Many thanks for this excellent explanation ! I have the following code now to set the thread priority :- 
$thispid = @ARGV[0];
$threadpriority = @ARGV[1]; 
use Win32::API;
$retcode =  Win32::API->Import( 'Kernel32', 
  q[ BOOL SetThreadPriority( HANDLE hThread, int nPriority ) ] );
print "import set threadpriority = $retcode \n";
$retcode =  SetThreadPriority( $thispid, $threadpriority );
print "set threadpriority = $retcode \n";

[download]
Value 1 is returned by Import, which I understand means OK. But value 0 is returned by SetThreadPriority. I tried using literals of 952 for the Handle of the thread I want to change and 0, 1, -1 for thread priority. Still no luck.
Am I using the wrong format for the parameters, or is the required Handle for the thread something else, not what I see in Task Manager as PID ? I think I haven't understood the relationship of Thread Handle to PID where there is only a single thread - If I use Win32::Process to dump all the process details, it shows 952 for Handle and ProcessId - is this the real internal picture or not ?
Is this the issue you were describing with "if you want a central thread to be able to adjust the priorities of other threads, then you will have to set up a mapping between threads->tids and Win32 Thread handles." - i.e. with my code example can I only change the thread priority of perl itself ?
thanks Rod

In reply to Re^6: how to change process & thread priority on Win32 ? by rbutcher
in thread how to change process & thread priority on Win32 ? by rbutcher

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