アプリケーション別に防止する

//---------------------------------------------------------------------------
// Project1.cpp
//---------------------------------------------------------------------------
namespace {
// 多重起動防止用ミューテックスの名前
const AnsiString AppInstanceLockName = "ExampleAuthor.ExampleApplication.AppInstanceLock";
} // End of namespace
//---------------------------------------------------------------------------
WINAPI WinMain(HINSTANCE, HINSTANCE, LPSTR, int)
{
        try
        {
                // 多重起動を防止する
                ::SetLastError(NO_ERROR);
                HANDLE instanceLock = ::CreateMutex(NULL, true, AppInstanceLockName.c_str());
                if(instanceLock == NULL || ::GetLastError() != NO_ERROR) {
                        return 0;
                }

                Application->Initialize();
                Application->CreateForm(__classid(TForm1), &Form1);
                Application->Run();
        }
        catch (Exception &exception)
        {
                // ...
        }
        catch (...)
        {
                // ...
        }
        return 0;
}
//---------------------------------------------------------------------------