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/*
* Licensed to the Apache Software Foundation (ASF) under one
* or more contributor license agreements. See the NOTICE file
* distributed with this work for additional information
* regarding copyright ownership. The ASF licenses this file
* to you under the Apache License, Version 2.0 (the
* "License"); you may not use this file except in compliance
* with the License. You may obtain a copy of the License at
*
* http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing,
* software distributed under the License is distributed on an
* "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
* KIND, either express or implied. See the License for the
* specific language governing permissions and limitations
* under the License.
*/
/**
* \file State.h
*/
#ifndef qpid_asyncStore_jrnl2_State_h_
#define qpid_asyncStore_jrnl2_State_h_
#include "qpid/asyncStore/jrnl2/Streamable.h"
namespace qpid {
namespace asyncStore {
namespace jrnl2 {
/**
* \brief Utility class to manage a simple state machine defined by an enumeration \a E.
*
* It is necessary that enumeration E has its default / initial value coded as value 0. This enumeration would
* be typically coded as follows:
* \code
* typedef enum {STATE1=0, STATE2, STATE3} myStates_t;
* class myStateMachine : State<myStates_t> {
* protected:
* void set(myStates_t s) { ... } // Implement state machine logic and transition checking here
* public:
* // State transition verbs
* void action1() { set(STATE2); }
* void action2() { set(STATE3); }
* };
* \endcode
*
* For child classes, the state machine transition logic is implemented in set(const E), and the state change
* verbs are implemented by calling set() with values from E. A call to reset() will return the state to the
* state numerically equal to 0, irrespective of the current state or state transition logic.
*
* Function getAsStr() returns the current state as a string, and is usually implemented by calling a local static
* function which translates the values of E into c-string literals.
*/
template <class E> class State : public Streamable {
public:
/**
* \brief Default constructor, which sets the internal state m_state to the state in E which is numerically
* equal to 0.
*/
State<E>() :
Streamable(),
m_state(E(0))
{}
/**
* \brief Constructor which sets the internal state m_state to the value \a s.
*/
State<E>(const E s) :
Streamable(),
m_state(s)
{}
/**
* \brief Copy constructor, which sets the internal state m_state to the same value as that of the copied
* instance \a s.
*/
State<E>(const State<E>& s) :
Streamable(),
m_state(s.m_state)
{}
/**
* \brief Virtual destructor
*/
virtual ~State()
{}
/**
* \brief Get the internal state m_state as an enumeration of type E.
*
* \returns The internal state m_state.
*/
virtual E get() const
{
return m_state;
}
/**
* \brief Get the internal state m_state as a c-string.
*
* \returns Internal state m_state as a c-string.
*/
virtual const char* getAsStr() const = 0;
/**
* \brief Reset the internal state m_state to the value of \a s or, if not supplied, to the state in E which is
* numerically equal to 0.
*
* \param s The state to which this instance should be reset. The default value is the member of E with a
* numerical value of 0.
*
* \note This call ignores the state transition logic in set() and forces the state to 0. This is not intended
* as a normal part of the state machine operation, but rather for reusing a state machine instance or in
* conditions where you need to force a change over the state machine logic. For cases where the normal state
* machine logic returns the state to its initial point, a verb should be created which uses set() and is
* subjected to the transition logic and checking of set().
*/
virtual void reset(const E s = E(0))
{
m_state = s;
}
/**
* \brief Stream the string representation of the internal state m_state.
*
* \param os Stream to which the string representation of the internal state m_state will be sent.
*/
virtual void toStream(std::ostream& os = std::cout) const
{
os << getAsStr();
}
protected:
E m_state; ///< Local state of this state machine instance.
private:
/**
* \brief Set (or change) the value of m_state. This function must implement the state machine checks for
* legal state change transitions, and throw an exception if an illegal state transition is requested.
*
* \param s State to which this machine should be changed.
*/
virtual void set(const E s) = 0;
/**
* \brief Compare the state \a s with the current state.
*
* \returns \b true if \a s is the same as internal state m_state, \b false otherwise.
*/
virtual bool is(const E s) const
{
return m_state == s;
}
};
}}} // namespace qpid::asyncStore::jrnl2
#endif // qpid_asyncStore_jrnl2_State_h_
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