The Boost Statechart Library

Reference

Contents

Concepts

Scheduler

FifoWorker

ExceptionTranslator

StateBase

SimpleState

State

Event

state_machine.hpp

Class template state_machine

asynchronous_state_machine.hpp

Class template asynchronous_state_machine

event_processor.hpp

Class template event_processor

fifo_scheduler.hpp

Class template fifo_scheduler

exception_translator.hpp

Class template exception_translator

null_exception_translator.hpp

Class null_exception_translator

 

simple_state.hpp

Enum history_mode

Class template simple_state

state.hpp

Class template state

shallow_history.hpp

Class template shallow_history

deep_history.hpp

Class template deep_history

 

event_base.hpp

Class event_base

event.hpp

Class template event

 

transition.hpp

Class template transition

in_state_reaction.hpp

Class template in_state_reaction

termination.hpp

Class template termination

deferral.hpp

Class template deferral

custom_reaction.hpp

Class template custom_reaction

result.hpp

Class result

Concepts

Scheduler concept

A Scheduler type defines the following:

• What is passed to the constructors of event_processor<> subtypes and how the lifetime of such objects is managed
• Whether or not multiple event_processor<> subtype objects can share the same queue and scheduler thread
• How events are added to the schedulers' queue
• Whether and how to wait for new events when the schedulers' queue runs empty
• Whether and what type of locking is used to ensure thread-safety
• Whether it is possible to queue events for no longer existing event_processor<> subtype objects and what happens when such an event is processed
• What happens when one of the serviced event_processor<> subtype objects propagates an exception

For a Scheduler type S and an object cpc of type const S::processor_context the following expressions must be well-formed and have the indicated results:

Expression	Type	Result
cpc.my_scheduler()	S &	A reference to the scheduler
cpc.my_handle()	S::processor_handle	The handle identifying the event_processor<> subtype object

To protect against abuse, all members of S::processor_context should be declared private. As a result, event_processor<> must be a friend of S::processor_context.

FifoWorker concept

A FifoWorker type defines the following:

• Whether and how to wait for new work items when the internal work queue runs empty
• Whether and what type of locking is used to ensure thread-safety

For a FifoWorker type F, an object f of that type, a const object cf of that type, a parameterless function object w of arbitrary type and an unsigned long value n the following expressions/statements must be well-formed and have the indicated results:

Expression/Statement	Type	Effects/Result
F::work_item	boost::function0< void >
F() or F( false )	F	Constructs a non-blocking (see below) object of the FifoWorker type. In single-threaded builds the second expression is not well-formed
F( true )	F	Constructs a blocking (see below) object of the FifoWorker type. Not well-formed in single-threaded builds
f.queue_work_item( w );		Constructs and queues an object of type F::work_item, passing w as the only argument
f.terminate();		Creates and queues an object of type F::work_item that, when later executed in operator()(), leads to a modification of internal state so that terminated() henceforth returns true
cf.terminated();	bool	true if terminate() has been called and the resulting work item has been executed in operator()(). Returns false otherwise Must only be called from the thread that also calls operator()()
f( n );	unsigned long	Enters a loop that, with each cycle, dequeues and calls operator()() on the oldest work item in the queue. The loop is left and the number of executed work items returned if one or more of the following conditions are met: f.terminated() == true The application is single-threaded and the internal queue is empty The application is multi-threaded and the internal queue is empty and the worker was created as non-blocking n != 0 and the number of work items that have been processed since operator()() was called equals n If the queue is empty and none of the above conditions are met then the thread calling operator()() is put into a wait state until f.queue_work_item() is called from another thread. Must only be called from exactly one thread
f();	unsigned long	Has exactly the same semantics as f( n ); with n == 0 (see above)

ExceptionTranslator concept

An ExceptionTranslator type defines how C++ exceptions occurring during state machine operation are translated to exception events.

For an ExceptionTranslator object et, a parameterless function object a of arbitrary type returning result and a function object eh of arbitrary type taking a const event_base & parameter and returning result the following expression must be well-formed and have the indicated results:

Expression	Type	Effects/Result
et( a, eh );	result	Attempts to execute return a(); If a() propagates an exception, the exception is caught Inside the catch block calls eh, passing a suitable stack-allocated model of the Event concept Returns the result returned by eh

StateBase concept

A StateBase type is the common base of all states of a given state machine type. state_machine<>::state_base_type is a model of the StateBase concept.

For a StateBase type S and a const object cs of that type the following expressions must be well-formed and have the indicated results:

Expression	Type	Result
cs.outer_state_ptr()	const S *	0 if cs is an outermost state, a pointer to the direct outer state of cs otherwise
cs.dynamic_type()	S::id_type	A value unambiguously identifying the most-derived type of cs. S::id_type values are comparable with operator==() and operator!=(). An unspecified collating order can be established with std::less< S::id_type >. In contrast to typeid( cs ), this function is available even on platforms that do not support C++ RTTI (or have been configured to not support it)
cs.custom_dynamic_type_ptr<   Type >()	const Type *	A pointer to the custom type identifier or 0. If != 0, Type must match the type of the previously set pointer. This function is only available if BOOST_STATECHART_USE_NATIVE_RTTI is not defined

SimpleState concept

A SimpleState type defines one state of a particular state machine.

For a SimpleState type S and a pointer pS pointing to an object of type S allocated with new the following expressions/statements must be well-formed and have the indicated effects/results:

Expression/Statement	Type	Effects/Result/Notes
simple_state<   S, C, I, h > * pB =     pS;		simple_state< S, C, I, h > must be an unambiguous public base of S. See simple_state<> documentation for the requirements and semantics of C, I and h
new S()	S *	Enters the state S. Certain functions must not be called from S::S(), see simple_state<> documentation for more information
pS->exit();		Exits the state S (first stage). The definition of an exit member function within models of the SimpleState concept is optional since simple_state<> already defines the following public member: void exit() {}. exit() is not called when a state is exited while an exception is pending, see simple_state<>::terminate() for more information
delete pS;		Exits the state S (second stage)
S::reactions	An mpl::list<> that is either empty or contains instantiations of the custom_reaction, in_state_reaction, deferral, termination or transition class templates. If there is only a single reaction then it can also be typedefed directly, without wrapping it into an mpl::list<>	The declaration of a reactions member typedef within models of the SimpleState concept is optional since simple_state<> already defines the following public member: typedef mpl::list<> reactions;

State concept

A State is a refinement of SimpleState (that is, except for the default constructor a State type must also satisfy SimpleState requirements). For a State type S, a pointer pS of type S * pointing to an object of type S allocated with new, and an object mc of type state< S, C, I, h >::my_context the following expressions/statements must be well-formed:

Expression/Statement	Type	Effects/Result/Notes
state< S, C, I, h > *   pB = pS;		state< S, C, I, h > must be an unambiguous public base of S. See state<> documentation for the requirements and semantics of C, I and h
new S( mc )	S *	Enters the state S. No restrictions exist regarding the functions that can be called from S::S() (in contrast to the constructors of models of the SimpleState concept). mc must be forwarded to state< S, C, I, h >::state()

Event concept

A Event type defines an event for which state machines can define reactions.

For a Event type E and a pointer pCE of type const E * pointing to an object of type E allocated with new the following expressions/statements must be well-formed and have the indicated effects/results:

Expression/Statement	Type	Effects/Result/Notes
const event< E > * pCB = pCE;		event< E > must be an unambiguous public base of E
new E( *pCE )	E *	Makes a copy of pE

Header <boost/statechart/state_machine.hpp>

Class template state_machine

This is the base class template of all synchronous state machines.

Class template state_machine parameters

Template parameter	Requirements	Semantics	Default
MostDerived	The most-derived subtype of this class template
InitialState	A model of the SimpleState or State concepts. The Context argument passed to the simple_state<> or state<> base of  InitialState must be MostDerived. That is, InitialState must be an outermost state of this state machine	The state that is entered when state_machine<> ::initiate() is called
Allocator	A model of the standard Allocator concept	Allocator::rebind<>::other is used to allocate and deallocate all simple_state subtype objects and internal objects of dynamic storage duration	std::allocator< void >
ExceptionTranslator	A model of the ExceptionTranslator concept	see ExceptionTranslator concept	null_exception_translator

Class template state_machine synopsis

namespace boost
{
namespace statechart
{
  template<
    class MostDerived,
    class InitialState,
    class Allocator = std::allocator< void >,
    class ExceptionTranslator = null_exception_translator >
  class state_machine : noncopyable
  {
    public:
      typedef MostDerived outermost_context_type;

      void initiate();
      void terminate();
      bool terminated() const;

      void process_event( const event_base & );

      template< class Target >
      Target state_cast() const;
      template< class Target >
      Target state_downcast() const;

      // a model of the StateBase concept
      typedef implementation-defined state_base_type;
      // a model of the standard Forward Iterator concept
      typedef implementation-defined state_iterator;

      state_iterator state_begin() const;
      state_iterator state_end() const;

      void unconsumed_event( const event_base & ) {}

    protected:
      state_machine();
      ~state_machine();

      void post_event(
        const intrusive_ptr< const event_base > & );
      void post_event( const event_base & );
  };
}
}

Class template state_machine constructor and destructor

state_machine();

Effects: Constructs a non-running state machine

~state_machine();

Effects: Destructs the currently active outermost state and all its direct and indirect inner states. Innermost states are destructed first. Other states are destructed as soon as all their direct and indirect inner states have been destructed. The inner states of each state are destructed according to the number of their orthogonal region. The state in the orthogonal region with the highest number is always destructed first, then the state in the region with the second-highest number and so on
Note: Does not attempt to call any exit member functions

Class template state_machine modifier functions

void initiate();

Effects:

1. Calls terminate()
2. Constructs a function object action with a parameter-less operator()() returning result that
   1. enters (constructs) the state specified with the InitialState template parameter
   2. enters the tree formed by the direct and indirect inner initial states of InitialState depth first. The inner states of each state are entered according to the number of their orthogonal region. The state in orthogonal region 0 is always entered first, then the state in region 1 and so on
3. Constructs a function object exceptionEventHandler with an operator()() returning result and accepting an exception event parameter that processes the passed exception event, with the following differences to the processing of normal events:
   • From the moment when the exception has been thrown until right after the execution of the exception event reaction, states that need to be exited are only destructed but no exit member functions are called
   • Reaction search always starts with the outermost unstable state
   • As for normal events, reaction search moves outward when the current state cannot handle the event. However, if there is no outer state (an outermost state has been reached) the reaction search is considered unsuccessful. That is, exception events will never be dispatched to orthogonal regions other than the one that caused the exception event
   • Should an exception be thrown during exception event reaction search or reaction execution then the exception is propagated out of the exceptionEventHandler function object (that is, ExceptionTranslator is not used to translate exceptions thrown while processing an exception event)
   • If no reaction could be found for the exception event or if the state machine is not stable after processing the exception event, the original exception is rethrown. Otherwise, a result object is returned equal to the one returned by simple_state<>::discard_event()
4. Passes action and exceptionEventHandler to ExceptionTranslator::operator()(). If ExceptionTranslator::operator()() throws an exception, the exception is propagated to the caller. If the caller catches the exception, the currently active outermost state and all its direct and indirect inner states are destructed. Innermost states are destructed first. Other states are destructed as soon as all their direct and indirect inner states have been destructed. The inner states of each state are destructed according to the number of their orthogonal region. The state in the orthogonal region with the highest number is always destructed first, then the state in the region with the second-highest number and so on. Continues with step 5 otherwise (the return value is discarded)
5. Processes all posted events (see process_event()). Returns to the caller if there are no more posted events

Throws: Any exceptions propagated from ExceptionTranslator::operator()(). Exceptions never originate in the library itself but only in code supplied through template parameters:

• Allocator::rebind<>::other::allocate()
• state constructors
• react member functions
• exit member functions
• transition-actions

void terminate();

Effects:

1. Constructs a function object action with a parameter-less operator()() returning result that terminates the currently active outermost state, discards all remaining events and clears all history information
2. Constructs a function object exceptionEventHandler with an operator()() returning result and accepting an exception event parameter that processes the passed exception event, with the following differences to the processing of normal events:
   • From the moment when the exception has been thrown until right after the execution of the exception event reaction, states that need to be exited are only destructed but no exit member functions are called
   • Reaction search always starts with the outermost unstable state
   • As for normal events, reaction search moves outward when the current state cannot handle the event. However, if there is no outer state (an outermost state has been reached) the reaction search is considered unsuccessful. That is, exception events will never be dispatched to orthogonal regions other than the one that caused the exception event
   • Should an exception be thrown during exception event reaction search or reaction execution then the exception is propagated out of the exceptionEventHandler function object (that is, ExceptionTranslator is not used to translate exceptions thrown while processing an exception event)
   • If no reaction could be found for the exception event or if the state machine is not stable after processing the exception event, the original exception is rethrown. Otherwise, a result object is returned equal to the one returned by simple_state<>::discard_event()
3. Passes action and exceptionEventHandler to ExceptionTranslator::operator()(). If ExceptionTranslator::operator()() throws an exception, the exception is propagated to the caller. If the caller catches the exception, the currently active outermost state and all its direct and indirect inner states are destructed. Innermost states are destructed first. Other states are destructed as soon as all their direct and indirect inner states have been destructed. The inner states of each state are destructed according to the number of their orthogonal region. The state in the orthogonal region with the highest number is always destructed first, then the state in the region with the second-highest number and so on. Otherwise, returns to the caller

Throws: Any exceptions propagated from ExceptionTranslator::operator(). Exceptions never originate in the library itself but only in code supplied through template parameters:

• Allocator::rebind<>::other::allocate()
• state constructors
• react member functions
• exit member functions
• transition-actions

void process_event( const event_base & );

Effects:

1. Selects the passed event as the current event (henceforth referred to as currentEvent)
2. Starts a new reaction search
3. Selects an arbitrary but in this reaction search not yet visited state from all the currently active innermost states. If no such state exists then continues with step 10
4. Constructs a function object action with a parameter-less operator()() returning result that does the following:
   1. Searches a reaction suitable for currentEvent, starting with the current innermost state and moving outward until a state defining a reaction for the event is found. Returns simple_state<>::forward_event() if no reaction has been found
   2. Executes the found reaction. If the reaction result is equal to the return value of simple_state<>::forward_event() then resumes the reaction search (step a). Returns the reaction result otherwise
5. Constructs a function object exceptionEventHandler returning result and accepting an exception event parameter that processes the passed exception event, with the following differences to the processing of normal events:
   • From the moment when the exception has been thrown until right after the execution of the exception event reaction, states that need to be exited are only destructed but no exit member functions are called
   • If the state machine is stable when the exception event is processed then exception event reaction search starts with the innermost state that was last visited during the last normal event reaction search (the exception event was generated as a result of this normal reaction search)
   • If the state machine is unstable when the exception event is processed then exception event reaction search starts with the outermost unstable state
   • As for normal events, reaction search moves outward when the current state cannot handle the event. However, if there is no outer state (an outermost state has been reached) the reaction search is considered unsuccessful. That is, exception events will never be dispatched to orthogonal regions other than the one that caused the exception event
   • Should an exception be thrown during exception event reaction search or reaction execution then the exception is propagated out of the exceptionEventHandler function object (that is, ExceptionTranslator is not used to translate exceptions thrown while processing an exception event)
   • If no reaction could be found for the exception event or if the state machine is not stable after processing the exception event, the original exception is rethrown. Otherwise, a result object is returned equal to the one returned by simple_state<>::discard_event()
6. Passes action and exceptionEventHandler to ExceptionTranslator::operator()(). If ExceptionTranslator::operator()() throws an exception, the exception is propagated to the caller. If the caller catches the exception, the currently active outermost state and all its direct and indirect inner states are destructed. Innermost states are destructed first. Other states are destructed as soon as all their direct and indirect inner states have been destructed. The inner states of each state are destructed according to the number of their orthogonal region. The state in the orthogonal region with the highest number is always destructed first, then the state in the region with the second-highest number and so on. Otherwise continues with step 7
7. If the return value of ExceptionTranslator::operator()() is equal to the one of simple_state<>::forward_event() then continues with step 3
8. If the return value of ExceptionTranslator::operator()() is equal to the one of simple_state<>::defer_event() then the return value of currentEvent.intrusive_from_this() is stored in a state-specific queue. Continues with step 11
9. If the return value of ExceptionTranslator::operator()() is equal to the one of simple_state<>::discard_event() then continues with step 11
10. Calls static_cast< MostDerived * >( this )->unconsumed_event( currentEvent ). If unconsumed_event() throws an exception, the exception is propagated to the caller. Such an exception never leads to the destruction of any states (in contrast to exceptions propagated from ExceptionTranslator::operator()())
11. If the posted events queue is non-empty then dequeues the first event, selects it as currentEvent and continues with step 2. Returns to the caller otherwise

Throws: Any exceptions propagated from MostDerived::unconsumed_event() or ExceptionTranslator::operator(). Exceptions never originate in the library itself but only in code supplied through template parameters:

• Allocator::rebind<>::other::allocate()
• state constructors
• react member functions
• exit member functions
• transition-actions
• MostDerived::unconsumed_event()

void post_event(
  const intrusive_ptr< const event_base > & );

Effects: Pushes the passed event into the posted events queue
Throws: Any exceptions propagated from Allocator::allocate()

void post_event( const event_base & evt );

Effects: post_event( evt.intrusive_from_this() );
Throws: Any exceptions propagated from Allocator::allocate()

void unconsumed_event( const event_base & evt );

Effects: None
Note: This function (or, if present, the equally named derived class member function) is called by process_event() whenever a dispatched event did not trigger a reaction, see process_event() effects, point 10 for more information.

Class template state_machine observer functions

bool terminated() const;

Returns: true, if the machine is terminated. Returns false otherwise
Note: Is equivalent to state_begin() == state_end()

template< class Target >
Target state_cast() const;

Returns: Depending on the form of Target either a reference or a pointer to const if at least one of the currently active states can successfully be dynamic_cast to Target. Returns 0 for pointer targets and throws std::bad_cast for reference targets otherwise. Target can take either of the following forms: const Class * or const Class &
Throws: std::bad_cast if Target is a reference type and none of the active states can be dynamic_cast to Target
Note: The search sequence is the same as for process_event()

template< class Target >
Target state_downcast() const;

Requires: For reference targets the compiler must support partial specialization of class templates, otherwise a compile-time error will result. The type denoted by Target must be a model of the SimpleState or State concepts
Returns: Depending on the form of Target either a reference or a pointer to const if Target is equal to the most-derived type of a currently active state. Returns 0 for pointer targets and throws std::bad_cast for reference targets otherwise. Target can take either of the following forms: const Class * or const Class &
Throws: std::bad_cast if Target is a reference type and none of the active states has a most derived type equal to Target
Note: The search sequence is the same as for process_event()

state_iterator state_begin() const;

state_iterator state_end() const;

Return: Iterator objects, the range [state_begin(), state_end()) refers to all currently active innermost states. For an object i of type state_iterator, *i returns a const state_base_type & and i.operator->() returns a const state_base_type *
Note: The position of a given innermost state in the range is arbitrary. It may change with each call to a modifier function. Moreover, all iterators are invalidated whenever a modifier function is called

Header <boost/statechart/
asynchronous_state_machine.hpp>

Class template asynchronous_state_machine

This is the base class template of all asynchronous state machines.

Class template asynchronous_state_machine parameters

Template parameter	Requirements	Semantics	Default
MostDerived	The most-derived subtype of this class template
InitialState	A model of the SimpleState or State concepts. The Context argument passed to the simple_state<> or state<> base of InitialState must be MostDerived. That is, InitialState must be an outermost state of this state machine	The state that is entered when the state machine is initiated through the Scheduler object
Scheduler	A model of the Scheduler concept	see Scheduler concept	fifo_scheduler<>
Allocator	A model of the standard Allocator concept		std::allocator< void >
ExceptionTranslator	A model of the ExceptionTranslator concept	see ExceptionTranslator concept	null_exception_translator

Class template asynchronous_state_machine synopsis

namespace boost
{
namespace statechart
{
  template<
    class MostDerived,
    class InitialState,
    class Scheduler = fifo_scheduler<>,
    class Allocator = std::allocator< void >,
    class ExceptionTranslator = null_exception_translator >
  class asynchronous_state_machine :
    public state_machine<
      MostDerived, InitialState, Allocator, ExceptionTranslator >,
    public event_processor< Scheduler >
  {
    protected:
      typedef asynchronous_state_machine my_base;

      asynchronous_state_machine(
        typename event_processor< Scheduler >::my_context ctx );
      ~asynchronous_state_machine();  
  };
}
}

Class template asynchronous_state_machine constructor and destructor

asynchronous_state_machine(
  typename event_processor< Scheduler >::my_context ctx );

Effects: Constructs a non-running asynchronous state machine
Note: Users cannot create asynchronous_state_machine<> subtype objects directly. This can only be done through an object of the Scheduler class

~asynchronous_state_machine();

Effects: Destructs the state machine
Note: Users cannot destruct asynchronous_state_machine<> subtype objects directly. This can only be done through an object of the Scheduler class

Header <boost/statechart/event_processor.hpp>

Class template event_processor

This is the base class template of all types that process events. asynchronous_state_machine<> is just one possible event processor implementation.

Class template event_processor parameters

Template parameter	Requirements	Semantics
Scheduler	A model of the Scheduler concept	see Scheduler concept

Class template event_processor synopsis

namespace boost
{
namespace statechart
{
  template< class Scheduler >
  class event_processor
  {
    public:
      virtual ~event_processor();

      Scheduler & my_scheduler() const;

      typedef typename Scheduler::processor_handle
        processor_handle;
      processor_handle my_handle() const;

      void initiate();
      void process_event( const event_base & evt );
      void terminate();

    protected:
      typedef const typename Scheduler::processor_context &
        my_context;
      event_processor( my_context ctx );

    private:
      virtual void initiate_impl() = 0;
      virtual void process_event_impl(
        const event_base & evt ) = 0;
      virtual void terminate_impl() = 0;
  };
}
}

Class template event_processor constructor and destructor

event_processor( my_context ctx );

Effects: Constructs an event processor object and stores copies of the reference returned by myContext.my_scheduler() and the object returned by myContext.my_handle()
Note: Users cannot create event_processor<> subtype objects directly. This can only be done through an object of the Scheduler class

virtual ~event_processor();

Effects: Destructs an event processor object
Note: Users cannot destruct event_processor<> subtype objects directly. This can only be done through an object of the Scheduler class

Class template event_processor modifier functions

void initiate();

Effects: initiate_impl();
Throws: Any exceptions propagated from the implementation of initiate_impl()

void process_event( const event_base & evt );

Effects: process_event_impl( evt );
Throws: Any exceptions propagated from the implementation of process_event_impl()

void terminate();

Effects: terminate_impl();
Throws: Any exceptions propagated from the implementation of terminate_impl()

Class template event_processor observer functions

Scheduler & my_scheduler() const;

Returns: The Scheduler reference obtained in the constructor

processor_handle my_handle() const;

Returns: The processor_handle object obtained in the constructor

Header <boost/statechart/fifo_scheduler.hpp>

Class template fifo_scheduler

This class template is a model of the Scheduler concept.

Class template fifo_scheduler parameters

Template parameter	Requirements	Semantics	Default
FifoWorker	A model of the FifoWorker concept	see FifoWorker concept	fifo_worker<>
Allocator	A model of the standard Allocator concept		std::allocator< void >

Class template fifo_scheduler synopsis

namespace boost
{
namespace statechart
{
  template<
    class FifoWorker = fifo_worker<>,
    class Allocator = std::allocator< void > >
  class fifo_scheduler : noncopyable
  {
    public:
      fifo_scheduler( bool waitOnEmptyQueue = false );

      typedef implementation-defined processor_handle;

      class processor_context : noncopyable
      {
        processor_context(
          fifo_scheduler & scheduler,
          const processor_handle & theHandle );

        fifo_scheduler & my_scheduler() const;
        const processor_handle & my_handle() const;

        friend class fifo_scheduler;
        friend class event_processor< fifo_scheduler >;
      };

      template< class Processor >
      processor_handle create_processor();
      template< class Processor, typename Param1 >
      processor_handle create_processor( Param1 param1 );

      // More create_processor overloads

      void destroy_processor( processor_handle processor );

      void initiate_processor( processor_handle processor );
      void terminate_processor( processor_handle processor );

      typedef intrusive_ptr< const event_base > event_ptr_type;

      void queue_event(
        const processor_handle & processor,
        const event_ptr_type & pEvent );

      typedef typename FifoWorker::work_item work_item;

      void queue_work_item( const work_item & item );

      void terminate();
      bool terminated() const;

      unsigned long operator()(
        unsigned long maxEventCount = 0 );
  };
}
}

Class template fifo_scheduler constructor

fifo_scheduler( bool waitOnEmptyQueue = false );

Effects: Constructs a fifo_scheduler<> object. In multi-threaded builds, waitOnEmptyQueue is forwarded to the constructor of a data member of type FifoWorker. In single-threaded builds, the FifoWorker data member is default-constructed
Note: In single-threaded builds the fifo_scheduler<> constructor does not accept any parameters and operator()() thus always returns to the caller when the event queue is empty

Class template fifo_scheduler modifier functions

template< class Processor >
processor_handle create_processor();

Requires: The Processor type must be a direct or indirect subtype of the event_processor class template
Effects: Creates and passes to FifoWorker::queue_work_item() an object of type FifoWorker::work_item that, when later executed in FifoWorker::operator()(), leads to a call to the constructor of Processor, passing an appropriate processor_context object as the only argument
Returns: A processor_handle object that henceforth identifies the created event processor object
Throws: Any exceptions propagated from FifoWorker::work_item() and FifoWorker::queue_work_item()
Caution: The current implementation of this function makes an (indirect) call to global operator new(). Unless global operator new() is replaced, care must be taken when to call this function in applications with hard real-time requirements

template< class Processor, typename Param1 >
processor_handle create_processor( Param1 param1 );

Requires: The Processor type must be a direct or indirect subtype of the event_processor class template
Effects: Creates and passes to FifoWorker::queue_work_item() an object of type FifoWorker::work_item that, when later executed in FifoWorker::operator()(), leads to a call to the constructor of Processor, passing an appropriate processor_context object and param1 as arguments
Returns: A processor_handle object that henceforth identifies the created event processor object
Throws: Any exceptions propagated from FifoWorker::work_item() and FifoWorker::queue_work_item()
Note: boost::ref() and boost::cref() can be used to pass arguments by reference rather than by copy. fifo_scheduler<> has 5 additional create_processor<> overloads, allowing to pass up to 6 custom arguments to the constructors of event processors
Caution: The current implementation of this and all other overloads make (indirect) calls to global operator new(). Unless global operator new() is replaced, care must be taken when to call these overloads in applications with hard real-time requirements

void destroy_processor( processor_handle processor );

Requires: processor was obtained from a call to one of the create_processor<>() overloads on the same fifo_scheduler<> object
Effects: Creates and passes to FifoWorker::queue_work_item() an object of type FifoWorker::work_item that, when later executed in FifoWorker::operator()(), leads to a call to the destructor of the event processor object associated with processor. The object is silently discarded if the event processor object has been destructed before
Throws: Any exceptions propagated from FifoWorker::work_item() and FifoWorker::queue_work_item()
Caution: The current implementation of this function leads to an (indirect) call to global operator delete() (the call is made when the last processor_handle object associated with the event processor object is destructed). Unless global operator delete() is replaced, care must be taken when to call this function in applications with hard real-time requirements

void initiate_processor( processor_handle processor );

Requires: processor was obtained from a call to one of the create_processor() overloads on the same fifo_scheduler<> object
Effects: Creates and passes to FifoWorker::queue_work_item() an object of type FifoWorker::work_item that, when later executed in FifoWorker::operator()(), leads to a call to initiate() on the event processor object associated with processor. The object is silently discarded if the event processor object has been destructed before
Throws: Any exceptions propagated from FifoWorker::work_item() and FifoWorker::queue_work_item()

void terminate_processor( processor_handle processor );

Requires: processor was obtained from a call to one of the create_processor<>() overloads on the same fifo_scheduler<> object
Effects: Creates and passes to FifoWorker::queue_work_item() an object of type FifoWorker::work_item that, when later executed in FifoWorker::operator()(), leads to a call to terminate() on the event processor object associated with processor. The object is silently discarded if the event processor object has been destructed before
Throws: Any exceptions propagated from FifoWorker::work_item() and FifoWorker::queue_work_item()

void queue_event(
  const processor_handle & processor,
  const event_ptr_type & pEvent );

Requires: pEvent.get() != 0 and processor was obtained from a call to one of the create_processor<>() overloads on the same fifo_scheduler<> object
Effects: Creates and passes to FifoWorker::queue_work_item() an object of type FifoWorker::work_item that, when later executed in FifoWorker::operator()(), leads to a call to process_event( *pEvent ) on the event processor object associated with processor. The object is silently discarded if the event processor object has been destructed before
Throws: Any exceptions propagated from FifoWorker::work_item() and FifoWorker::queue_work_item()

void queue_work_item( const work_item & item );

Effects: FifoWorker::queue_work_item( item );
Throws: Any exceptions propagated from the above call

void terminate();

Effects: FifoWorker::terminate()
Throws: Any exceptions propagated from the above call

unsigned long operator()( unsigned long maxEventCount = 0 );

Requires: Must only be called from exactly one thread
Effects: FifoWorker::operator()( maxEventCount )
Returns: The return value of the above call
Throws: Any exceptions propagated from the above call

Class template fifo_scheduler observer functions

bool terminated() const;

Requires: Must only be called from the thread that also calls operator()()
Returns: FifoWorker::terminated();

Header <boost/statechart/exception_translator.hpp>

Class template exception_translator

This class template is a model of the ExceptionTranslator concept.

Class template exception_translator parameters

Template parameter	Requirements	Semantics	Default
ExceptionEvent	A model of the Event concept	The type of event that is dispatched when an exception is propagated into the framework	exception_thrown

Class template exception_translator synopsis & semantics

namespace boost
{
namespace statechart
{
  class exception_thrown : public event< exception_thrown > {};

  template< class ExceptionEvent = exception_thrown >
  class exception_translator
  {
    public:
      template< class Action, class ExceptionEventHandler >
      result operator()(
        Action action,
        ExceptionEventHandler eventHandler )
      {
        try
        {
          return action();
        }
        catch( ... )
        {
          return eventHandler( ExceptionEvent() );
        }
      }
  };
}
}

Header <boost/statechart/
null_exception_translator.hpp>

Class null_exception_translator

This class is a model of the ExceptionTranslator concept.

Class null_exception_translator synopsis & semantics

namespace boost
{
namespace statechart
{
  class null_exception_translator
  {
    public:
      template< class Action, class ExceptionEventHandler >
      result operator()(
        Action action, ExceptionEventHandler )
      {
        return action();
      }
  };
}
}

Header <boost/statechart/simple_state.hpp>

Enum history_mode

Defines the history type of a state.

namespace boost
{
namespace statechart
{
  enum history_mode
  {
    has_no_history,
    has_shallow_history,
    has_deep_history,
    has_full_history // shallow & deep
  };
}
}

Class template simple_state

This is the base class template for all models of the SimpleState concept. Such models must not call any of the following simple_state<> member functions from their constructors:

void post_event(
  const intrusive_ptr< const event_base > & );
void post_event( const event_base & );

template<
  class HistoryContext,
  implementation-defined-unsigned-integer-type
    orthogonalPosition >
void clear_shallow_history();
template<
  class HistoryContext,
  implementation-defined-unsigned-integer-type
    orthogonalPosition >
void clear_deep_history();

outermost_context_type & outermost_context();
const outermost_context_type & outermost_context() const;

template< class OtherContext >
OtherContext & context();
template< class OtherContext >
const OtherContext & context() const;

template< class Target >
Target state_cast() const;
template< class Target >
Target state_downcast() const;

state_iterator state_begin() const;
state_iterator state_end() const;

States that need to call any of these member functions from their constructors must derive from the state class template.

Class template simple_state parameters

Template parameter	Requirements	Semantics	Default
MostDerived	The most-derived subtype of this class template
Context	A most-derived direct or indirect subtype of the state_machine or asynchronous_state_machine class templates or a model of the SimpleState or State concepts or an instantiation of the simple_state<>::orthogonal class template. Must be a complete type	Defines the states' position in the state hierarchy
InnerInitial	An mpl::list<> containing models of the SimpleState or State concepts or instantiations of the shallow_history or deep_history class templates. If there is only a single inner initial state that is not a template instantiation then it can also be passed directly, without wrapping it into an mpl::list<>. The Context argument passed to the simple_state<> or state<> base of each state in the list must correspond to the orthogonal region it belongs to. That is, the first state in the list must pass MostDerived::orthogonal< 0 >, the second MostDerived::orthogonal< 1 > and so forth. MostDerived::orthogonal< 0 > and MostDerived are synonymous	Defines the inner initial state for each orthogonal region. By default, a state does not have inner states	unspecified
historyMode	One of the values defined in the history_mode enumeration	Defines whether the state saves shallow, deep or both histories upon exit	has_no_history

Class template simple_state synopsis

namespace boost
{
namespace statechart
{
  template<
    class MostDerived,
    class Context,
    class InnerInitial = unspecified,
    history_mode historyMode = has_no_history >
  class simple_state : implementation-defined
  {
    public:
      // by default, a state has no reactions
      typedef mpl::list<> reactions;

      // see template parameters
      template< implementation-defined-unsigned-integer-type
        innerOrthogonalPosition >
      struct orthogonal
      {
        // implementation-defined
      };

      typedef typename Context::outermost_context_type
        outermost_context_type;

      outermost_context_type & outermost_context();
      const outermost_context_type & outermost_context() const;

      template< class OtherContext >
      OtherContext & context();
      template< class OtherContext >
      const OtherContext & context() const;

      template< class Target >
      Target state_cast() const;
      template< class Target >
      Target state_downcast() const;

      // a model of the StateBase concept
      typedef implementation-defined state_base_type;
      // a model of the standard Forward Iterator concept
      typedef implementation-defined state_iterator;

      state_iterator state_begin() const;
      state_iterator state_end() const;

      void post_event(
        const intrusive_ptr< const event_base > & );
      void post_event( const event_base & );

      result discard_event();
      result forward_event();
      result defer_event();
      template< class DestinationState >
      result transit();
      template<
        class DestinationState,
        class TransitionContext,
        class Event >
      result transit(
        void ( TransitionContext::* )( const Event & ),
        const Event & );
      result terminate();

      template<
        class HistoryContext,
        implementation-defined-unsigned-integer-type
          orthogonalPosition >
      void clear_shallow_history();
      template<
        class HistoryContext,
        implementation-defined-unsigned-integer-type
          orthogonalPosition >
      void clear_deep_history();

      static id_type static_type();

      template< class CustomId >
      static const CustomId * custom_static_type_ptr();

      template< class CustomId >
      static void custom_static_type_ptr( const CustomId * );

      // see transit() or terminate() effects
      void exit() {}

    protected:
      simple_state();
      ~simple_state();
  };
}
}

Class template simple_state constructor and destructor

simple_state();

Effects: Constructs a state object

~simple_state();

Effects: Pushes all events deferred by the state into the posted events queue

Class template simple_state modifier functions

void post_event(
  const intrusive_ptr< const event_base > & pEvt );

Requires: If called from a constructor of a direct or indirect subtype then the most-derived type must directly or indirectly derive from the state class template. All direct and indirect callers must be exception-neutral
Effects: outermost_context().post_event( pEvt );
Throws: Whatever the above call throws

void post_event( const event_base & evt );

Requires: If called from a constructor of a direct or indirect subtype then the most-derived type must directly or indirectly derive from the state class template. All direct and indirect callers must be exception-neutral
Effects: outermost_context().post_event( evt );
Throws: Whatever the above call throws

result discard_event();

Requires: Must only be called from within react member functions, which are called by custom_reaction<> instantiations. All direct and indirect callers must be exception-neutral
Effects: Instructs the state machine to discard the current event and to continue with the processing of the remaining events (see state_machine<>::process_event() for details)
Returns: A result object. The user-supplied react member function must return this object to its caller

result forward_event();

Requires: Must only be called from within react member functions, which are called by custom_reaction<> instantiations. All direct and indirect callers must be exception-neutral
Effects: Instructs the state machine to forward the current event to the next state (see state_machine<>::process_event() for details)
Returns: A result object. The user-supplied react member function must return this object to its caller

result defer_event();

Requires: Must only be called from within react member functions, which are called by custom_reaction<> instantiations. All direct and indirect callers must be exception-neutral
Effects: Instructs the state machine to defer the current event and to continue with the processing of the remaining events (see state_machine<>::process_event() for details)
Returns: A result object. The user-supplied react member function must return this object to its caller
Throws: Any exceptions propagated from Allocator::rebind<>::other::allocate() (the template parameter passed to the base class of outermost_context_type)

template< class DestinationState >
result transit();

Requires: Must only be called from within react member functions, which are called by custom_reaction<> instantiations. All direct and indirect callers must be exception-neutral
Effects:

1. Exits all currently active direct and indirect inner states of the innermost common context of this state and DestinationState. Innermost states are exited first. Other states are exited as soon as all their direct and indirect inner states have been exited. The inner states of each state are exited according to the number of their orthogonal region. The state in the orthogonal region with the highest number is always exited first, then the state in the region with the second-highest number and so on.
   The process of exiting a state consists of the following steps:
   1. If there is an exception pending that has not yet been handled successfully then only step 5 is executed
   2. Calls the exit member function (see synopsis) of the most-derived state object. If exit() throws then steps 3 and 4 are not executed
   3. If the state has shallow history then shallow history information is saved
   4. If the state is an innermost state then deep history information is saved for all direct and indirect outer states that have deep history
   5. The state object is destructed
2. Enters (constructs) the state that is both a direct inner state of the innermost common context and either the DestinationState itself or a direct or indirect outer state of DestinationState
3. Enters (constructs) the tree formed by the direct and indirect inner states of the previously entered state down to the DestinationState and beyond depth first. The inner states of each state are entered according to the number of their orthogonal region. The state in orthogonal region 0 is always entered first, then the state in region 1 and so on
4. Instructs the state machine to discard the current event and to continue with the processing of the remaining events (see state_machine<>::process_event() for details)

Returns: A result object. The user-supplied react member function must return this object to its caller
Throws: Any exceptions propagated from:

• Allocator::rebind<>::other::allocate() (the template parameter passed to the base class of outermost_context_type)
• state constructors
• exit member functions

Caution: Inevitably destructs this state before returning to the calling react member function, which must therefore not attempt to access anything except stack objects before returning to its caller

template<
  class DestinationState,
  class TransitionContext,
  class Event >
result transit(
  void ( TransitionContext::* )( const Event & ),
  const Event & );

Requires: Must only be called from within react member functions, which are called by custom_reaction<> instantiations. All direct and indirect callers must be exception-neutral
Effects:

1. Exits all currently active direct and indirect inner states of the innermost common context of this state and DestinationState. Innermost states are exited first. Other states are exited as soon as all their direct and indirect inner states have been exited. The inner states of each state are exited according to the number of their orthogonal region. The state in the orthogonal region with the highest number is always exited first, then the state in the region with the second-highest number and so on.
   The process of exiting a state consists of the following steps:
   1. If there is an exception pending that has not yet been handled successfully then only step 5 is executed
   2. Calls the exit member function (see synopsis) of the most-derived state object. If exit() throws then steps 3 and 4 are not executed
   3. If the state has shallow history then shallow history information is saved
   4. If the state is an innermost state then deep history information is saved for all direct and indirect outer states that have deep history
   5. The state object is destructed
2. Executes the passed transition action, forwarding the passed event
3. Enters (constructs) the state that is both a direct inner state of the innermost common context and either the DestinationState itself or a direct or indirect outer state of DestinationState
4. Enters (constructs) the tree formed by the direct and indirect inner states of the previously entered state down to the DestinationState and beyond depth first. The inner states of each state are entered according to the number of their orthogonal region. The state in orthogonal region 0 is always entered first, then the state in region 1 and so on
5. Instructs the state machine to discard the current event and to continue with the processing of the remaining events (see state_machine<>::process_event() for details)

Returns: A result object. The user-supplied react member function must return this object to its caller
Throws: Any exceptions propagated from:

• Allocator::rebind<>::other::allocate() (the template parameter passed to the base class of outermost_context_type)
• state constructors
• exit member functions
• the transition action

Caution: Inevitably destructs this state before returning to the calling react member function, which must therefore not attempt to access anything except stack objects before returning to its caller

result terminate();

Requires: Must only be called from within react member functions, which are called by custom_reaction<> instantiations. All direct and indirect callers must be exception-neutral
Effects: Exits this state and all its direct and indirect inner states. Innermost states are exited first. Other states are exited as soon as all their direct and indirect inner states have been exited. The inner states of each state are exited according to the number of their orthogonal region. The state in the orthogonal region with the highest number is always exited first, then the state in the region with the second-highest number and so on.
The process of exiting a state consists of the following steps:

1. If there is an exception pending that has not yet been handled successfully then only step 5 is executed
2. Calls the exit member function (see synopsis) of the most-derived state object. If exit() throws then steps 3 and 4 are not executed
3. If the state has shallow history then shallow history information is saved
4. If the state is an innermost state then deep history information is saved for all direct and indirect outer states that have deep history
5. The state object is destructed

Also instructs the state machine to discard the current event and to continue with the processing of the remaining events (see state_machine<>::process_event() for details)
Returns: A result object. The user-supplied react member function must return this object to its caller
Throws: Any exceptions propagated from:

• Allocator::rebind<>::other::allocate() (the template parameter passed to the base class of outermost_context_type, used to allocate space to save history)
• exit member functions

Note: If this state is the only currently active inner state of its direct outer state then the direct outer state is terminated also. The same applies recursively for all indirect outer states
Caution: Inevitably destructs this state before returning to the calling react member function, which must therefore not attempt to access anything except stack objects before returning to its caller

template<
  class HistoryContext,
  implementation-defined-unsigned-integer-type
    orthogonalPosition >
void clear_shallow_history();

Requires: If called from a constructor of a direct or indirect subtype then the most-derived type must directly or indirectly derive from the state class template. The historyMode argument passed to the simple_state<> or state<> base of HistoryContext must be equal to has_shallow_history or has_full_history
Effects: Clears the shallow history of the orthogonal region specified by orthogonalPosition of the state specified by HistoryContext
Throws: Any exceptions propagated from Allocator::rebind<>::other::allocate() (the template parameter passed to the base class of outermost_context_type)

template<
  class HistoryContext,
  implementation-defined-unsigned-integer-type
    orthogonalPosition >
void clear_deep_history();

Requires: If called from a constructor of a direct or indirect subtype then the most-derived type must directly or indirectly derive from the state class template. The historyMode argument passed to the simple_state<> or state<> base of HistoryContext must be equal to has_deep_history or has_full_history
Effects: Clears the deep history of the orthogonal region specified by orthogonalPosition of the state specified by HistoryContext
Throws: Any exceptions propagated from Allocator::rebind<>::other::allocate() (the template parameter passed to the base class of outermost_context_type)

Class template simple_state observer functions

outermost_context_type & outermost_context();

Requires: If called from a constructor of a direct or indirect subtype then the most-derived type must directly or indirectly derive from the state class template. If called from a destructor of a direct or indirect subtype then the state_machine<> subclass portion must still exist
Returns: A reference to the outermost context, which is always the state machine this state belongs to

const outermost_context_type & outermost_context() const;

Requires: If called from a constructor of a direct or indirect subtype then the most-derived type must directly or indirectly derive from the state class template. If called from a destructor of a direct or indirect subtype then the state_machine<> subclass portion must still exist
Returns: A reference to the const outermost context, which is always the state machine this state belongs to

template< class OtherContext >
OtherContext & context();

Requires: If called from a constructor of a direct or indirect subtype then the most-derived type must directly or indirectly derive from the state class template. If called from a destructor of a direct or indirect subtype with a state_machine<> subtype as argument then the state_machine<> subclass portion must still exist
Returns: A reference to a direct or indirect context

template< class OtherContext >
const OtherContext & context() const;

Requires: If called from a constructor of a direct or indirect subtype then the most-derived type must directly or indirectly derive from the state class template. If called from a destructor of a direct or indirect subtype with a state_machine<> subtype as argument then the state_machine<> subclass portion must still exist
Returns: A reference to a const direct or indirect context

template< class Target >
Target state_cast() const;

Requires: If called from a constructor of a direct or indirect subtype then the most-derived type must directly or indirectly derive from the state class template
Returns: Has exactly the same semantics as state_machine<>::state_cast<>()
Throws: Has exactly the same semantics as state_machine<>::state_cast<>()
Note: The result is unspecified if this function is called when the machine is unstable

template< class Target >
Target state_downcast() const;

Requires: If called from a constructor of a direct or indirect subtype then the most-derived type must directly or indirectly derive from the state class template. Moreover, state_machine<>::state_downcast<>() requirements also apply
Returns: Has exactly the same semantics as state_machine<>::state_downcast<>()
Throws: Has exactly the same semantics as state_machine<>::state_downcast<>()
Note: The result is unspecified if this function is called when the machine is unstable

state_iterator state_begin() const;

state_iterator state_end() const;

Require: If called from a constructor of a direct or indirect subtype then the most-derived type must directly or indirectly derive from the state class template
Return: Have exactly the same semantics as state_machine<>::state_begin() and state_machine<>::state_end()
Note: The result is unspecified if these functions are called when the machine is unstable

Class template simple_state static functions

static id_type static_type();

Returns: A value unambiguously identifying the type of MostDerived
Note: id_type values are comparable with operator==() and operator!=(). An unspecified collating order can be established with std::less< id_type >

template< class CustomId >
static const CustomId * custom_static_type_ptr();

Requires: If a custom type identifier has been set then CustomId must match the type of the previously set pointer
Returns: The pointer to the custom type identifier for MostDerived or 0
Note: This function is not available if BOOST_STATECHART_USE_NATIVE_RTTI is defined

template< class CustomId >
static void custom_static_type_ptr( const CustomId * );

Effects: Sets the pointer to the custom type identifier for MostDerived
Note: This function is not available if BOOST_STATECHART_USE_NATIVE_RTTI is defined

Header <boost/statechart/state.hpp>

Class template state

This is the base class template for all models of the State concept. Such models typically need to call at least one of the following simple_state<> member functions from their constructors:

void post_event(
  const intrusive_ptr< const event_base > & );
void post_event( const event_base & );

template<
  class HistoryContext,
  implementation-defined-unsigned-integer-type
    orthogonalPosition >
void clear_shallow_history();
template<
  class HistoryContext,
  implementation-defined-unsigned-integer-type
    orthogonalPosition >
void clear_deep_history();

outermost_context_type & outermost_context();
const outermost_context_type & outermost_context() const;

template< class OtherContext >
OtherContext & context();
template< class OtherContext >
const OtherContext & context() const;

template< class Target >
Target state_cast() const;
template< class Target >
Target state_downcast() const;

state_iterator state_begin() const;
state_iterator state_end() const;

States that do not need to call any of these member functions from their constructors should rather derive from the simple_state class template, what saves the implementation of the forwarding constructor.

Class template state synopsis

namespace boost
{
namespace statechart
{
  template<
    class MostDerived,
    class Context,
    class InnerInitial = unspecified,
    history_mode historyMode = has_no_history >
  class state : public simple_state<
    MostDerived, Context, InnerInitial, historyMode >
  {
    protected:
      struct my_context
      {
        // implementation-defined
      };

      typedef state my_base;

      state( my_context ctx );
      ~state();
  };
}
}

Direct and indirect subtypes of state<> must provide a constructor with the same signature as the state<> constructor, forwarding the context parameter.

Header <boost/statechart/shallow_history.hpp>

Class template shallow_history

This class template is used to specify a shallow history transition target or a shallow history inner initial state.

Class template shallow_history parameters

Template parameter	Requirements	Semantics
DefaultState	A model of the SimpleState or State concepts. The type passed as Context argument to the simple_state<> or state<> base of DefaultState must itself pass has_shallow_history or has_full_history as historyMode argument to its simple_state<> or state<> base	The state that is entered if shallow history is not available

Class template shallow_history synopsis

namespace boost
{
namespace statechart
{
  template< class DefaultState >
  class shallow_history
  {
    // implementation-defined
  };
}
}

Header <boost/statechart/deep_history.hpp>

Class template deep_history

This class template is used to specify a deep history transition target or a deep history inner initial state. The current deep history implementation has some limitations.

Class template deep_history parameters

Template parameter	Requirements	Semantics
DefaultState	A model of the SimpleState or State concepts. The type passed as Context argument to the simple_state<> or state<> base of DefaultState must itself pass has_deep_history or has_full_history as historyMode argument to its simple_state<> or state<> base	The state that is entered if deep history is not available

Class template deep_history synopsis

namespace boost
{
namespace statechart
{
  template< class DefaultState >
  class deep_history
  {
    // implementation-defined
  };
}
}

Header <boost/statechart/event_base.hpp>

Class event_base

This is the common base of all events.

Class event_base synopsis

namespace boost
{
namespace statechart
{
  class event_base
  {
    public:
      intrusive_ptr< const event_base >
        intrusive_from_this() const;

      typedef implementation-defined id_type;

      id_type dynamic_type() const;

      template< typename CustomId >
      const CustomId * custom_dynamic_type_ptr() const;
      
    protected:
      event_base( unspecified-parameter );
      virtual ~event_base();
  };
}
}

Class event_base constructor and destructor

event_base( unspecified-parameter );

Effects: Constructs the common base portion of an event

virtual ~event_base();

Effects: Destructs the common base portion of an event

Class event_base observer functions

intrusive_ptr< const event_base > intrusive_from_this() const;

Returns: Another intrusive_ptr< const event_base > referencing this if this is already referenced by an intrusive_ptr<>. Otherwise, returns an intrusive_ptr< const event_base > referencing a newly created copy of the most-derived object

id_type dynamic_type() const;

Returns: A value unambiguously identifying the most-derived type
Note: id_type values are comparable with operator==() and operator!=(). An unspecified collating order can be established with std::less< id_type >. In contrast to typeid( cs ), this function is available even on platforms that do not support C++ RTTI (or have been configured to not support it)

template< typename CustomId >
const CustomId * custom_dynamic_type_ptr() const;

Requires: If a custom type identifier has been set then CustomId must match the type of the previously set pointer
Returns: A pointer to the custom type identifier or 0
Note: This function is not available if BOOST_STATECHART_USE_NATIVE_RTTI is defined

Header <boost/statechart/event.hpp>

Class template event

This is the base class template of all events.

Class template event parameters

Template parameter	Requirements	Semantics	Default
MostDerived	The most-derived subtype of this class template
Allocator	A model of the standard Allocator concept	Allocator::rebind< MostDerived >::other is used to allocate and deallocate all event subtype objects of dynamic storage duration, see operator new	std::allocator< void >

Class template event synopsis

namespace boost
{
namespace statechart
{
  template< class MostDerived, class Allocator = std::allocator< void > >
  class event : implementation-defined
  {
    public:
      static void * operator new( std::size_t size );
      static void * operator new( std::size_t size, void * p );
      static void operator delete( void * pEvent );

      static id_type static_type();

      template< class CustomId >
      static const CustomId * custom_static_type_ptr();

      template< class CustomId >
      static void custom_static_type_ptr( const CustomId * );

    protected:
      event();
      virtual ~event();
  };
}
}

Class template event constructor and destructor

event();

Effects: Constructs an event

virtual ~event();

Effects: Destructs an event

Class template event static functions

static void * operator new( std::size_t size );

Effects: Allocator::rebind< MostDerived >::other().allocate( 1, static_cast< MostDerived * >( 0 ) );
Returns: The return value of the above call
Throws: Whatever the above call throws

static void * operator new( std::size_t size, void * p );

Effects: None
Returns: p

static void operator delete( void * pEvent );

Effects: Allocator::rebind< MostDerived >::other().deallocate( static_cast< MostDerived * >( pEvent ), 1 );

static id_type static_type();

Returns: A value unambiguously identifying the type of MostDerived
Note: id_type values are comparable with operator==() and operator!=(). An unspecified collating order can be established with std::less< id_type >

template< class CustomId >
static const CustomId * custom_static_type_ptr();

Requires: If a custom type identifier has been set then CustomId must match the type of the previously set pointer
Returns: The pointer to the custom type identifier for MostDerived or 0
Note: This function is not available if BOOST_STATECHART_USE_NATIVE_RTTI is defined

template< class CustomId >
static void custom_static_type_ptr( const CustomId * );

Effects: Sets the pointer to the custom type identifier for MostDerived
Note: This function is not available if BOOST_STATECHART_USE_NATIVE_RTTI is defined

Header <boost/statechart/transition.hpp>

Class template transition

This class template is used to specify a transition reaction. Instantiations of this template can appear in the reactions member typedef in models of the SimpleState and State concepts.

Class template transition parameters

Template parameter	Requirements	Semantics	Default
Event	A model of the Event concept or the class event_base	The event triggering the transition. If event_base is specified, the transition is triggered by all models of the Event concept
Destination	A model of the SimpleState or State concepts or an instantiation of the shallow_history or deep_history class templates. The source state (the state for which this transition is defined) and Destination must have a common direct or indirect context	The destination state to make a transition to
TransitionContext	A common context of the source and Destination state	The state of which the transition action is a member	unspecified
pTransitionAction	A pointer to a member function of TransitionContext. The member function must accept a const Event & parameter and return void	The transition action that is executed during the transition. By default no transition action is executed	unspecified

Class template transition synopsis

namespace boost
{
namespace statechart
{
  template<
    class Event,
    class Destination,
    class TransitionContext = unspecified,
    void ( TransitionContext::*pTransitionAction )(
      const Event & ) = unspecified >
  class transition
  {
    // implementation-defined
  };
}
}

Class template transition semantics

When executed, one of the following calls to a member function of the state for which the reaction was defined is made:

• transit< Destination >(), if no transition action was specified
• transit< Destination >( pTransitionAction, currentEvent ), if a transition action was specified

Header <boost/statechart/in_state_reaction.hpp>

Class template in_state_reaction

This class template is used to specify an in-state reaction. Instantiations of this template can appear in the reactions member typedef in models of the SimpleState and State concepts.

Class template in_state_reaction parameters

Template parameter	Requirements	Semantics	Default
Event	A model of the Event concept or the class event_base	The event triggering the in-state reaction. If event_base is specified, the in-state reaction is triggered by all models of the Event concept
ReactionContext	Either the state defining the in-state reaction itself or one of it direct or indirect contexts	The state of which the action is a member	unspecified
pAction	A pointer to a member function of ReactionContext. The member function must accept a const Event & parameter and return void	The action that is executed during the in-state reaction	unspecified

Class template in_state_reaction synopsis

namespace boost
{
namespace statechart
{
  template<
    class Event,
    class ReactionContext = unspecified,
    void ( ReactionContext::*pAction )(
      const Event & ) = unspecified >
  class in_state_reaction
  {
    // implementation-defined
  };
}
}

Class template in_state_reaction semantics

When executed then the following happens:

1. If an action was specified, pAction is called, passing the triggering event as the only argument
2. A call is made to the discard_event member function of the state for which the reaction was defined

Header <boost/statechart/termination.hpp>

Class template termination

This class template is used to specify a termination reaction. Instantiations of this template can appear in the reactions member typedef in models of the SimpleState and State concepts.

Class template termination parameters

Template parameter	Requirements	Semantics
Event	A model of the Event concept or the class event_base	The event triggering the termination. If event_base is specified, the termination is triggered by all models of the Event concept

Class template termination synopsis

namespace boost
{
namespace statechart
{
  template< class Event >
  class termination
  {
    // implementation-defined
  };
}
}

Class template termination semantics

When executed, a call is made to the terminate member function of the state for which the reaction was defined.

Header <boost/statechart/deferral.hpp>

Class template deferral

This class template is used to specify a deferral reaction. Instantiations of this template can appear in the reactions member typedef in models of the SimpleState and State concepts.

Class template deferral parameters

Template parameter	Requirements	Semantics
Event	A model of the Event concept or the class event_base	The event triggering the deferral. If event_base is specified, the deferral is triggered by all models of the Event concept

Class template deferral synopsis

namespace boost
{
namespace statechart
{
  template< class Event >
  class deferral
  {
    // implementation-defined
  };
}
}

Class template deferral semantics

When executed, a call is made to the defer_event member function of the state for which the reaction was defined.

Header <boost/statechart/custom_reaction.hpp>

Class template custom_reaction

This class template is used to specify a custom reaction. Instantiations of this template can appear in the reactions member typedef in models of the SimpleState and State concepts.

Class template custom_reaction parameters

Template parameter	Requirements	Semantics
Event	A model of the Event concept or the class event_base	The event triggering the custom reaction. If event_base is specified, the custom reaction is triggered by all models of the Event concept

Class template custom_reaction synopsis

namespace boost
{
namespace statechart
{
  template< class Event >
  class custom_reaction
  {
    // implementation-defined
  };
}
}

Class template custom_reaction semantics

When executed, a call is made to the user-supplied react member function of the state for which the reaction was defined. The react member function must have the following signature:

result react( const Event & );

and must call exactly one of the following reaction functions and return the obtained result object:

result discard_event();
result forward_event();
result defer_event();
template< class DestinationState >
result transit();
template<
  class DestinationState,
  class TransitionContext,
  class Event >
result transit(
  void ( TransitionContext::* )( const Event & ),
  const Event & );
result terminate();

Header <boost/statechart/result.hpp>

Class result

Defines the nature of the reaction taken in a user-supplied react member function (called when a custom_reaction is executed). Objects of this type are always obtained by calling one of the reaction functions and must be returned from the react member function immediately.

namespace boost
{
namespace statechart
{
  class result
  {
    public:
      result( const result & other );
      ~result();

    private:
      // Result objects are not assignable
      result & operator=( const result & other );
  };
}
}

Class result constructor and destructor

result( const result & other );

Requires: other is not consumed
Effects: Copy-constructs a new result object and marks other as consumed. That is, result has destructive copy semantics

~result();

Requires: this is marked as