wxWidgets/interface/wx/snglinst.h

/////////////////////////////////////////////////////////////////////////////
// Name:        snglinst.h
// Purpose:     interface of wxSingleInstanceChecker
// Author:      wxWidgets team
// RCS-ID:      $Id$
// Licence:     wxWindows license
/////////////////////////////////////////////////////////////////////////////

/**
    @class wxSingleInstanceChecker

    wxSingleInstanceChecker class allows to check that only a single instance of a
    program is running.

    To do it, you should create an object of this class. As long as this object
    is alive, calls to wxSingleInstanceChecker::IsAnotherRunning from other
    processes will return @true.

    As the object should have the life span as big as possible, it makes sense to
    create it either as a global or in wxApp::OnInit.
    For example:

    @code
    bool MyApp::OnInit()
    {
        const wxString name = wxString::Format("MyApp-%s", wxGetUserId().c_str());
        m_checker = new wxSingleInstanceChecker(name);
        if ( m_checker-IsAnotherRunning() )
        {
            wxLogError(_("Another program instance is already running, aborting."));

            delete m_checker; // OnExit() won't be called if we return false
            m_checker = NULL;

            return false;
        }

        ... more initializations ...

        return true;
    }

    int MyApp::OnExit()
    {
        delete m_checker;

        return 0;
    }
    @endcode

    Note using wxGetUserId() to construct the name: this allows different user
    to run the application concurrently which is usually the intended goal.
    If you don't use the user name in the wxSingleInstanceChecker name, only
    one user would be able to run the application at a time.

    This class is implemented for Win32 and Unix platforms (supporting @c fcntl()
    system call, but almost all of modern Unix systems do) only.

    @library{wxbase}
    @category{misc}
*/
class wxSingleInstanceChecker
{
public:
    /**
        Default ctor, use Create() after it.
    */
    wxSingleInstanceChecker();

    /**
        Like Create() but without error checking.
    */
    wxSingleInstanceChecker(const wxString& name,
                            const wxString& path = wxEmptyString);

    /**
        Destructor frees the associated resources.
        Note that it is not virtual, this class is not meant to be used polymorphically.
    */
    ~wxSingleInstanceChecker();

    /**
        Initialize the object if it had been created using the default constructor.
        Note that you can't call Create() more than once, so calling it if the
        @ref wxSingleInstanceChecker() "non default ctor" had been used is an error.

        @param name
            Must be given and be as unique as possible. It is used as the
            mutex name under Win32 and the lock file name under Unix.
            GetAppName() and wxGetUserId() are commonly used to construct
            this parameter.
        @param path
            The path is optional and is ignored under Win32 and used as the
            directory to create the lock file in under Unix
            (default is wxGetHomeDir()).

        @return Returns @false if initialization failed, it doesn't mean that
                another instance is running - use  IsAnotherRunning() to check
                for it.

        @note
            One of possible reasons while Create may fail on Unix is that the lock
            file used for checking already exists but was not created by the user.
            Therefore applications shouldn't treat failure of this function as fatal
            condition, because doing so would open them to the possibility of a
            Denial of Service attack. Instead, they should alert the user about
            the problem and offer to continue execution without checking if
            another instance is running.
    */
    bool Create(const wxString& name,
                const wxString& path = wxEmptyString);

    /**
        Returns @true if another copy of this program is already running, @false
        otherwise.
    */
    bool IsAnotherRunning() const;
};