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

6.3 Communication 173
∞
client retrieve(PersonName)
dataBaseA
1. Buffered message flow with infinite buffer
n
client retrieve(PersonName)
dataBaseA
2. Buffered message flow with finite buffer
1
client retrieve(PersonName)
dataBaseA
3. Buffered message flow with one place buffer
Figure 6.8: Various Sorts of Buffered Message Flows
Summary:
A buffered message flow symbol represents an asynchronous message passing. The
sender can always send. A buffer always finishes the rendezvous with the sender. The
receiver can always read an available message from the buffer. The interpretation of the
buffered message flow symbol can be refined by adding information about the buffer
depth and the behaviour when the buffer is full. We recommend to create buffer full
notification and message discard notification.
6.3.6.5 Interrupt Message Symbol
The description of complex real-time reactive systems typically requires an interrupt
primitive. A hard real-time requirement will often require that the current course of
behaviour is postponed or ended in order to perform the required behaviour. The
modelling of an interrupt with the use of synchronous message passing means that the
receiving object must always be prepared to do the rendezvous for an interrupt message.
This message can always pass the object’s outer shell. The behaviour is constructed
such that the message interface cannot refuse the message. This notion is visualised
in the message symbol that breaks through the object’s shell. See Figure 6.10. The
description of the internal behaviour of an object that is specified to receive an interrupt