A synchronization semaphore. A synchronization semaphore which can be used to synchronize multiple [Thread]s. Initialized to zero on creation. Be careful to avoid deadlocks. For a binary version, see [Mutex]. $DOCS_URL/tutorials/performance/threads/using_multiple_threads.md Lowers the [Semaphore], allowing one more thread in. [b]Note:[/b] This method internals' can't possibly fail, but an error code is returned for backwards compatibility, which will always be [constant OK]. Like [method wait], but won't block, so if the value is zero, fails immediately and returns [constant ERR_BUSY]. If non-zero, it returns [constant OK] to report success. Waits for the [Semaphore], if its value is zero, blocks until non-zero. [b]Note:[/b] This method internals' can't possibly fail, but an error code is returned for backwards compatibility, which will always be [constant OK].