Quelle TimeStamp.vdmpp Sprache: VDM

\begin{vdm_al}
class TimeStamp

\end{vdm_al}
Class used for concurrent VDM++ models. All threads should call the following operations:
- WaitRelative(t): makes the thread periodic with t = the period
- NotifyAll(): notified all threads sleeping in the wakeUpMap
- Awake(): puts the thread to sleep - will wakeup when t time units has passed

The step length with which the currentTime is incremented
\begin{vdm_al}
values

public stepLength : nat = 1;

instance variables

currentTime  : nat   := 0;
wakeUpMap    : map nat to nat := {|->};
--syncWithTimeInc : set of nat := {};
--syncWithTimeIncCurrent : set of nat := {};

operations

\end{vdm_al}
WaitRelative: sleeps the calling thread for 'val' time units - relative to the currentTime
\begin{vdm_al}

public WaitRelative : nat ==> ()
WaitRelative(val) ==
  AddToWakeUpMap(threadid, currentTime + val);

\end{vdm_al}
WaitAbsolute: sleeps the calling thread undtil a specific time
\begin{vdm_al}

public WaitAbsolute : nat ==> ()
WaitAbsolute(val) ==
  AddToWakeUpMap(threadid, val);

\end{vdm_al}
AddToWakeUpMap: Utility operation - adding the thread to the wakeUpMap
\begin{vdm_al}

AddToWakeUpMap : nat * nat ==> ()
AddToWakeUpMap(tId, val) ==
   wakeUpMap := wakeUpMap ++ { tId |-> val };

\end{vdm_al}
NotifyThread: notified a specific thread - removing it from the wakeUpMap
\begin{vdm_al}

public NotifyThread : nat ==> ()
NotifyThread(tId) ==
wakeUpMap := {tId} <-: wakeUpMap;

\end{vdm_al}
NotifyAll: notifies all threads - waking up threads which wakeUpTime is up
\begin{vdm_al}

public NotifyAll : () ==> ()
NotifyAll() ==
  let threadSet : set of nat = {th | th in set dom wakeUpMap & wakeUpMap(th) <= currentTime }
  in
    for all t in set threadSet
    do
      NotifyThread(t);

\end{vdm_al}
NotifyAndIncTime: Must only be used by ONE thread - usually the Environment thread.
Increments the currentTime with stepLength time units, and notifies all threads.
\begin{vdm_al}

public NotifyAndIncTime : () ==> ()
NotifyAndIncTime() ==
(
    currentTime := currentTime + stepLength;
    NotifyAll();
-- syncWithTimeIncCurrent := syncWithTimeInc;
);

\end{vdm_al}
GetTime: Returns the currentTime.
\begin{vdm_al}

public GetTime : () ==> nat
GetTime() ==
  return currentTime;

\end{vdm_al}
Awake: Used to sleep threads - will not wake up until threadid is removed from wakeUpMap
\begin{vdm_al}

public Awake: () ==> ()
Awake() == skip;

\end{vdm_al}
SyncWithTimeIncrement: Called by threads which need to finish their loop/operation before time can be increased.
YieldTimeIncrement is call when a thread is ready to a time increment.
Once a thread has call SyncWithTimeIncrement is must call YieldTimeIncrement eventually, otherwise time increment
will be prevented
\begin{vdm_al}

--public SyncWithTimeIncrement : () ==> ()
--SyncWithTimeIncrement() ==
--(
-- syncWithTimeInc := syncWithTimeInc union {threadid}; --keep track of all
-- syncWithTimeIncCurrent := syncWithTimeIncCurrent union {threadid}; --include in current sync round
-- skip;
--);

--public YieldTimeIncrement: () ==> ()
--YieldTimeIncrement()==
--(
-- syncWithTimeIncCurrent := syncWithTimeIncCurrent \ {threadid};
-- skip
--);

sync
  per Awake => threadid not in set dom wakeUpMap;

  per NotifyAndIncTime => (card {th | th in set dom wakeUpMap & wakeUpMap(th) = currentTime +1} > 0) ;  --The magic one,  only allow run
--  per NotifyAndIncTime => ({th | th in set dom wakeUpMap & wakeUpMap(th) <= currentTime} inter syncWithTimeIncCurrent) = {};

  mutex(NotifyAll);
  mutex(AddToWakeUpMap);
  mutex(AddToWakeUpMap, NotifyAll);
--  mutex(SyncWithTimeIncrement);
--  mutex(YieldTimeIncrement);
--  mutex(SyncWithTimeIncrement, YieldTimeIncrement, NotifyAndIncTime);

end TimeStamp
\end{vdm_al}

\begin{rtinfo}[TimeStamp`NotifyAndIncTime]
{vdm.tc}[TimeStamp]
\end{rtinfo}

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