The Need for a COMPLETED Queue

Question Text

Why does the scheduler need a COMPLETED queue and not simply terminate one thread once its function finishes?

Question Answers

• The COMPLETED queue is an implementation preference. The scheduler can expose the same functions without it

• Because the OS’s scheduler may kill the main kernel-level thread unless we keep the user-level thread in a queue

• The COMPLETED queue is needed to save the value returned by the thread so that it can later be retrieved by threads_join().

Feedback

Take a look at the handle_thread_start() function. It is used by threads_create() to start executing the given function. This is a wrapper that calls the function associated with the thread (this->start_routine), saves its result and then calls threads_exit() to store this result in the COMPLETED queue.