Guide: ULT Library

Go to labs/lab-08/guides/libult/support. It contains a minimalist user-level threads scheduler. Compiling it produces a shared library called libult.so. You can also consult its documentation. It explains the API as well as its implementation. The API exposed by the scheduling library is very simple. It is only made up of 3 functions:

• threads_create() creates a new ULT
• threads_exit() moves the current ULT to the COMPLETED state
• threads_join() waits for a given thread to end and saves its return value in the result argument

Look inside labs/lab-08/guides/libult/support/threads.c. Here you will find the 3 functions mentioned above.

The scheduler only uses 3 states: RUNNING, READY, COMPLETED.

Quiz

The threads in the READY and COMPLETED states are kept in 2 separate queues. When the scheduler wants to run a new thread, it retrieves it from the READY queue. When a thread ends its execution, it is added to the COMPLETED queue, together with its return value.

Quiz