Windows message pump problems

[Cantankerous Old Git]

I am trying to write a program that I hope to get working as a 
command-line app to start with, and then eventually use a windows 
service wrapper to call it as a service. Its purpose is to attach 
to an already running (not ours) service using an API DLL, where 
it will do houskeeping and monitoring tasks.

This is where it all gets strange. Although I can make calls into 
the API and do things proactively, when I register a callback for 
event notification, this callback doesn't get called. I am told 
that if I want event notifications, I must create a window and 
run a "message pump" on it, and pass the window handle to the API 
when I register my callback function. This is despite the fact 
that I don't want my service to ever display a window. I gather I 
don't have to act on any messages either, but somehow the API 
won't tell me about any events unless I do this.

So I am trying to create a skeleton that will create a window and 
run a "Message Pump". This is fairly succesful, in that I can 
create the window and the API then magically calls my event handler.

But I want to be able to stop my service on demand, and this 
involved killing the message pump loop and destroying the window. 
I can't figure out how to do that.

Problem 1:
If I have another thread call DestroyWindow after a delay, it 
gets an error "permission denied". I really can't see why.

Problem 2:
I thought that maybe catching some kind of message might help. I 
have tried registering both a message-map and a wndProc handler. 
In both instances (see the code below) I don't get the WM_CREATE 
message that I hope to see first. Also, if I use the wndProc 
method, the CPU slams to 100% and I seem to receive an infinite 
number of messages of some sort.

Problem 3:
I thought if I pump the messages using GetMessage and 
DispatchMessage in my own loop, I might be able to check a flag 
and exit the loop when required. But I can't figure out the 
callling arguments to these calls.


Below is the code I have done so far. I have stripped to as 
simple as I can make it. I would really appreciate some guidance 
or links to articles. I am struggling to understand even the 
basics, I think.

The Cog.



import win32gui
import win32api
import win32con
import traceback, time, threading

def onCreate():
     print 'GOT WM_CREATE'

def onDestroy():
     print 'GOT WM_DESTROY'

def wndProc(hwnd, msg, wparam, lparam):
     #print '~~~wndProc get a message'
     if msg == win32con.WM_CREATE:
         onCreate()
     if msg == win32con.WM_DESTROY:
         onDestroy()
     return 0

def registerWindowClass():
     wc = win32gui.WNDCLASS()
     wc.hInstance = hinst
     wc.lpszClassName = "Eric the half-a-bee"
     messageMap = {win32con.WM_CREATE : onCreate , 
win32con.WM_DESTROY : onDestroy }
     wc.lpfnWndProc = messageMap     # no messages if I do this
     #wc.lpfnWndProc = wndProc       # infinite stream of 
messages if I do this
     return win32gui.RegisterClass(wc)


def createWindow(registeredClassAtom):
     return win32gui.CreateWindow(
         registeredClassAtom, "This is a window",
         0, 0, 0, win32con.CW_USEDEFAULT, win32con.CW_USEDEFAULT, 
0, 0, hinst, None)


hinst = win32api.GetModuleHandle(None)

hwnd = createWindow(registerWindowClass())

win32gui.ShowWindow(hwnd, True)     # I'll try hide it later
win32gui.UpdateWindow(hwnd)


# wait 10 secs then kill the window
def timeKill():
     print 'sleeping...'
     time.sleep(10)
     print 'killing'
     win32gui.DestroyWindow(hwnd)


print 'starting killer timer'
threading.Thread(target=timeKill).start()

# This message pump traps the thread and never returns
win32gui.PumpMessages()