Hello Mike!

Saturday April 06 1996 19:01, Mike Bilow wrote to All:

MB> I have a situation in which I want to run a REXX script periodically, but
MB> with the ability to time out if something goes wrong.  For example, I have
MB> a program (BinkleyTerm) which is started from a batch file and which
MB> is usually running, but which exits with certain errorlevels at
MB> scheduled times.  One of these errorlevels causes the parent batch file to
MB> run a particular REXX script.  Because there are certain real-time
MB> constraints, I need to be able to limit the amount of time that the REXX
MB> script runs, killing it ungracefully if necessary as a last ditch effort to
MB> keep the system running.

I spent a few hours learning rexx to solve this. (Thank's for the excuse,
I've been meaning to get around to it for awhile :-)

MB> If the program in question was an EXE rather than a REXX script, then
MB> I
MB> could use something like DosKillProcess().  But this does not work because
MB> simply killing the REXX script process has the effect of killing the parent
MB> batch, too, since CMD itself is the process.

I looked first as DosSendSignalException() but rexx doesn't use signal's to
handle ctrl-c AFAICT.

MB> The ideal approach to doing a time out would be to build it directly
MB> into
MB> the program, which would naturally be accomplished by multithreading.
MB> However, there is no way to multithread a REXX program, as far as I know.

Here is where you go astray! I fooled around with some functions and came
up with a multithreaded rexx program  (ok, it does use some c
functions)

MB> The second approach is to devise some sort of REXX DLL which the REXX
MB> script could use to set a time out on itself.  The problem here is again
MB> that the DLL would only be able to kill the REXX process, which is really
MB> that of the parent batch.  I would think that there is some way to do this,
MB> since hitting Ctrl-Break during a REXX script will terminate it
MB> without terminating the parent batch, but I am not sure exactly how to make
MB> that distinction.

It's sorta like this idea. I've setup 4 rexx functions, it could be done in
two however.

GetPID()
   -   just returns the process id
GetTID()
   -   same for the thread id
TimeOut(PID, TID, milliseconds)
   -   sets up the thread and starts it
CancelTimeOut(PID,TID)
   -   posts the event semaphore
RexxTimeoutThread(ULONG)
   -   does the dirty work

What basically happens is you call TimeOut() with the relevant data. It
starts the thread which in turn creates an event semaphore derived from the
pid & tid. It then blocks on the semaphore until either you call
CancelTimeOut() or it times out. In the event of it timing out, it calls
the rexx function RexxSetHalt() which sends a halt to the rexx interpreter.

In your rexx script, you set in to jump to a label on reciept of a halt and
volia! you even get to do cleanup .

The source is pretty messy as I was mostly just experimenting but it should
be understandable. I think it's even pretty portable as I tried to stick to
OS/2 API's.

There are 5 files,

test.cpp   :source
test.h     :header
test.def   :just has 'LIBRARY TEST'
test1.cmd  :parent rexx script
test2.cmd  :child rexx script

I'll post them in the next few messages.

Doug

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