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\begin{vdm_al}
class MissileDetector is subclass of GLOBAL, BaseThread
-- the primary task of the MissileDetector is to
-- collect all sensor data and dispatch each event
-- to the appropriate FlareController
instance variables
-- maintain a link to each controller
ranges : map nat to (Angle * Angle) := {|->};
controllers : map nat to FlareController := {|->};
inv dom ranges = dom controllers;
-- collects the observations from all attached sensors
threats : seq of (EventId * MissileType * Angle * Time) := [];
-- status of the missile detector
busy : bool := false
operations
public MissileDetector: [ThreadDef] ==> MissileDetector
MissileDetector(tDef)==
(if tDef <> nil
then (period := tDef.p;
isPeriodic := tDef.isP;
);
BaseThread(self);
);
-- addController is only used to instantiate the model
public addController: FlareController ==> ()
addController (pctrl) ==
(dcl nid : nat := card dom ranges + 1;
atomic
(ranges := ranges munion {nid |-> pctrl.getAperture()};
controllers := controllers munion {nid |-> pctrl}
);
);
-- addThreat is a helper operation to modify the event
-- list. currently events are stored first come first served.
-- one could imagine using a different ordering instead.
public addThreat: EventId * MissileType * Angle * Time ==> ()
addThreat (evid,pmt,pa,pt) ==
(threats := threats ^ [mk_ (evid,pmt,pa,pt)];
busy := true );
-- getThreat is a local helper operation to modify the event list
private getThreat: () ==> EventId * MissileType * Angle * Time
getThreat () ==
(dcl res : EventId * MissileType * Angle * Time := hd threats;
threats := tl threats;
return res );
public isFinished: () ==> ()
isFinished () ==
for all id in set dom controllers do
controllers(id).isFinished();
protected Step: () ==> ()
Step() ==
( if threats <> []
then (def mk_ (evid,pmt, pa, pt) = getThreat() in
for all id in set dom ranges do
def mk_(papplhs, pappsize) = ranges(id) in
if canObserve(pa, papplhs, pappsize)
then controllers(id).addThreat(evid,pmt,pa,pt);
busy := len threats > 0);
);
sync
mutex (Step);
-- addThreat and getThreat modify the same instance variables
-- therefore they need to be declared mutual exclusive
mutex (addThreat,getThreat);
-- getThreat is used as a 'blocking read' from the main
-- thread of control of the missile detector
per getThreat => len threats > 0;
per isFinished => not busy
end MissileDetector
\end{vdm_al}
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