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From: eachus@spectre.mitre.org (Robert I. Eachus)
Subject: Re: is there a 'wait' command in Ada
Date: 1996/12/10
Message-ID: <EACHUS.96Dec9193401@spectre.mitre.org>#1/1
X-Deja-AN: 203264260
references: <Pine.SOL.3.91.961129204410.12801A-100000@sirius>
organization: The Mitre Corp., Bedford, MA.
newsgroups: comp.lang.ada
Date: 1996-12-10T00:00:00+00:00
List-Id: <comp.lang.ada>



   "David C. Hoos, Sr." <david.c.hoos.sr@ada95.com> writes:

   >Have you ever thought of using the UNIX select function to implement a
   >"delay that doesn't burn CPU cycles or issue s shell command?
   >All you need to do is set all three of the file descriptor mask addresses
   >to null addresses, and point to a timeval structure initialized with the
   >desired delay time, and the UNIX kernel will swap you out until the time
   >has expired.  Works like a champ!

   It looks like what everyone is looking for is an implementation of
delay with the effective logic:

   if Number_of_Tasks = 1
   then Unix.Sleep(N) 
   else Ada.Runtime.Delay(N);
   end if;

   (I plan on general prinicples to ignore any discussion of the
"extra overhead" in doing things this way. If you execute a delay
statement you should only complain if it doesn't take as long as
requested, and a busy wait is an appropriate implementation for very
short delays.)

   Also it should be the case that a runtime which supports pragma
Restrictions(Max_Tasks => 0) should not load the tasking runtime, even
if this requires special support for (more efficient) protected types.

--

					Robert I. Eachus

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