Specification of Reactive Hardware/Software Systems - Electronic ...

12.3 The Essential Specification 391
immediately starts executing the initial loopForever method:
initial method call
loopForever
The loopForever method is defined as follows:
loopForever
acceptProduct;
storeProductInfo;
scheduleServices;
waitTilNextProductArrivalIsSafe;
loopForever
"Enter new product information and physical product."
"Fill a free Product Info Keeper with the accepted PI."
"Notify scheduler of product entrance and initial position."
"Arrange a wake up for a new arrival based
on the appropriate packet distance."
The loopForever method repeatedly executes the sequence of methods acceptProduct,
storeProductInfo, scheduleServices and waitTilNextProductArrivalIsSafe. These methods,
their names and their internal behaviour are derived from the narrative description of the
Product Flow Scenario (Subsection 12.3.3). After the waitTilNextProductArrivalIsSafe has
terminated, the loopForever method calls itself in a tail recursive manner. In the following
the acceptProduct, storeProductInfo, scheduleServices and waitTilNextProductArrivalIsSafe
methods are defined. The method behaviours are explained by comment listed between
quotes.
acceptProduct
i?accept(productInfo);
piti?productArrived;
piti?currentPosition
(initialPosition)
"Accept next product information."
"Wait until corresponding mailing product arrives."
"Read the initial position of the arrived product."
storeProductInfo
pihp?free(piKeeperId); "Read identification of free Product Info Keeper."
pihp!store
"Store product info in free Product Info Keeper."
(piKeeperId,productInfo)
scheduleServices
pihs!schedule
(piKeeperId,initialPosition)
waitTilNextProductArrivalIsSafe
id : ProductInputHandlerId
wake!wakeAt(initialPosition
+productDistance,myId);
wake?wakeup(id ¡ id = myId)
"Send schedule message to Service Scheduler."
"Declare local variable id."
"Ask Transporter Image to get woken when
the previous product has been transported
over a productDistance of distance."
Notice that the condition id=myId in the conditional receive statement wake?wakeup(id
id=myId) makes sure that the wakeup message is only accepted if it carries the correct
object identifier.