VDM-10 Language Manual

Chapter 6. Expressions
Examples: Using threadid’s it is possible to provide a VDM++ base class that implements a Javastyle
wait-notify in VDM++ using permission predicates. Any object that should be available
for the wait-notify mechanism must derive from this base class.
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class WaitNotify
instance variables
waitset : set of nat := {};
operations
protected wait: () ==> ()
wait() ==
let p = threadid
in (
AddToWaitSet( p );
Awake();
);
AddToWaitSet : nat ==> ()
AddToWaitSet( p ) ==
waitset := waitset union { p };
Awake: () ==> ()
Awake() ==
skip;
protected notify: () ==> ()
notify() ==
if waitset {}
then let arbitrary_process in set waitset
in waitset := waitset \ {arbitrary_process};
protected notifyAll: () ==> ()
notifyAll() ==
waitset := {};
sync
mutex(notifyAll, AddToWaitSet, notify);
per Awake => threadid not in set waitset;
end WaitNotify
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