C# Signature:
[DllImport("kernel32.dll")]
static extern IntPtr CreateMutex(IntPtr lpMutexAttributes, bool bInitialOwner,
string lpName);
User-Defined Types:
None.
Notes:
None.
Tips & Tricks:
Please add some!!!
Sample Code:
Here's how I use CreateMutex() to prevent more than one instance of my application from running at any given time.
//// Win32Calls.cs ////////////////////////////
namespace nsWin32Calls
{
/// <summary>
/// Win32 calls encapsulation object.
/// </summary>
public class Win32Calls
{
...
[DllImport("kernel32.dll", SetLastError = true)]
public static extern IntPtr CreateMutex( IntPtr lpMutexAttributes,
bool bInitialOwner, string lpName );
[DllImport("kernel32.dll")]
public static extern bool ReleaseMutex( IntPtr hMutex );
...
/// <summary>
/// This value can be returned by CreateMutex() and is found in
/// C++ in the error.h header file.
/// </summary>
public const int ERROR_ALREADY_EXISTS = 183;
...
}
}
//// frmMain.cs ///////////////////////////////
...
using nsWin32Calls; // encapsulates Win32 calls
...
namespace dsh
{
public class frmMain : System.Windows.Forms.Form
{
...
// helper objects
private static frmMain form = null;
...
/// <summary>
/// Main entry point for the application.
/// </summary>
[STAThread]
public static void Main()
{
// create IntPtrs for use with CreateMutex()
IntPtr ipMutexAttr = new IntPtr( 0 );
IntPtr ipHMutex = new IntPtr( 0 );
try
{
// Create the mutex and verify its status BEFORE construction
// of the main form.
ipHMutex = Win32Calls.CreateMutex( ipMutexAttr,
true, "CompanyName_AppName_MUTEX" );
if (ipHMutex != (IntPtr)0)
{
// check GetLastError value (MUST use this call. See MSDN)
int iGLE = Marshal.GetLastWin32Error();
// if we get the ERROR_ALREADY_EXISTS value, there is
// already another instance of this application running.
if (iGLE == Win32Calls.ERROR_ALREADY_EXISTS)
// So, don't allow this instance to run.
return;
}
else
{ // CreateMutex() failed.
// once the app is up and running, I log the failure from
// within the frmMain constructor.
m_bMutexFailed = true;
}
// construct the main form object and
form = new frmMain();
// run the app.
Application.Run( form );
}
catch( Exception oEx )
{
...handle it...
}
finally
{
// release the mutex
if (ipHMutex != (IntPtr)0)
Win32Calls.ReleaseMutex( ipHMutex );
// cleanup the main form object instance.
if (form != null) {
form.Dispose();
}
}
}
...
}
}
I tried to format as well as possible, but this thing is a bit weird. If I leave one blank line, this darn thing leaves two. If I leave none, it leaves none. :s
Alternative Managed API:
