ERROR_SEM_NOT_FOUND - 187 (0xBB)
The specified system semaphore name was not found.
Updated: Feb 21, 2026
Technical Meaning
The ERROR_SEM_NOT_FOUND error code indicates that the system was unable to locate a semaphore object by its specified name. Semaphores are synchronization objects used in Windows for managing access to shared resources or controlling the number of threads that can simultaneously execute certain operations.
Error Details
This error typically occurs when an application attempts to open or reference a semaphore using a name that does not exist within the system's semaphore namespace. The error code 187 (0xBB) is returned by the Windows API functions such as CreateSemaphore, OpenSemaphore, and others, which are used for semaphore operations.
Usage Context
This error can be encountered in various scenarios where semaphores are utilized, including but not limited to:
- Synchronization between threads or processes
- Controlling access to shared resources
- Managing the number of concurrent operations
Developer Interpretation
When this error is returned, it signifies that the specified semaphore name does not exist. This could be due to several reasons such as incorrect naming, the semaphore being deleted, or never having been created in the first place.
Common Causes
- Incorrect semaphore name provided during operation
- Semaphore was deleted after creation but before reference
- Semaphore was never created
Related Errors
ERROR_INVALID_NAME(123) - Indicates an invalid object name was specified, which could be a precursor to this error if the name is syntactically incorrect.ERROR_ACCESS_DENIED(5) - If the operation requires specific permissions and they are not granted.
FAQ
Q: What does ERROR_SEM_NOT_FOUND mean?
A: It means that the specified semaphore name was not found in the system's namespace.
Q: How can I resolve this error?
A: Ensure that the correct semaphore name is used and that the semaphore exists before attempting to reference it.
Summary
The ERROR_SEM_NOT_FOUND (187) error code indicates a failure to locate a specified semaphore by its name. This error should be handled by validating the semaphore name and ensuring that the semaphore has been properly created in the system.