Whether this is a single-threaded program. In this case, a number of methods change their meaning, as described below.

In a multi-threaded program: Starts a new thread, and calls the passed function with the passed argument in the new thread (like Thread.create). In a single-threaded program: fails.

In a multi-threaded program: Returns the currently running thread. Subsequent calls of self can return different objects for the same thread, but the id method will always return the same number. In a single-threaded program: Returns a dummy object (see below).

In a multi-threaded program: gives a hint that another thread should better run now. In a single-threaded program: this is a no-op.

In a multi-threaded program: Creates a mutex and returns the object. In a single-threaded program: Returns a dummy mutex object (see below).

In a multi-threaded program: Creates a condition variable and returns the object. In a single-threaded program: Returns a dummy variable (see below).