title: Detect if an instance is running with kernel32::CreateMutexA
body: <p>I'm working on an NSIS installer, and trying to check if a certain application is running before uninstalling. So, I use <code>kernel32::CreateMutexA</code> call. Here is the chunk:</p>
  
  <pre><code>System::Call 'kernel32::CreateMutexA(i 0, i 0, t "cmd.exe") i .r1 ?e'
  Pop $R0
  StrCmp $R0 0 +3
      MessageBox MB_USERICON "The application is already running."
  Abort
  </code></pre>
  
  <p>I put it into <code>un.onInit</code>. Trouble is, the process (<code>cmd.exe</code> here) is never detected.</p>
  
  <p>Did I miss something?</p>
  
  <p>Tx.</p>