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RPC_E_NO_SYNC
No synchronization objects are available to wait on
RPC_E_NO_SYNC is HRESULT 2147549472 (0x80010120) from winerror.h. AllStat describes it as “There are no synchronize objects to wait on.” 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.
A generic “operation failed” message is insufficient for it because the recovery decision depends on the exact lifecycle, security, marshaling, or state condition.
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 COM call-control code asked to wait or coordinate when the call or operation exposes no valid synchronization handles. Keep this result 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 API contract actually promises a waitable object and the handle list has not been consumed, closed, or left uninitialized. The decisive boundary for it determines whether the same object can continue, a new object is required, or policy must change.
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.
Correct handling and recovery
Use the documented callback or completion mechanism, initialize synchronization state before waiting, and avoid waiting on empty handle sets.
An unchanged retry loop for it can duplicate effects, deepen reentrancy, or hide an invalid lifetime transition.
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.
Practical scenario
A cancellation controller calls a wait helper before registering any outstanding calls. It skips the wait and reports that no cancellable operations exist.
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.
Difference from nearby HRESULTs
It is missing synchronization infrastructure; RPC_E_TIMEOUT means a valid wait existed but did not finish in time.
The distinction around it should be represented explicitly in control flow and operational dashboards.
References
- Microsoft: COM RPC error codes
- Microsoft: IMessageFilter
- Microsoft: RetryRejectedCall
- Microsoft: CoInitialize
- Microsoft: CoInitializeSecurity
- Microsoft: marshaling rules
- Microsoft: HRESULT values
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