************************
wx.SingleInstanceChecker
************************

Inheritance diagram for `wx.SingleInstanceChecker`:

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.. inheritance-diagram:: wx.SingleInstanceChecker

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Description
===========

`wx.SingleInstanceChecker` 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 <#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 
`wx.App.OnInit`. For example::


    def OnInit(self):

        # Give a name to the wx.App
        name = "MyApp-%s"%wx.GetUserId()

        self._checker = wx.SingleInstanceChecker(name)
        if self._checker.IsAnotherRunning():
            raise Exception("Another program instance is already running, aborting.")
            return False

        # ... more initializations here ...      

        return True


    def OnExit(self):

        del self._checker
        return 0


.. note:: Note using `wx.GetUserId <../wxFunctions.html#GetUserId>`_ 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 `wx.SingleInstanceChecker`
   name, only one user would be able to run the application at a time.


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


Methods Summary
^^^^^^^^^^^^^^^

* `__init__ <#__init__>`_ 
* `Create <#Create>`_ 
* `IsAnotherRunning <#IsAnotherRunning>`_ 

Class API
=========

Methods
^^^^^^^


.. method:: __init__(name, path="")

   Default constructor.

   **Parameters:**

   * `name` (string): 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() <wx.App.html#GetAppName>`_ and `wx.GetUserId() <../wxFunctions.html#GetUserId>`_ 
     are commonly used to construct this parameter.
   * `path` (string): is optional and is ignored under Win32 and used as the directory to create the lock file in under 
     Unix (default is `wx.GetHomeDir() <../wxFunctions.html#GetHomeDir>`_)

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   **Returns:**

   `wx.SingleInstanceChecker <wx.SingleInstanceChecker.html>`_
 

--------

.. method:: Create(name, path="")

   Initialize the object if it had been created using the default constructor.

   Returns ``False`` if initialization failed, it doesn't mean that another instance is running - use `IsAnotherRunning() <#IsAnotherRunning>`_ to check for it.

   **Parameters:**

   * `name` (string): 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() <wx.App.html#GetAppName>`_ and `wx.GetUserId() <../wxFunctions.html#GetUserId>`_ 
     are commonly used to construct this parameter.
   * `path` (string): is optional and is ignored under Win32 and used as the directory to create the lock file in under 
     Unix (default is `wx.GetHomeDir() <../wxFunctions.html#GetHomeDir>`_)

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   **Returns:**

   `bool` 

.. note:: Note that you can't call `Create` more than once, so calling it if the non default constructor had been used is an error.

.. tip:: 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.


--------

.. method:: IsAnotherRunning()

   Returns ``True`` if another copy of this program is already running, ``False`` otherwise.

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   **Returns:**

   `bool`