They plant dead trees for living, and the dead
They string together with a living thread . . .
But in no hush they string it . . . With a laugh, . . .
They bring the telephone and telegraph.
—Robert Frost, The Line-gang (1920)
Threads are created and managed by the built-in classes Thread (§20.20) and
ThreadGroup (§20.21). Creating a Thread object creates a thread and that is the
only way to create a thread. When the thread is created, it is not yet active; it
begins to run when its start method (§20.20.14) is called.
Every thread has a priority. When there is competition for processing resources, threads with higher priority are generally executed in preference to threads with lower priority. Such preference is not, however, a guarantee that the highest priority thread will always be running, and thread priorities cannot be used to reliably implement mutual exclusion.