Wsrtjtyk

I'm wondering if it's possible to programmatically restart an application that has been terminated in the beginning of a shutdown that will be canceled later.

On Windows, if an application calls ShutdownBlockReasonCreate on shutdown , it can know whether the user has cancelled it or not, by checking if the ENDSESSION_CRITICAL bit is set in the lParam.

In my case I don't want to block any shutdown .

Is this possible ? Thanks for any suggestion.

I think I found a solution :

I created a hidden window using CreateWindowEx to handle the WM_QUERYENDSESSION and WM_ENDSESSION messages:

LRESULT CALLBACK WndProc(HWND hwnd, UINT msg, WPARAM wParam, LPARAM lParam)

{

    switch(msg)

    {

        case WM_QUERYENDSESSION:

        {

            //clean up ...



            ShutdownBlockReasonCreate(hwnd, L"      ");

            // What ? You said you don't want to block the shutdown ?

            // Yes I do. It seems to work different with a hidden window.



            return 1;

        }

        case WM_ENDSESSION:

        {

            // GetSystemMetrics(SM_SHUTTINGDOWN) return Nonzero if the current session is shutting down

            // This loop waits for the user to cancel the shutdown

            while(GetSystemMetrics(SM_SHUTTINGDOWN) != 0)

               Sleep(100);

            // The user has cancelled the shutdown here

            // I can run the process again using CreateProcess or what ever...

            // Once this line is executed this instance will be terminated



        return 0;

        }

        default:

        return DefWindowProc(hwnd, msg, wParam, lParam);

    }

}

The return values are very important (see this).

As I didn't expected, a process without a top level visible window, even if it calls ShutdownBlockReasonCreate (with a hidden window handle), it will not be shown in the list of applications blocking the shutdown. And if there's no other application blocking the shutdown, Windows will only wait for a few seconds, and then shutdown.

For the loop, I took the idea from here. I don't know if there's a better alternative.

That's it.

Please test it, and correct me if I'm wrong.
Thanks.

[EDIT]
Here's the program main for a ready test:

#include <string>

#include <Windows.h>



using namespace std;



string getExePath()

{

    TCHAR wpath[MAX_PATH];

    GetModuleFileName (NULL, wpath, MAX_PATH);

    size_t i;

    char path[MAX_PATH];

    wcstombs_s(&i, path, MAX_PATH, wpath, MAX_PATH);



    return path;

}



LRESULT CALLBACK WndProc(HWND hwnd, UINT msg, WPARAM wParam, LPARAM lParam)

{

    switch(msg)

    {

        case WM_QUERYENDSESSION:

        {

            // A shutdown has been initiated

            ShutdownBlockReasonCreate(hwnd, L"      ");



            return 1;

        }

        case WM_ENDSESSION:

        {

            // GetSystemMetrics(SM_SHUTTINGDOWN) return Nonzero if the current session is shutting down

            // This loop waits for the user to cancel the shutdown



            while(GetSystemMetrics(SM_SHUTTINGDOWN) != 0)

               Sleep(100);            



            // The user has cancelled the shutdown here

            // I can run the process again



            WinExec(string(""" + getExePath() + """).c_str(), SW_HIDE);



            TerminateProcess(OpenProcess(PROCESS_TERMINATE, FALSE, GetCurrentProcessId()), 0);



        return 0;

        }

        default:

        return DefWindowProc(hwnd, msg, wParam, lParam);

    }

}





int WINAPI WinMain(HINSTANCE hInstance, HINSTANCE hPrevInstance, LPSTR lpCmdLine, int nCmdShow)

{

    HWND hwnd;

    WNDCLASSEXA wc;



    wc.cbSize        = sizeof(WNDCLASSEX);

    wc.style         = 0;

    wc.lpfnWndProc   = WndProc;

    wc.cbClsExtra    = 0;

    wc.cbWndExtra    = 0;

    wc.hInstance     = hInstance;

    wc.hIcon         = LoadIcon(NULL, IDI_APPLICATION);

    wc.hCursor       = LoadCursor(NULL, IDC_ARROW);

    wc.hbrBackground = (HBRUSH)(COLOR_WINDOW+1);

    wc.lpszClassName = "TestShutDownAbortClass";

    wc.hIconSm       = LoadIcon(NULL, IDI_APPLICATION);



    if( RegisterClassExA(&wc) == 0 )

        return 1;



    hwnd = CreateWindowExA(0,"TestShutDownAbortClass", "", WS_OVERLAPPEDWINDOW, CW_USEDEFAULT, CW_USEDEFAULT, CW_USEDEFAULT, CW_USEDEFAULT,NULL, NULL, hInstance, NULL);



    if(hwnd == NULL)

        return 1;



    MSG msg;

    while(GetMessageA(&msg, hwnd, 0, 0) > 0)

    {

        TranslateMessage(&msg);

        DispatchMessageA(&msg);

    }





    return 0;

}