system wide key/mouse hook does NOT work on NT4.0 if a background process

Based on the prior expert's advice (thanks) I implemented system-wide (I wish) hook in C on NT 4.0.
It has two components: a hook DLL and the main test program. When I run the main test program in DOS console it does capture keyboard/mouse events.

However, if I start the test program in the background (EITHER via a home-grown network messaging mechanism where I issue system("start /B c:\path\main.exe") from an already running background program OR via a remote cmd console (using psexec)); it does not work.

Visual C++ source code is below (Main starts up, waits for an event and when detects one, it exits).

What am I doing wrong ?

#include <windows.h>
#include <stdio.h>

HINSTANCE instance_handle;

#pragma data_seg (".hookdat")
HHOOK g_hHookKbd = NULL;
HHOOK g_hHookMse = NULL;
DWORD g_dwLastInputTick = 0;
#pragma data_seg()
#pragma comment (linker,"/section:.hookdat,rws")

// Get tick count of last keyboard or mouse event
__declspec( dllexport ) DWORD IdleCPUGetLastInputTime()
     return g_dwLastInputTick;

// Keyboard hook: record tick count
LRESULT CALLBACK MyKbdHook(int code, WPARAM wParam, LPARAM lParam)
    if (code==HC_ACTION)
          g_dwLastInputTick = GetTickCount();
    return CallNextHookEx(g_hHookKbd, code, wParam, lParam);
// Mouse hook: record tick count
LRESULT CALLBACK MyMouseHook(int code, WPARAM wParam, LPARAM lParam)
    if (code==HC_ACTION)
       g_dwLastInputTick = GetTickCount();
    return CallNextHookEx(g_hHookMse, code, wParam, lParam);
// Initialize DLL: install kbd/mouse hooks.
__declspec( dllexport ) bool IdleCPUInit()
   if (g_hHookKbd == NULL)
          g_hHookKbd = SetWindowsHookEx(WH_KEYBOARD, (HOOKPROC) MyKbdHook, instance_handle, 0);
          g_hHookMse = SetWindowsHookEx(WH_MOUSE,    (HOOKPROC) MyMouseHook, instance_handle, 0);
          g_dwLastInputTick = GetTickCount(); // init count
    return TRUE;
// Terminate DLL: remove hooks.
__declspec( dllexport ) void IdleCPUTerm()
    BOOL bRet1 = UnhookWindowsHookEx(g_hHookKbd);
    BOOL bRet2 = UnhookWindowsHookEx(g_hHookMse);

int WINAPI DllMain(HINSTANCE hinst, unsigned long reason, void* lpReserved)
     switch(reason) {
          instance_handle = hinst;
          return TRUE;
          if ((g_hHookKbd != NULL) || (g_hHookMse != NULL))
          return TRUE;
          return TRUE;

//COMMENT: I am using ordinal numbers for hook dll lookup because had some problems with passing the name
#include <stdio.h>
#include <windows.h>

typedef BOOL (*INITPROC) ();
typedef DWORD (*TIMEPROC) ();
typedef VOID (*TERMPROC) ();

int main(int argc,char *argv[]) {
    HINSTANCE hinstLib;
    INITPROC ProcInit = NULL;
    TIMEPROC ProcTime = 0;
    TERMPROC ProcTerm;
    BOOL fFreeResult;
    long last_input_time, time_running, time_started, time_diff;
    BOOL no_interrupt;

    hinstLib = LoadLibrary("hook");
    if (hinstLib != NULL) {
        ProcInit = (INITPROC) GetProcAddress(hinstLib, 2);
        if (ProcInit)  {
         fFreeResult=ProcInit ();
// initial time tick
    time_started = (long) GetTickCount();
    ProcTime = (TIMEPROC) GetProcAddress(hinstLib, 1);
    if (ProcTime) {
        while (no_interrupt) {
            last_input_time = (long) ProcTime();
            time_running = (long)((GetTickCount() - time_started)/1000);
            time_diff = (long)((GetTickCount() - last_input_time)/1000);
            if ((time_diff + 4) < time_running) {
            if (no_interrupt==TRUE) {
                Sleep (5000);
    ProcTerm = (TERMPROC) GetProcAddress(hinstLib, 3);
    if (NULL != ProcTerm) {
        (ProcTerm) ();
    fFreeResult = FreeLibrary(hinstLib);

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>>However, if I start the test program in the background (EITHER via a home-grown network
>>messaging mechanism where I issue system("start /B c:\path\main.exe") from an already running
>>background program OR via a remote cmd console (using psexec)); it does not work.

That's not surprising, as there is a different desktop assiciated with the process than the one of the logged on user. You should put that in the autostart group for every user.
jerzybAuthor Commented:
There are lots of users.
The job of the background process is to do heavy calculations (which have nothing to do with the logged in user) and suspend itself if a keyboard/mouse activity detected (to minimize any effects on the user).

The process is already LOW priority but sometimes its not enough.

The screensavers somehow do it so, there must be a different way.

>>The screensavers somehow do it

Yes, but they are launched in the user's context...
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jerzybAuthor Commented:
OK, since my program runs with admin priviledges, can I somehow start my key/mouse detection program in the context of the logged-in user?
That is, the program will monitor who is logged in and restart appropriately (but how?).
>>can I somehow start my key/mouse detection program in the context of the logged-in user?

Yes, you can, but it ain't that simple :o)

You have to obtain a token from a process the user is running (explorer.exe is a good choice <s>). You'll need the PID to call 'OpenProcess()', then 'OpenProcessToken()' with 'TOKEN_IMPERSONATE' access. See;EN-US;q175030 ("HOWTO: Enumerate Applications Using Win32 APIs (Q175030)") on how to get that PID - it comes with sample code. Then, once you have the token, you have to call 'ImpersonateLoggedOnUser()', et voilà, you are there - either launch the program or do that inside the program before initializing the hooks.

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You are using #pragma data_seg()

You must use #pragma bss_seg because the shared variables are uninitialized. You are initializing them to zero, but zero doesn't count as initializing. Instead of #pragma data_seg use #pragma bss_seg, or even both (haven't tried both).

text_seg: program code
data_seg: NONZERO initialized variables
bss_seg: zero initialized variables

The idea is that the linker does not neet to write the bss_seg content to the output file because it is understood to be all-zeros, reducing executable size.

Use DUMPBIN in the msvc tools directory to verify that the output file does contain a .hookdat section.
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