What does Windows error code 121 (ERROR_SEM_TIMEOUT) mean?

 
Could be also:
ConstantTypeOS
EREMOTEIOerrnoLinux
ESOCKTNOSUPPORTerrnoSolaris
ENOLINKerrnoWindows
MISMATCHED_HALBugCheck CodeWindows
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ERROR_CALL_NOT_IMPLEMENTED ERROR_INSUFFICIENT_BUFFER

ERROR_SEM_TIMEOUT

The synchronization wait timed out

ERROR_SEM_TIMEOUT reports that a synchronization or device operation waited for a semaphore-related condition and the configured timeout elapsed first. It often points to a stalled peer, slow hardware, or an operation whose timeout is too aggressive.

What to check

  • Measure the actual wait duration and record the timeout value.
  • Inspect the thread or device expected to signal completion.
  • Check for deadlocks, lost notifications, blocked I/O, and overloaded hardware.
  • Do not assume that a longer timeout fixes the underlying cause.

How to handle it

Treat the result according to whether the operation is safe to retry. Cancel or unwind outstanding work before retrying so that a late completion cannot corrupt state.

References


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