Type start /? on your command line for how to start a command with a low or background priory.

Hit ctrl-alt-del to bring up the task manager, right-clock the name on the processes tab and use "set Priority" ona running process.

See Win32::Process and use the appropriate constant from:

        HIGH_PRIORITY_CLASS
        IDLE_PRIORITY_CLASS
        NORMAL_PRIORITY_CLASS
        REALTIME_PRIORITY_CLASS
        THREAD_PRIORITY_ABOVE_NORMAL
        THREAD_PRIORITY_BELOW_NORMAL
        THREAD_PRIORITY_ERROR_RETURN
        THREAD_PRIORITY_HIGHEST
        THREAD_PRIORITY_IDLE
        THREAD_PRIORITY_LOWEST
        THREAD_PRIORITY_NORMAL
        THREAD_PRIORITY_TIME_CRITICAL
        ABOVE_NORMAL_PRIORITY_CLASS
        BELOW_NORMAL_PRIORITY_CLASS
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if you are starting the process from within perl.

Personally, I find the first option the simplest even when starting a process from with a perl script:

system q[start /low notepad.exe];;
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as it also allows me to set the affinity mask.

Thanks a lot. These seem to be useful starting points. But my main goal is to do this on a constant basis (ie. not having to look my process up in the table manually every time rather do it automatically from the script) and having a look at the Win32::Process module it seems to me that if I open the process that way I won't have handles to the STDIN and STDOUT of the process, while if I open it through Open2 (as I do currently) there is not a Win32::Process object on which I can perform $ProcessObj->SetPriorityClass($class). There seems to be no method for creating a Win32::Process object from a pid.

There seems to be no method for creating a Win32::Process object from a pid.

Actually there is:

Win32::Process::Open( $obj, $pid, $iflags );
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$pid is an existingprocess id as return by open2(), $obj is a variable you pass in which gets set to a Win32::Process object handle. You can the call ->SetPriority() on that. Eg.

use Win32::Process;;

$pid = system 1, 'notepad';; ## The return from open2 should work just
+ as well.

Win32::Process::Open( $o, $pid, 0 );;

print $o;;
Win32::Process=SCALAR(0x4073208)

$o->SetPriorityClass( IDLE_PRIORITY_CLASS );;
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With the rise and rise of 'Social' network sites: 'Computers are making people easier to use everyday'

Examine what is said, not who speaks -- Silence betokens consent -- Love the truth but pardon error.

"Science is about questioning the status quo. Questioning authority".

In the absence of evidence, opinion is indistinguishable from prejudice.

The start of some sanity?

It would surprise me greatly, indeed, if it proved to be the over-consumption of CPU time that is causing “everything else to become painstakingly slow” such that “web pages time out,” etc.   It is almost axiomatic to me that such disruption actually comes from the over-consumption of virtual memory (leading to thrashing), or very inefficient use of the file system, or sometimes, simply having too many processes or threads fighting for available milliseconds.   If this be so, then changing the dispatching-priority of a thread won’t help much at all, if at all.

Now, thread priorities do make a noticeable difference in some GUI systems, most notably Microsoft Windows, which still to this day is very sensitive to main-threads which do not timely respond to GUI messages.   But this manifests itself as “visual jitterbugs,” such as mouse cursors that don’t move smoothly, even as other activities which do not directly involve the GUI continue apace.

It is true that a chess engine tends to use a great amount of memory for its hash to store generated moves (of which there are tipically tens of millions). On the other hand once started it never 'sleeps' so consumes CPU resources as well - all the way long.

Still: lowering the priority of the engine process has worked for me. Now I can open web pages even play online with the engine running in the background.