UMS Scheduler Entry Point Function

An application’s scheduler entry point function is implemented as a ums_scheduler_entry_point_t function. The system calls the application’s scheduler entry point function at the following times:

• When a non-UMS thread is converted to a UMS scheduler thread by calling enter_ums_scheduling_mode().

• When a UMS worker thread calls ums_thread_yield().

• When a UMS worker thread terminates.

The ums_reason_t parameter of the ums_scheduler_entry_point_t function specifies the reason that the entry point function was called. If the entry point function was called because a new UMS scheduler thread was created, the scheduler_param parameter contains data specified by the caller of enter_ums_scheduling_mode(). If the entry point function was called because a UMS worker thread yielded, the scheduler_param parameter contains data specified by the caller of ums_thread_yield(). If the entry point function was called because a UMS worker thread terminated, the scheduler_param parameter is NULL.

The scheduler entry point function is responsible for determining the appropriate next action for the specified thread.

When the scheduler entry point function is called, the application’s scheduler should attempt to retrieve all of the items in its associated completion list by calling the dequeue_ums_completion_list_items() function. This function retrieves a list of UMS thread contexts that have finished processing in the kernel and are ready to run. The application’s scheduler should not run UMS threads directly from this list because this can cause unpredictable behavior in the application. Instead, the scheduler should retrieve all UMS thread contexts by calling the get_next_ums_list_item() function once for each context, insert the UMS thread contexts in the scheduler’s ready thread queue, and only then run UMS threads from the ready thread queue.