wx.SingleInstanceChecker

Inheritance diagram for wx.SingleInstanceChecker:

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 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 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__
• Create
• IsAnotherRunning

Class API

Methods

__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() and wx.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())

Returns:

wx.SingleInstanceChecker

---

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() 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() and wx.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())

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.

---

IsAnotherRunning()

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

Returns:

bool