Recognize frozen applications (Watchdog)

Windows with Delphi
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Recognize frozen applications (Watchdog)

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Question:

I am developing a sort of watchdog and I need to programatically check from an application, if another application is not responding. How can I do this?

Answer:

Try by sending a message with SendMessageTimeOut. If the another application is not responding, there is a timout. The example below searches for application 'MyApplication' in the main window's caption bar and gives it 3 seconds to respond to a message.

function AppFrozen(H: HWND) : Boolean;
var
  dwResult: DWord;
const
  timeout = 3000; // ms
begin
  AppFrozen := SendMessageTimeout(H, WM_NULL, 0, 0, 
                                  SMTO_ABORTIFHUNG or SMTO_BLOCK, 
                                  timeout, dwResult) <> 0
end;


var
  H: HWND;

begin
  // enumerate top level windows or search for an
  // application that you are monitoring
  H := FindWindow(nil, 'MyApplication');
  if H<>0 then
    if AppFrozen(H) then
      ShowMessage('MyApplication is Frozen!')
end.

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