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

176 Modelling of Concurrent Reactive Behaviour
reply flow. Like the message on an interrupt message flow this message can always pass
the object’s outer shell. The behaviour at the receiver side must prepare an answer. The
sender must wait for this answer. This notion is visualised in the message symbol that
breaks through the object’s shell and also shows a reversed reply arrow head, see Figure
6.11. Like the interrupt message flow, the interrupt with reply flow can be used to model
two cases:
reliable
guard
an abort with reply and waiting;
emergency/
received,notReceived
process B
Figure 6.11: An Interrupt with Reply Flow
an interrupt with reply and waiting.
An abort statement specifies that a piece of behaviour description can be stopped at
the instants between the execution of the individual process statements. The behaviour
specified after the abort statement must produce a reply. Alternative continuing behaviour
can be specified as well. The original behaviour which was interrupted by the
abort is not resumed.
An interrupt statement specifies that a piece of behaviour description can be interrupted
at the instants between the execution of the statements, and can be resumed later, so that
the original behaviour is continued from the place where it was interrupted. Since the
production of reply is specified, the interrupt behaviour must produce a reply.
Summary:
An interrupt with reply symbol represents a synchronous message passing that can be
forced to happen after the current atomic process statement is finished. In addition the
symbol shows that the sender must wait for a reply. POOSL offers two primitives for the
description of the behaviour of an interrupt flow. An interrupt specifies that the current
behaviour can be resumed. An abort specifies that the current behaviour is interrupted
but cannot be resumed.
6.3.7 Multi-Way Communication
Multi-way communication means that a message can be received simultaneously by more
than one receiver, see Figure 6.12. The sender process sends one single message m that
can be received simultaneously by three processes A, B and C. This implies that we
need a common channel with the four process objects connected to it. By splitting the
message flow we visualise that message m sent must be received simultaneously by all