Information Technology Reference
In-Depth Information
Fig. 11.
Synchronization between parallel execution threads
to the call for proposals or some specified deadline has passed. Only then the
protocol can proceed and the best bidder be selected. To define this kind of
synchronization at the modelling level we provide the following concepts:
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For each protocol instance in each actor we maintain a context in which the
state of the ongoing protocol execution can be maintained.
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In the protocol context we maintain a table which allows us to find for each
message sent all replies that have been received so far.
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Message flows can be marked as synchronized. A condition specifies what
needs to happen before the synchronization is successfully achieved. Such a
condition can be that a specific number of replies has been received or that a
specific event (e.g. a timeout) has occurred. All replies to a sent message that
are received after the synchronization was successfully achieved are ignored.
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A special variable MaxMessages in the protocol context gives the number of
how many messages were actually sent in the start message flow.
With this basic machinery it is already possible to design a large number of
complex protocols. A limitation of the presented concepts is that it is not possible
to model protocols where messages are sent out to more than one actor while the
sender waits for the replies to these messages in a concurrent manner. However,
because several agent instances can hide behind an actor the only limitation
is that sending concurrent messages to more than one group of agents hiding
behind one of the actors in the protocol diagram is not possible in one model.
However, because each of the agent instances at any specific stage of the protocol
execution (i.e. a specific message flow), where it receives a message, spawns off
an achieve goal event to produce the message that should be sent next, in the
process of achieving this event can of course again initiate the execution of an
