ReleaseSemaphoreHANDLE

ReleaseSemaphoreHANDLE is not an official Windows API name. The correct API is ReleaseSemaphore, which operates on a semaphore object identified by a HANDLE. Semaphores are kernel objects used to control access to a limited resource by maintaining a count.

The function signature is BOOL ReleaseSemaphore(HANDLE hSemaphore, LONG lReleaseCount, LPLONG lpPreviousCount). hSemaphore is a handle to a semaphore created by CreateSemaphore or opened with OpenSemaphore. lReleaseCount specifies how many units to release (signal) the semaphore. lpPreviousCount, if non-NULL, receives the semaphore’s previous count before the release.

Behavior and usage: ReleaseSemaphore increments the semaphore’s current count by lReleaseCount. If the new count would exceed the semaphore’s maximum count (established when the semaphore was created), the call fails and the semaphore’s count is not changed. The operation may unblock threads waiting in wait calls such as WaitForSingleObject or WaitForMultipleObjects, allowing them to proceed according to the new count.

Return value and errors: The function returns a nonzero value on success and zero on failure. Use GetLastError to obtain extended error information when it fails. Possible failure reasons include an invalid handle, a parameter that would exceed the maximum count, or insufficient permissions to operate on the semaphore.

Notes: ReleaseSemaphore does not itself acquire ownership or require prior ownership of the semaphore—its primary role is to signal resource availability. The lpPreviousCount parameter is optional but can be useful for debugging or for coordinating complex synchronization.

See also: CreateSemaphore, OpenSemaphore, WaitForSingleObject, WaitForMultipleObjects, synchronization objects.