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

On 3/5/2010 1:10 PM, Dilip wrote:
> 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 ?

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 hasn't 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)
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www.fortechembeddedlabs.it
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www.geekswithblogs.net/WindowsEmbeddedCookbook
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