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How To Detect If an Application Has Stopped Responding

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In many situations you may want to know if an application is blocked. For example when you automate Microsoft Internet Explorer, you want to know whether Internet Explorer stops responding.

This article describes how to detect whether an automated instance of Internet Explorer stops responding. Although the code is written for Internet Explorer and Visual Basic, you can also use the following instructions for other applications.

The code uses the Win32 API SendMessageTimeout function to determine whether the target application responds and then the API call TerminateProcess to kill the hung instance of Internet Explorer.

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More information

There is no clear definition of an application hanging. Typically the application is "busy" with some processing. However from a user's perspective, the application has stopped responding.

The idea is to periodically detect if the application is still responding in a timer and depending on application logic, the target application can be killed or other necessary action can be taken.
The following steps demonstrate this. The code assumes that Internet Explorer is installed on the target machine.
  1. Start a new Standard EXE project in Visual Basic.
  2. Form1 is created by default. Place three command buttons on the form and name them cmdCheck, cmdLaunch, and cmdKill. Change their Caption property to Check, Launch, and Kill, respectively.
  3. Add the following code to Form1:
    Option Explicit
    'API Constants
    Const SMTO_BLOCK = &H1
    Const WM_NULL = &H0
    Const WM_CLOSE = &H10
    'API functions
    Private Declare Function GetWindowThreadProcessId Lib "user32" (ByVal hwnd As Long, _
    lpdwProcessId As Long) As Long
    Private Declare Function OpenProcess Lib "kernel32" (ByVal dwDesiredAccess As Long, _
    ByVal bInheritHandle As Long, ByVal dwProcessId As Long) As Long
    Private Declare Function SendMessageTimeout Lib "user32" Alias "SendMessageTimeoutA" _
    (ByVal hwnd As Long, ByVal msg As Long, ByVal wParam As Long, ByVal lParam As _
    Long, ByVal fuFlags As Long, ByVal uTimeout As Long, lpdwResult As Long) As Long
    Private Declare Function TerminateProcess Lib "kernel32" (ByVal hProcess As Long, _
    ByVal uExitCode As Long) As Long
    Private modObjIE As Object
    Private modlngWndIE As Long
    Private Sub cmdCheck_Click()
        Dim lngResult As Long
        Dim lngReturnValue As Long
        lngReturnValue = SendMessageTimeout(modlngWndIE, WM_NULL, 0&, 
          0&, SMTO_ABORTIFHUNG And SMTO_BLOCK, 1000, lngResult)
        If lngReturnValue Then
            MsgBox "Responding"
            MsgBox "Not Responding","Block tester"
        End If
    End Sub
    Private Sub cmdLaunch_Click()
        Set modObjIE = Nothing
        Set modObjIE = CreateObject("InternetExplorer.Application")
        modObjIE.Visible = True
        modObjIE.Navigate2 ""
        modlngWndIE = modObjIE.hwnd
    End Sub
    Private Sub cmdKill_Click()
        Dim lngProcessID As Long
        Dim lngReturnValue As Long
        Dim lngProcess As Long
        lngReturnValue = GetWindowThreadProcessId(modlngWndIE, lngProcessID)
        lngProcess = OpenProcess(PROCESS_ALL_ACCESS, 0&, lngProcessID)
        lngReturnValue = TerminateProcess(lngProcess, 0&)
    End Sub
  4. Run this program and click the Launch button.
  5. Click the Check button. You should see Responding appear.
Enter your own URL in the navigate2 command if you have one that causes blocking.

NOTE: None of the automation properties of Internet Explorer will be accessible once Internet Explorer stops responding, which is the reason for storing hwnd in a form level variable.

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For additional information, click the article numbers below to view the articles in the Microsoft Knowledge Base:
129797 How To Launch a Win32 Application from Visual Basic
178893 How To Terminate an Application Cleanly in Win32
176391 How To Programmatically Close a Single Instance of a Windows-Based Program

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Keywords: KB231844, kbhowto

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Article Info
Article ID : 231844
Revision : 5
Created on : 7/1/2004
Published on : 7/1/2004
Exists online : False
Views : 458