A state machine that formalizes a distributed mutual exclusion protocol called the Suzuki-Kasami protocol is graphically animated. The network with which messages are exchanged among nodes in the protocol is displayed as follows: some limited number of messages in the network are displayed and the others are depressed when there are many messages in the network. We prepare one place dedicated to the message that has been just put into the network by a node (or just sent by a node) and one place dedicated to the message that has been just received by a node (just deleted from the network by a node). The main purpose of graphically animating state machines is to make it possible for humans to perceive characteristics or properties of the state machines by observing their graphical animations. We can guess some properties of the state machine formalizing the Suzuki-Kasami protocol by observing graphical animations of the state machine and confirm them by model checking, which demonstrates that state machine graphical animations could make humans perceive state machine properties.
MCS shared-memory mutual exclusion protocol is used as an example to demonstrate that state picture designs should be better visualized. A case study has been conducted in which we demonstrate that better visualized state pictures make it possible to conjecture more non-trivial characteristics of state machines than the old state pictures. The lessons learned acquired through the case study are summarized as new tips on how to make state picture designs.
The mutual exclusion protocol invented by Mellor-Crummey and Scott (called MCS protocol) is used to exemplify that state picture designs based on which the state machine graphical animation (SMGA) tool produces graphical animations should be better visualized. Variants of MCS protocol have been used in Java virtual machines and therefore the 2006 Edsger W. Dijkstra Prize in Distributed Computing went to their paper on MCS protocol. The new state picture design of a state machine formalizing MCS protocol is assessed based on Gestalt principles, more specifically proximity principle and similarity principle. We report on a core part of a formal verification case study in which the new state picture design and the SMGA tool largely contributed to the successful completion of the formal proof that MCS protocol enjoys the mutual exclusion property. The lessons learned acquired through our experiments are summarized as two groups of tips. The first group is some new tips on how to make state picture designs. The second one is some tips on how to conjecture state machine characteristics by using the SMGA tool. We also report on one more case study in which the state picture design has been made for the mutual exclusion protocol invented by Anderson (called Anderson protocol) and some characteristics of the protocol have been discovered based on the tips.
A state machine that formalizes a distributed mutual exclusion protocol called the Suzuki-Kasami protocol is graphically animated. The messages that have been just put into (or sent) and deleted from (or received) the network are crucial information and then visually explicitly displayed on the designated places in a state picture. The protocol uses some pieces of information that are seemingly owned by each node but actually shared by all nodes. The pieces of information are visually explicitly displayed on two designated places. One main purpose of graphically animating state machines is to make it possible for humans to visually perceive characteristics or properties of the state machines. We demonstrate that carefully observing graphical animations makes it possible for human users to perceive some characteristics or properties of the state machine formalizing the Suzuki-Kasami protocol and the properties are confirmed by model checking. To make it more likely for human users to be able to perceive such properties, it is necessary to design good state pictures. We summarize some tips on how to design good state pictures for mutual exclusion protocols.
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