Hi David--

    It seems that learning PL/I is two steps forward and one step back!
It may be almost as bad as C++ .

    I have a little PL/I utility that I use frequently.  It is a local
alarm clock, used to interrupt my session at the console when it is time
to go do something else.  When I invoke it (from a program-object icon)
the window tells me the current system time and asks me to set an alarm
time.  It corrects the time I give it, by 12-hour increments, until that
time is at least 1 minute later than the current system time (up to noon
the following day) and then goes into a coma (DELAY) until the set-time
arrives.  To activate the alarm, it attaches a second thread that beeps
for half of each second while the first thread is blocked until I press
a key (while its window has the focus).  At the keypress, it issues a
DETACH for the second thread and terminates the program with EXIT.  The
beeping stops, the window closes, and all is serene.

    It works as advertised, except for the wrong reasons!  I was doing a
little testing with OS20MEMU to check memory usage in the several phases
of the program, and decided I wanted to see how much of the resources
devoted to the second thread were recovered after that thread was
DETACHed.  So I put in a second "press any key" between the DETACH and
the EXIT.  I discovered that the beeping didn't stop until the second
keypress, which meant that DETACH didn't, EXIT did!  Back to RTFM!  It
appears that I should have used STOP to stop the beeping, not DETACH.
This worked as it should have. 

    Big question:  What does DETACH do, if anything?  I find the manual
very murky on this point.  A small exposition on the subject would be
appreciated.

    Thanks,

          --Murray
 (back to novice class)
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 * MR/2 2.25 #120 * Which direction is forward?
                                                                                 
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