## 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 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:

    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."));

            return false;
        }

        ... more initializations ...

        return true;
    }

    int MyApp::OnExit()
    {
        delete m_checker;

        return 0;
    }

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 `fcntl()` system call, but almost all of modern Unix systems do) only.

Derived from

No base class

Include files

<wx/snglinst.h>

Members

wxSingleInstanceChecker::wxSingleInstanceChecker
wxSingleInstanceChecker::wxSingleInstanceChecker
wxSingleInstanceChecker::Create
wxSingleInstanceChecker::IsAnotherRunning
wxSingleInstanceChecker::~wxSingleInstanceChecker

### wxSingleInstanceChecker::wxSingleInstanceChecker

wxSingleInstanceChecker()

Default ctor, use Create() after it.

### wxSingleInstanceChecker::wxSingleInstanceChecker

wxSingleInstanceChecker(const wxString& name, const wxString& path = wxEmptyString)

Like Create() but without error checking.

### wxSingleInstanceChecker::Create

bool Create(const wxString& name, const wxString& path = wxEmptyString)

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 non default ctor had been used is an error.

Parameters

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.

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 value

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.

### wxSingleInstanceChecker::IsAnotherRunning

bool IsAnotherRunning() const

Returns `true` if another copy of this program is already running, `false` otherwise.

### wxSingleInstanceChecker::~wxSingleInstanceChecker

~wxSingleInstanceChecker()

Destructor frees the associated resources.

Note that it is not virtual, this class is not meant to be used polymorphically