# wxSingleInstanceChecker Class Reference
[Application and Process Management]

`#include <wx/snglinst.h>`

## Detailed Description

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:

        bool MyApp::OnInit()
        {
            m_checker = new wxSingleInstanceChecker;
            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;
        }

Note that by default wxSingleInstanceChecker::CreateDefault() is used to create the checker meaning that it will be initialized differently for different users and thus will allow different users to run the application concurrently which is usually the required behaviour. However if only a single instance of a program should be running system-wide, you need to call Create() with a custom name which does not include wxGetUserId().

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

##

Library: wxBase

Category: Application and Process Management

## Public Member Functions
| wxSingleInstanceChecker ()
| Default constructor.
| wxSingleInstanceChecker (const wxString &name, const wxString &path=wxEmptyString)
| Constructor calling Create().
| ~wxSingleInstanceChecker ()
| Destructor frees the associated resources.
bool | Create (const wxString &name, const wxString &path=wxEmptyString)
| Initialize the object if it had been created using the default constructor.
bool | CreateDefault ()
| Calls Create() with default name.
bool | IsAnotherRunning () const
| Returns true if another copy of this program is already running and false otherwise.

List of all members.

## Constructor & Destructor Documentation

wxSingleInstanceChecker::wxSingleInstanceChecker | ( |  | ) |

Default constructor.

You may call Create() after using it or directly call IsAnotherRunning() in which case CreateDefault() will be implicitly used.

wxSingleInstanceChecker::wxSingleInstanceChecker | ( | const wxString & | name,
|  | const wxString & | path = `wxEmptyString` |
| ) |  |  |

Constructor calling Create().

This constructor does exactly the same thing as Create() but doesn't allow to check for errors.

wxSingleInstanceChecker::~wxSingleInstanceChecker | ( |  | ) |

Destructor frees the associated resources.

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

## Member Function Documentation

bool wxSingleInstanceChecker::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. wxApp::GetAppName() and wxGetUserId() are commonly used to construct this parameter.
  | 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()).

Returns:
  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 wxSingleInstanceChecker::CreateDefault | ( |  | ) |

Calls Create() with default name.

This method simply calls Create() with a string composed of wxApp::GetAppName() and wxGetUserId().

Because this method uses wxApp::GetAppName(), it may only be called after the global application was constructed.

Since:
  2.9.1

bool wxSingleInstanceChecker::IsAnotherRunning | ( |  | ) | const

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

Notice that if the object was created using the default constructor Create() hadn't been called before this method, it will call CreateDefault() automatically.

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