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Newsgroups: comp.lang.ada
Date: Sun, 4 Mar 2018 20:08:23 -0800 (PST)
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Subject: Re: multiple delay alternative
From: Bojan Bozovic <bozovic.bojan@gmail.com>
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Xref: reader02.eternal-september.org comp.lang.ada:50819
Date: 2018-03-04T20:08:23-08:00
List-Id: <comp.lang.ada>

On Sunday, March 4, 2018 at 7:22:58 PM UTC+1, Mehdi Saada wrote:
> Hello !
>=20
> In https://perso.telecom-paristech.fr/pautet/Ada95/chap28.htm, Ada tutori=
al's paragraph on the delayed rendezvous, it says the general form of this =
construct is:
> select=20
>          delay <time>;
>          <entry call>;
>     or=20
>          delay <time>;
>          <entry call>;
>     or
>          delay <time>;
>          <entry call>;
>     end select;
>=20
> But in the RM timed entry calls are featured like this:
> timed_entry_call ::=3D=20
>   select
>    entry_call_alternative
>   or
>    delay_alternative
>   end select;
>=20
> What should I understand ?
> I have trouble understanding the first construct, otherwise than "if noth=
ing happens before n seconds, do that, AND THEN, if nothing happens before =
n2 seconds, do that, etc... as if
> select
>      delay 11.0;
>      A;
> or
>      delay 12.0
>      B;
> end select;
>=20
> is equivalent to
> delay 10.0
> select
>      delay 1.0;
> or
>      delay 2.0;
> end select;
> But it's likely that I didn't guess right.

http://www.adaic.org/resources/add_content/docs/95style/html/sec_6/6-1-7.ht=
ml

"The Ada language definition only guarantees that the delay time is a minim=
um. The meaning of a delay or delay until statement is that the task is not=
 scheduled for execution before the interval has expired. In other words, a=
 task becomes eligible to resume execution as soon as the amount of time ha=
s passed. However, there is no guarantee of when (or if) it is scheduled af=
ter that time because the required resources for that task might not be ava=
ilable at the expiration of the delay . "

Delay will simply stop execution (not schedule the task) for an amount of t=
ime until the condition needed is met, and then process the task entry. If =
you have both delayed and non-delayed entries for the same "accept" in "sel=
ect" non-delayed will be executed (as far as I can tell).

I myself am willing to wait and see what the more experienced have to say o=
n this matter, as AdaTutor by John J. Herro I'm using don't cover delayed t=
ask entries at all.