JF>  I am attempting to learn to program under OS/2 and 
 JF> well still need to do alot of reading. Can anyone 
 JF> explain what an Object Window is, and perhaps provide 
 JF> a scenario as to why one is created ?

An object window is a window that will never be seen.  Instead of having
HWND_DESKTOP as the ultimate parent -- as all visible windows do -- an
object window has HWND_OBJECT as the parent.

Because PM uses one special queue for mouse, keyboard and focus change
messages,  it is important that this queue always remain responsive.  If a
PM program does not return instantly from one of these messages, the user
can not do much (PM is not "hung" as some would say -- pm
programs will continue to run and update their windows;  the problem is
that the user has been locked out of the system).

Since an object window (in a different thread, with a different queue)
never receives any of these messages (mouse, keyboard, focus change), it is
incapable of locking the user out. Therefore,  you can take your bloody
time processing a message in this "worker thread".

Messages are usually Posted (not Sent) from your main thread,  which DOES
create windows the user can see.

Actually creating an Object window is an unnecessary step.  All you really
need to so is create a queue and use WinPostQueueMsg() to communicate with
it,  instead of WinPostMsg().  I actually prefer this method, since it
removes one layer,  and removes any possibility of calling WinSendMsg(),
which defeats the whole purpose of the worker thread.

A specific circumstance:

        You should never, ever, ever call DosOpen (and therefore open(),
        fopen(), etc) during a PM message.  If the file is on
        a floppy, cdrom, or network, unexpected delays will cause
        the PM queue to get stuck.

        For an example of a bad program,  make sure you don't have
        a disk in A:,  and go to your desktop and right-click on
        your A: icon (to bring up its pop-up menu).  The system will
        be stuck while it tries to read from the disk that isn't
        in drive A:.  (later: I just tried this with FP17,  and it
        looks like they finally fixed this one).



--- Maximus/2 3.00