[mkc2008] Thread Creation, Destruction and Synchronization - side effects of task destruction

Torsten Frenzel frenzel at os.inf.tu-dresden.de
Mon Apr 6 11:06:03 CEST 2009

Jan Bierbaum(s3306700 at mail.inf.tu-dresden.de)@2009.04.05 22:15:14 +0200:
> Hi!
> What happens to mappings created by a (thread of a) task that is
> destroyed? Intuitively I'd say they continue to exist and in the mapping
> data base the "parent task inherits the mappings". That sounds a bit
> awkward, so I'll try a picture:
> A --> B ---> C
>          \-> D
> Some thread in task A established a mapping (of some page) to task B.
> Task B did map that page to tasks C and D afterwards. Now we destroy
> task B. Does the MDB look like this afterwards?
> A ---> C
>    \-> D
No the mapping will be revoked from C and D. This makes sense because A
doesn't know anything about C and D.
> Another question:
> On slide 32, as a solution to the problem of trying to access an invalid
> thread lock, there's the approach to "Check [the] validity of [any]
> thread lock before every try [to acquire it]". How is this done? How can
> the validity of a lock be checked without actually touching it in memory?

Of course you need to touch the memory. Practically the thread-lock
lives in the TCB. There is a special function called is_tcb_mapped()
that returns the required information. There is a special case in the
page-fault handler to check whether the pagefault came from this
function and if so, set some flag that the function can evaluate


More information about the mkc2008 mailing list