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POImplementing Hierarchical State Machines in C
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2010-08-17T23:07:58.853
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2014-12-29T11:19:35.167
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I'm a bit confused about how to implement my state machine. I already know it's hierarchical since some states share the same action. I determine what I need to do by these parameters: <ul> <li>Class (Values are: Base, Derived, Specific)</li> <li>OpCode</li> <li>Parameter 1 - optional</li> <li>Parameter 2 - optional</li> </ul> My hierarchy is determined by the Class and the OpCode represents the action. Derived can use the OpCodes of Base and Specific can use OpCodes of both Base and Derived. The naive implementation is the following: <pre><code>void (*const state_table [MAX_CLASSES][MAX_OPCODES]) (state *) { {base_state1, base_state2, NULL, NULL}, {base_state1, base_state2, derived_state1, NULL}, {base_state1,base_state2, derived_state1, specific_state3}, }; void dispatch(state *s) { if (state_table[s->Class][s->OpCode] != NULL) state_table[s->Class][s->OpCode](s); } </code></pre> This will turn unmaintainable really quick. Is there another way to map the state to a superclass? EDIT: Further calcualtion leads me to think that I'll probably use most if not all OpCodes but I will not use all of the Classes available to me. Another clarification: Some OpCodes might be shared through multiple derived and base Classes. For example: <ul> <li>I have a Class called Any which is a Base class. It has the OpCodes: STATE_ON, STATE_OFF, STATE_SET.</li> <li>I have another Class called MyGroup which is a Derived class. It has the OpCodes: STATE_FLIP, STATE_FLOP.</li> <li>The third Class is a Specific class called ThingInMyGroup which has the OpCode: STATE_FLIP_FLOP_AND_FLOOP.</li> </ul> So a message with class Any is sent from the server, recieved in all clients and processed. A message with class MyGroup is sent from the server, recieved in all clients and processed only on clients that belong to MyGroup, any OpCodes that are valid for the Any class are valid for the MyGroup class. A message with class ThingInMyGroup is sent from the server, recieved in all clients and processed only on clients that belong to MyGroup and are a ThingInMyGroup*, any **OpCodes that are valid for the Any class and MyGroup class are valid for the ThingInMyGroup class. After a message is received the client will ACK/NACK accordingly. I prefer not to use switch cases or const arrays as they will become unmaintainable when they get bigger. I need a flexible design that allows me: <ol> <li>To specify which OpCodes are available for each Class.</li> <li>To specify a superclass for each Class and through that specification to allow me to call the function pointer that is represented by the current OpCode.</li> </ol>
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<c><design><finite-state-machine><hsm>
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Implementing Hierarchical State Machines in C
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