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

286 Process Part of POOSL
in
x
Sender Receiver
y
Figure 9.1: A Simple Handshake Protocol
will demonstrate that the protocol behaves as a 1-place buffer. The protocol, consisting
of a Sender process and a Receiver process, is visualised in figure 9.1.
The Sender can receive some data from channel in and this data is delivered by the
Receiver at channel out. Externally the protocol behaves as a 1-place buffer. The protocol
is specified as follows:
(Sender ¢ Receiver) £
x¥ y¦ ¥
¥ Sys p Sys ¥
For reasons of simplicity we assume that there are no non-primitive data classes, so
Sys . Sysp consists of process classes Sender and Receiver. It is defined as Sysp
7
process class Sender
instance variables
communication channels in x y
message interface in?receive(dS) x!transfer(dS) y?ack
initial method call start
instance methods start ¡ dS ¡
in?receive(dS); x!transfer(dS); y?ack; start
¡ ¡
process class
instance variables
Receiver
communication channels x y out
message interface x?transfer(dR) out!deliver(dR) y!ack
initial method call start
instance methods start dR
x?transfer(dR); out!deliver(dR); y!ack; start
Configuration ¢ (Sender Receiver) £
¥ x¥ y¦ ¥ Sysp ¥ Sys reflects the state of the protocol
where both the sender and the receiver are not initialised yet. The actual computation
starts by initialising either the sender or the receiver. By axiom (8’) we have
Sys ¥ Sender¥ p ¥
Sys £ £
Sender £ ¤ ¦ ¥
¥ proc start §
¥ ¤ ¥ Sys p ¥ Sys
7 The specifications and configurations use some obvious syntactic simplifications.
ou t