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Hierarchical_State_Machine Class Reference

Collaboration diagram for Hierarchical_State_Machine:

Detailed Description

For details refer to the article on Hierarchical State Machines

In conventional state machine design, all states are considered at the same level. The design does not capture the commonality that exists among states. In real life, many states handle most messages in similar fashion and differ only in handling of few key messages. Even when the actual handling differs, there is still some commonality. Hierarchical state machine design captures the commonality by organizing the states as a hierarchy. The states at the higher level in hierarchy perform the common message handling, while the lower level states inherit the commonality from higher level ones and perform the state specific functions. This examples explores hierarchichal state machines using an example of a hardware unit that can be in the following states:

• Inservice state
  • Active state
  • Standby state
• Out_Of_Service
  • Suspect state
  • Failed state

Definition at line 32 of file Hierarchical_State_Machine.h.

Public Member Functions
void	On_Message (const Message *p_Message)
	Receive methods and invoke the handler for the currently active state.
Private Member Functions
void	Next_State (Unit_State &r_State)
	This private method changes the state for the state machine.
Private Attributes
Unit_State *	p_Current_State
	Pointer to the current state.
Static Private Attributes
Active	Active_State
	Static declaration of Active state. Static declarations share the same states across multiple instances.
Standby	Standby_State
	Static declaration of Standby state.
Suspect	Suspect_State
	Static declaration of Suspect state.
Failed	Failed_State
	Static declaration of Failed State.

Member Function Documentation

void Hierarchical_State_Machine::Next_State (  Unit_State &  r_State  )  [private]

This private method changes the state for the state machine. The p_Current_State variable is updated with the new state Parameters: r_State  Reference to the desired next state Definition at line 169 of file Hierarchical_State_Machine.h. 00170 { 00171 p_Current_State = &r_State; 00172 }

void Hierarchical_State_Machine::On_Message (  const Message *  p_Message  )

Receive methods and invoke the handler for the currently active state. Note that p_Current_State has already been set to the current state. Parameters: p_Message  Pointer to the message being processed. Definition at line 17 of file Hierarchical_State_Machine.cpp. 00018 { 00019 switch (p_Message->GetType()) 00020 { 00021 case Message::FAULT_TRIGGER: 00022 p_Current_State->On_Fault_Trigger(*this, p_Message); 00023 break; 00024 00025 case Message::SWITCHOVER: 00026 p_Current_State->On_Switchover(*this, p_Message); 00027 break; 00028 00029 case Message::DIAGNOSTICS_PASSED: 00030 p_Current_State->On_Diagnostics_Passed(*this, p_Message); 00031 break; 00032 00033 case Message::DIAGNOSTICS_FAILED: 00034 p_Current_State->On_Diagnostics_Failed(*this, p_Message); 00035 break; 00036 00037 case Message::OPERATOR_INSERVICE: 00038 p_Current_State->On_Operator_Inservice(*this, p_Message); 00039 break; 00040 00041 default: 00042 assert(false); 00043 break; 00044 } 00045 }

• Hierarchical_State_Machine.h
• Hierarchical_State_Machine.cpp

Generated on Sun Feb 13 21:30:28 2005 for Object Oriented Design Examples by 1.3.4

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