A unit of execution in a process. A unit of execution in a process. Can run methods on [Object]s simultaneously. The use of synchronization via [Mutex], [Semaphore] is advised if working with shared objects. Returns the current [code]Thread[/code]s id, uniquely identifying it among all threads. Returns [code]true[/code] if this [code]Thread[/code] is currently active. An active [code]Thread[/code] cannot start work on a new method but can be joined with [method wait_to_finish]. Starts a new [code]Thread[/code] that runs "method" on object "instance" with "userdata" passed as an argument. The "priority" of the [code]Thread[/code] can be changed by passing a PRIORITY_* enum. Returns OK on success, or ERR_CANT_CREATE on failure. Joins the [code]Thread[/code] and waits for it to finish. Returns what the method called returned.