Processing Messages in WIN32 applications

Question

Can any one help me ?
I have developed a multithreaded application for Windows
using VisualCafe.
There are two threads in this application.
The main thread is associated with the main frame
and it is responsible for user interactions.
The other thread is used to communicate with hardware;
it executes commands that require some time to be completed.
The main thread starts the second thread and
waits till the second thread is completed :
Thread mainThread = Thread.currentThread();
secondThread cfThread = new SecondThread();
cfThread.start();
while (! SecondThreadStatus.Finished)
try
// ProcessMessages(); !!!!! ?????????
mainThread.sleep(100);
catch (InterruptedException e) {
Class SecondThreadStatus contains static variable Finished
and is used to check the status of the second thread.
The problem is that I do not know how to process Windows
messages. I could not find a procedure like ProcessMessages
in Java libraries and I do not know how to implement
ProcessMessages using Java.
I have developed similar applications using Delphi that work well. The related procedure looks like this :
procedure WaitForCompletion;
begin
while not Finished do begin
Application.ProcessMessages;
Sleep(100);
end;
end;
The code for TApplication.ProcessMessages (unit Forms)
function TApplication.ProcessMessage(var Msg: TMsg): Boolean;
var
Handled: Boolean;
begin
Result := False;
if PeekMessage(Msg, 0, 0, 0, PM_REMOVE) then
begin
Result := True;
if Msg.Message <> WM_QUIT then
begin
Handled := False;
if Assigned(FOnMessage) then FOnMessage(Msg, Handled);
if not IsHintMsg(Msg) and not Handled and
not IsMDIMsg(Msg) and
not IsKeyMsg(Msg) and not IsDlgMsg(Msg) then
begin
TranslateMessage(Msg);
DispatchMessage(Msg);
end;
end
else
FTerminate := True;
end;
end;
procedure TApplication.ProcessMessages;
var
Msg: TMsg;
begin
while ProcessMessage(Msg) do {loop};
end;
Thank you in advance for your advice,
Dmitri

Answer 1

I initially used one thread in my application.
This application may call procedures that
require some time to be completed;
these procedures perform hardware related
commands.Good idea to split these procedures into another thread...
>
This application does not respond to user actions
(pressing buttons etc) after such a procedure
is called until this procedure is completed.
The cause of this effect is that application
does not process messages while this procedure
is running.What messages are you talking about?
If you are talking about Windows messages (ie. WM_CLOSE, WM_MINIMIZED, etc) then see my above posts. Java does not use these messages (how could Java be portable across multiple platforms if it did use Windows messages).
What I think you are saying is that when the intensive tasks are being processed (ie in SecondThread), your application locks up and refuses to respond to clicks, etc.
What you have done is correct, separate out these tasks into a second worker thread and handle your GUI events in a separate thread as you've shown.
The following code shows an example. Let me know if it works:
class MyFrame extends JFrame
MyRunnable Worker = new MyRunnable();
public static void main(String[] args)
MyFrame app = new MyFrame();
public MyFrame()
super("Thread Tester");
this.addWindowListener(new WindowAdapter()
public void windowClosing(WindowEvent we)
closeWindow();
this.setSize(300,200);
this.show();
new Thread(Worker).start();
while(!Worker.isDone())
Thread.sleep(100); // sleep this thread for 100 ms
public void closeWindow()
Worker.stop();
while(!Worker.isDone()) ; // wait until worker finishes
// current task
this.dispose();
System.exit(0);
class MyRunnable implements Runnable
boolean Done = false;
public boolean isDone() {return Done;}
boolean Stop = false;
public void stop() {Stop = true;}
public void run()
for(int loop = 0; loop < 1000; loop++)
if(Stop)
break;
// process some long task here...
Thread.sleep(2000);
System.out.println("Task # " + loop + " accomplished.");
Done = true;
} // void run() method
} // end class MyRunnable
} // end class MyFrame
>
I allocated the second thread for these hardware
related procedures in order to enable the main thread
to process messages.
But this didn't help. The application does not
respond to user actions till the second thread is
stopped.
I solved this problem in Delphi calling procedure
ProcessMessages, you may see my code.
But I do not know what I should do in Java.
Dmitri