[okl4-developer] threads linked to ThreadControl

[Nelson Tam]

Hi Charles,

On 05/06/2008, at 10:11 PM, Charles.VANWITTENBERGHE at fr.thalesgroup.com  
wrote:

> Hello,
>
> I'd like to have some explanations about the exception_handler_thread,
> scheduler_thread, and pager_thread.
>
> *	Are the three of them user defined ?

Yes, they are defined by the user when L4_ThreadControl() is called to  
create a thread.

> *	The purpose of the exception_handler_thread is obvious, but what are
> the purpose of the scheduler_thread and the pager_thread ?

The short answer is that the scheduler thread will have permissions to  
call L4_Schedule() on the newly-created thread, which means it can  
modify the timeslice and priority of said thread.  The details of who  
can call L4_Schedule() is documented in the L4 Reference Manual.

The pager thread is the thread who gets sent an IPC from the kernel  
when the target thread pagefaults.  The IPC is called a pagefault IPC  
because it contains information about the pagefault, which allows the  
pager to allocate and map memory appropriately.

> *	Do exception_handler and scheduler really have to be set to the same
> thread when using SYS_THREAD_CONTROL ?

No.  There are no restrictions that they have to be the same, but it  
is the general practice for pragmatic reasons.

--
(nt)

Nelson Tam

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