Windows 7 - Thread scheduling vs Process scheduling

Asked By Dilip on 05-Mar-10 07:10 AM
Hi

In WinCE, the scheduler does a thread scheduling instead of process
scheduling? What is the difference between the thread scheduling and the
process scheduling and what are the advantages of the thread scheduling over
process scheduling ?

regards,
T Dilip Chakravarthy




Valter Minute [eMVP] replied to Dilip on 05-Mar-10 08:13 AM
In windows CE the threads are scheduled based on their priority. There
is no concept of "process priority" and the scheduler is quite simple.
Round robin between all the highest priority threads and a single level
of priority inversion. No dynamic priority changes controlled by the
scheduler (to rise the priority of a thread that has not been running for
a long time, for example), but dynamic priority management allowed with
specific APIs.
The process is an address space where one or more threads can run.
When the scheduler activate a thread it checks if it should remap the
MMU to active the process address space where that thread is supposed to
run.
Working with threads instead of processes where an execution flow and an
address space are coupled will allow you to have multiple flows of
execution (thread) sharing the same data and resources (inside the
process address space), without requiring any marshaling of those
resources (no copies, no remaps).
On the other side all the resources shared by multiple threads may need
to be syncronized and this makes development more complex.
When you design a system based on Windows CE you should carefully choose
what to implement as a thread inside a shared process and what to
implement as a distinct process. Using too many processes may involve
some overhead to share information, using only threads may lead to a
less reliable system because a failure in a single thread may impact all
the thread sharing the same process space.

--
Valter Minute (eMVP)
Training, support and development for Windows CE:
www.fortechembeddedlabs.it
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