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From: rommel@lan.informatik.tu-muenchen.dbp.de (Kai-Uwe Rommel)
Newsgroups: comp.windows.ms
Subject: spawning under Windows
Message-ID: <2568@tuminfo1.lan.informatik.tu-muenchen.dbp.de>
Date: 31 May 90 13:41:58 GMT
Sender: news@lan.informatik.tu-muenchen.dbp.de
Reply-To: rommel@lan.informatik.tu-muenchen.dbp.de (Kai-Uwe Rommel)
Distribution: comp.windows.ms
Organization: Inst. fuer Informatik, TU Muenchen, W. Germany
Lines: 44

Some time ago I asked for information about controlling spawned child
applications under Windows. Spawning applications itself is rather easy
if you read the discussion about this topic here last year. What I
needed was a "handle" to the child program and a way of at least asking
if it still exists. This is an odd situation. MS-DOS has only
synchronous spawn (clear) but Windows has only asynchronous spawn
(well, better than having only the other type) but nothing like wait()
or so. In a program I need to call an external editor (with a text file
as an argument) and to read the text file in back after the editor
exited WITHOUT user interaction. That means I have to be informed of
the childs exit.

I did not get any response, this may either be of no interest to others
:-( or nothing has done this and some may be interested in a result :-).

I played for a while and finally found a way. Well, it uses one
undocumented feature but even spawning under Windows itself is not
officially documented by Microsoft in the SDK documentation.

1. When you spawn a child program with INT 21 using the Microsoft
sample code posted here during the spawn-discussion, you get the
instance handle of the child program back in AX from the INT 21. For
old applications called using a PIF file (spawn with "PROG.PIF" as
executable name) you get the instance handle of WINOLDAP.MOD but this
works reliable only if not more than one old app is called.

2. You can test if the application still exists using the
GetModuleFilename() call with the handle from 1. The call returns the
length of the pathname of the program copied to your buffer or zero, if
it does not longer exist. Unexpectedly, the GetModuleUsage() call
returns one even if the instance handle given as argument is invalid

Now I test for existence of the child app using GetModuleFilename() in
a timer callback function after spawning the child and it seems to work
reliable even if I call an old application like MicroEMACS as the
editor via a PIF file.

I HOPE that Windows 3.0 provides an API extension for control of child
programs and spawning, the use of INT 21 is SO ugly ....


Kai Uwe Rommel
Munich
rommel@lan.informatik.tu-muenchen.dbp.de