous cross-apartment call from the handler.
Backoff alone is not a repair for it; a measurable state or configuration transition must justify another attempt.
Practical scenario
A window procedure invoked by COM attempts to call another automation server. The handler posts a private message and performs the call after returning.
A regression test should reproduce it, assert the raw HRESULT and all relevant outputs, then correct only the decisive condition and verify the intended success or neighboring failure result.
Lifetime, retry, and cleanup rules
After it, determine whether the current object, interface pointer, call context, token, stream, metadata reader, asynchronous operation, or access-control instance remains valid. Release only resources owned by the failing attempt, cancel callbacks through their documented mechanism, and avoid double close, double commit, repeated activation, or replay of a non-idempotent remote method.
The retry policy for it should state the trigger, maximum attempts, cancellation owner, and reconciliation step for effects that may have completed elsewhere.
References
- Microsoft: COM RPC error codes
- Microsoft: IMessageFilter
- Microsoft: RetryRejectedCall
- Microsoft: CoInitialize
- Microsoft: CoInitializeSecurity
- Microsoft: marshaling rules
- Microsoft: HRESULT values
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