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From: ncohen@watson.ibm.com (Norman H. Cohen)
Subject: Re: ADA task
Date: 1996/09/16
Message-ID: <51jnm6$16qc@watnews1.watson.ibm.com>#1/1
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distribution: world
references: <5174qu$o1p@nr1.ottawa.istar.net>
 <51cjp0$q7k@watnews1.watson.ibm.com> <51ep6c$cut@nr1.ottawa.istar.net>
organization: IBM T.J. Watson Research Center
reply-to: ncohen@watson.ibm.com
newsgroups: comp.lang.ada
Date: 1996-09-16T00:00:00+00:00
List-Id: <comp.lang.ada>


In article <51ep6c$cut@nr1.ottawa.istar.net>, "Roumen Roupski"
<Roumen.Roupski@Pika.Ca> writes: 

|> In your example above you use Calendar package. I saw GNAT has
|> Ada.Real_Time package. Should I use it instead of Calendar?

Old habits die hard.  Yes, you should.

Ada.Real_Time is provided by every Ada-95 compiler that supports the
Real-Time Annex and is guaranteed to provide more accurate time
measurement than Ada.Calendar is guaranteed to provide.  The delay-until
statement works not only with type Ada.Calendar.Time, but also with type
Ada.Real_Time.Time.

Paragraph D.9(13) of the Ada-95 RM requires an implementation supporting
the Real-Time Annex to guarantee an upper bound on the difference between
the delay time specified in the delay-until statement and the time at
which execution of the delayed task actually resumes.  This can be used
to address Ken Garlington's concerns about guaranteeing on-time execution
of a periodic piece of work.  (Careful analysis, such as rate-monotonic
scheduling, is necessary to ensure that the processor will be available,
i.e., that all other tasks of equal or higher priority will be suspended,
when a delay expires; the guarantees in paragraph D.9(13) ensure that
under those conditions a sleeping task awakens quickly when the delay
expires.)

--
Norman H. Cohen    ncohen@watson.ibm.com