How can I freeze the execution of a program?

Question

Say I have got a program that hogs the processor and/or hard disk to the point that it makes it nearly impossible to do anything else on that computer. Now I don't want to kill that program because what it does is useful (it's a batch job that really is that CPU or disk heavy, e.g. it could ZIP a few gigabytes of data files) but for a short time I need to do something else on that computer. Is there any way an external program could do to freeze that performance killer for a while?

It's like the old DOS option to switch between programs without actually having multitasking.

Assume that the hypothetical program in question is a 3rd party product for which I don't have the source code and there is no way to tell it to pause.

I know I can change the program's priority class e.g. in TaskManager but that's not enough, I want to freeze it.

I am talking about Windows XP as the OS and would like to program a solution with Delphi. I have got all rights on the machine, so I could start something as administrator, replace files and I could also install a service if that is necessary.

Answer 1

You can freeze it with Process Explorer: Right-click on your program and select Suspend.

Here is some sample code for programmatic freezing from http://www.c-plusplus.de/forum/viewtopic-var-p-is-1460293.html, edited and omitted error checking for brevity:

#include <windows.h>

_NtSuspendProcess NtSuspendProcess =
    (_NtSuspendProcess) GetProcAddress( GetModuleHandle( "ntdll" ),
                                        "NtSuspendProcess" ); 
HANDLE ProcessHandle = OpenProcess( PROCESS_ALL_ACCESS, FALSE, pid);
NtSuspendProcess( ProcessHandle );