🚀 go-pugleaf

"Nate Lockwood" <RNLockwoodREMOVE@attglobal.net> wrote in message 
news:43ff726e$1@newsgroups.borland.com...
> I'm trying to have my program detect that another instance is 
> running, send a "Show" message to the already running instance, and 
> then return. I'm using Builder 6.
>
> It appears that I always get a non null mutex so the message is 
> never sent.  Here's some code.
>

You *should* get the handle to the existing mutex. You have to call 
GetLastError() after CreateMutex() to see if it returns 
ERROR_ALREADY_EXISTS.

-- 
Bruce 

  Bruce Salzman wrote:


> You *should* get the handle to the existing mutex. You have to call 
> GetLastError() after CreateMutex() to see if it returns 
> ERROR_ALREADY_EXISTS.

Thanks, I got that thought after I posted and changed my code to that 
below.  The first instance is detected but the message doesn't get through.

Nate

HANDLE CheckForInstance(const UINT WM_MYMSG)
{
   SetLastError(0) ;
   char * m_Name = "USDA.FS.FireScience.GooleEarthTool";
   HANDLE m_Handle = CreateMutex(NULL, false, m_Name);
   if(m_Handle != NULL)
     if(GetLastError() != ERROR_ALREADY_EXISTS)
       return m_Handle;      // this is the first instance

   PostMessage(HWND_BROADCAST, WM_MYMSG, NULL, NULL);
   return NULL;     //  NULL handle
}

I'll start another thread now that I have the mutex problem fixed.

"Nate Lockwood" <RNLockwoodREMOVE@attglobal.net> wrote in message
news:43ff726e$1@newsgroups.borland.com...

> It appears that I always get a non null mutex

As you should be.  That is what CreateMutex() does.  You are not taking into
account that the returned pointer is always non-NULL even if the pointer
belongs to another existing mutex.  The only time CreateMutex() returns NULL
is when a real error occurs (out of resources, etc).

> Here's some code.

Use something more like the following code instead:

    --- Project .cpp---

    UINT WM_MYMSG = 0;

    WINAPI WinMain(HINSTANCE, HINSTANCE, LPSTR, int)
    {
        WM_MYMSG =
RegisterWindowMessage("USDA.FS.FireScience.GooleEarthTool.Awake");

        HANDLE mutex = ::CreateMutex(NULL, TRUE,
"USDA.FS.FireScience.GooleEarthTool");
        if( m_Handle == NULL )
            return 0;

        if( ::GetLastError() == ERROR_ALREADY_EXISTS )
        {
            if( WM_MYMSG != 0 )
            {
                Application->Title = "";
                HWND hWnd = ::FindWindow("TApplication", "Google Earth (C)
Tool");
                if( hWnd )
                    ::PostMessage(hWnd, WM_MYMSG, NULL, NULL);
            }
        }
        else
        {
            try
            {
                Application->Title = "Google Earth (C) Tool";
                Application->Initialize();
                Application->CreateForm(__classid(TFormMain), &FormMain);
                Application->CreateForm(__classid(TAboutBox), &AboutBox);
                Application->Run();
            }
            catch(Exception &exception)
            {
                SysUtils::ShowException(&exception);
            }
        }

        if( mutex )
            ::CloseHandle(mutex);

        return 0;
    }


    --- Form.cpp ---

    extern UINT WM_MYMSG;

    __fastcall TFormMain::TFormMain(TComponent *Owner)
        : TForm(Owner)
    {
        Application->OnMessage = AppMessage;
    }

    __fastcall TFormMain::~TFormMain()
    {
        Application->OnMessage = NULL;
    }

    void __fastcall TFormMain::AppMessage(MSG &Msg, bool &Handled)
    {
        if( (Msg.message == WM_MYMSG) && (WM_MYMSG != 0) )
        {
            Handled = true;
            Show();
        }
        else
            Handled = false;
    }


Gambit

"Nate Lockwood" <RNLockwoodREMOVE@attglobal.net> wrote in message
news:43ff748a$1@newsgroups.borland.com...

> The first instance is detected but the message doesn't get through.

You are not catching the message properly.  You are trying to catch it at
from TForm, but you are doing a broadcast post which means the TApplication
will catch the message instead.  See my other reply.

>    PostMessage(HWND_BROADCAST, WM_MYMSG, NULL, NULL);
>    return NULL;     //  NULL handle

You are not freeing the mutex before returning.


Gambit

Remy Lebeau (TeamB) wrote:


> You are not freeing the mutex before returning.
> 

Thanks for the warning, I did free is some lines later.  Forgot to 
mention it.

Nate

Thanks very much, I learned a lot and it works just as I wanted it to 
after I changed the Show to Application->Restore(). <G>

I'd like to pass a string, too, do I understand correctly that I can 
create a string in the heap and pass it by reference?

Nate