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Path: utzoo!attcan!uunet!tut.cis.ohio-state.edu!zaphod.mps.ohio-state.edu!sunybcs!planck!corsair!westley
From: westley@corsair.uucp (Terry J. Westley)
Newsgroups: comp.lang.ada
Subject: Re: Missing accept statement
Summary: Verdix detects deadlock; 9X Project Report includes this issue
Message-ID: <1990Mar19.182938.17283@planck.uucp>
Date: 19 Mar 90 18:29:38 GMT
References: <1990Mar15.203521.28171@planck.uucp> <4623@cbnewsl.ATT.COM>
Sender: news@planck.uucp (Usenet News)
Reply-To: westley%hercules@planck.UUCP (Terry J. Westley)
Organization: Calspan Corporation ATC  Buffalo, NY
List-Id: <comp.lang.ada>

In article <4623@cbnewsl.ATT.COM> arny@cbnewsl.ATT.COM (arny.b.engelson,wh,) writes:
>I could not find anything in the ARM (or the commentaries) that says a task
>MUST have an accept statement for every one of its declared entries, just
>that there may be more than one.  At a minimum, the ARM should be clarified
>on this point.  Assuming that this situation is therefore allowed, I would
>hope a compiler would at least produce a warning message.  I would expect
>any call to the entry to hang (unless it's a conditional/timed entry call).
>In the above example, since there are no calls to the entry, the compiler may
>have chosen not to bother with a warning message.  Try adding an entry call
>and see if the compiler warns you about the impending deadlock.

Yes, I had already tried calling the entry from within the procedure
body.  TASKING_ERROR occurred, presumably because the task terminated
before the rendezvous could occur.  The following mod to prevent
termination gets no warning from the compiler concerning the missing
entry.  But, happily, the run-time detects DEADLOCK.

procedure Missing_Task_Entry is
   task A_Task is
      entry Missing_Entry;
      entry Stop;
   end A_Task;
   task body A_Task is
   begin -- A_Task
      loop
         select
            accept Stop;
      	 or
            terminate;
	 end select;
      end loop;
   end A_Task;
begin -- Missing_Task_Entry
   A_Task.Missing_Entry;
end Missing_Task_Entry;

Detection is really only this implementation, however.  Since posting
the first message concerning this, I have received the January, 1990,
Supplement 1 of the Ada 9X Project Report.  Page 9-110, Revision Request
#0216, addresses this issue.

Terry J. Westley
Arvin/Calspan Advanced Technology Center
P.O. Box 400, Buffalo, NY 14225
acsu.buffalo.edu!planck!hercules!westley