PHP Manual: sem

function sem_release(SysvSemaphore $semaphore): bool

sem_release() releases the semaphore if it is currently acquired by the calling process, otherwise a warning is generated.

After releasing the semaphore, sem_acquire() may be called to re-acquire it.

Returns true on success or false on failure.

Version	Description
8.0.0	`semaphore` expects a SysvSemaphore instance now; previously, a resource was expected.

sem_release