* (Newbie) intertask communication
@ 2001-04-06 17:37 Pieter Thysebaert
2001-04-06 20:46 ` Mark Lundquist
0 siblings, 1 reply; 2+ messages in thread
From: Pieter Thysebaert @ 2001-04-06 17:37 UTC (permalink / raw)
Hi....
I'm trying to have two tasks interact (using entry/accept).
In fact we have this assignment where we are supposed to (not in reality)
monitor some patient's heartbeat.
So I created two task types : patient and monitor
The idea is that the patient will call the function (entry) beat on his/her
associated monitor;
the monitor will accept beat() calls and will display a warning when not
receiving a heartbeat for two (or x) seconds
So this is my monitor:
task body monitortask is
id : Integer;
begin
accept start(patient_id : Integer) do
id := patient_id;
end;
loop
select
accept beat do
PutLine(<patient id is alivestuff>);
end;
or
delay 2;
sound_alarm();
end loop;
end monitortask;
And the patient :
task body patienttask is
begin
accept start(m : monitortask) do
loop
delay <random value between 1 and 4 seconds>;
m.beat;
end loop;
end;
end patienttask;
My problem/question is : this stuff only works when m.start is called first
in a testprogram, end then p.start
(m : monitortask and p : patientask) - the testprogram blosk on the
patient.start thing
That's because I have the loop _IN_ the patient's accept statement.
Of course what I want is more like :
task body patienttask is
mymonitor : monitortask;
begin
accept start(m : monitortask) do
mymonitor := m;
end;
loop
.....do stuff but call mymonitor.beat;
which will not block the testprogram calling p.start;
Unfortunately, the assignment to mymonitor does not work like this.
How would I pass the "name" of a task to antoher task to have it use that
one ?
And how can I save a "reference"to a task ?
Pieter
^ permalink raw reply [flat|nested] 2+ messages in thread
* Re: (Newbie) intertask communication
2001-04-06 17:37 (Newbie) intertask communication Pieter Thysebaert
@ 2001-04-06 20:46 ` Mark Lundquist
0 siblings, 0 replies; 2+ messages in thread
From: Mark Lundquist @ 2001-04-06 20:46 UTC (permalink / raw)
Pieter Thysebaert <pieter.thysebaert@pandora.be> wrote in message
news:q9nz6.15400$ii5.1263786@afrodite.telenet-ops.be...
> Hi....
>
> I'm trying to have two tasks interact (using entry/accept).
> In fact we have this assignment where we are supposed to (not in reality)
> monitor some patient's heartbeat.
>
>
[example snipped...]
OK, this post was a prime example of the right way to ask for help with a
homework assignment! Thanks, Pieter!
> How would I pass the "name" of a task to antoher task to have it use that
> one ?
> And how can I save a "reference"to a task ?
Use an access type designating a task type. This can be used for any formal
parameter (to a "callable entity", i.e. subprogram or entry, or to a
generic), and of course you can declare a variable of this type in your
Patient task and assign to it, to save your reference to the other task. So
for example:
task type Monitor is
.
.
type Access_Monitor is access all Monitor;
.
.
Monitor_1 : aliased Monitor;
Patient_1.Start (Monitor_1'Access);
Also, a task type can have discriminants. So you can do this:
task type Patient (Associated_Monitor : Access_Monitor)
For that matter, it can be an "access discriminant" (then you no longer need
the access type, and you get a built-in null check):
task type Patient (Associated_Monitor : access Monitor);
Hope this helps,
-- mark
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