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# Wx::SingleInstanceChecker

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
is_another_running 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 App#on_init. For
example:

bool MyApp::OnInit() { const String name = String::Format("MyApp- m_checker = new SingleInstanceChecker(name); if ( m_checker→IsAnotherRunning() ) { LogError(_(“Another program instance is already running, aborting.”)); return false; } … more initializations … return true; } int MyApp::OnExit() { delete m_checker; return 0; }

Note using 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 SingleInstanceChecker
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

## Methods

- SingleInstanceChecker.new
- SingleInstanceChecker.new
- SingleInstanceChecker#create
- SingleInstanceChecker#is_another_running

### SingleInstanceChecker.new

SingleInstanceChecker.new(%(arg-type)String% name, String path = ’’)

Like Create but without
error checking.

### SingleInstanceChecker#create

Boolean create(%(arg-type)String% name, String path = ’’)

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.
  get_app_name and GetUserId
  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
  GetHomeDir)

#### Return value

Returns `false` if initialization failed, it doesn’t mean that another
instance is running – use
is_another_running 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.

### SingleInstanceChecker#is_another_running

Boolean is_another_running()

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

destructor()

Destructor frees the associated resources.

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

[This page automatically generated from the Textile source at 2023-06-09 00:45:29 +0000]