Re: Problem with XP scheduler?

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Tim Roberts wrote:
Grzegorz Wróbel </dev/null@xxxxxxxxxxxxxxxxxxxxx> wrote:

Tim Roberts wrote:
Get real. A software problem cannot cause your machine to lock up so hard
that even mouse and keyboard stop.
Get rational. User mode app can lock up mouse and keyboard just by starving system processes that manage mouse and keyboard input. On the single CPU/core machines it was very common to happen. On the multi core machines much less likely to happen "naturally", but still possible.

No. A user mode app can certainly prevent other user mode apps from
processing mouse and keyboard input, yes, but the mouse pointer keeps
moving, and pressing the caps lock key still toggles the caps lock
indicator. Stopping those requires the "assistance" of kernel code.

No. The point is you can lock mouse and keyboard to the point that the mouse cursor stops moving and no other application (including Windows shell) can receive/process mouse and keyboard input.

This is known issue, if you have never experienced it as a programmer, you still can read about it in MSDN: http://msdn.microsoft.com/en-us/library/ms685100(VS.85).aspx

You can of course argue this is still "kernel code" that freezes the box, but such argumentation doesn't have much sense since this code is executed directly by user mode API calls.


This is the sample test code I once wrote to effectively freeze the single CPU/core Windows box for 30 seconds (on post XP system you'll need to run it elevated otherwise SetPriorityClass() will fail):

//lockme.cpp

# include <windows.h>
# include <math.h>

int main()
{
int i,j,k;
double a,b,c;
ULARGE_INTEGER start,current;
SYSTEMTIME st;
FILETIME ft;

SetPriorityClass(GetCurrentProcess(),REALTIME_PRIORITY_CLASS);
SetThreadPriority(GetCurrentThread(),THREAD_PRIORITY_TIME_CRITICAL);

GetSystemTime(&st);
SystemTimeToFileTime(&st,&ft);
memcpy(&start,&ft,sizeof(ft));

for(;;){ //lets do some heavy computation;
c = 0.9;
a = sin(c);
b = cos(c);
c = log(pow(a,b)+c);
k = int(c)+5;
j = 4*k*k*k + 2*k*k + k + 1;

GetSystemTime(&st);
SystemTimeToFileTime(&st,&ft);
memcpy(&current,&ft,sizeof(ft));
if(current.QuadPart-start.QuadPart>300000000) // release the lock after 30 seconds
break;
}

return 0;
}


The above code simply sets its base priority to 31 and then occupy CPU.

Haven't tried it on multicore box, but presumably if you run it from elevated console n times (when n is number of the CPU cores) you should freeze the box too. Unless OS tries to reserve one core for itself (unlikely).


--
Grzegorz Wróbel
677265676F727940346E6575726F6E732E636F6D
.

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