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• The class PowerSupply simulates the behaviour of a power supply.
• (…doxygen comment…)
  */
  class acsexmpl_EXPORT PowerSupply:public virtual CharacteristicComponentImpl,
  public virtual POA_PS::PowerSupply,
  public ActionImplementator
  {
  Asynchronous call handling implementation requires that action numbers are defined for each call (here on(), off() and reset()).
  PowerSupply must inherit from the class CharacteristicComponentImpl because the IDL interface does, ActionImplementator for asynchronous methods, and POA_<name of module in IDL>::<name of interface in IDL> which is auto-generated by tao_idl. The CharacteristicComponentImpl class incorporates standard methods and macros necessary for the CORBA interface implementation and MACI-DLL support.
  Now we can define public methods and fields (note: because of inheritance, you should put virtual before the destructor and other methods):
  public:
  /**
• Constructor
• @param poa poa which will activate this and also all other COBs
• @param name Component name
  */
  PowerSupply(const ACE_CString& name, maci::ContainerServices* containerServices);
  /**
• Destructor
  */
  virtual ~PowerSupply();
  /**

• 
  

  Wiki Markup
  Override component lifecycles method */ virtual void *execute{*}() throw (acsErrTypeLifeCycle::LifeCycleExImpl); \\ /* --------------- \[ Action implementator interface \] -------------- */ \\ /**

  
  

• Action dispatcher function – called from a method inherited from
• ActionImplementator class whenever there is an asynchronous method waiting in a
• queue.
• (…doxygen comment…)
  */
  virtual ActionRequest
  invokeAction(int function, BACIComponent* cob_p, const int& callbackID,
  const CBDescIn& descIn, BACIValue* value, Completion& completion,
  CBDescOut& descOut);
  /***
• Implementation of async. on() method – called by invokeAction
  */
  virtual ActionRequest
  onAction(BACICComponent* cob, const int& callbackID, const CBDescIn& descIn,
  BACIValue* value, Completion& completion, CBDescOut& descOut);
  /***
• Implementation of async. off() method – called by invokeAction
  */
  virtual ActionRequest
  offAction(BACICComponent * cob, const int& callbackID, const CBDescIn& descIn,
  BACIValue* value, Completion& completion, CBDescOut& descOut);
  /**

• 
  

  Wiki Markup
  Implementation of async. *reset{*}() method - called by invokeAction */ virtual ActionRequest *reset{*}Action(BACICComponent * cob, const int& callbackID, const CBDescIn& descIn, BACIValue* value, Completion& completion, CBDescOut& descOut); \\ \\ /* --------------------- \[ CORBA interface \] ----------------------*/ \\ /**

  
  

• Switches on the power supply – registers the call to the asynch. queue
• (…doxygen comment…)
  */
  virtual void
  on (ACS::CBvoid_ptr cb, const ACS::CBDescIn & desc)
  throw(CORBA::SystemException);
  /**
• Switches off the power supply - registers the call to the asynch. queue
• (…doxygen comment…)
  */
  virtual void
  off (ACS::CBvoid_ptr cb, const ACS::CBDescIn & desc)
  throw(CORBA::SystemException);
  /**
• Resets the power supply - registers the call to the asynch. queue
• (…doxygen comment…)
  */
  virtual void
  reset (ACS::CBvoid_ptr cb, const ACS::CBDescIn & desc)
  throw(CORBA::SystemException);
  /**
• Property current contains the commanded current of the power supply.
  */
  virtual ACS::RWdouble_ptr
  current ()
  throw(CORBA::SystemException);
  /**
• Property readback is the actual current obtained from the physical device.
  */
  virtual ACS::ROdouble_ptr
  readback ()
  throw(CORBA::SystemException);
  /**

• Property status contains the status of the power supply.
  */
  virtual ACS::ROpattern_ptr
  status ()
  throw(CORBA::SystemException);
  The private fields usually consist of all variables that are in the program. We use a smart pointer for each property. The type of each smart pointer is a template based on the type of the related property. The smart pointers for the properties take care of all the CORBA detail in behalf of the developer making the programming of a device server easier, faster and safer.
  private:
  /// Properties
  SmartPropertyPointer<ROdouble> m_readback_sp;
  SmartPropertyPointer<RWdouble> m_current_sp;
  SmartPropertyPointer<ROpattern> m_status_sp;
  };
  #endif /* acsexmplPowerSupplyImpl_h */
  
  The execute method is part of the life cycle methods. Ther are four methods for the life cycle. They are defined in acscomponent and can be overridden by the developer.
  virtual void initialize()
  throw (acsErrTypeLifeCycle::acsErrTypeLifeCycleExImpl);
  virtual void execute()
  throw (acsErrTypeLifeCycle::acsErrTypeLifeCycleExImpl);
  */
  virtual void cleanUp();
  virtual void aboutToAbort();
  The intialize method is called by the container after instantiating the component i.e. after executing the constructor. The developer should insert here all the code related to the initialization of the component like, for example retrieve connections, read in configuration files orparameters, build up in-memory tables and so on. This method is called before any functional requests can be sent to the component.
  The execute method is called by the container after the initialize to signal that the server has to be ready to accept functional requests.
  The developer in the execute and the initialize can throw an exception to signal a malfunction to the container. In this case the exception is catched by the container and the component will be released and unloaded.
  The aboutToAbort is called by the container in case of an error and an emergency sistuation requests the component to be destroyed. The developer should insert here the code to handle this situation trying to release resources and so on. This method is called in an emergency situation and there is no warranty that the container will wait its termination before destroying the component.
  Finally, the cleanUp method is called by the container before destroying the server in a normal situation. The developer should release all the reasource and perform all the clean up here.
  As a guideline, we suggest to leave the constructor and the destructor of the server empty moving the code in the life cycle method. This should help in writing more reliable servers.
  There is no need to call the parent life cycle method
  In the power supply component, execute is the only life cycle method overridden.
  Together with the life cycle methods there is the concept of the state of the component i.e. the component passes through different states during its life, since it is built until it is destroyed. The state is transparent to the user and managed by the ComponentStateManager object that is part of the ContainerServices. The state of the component is managed by the container and must not be accessed nor modified by the developer. For completeness I report here the states that a component can assume, as defined in acscomponent.idl:

  COMPSTATE_NEW	This is the initial state of the component
  COMPSTATE_INITIALIZING	When the component is executing the initialize method
  COMPSTATE_INITIALIZED	When the initialize method terminates
  COMPSTATE_OPERATIONAL	When the execute method terminates
  COMPSTATE_ERROR	An error occurred
  COMPSTATE_DESTROYING	Before executing the cleanUp method
  COMPSTATE_ABORTING	Before executing the aboutToAbort method
  COMPSTATE_DEFUNCT	Before destroying the component

  
  

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  Implementation files

  (If you are using ALMA directory structure, implementation files should be located in <xxxx>/ws/src or <xxxx>/src directory.)
  Tao has already generated some files needed for client-server communication, but now we have to implement our device server. I will divide the C++ file into smaller parts and explain each of them. The beginning of the program is pretty much standard, so I will just write about unusual lines. (Note: code marked with bold should be adapted for new applications):

...

\\
\\
\\
The destructor is empty. The entire cleanup for the properties is managed by the smart pointers.
\\
*PowerSupply{*}::~{*}PowerSupply{*}()
\{
\}
\\
Let us come to actions now. All requests for asynchronous actions go through the Activator, which sends this request back to the device server. This is done through the invokeAction() method, where you define what has to be done when a call is received:
 \\
/* --------------- \[ Action implementator interface \] -------------- */
\\
ActionRequest 
PowerSupply::invokeAction(int function, BACIComponent* cob, const int& callbackID,
    const CBDescIn& descIn, BACIValue* value, Completion& completion,
    CBDescOut& descOut) 
\{
  switch (function) 
    \{
    case *ON{*}_ACTION:
      return *on{*}Action(cob, callbackID, descIn, value, completion, descOut);
    case *OFF{*}_ACTION:
      return *off{*}Action(cob, callbackID, descIn, value, completion, descOut);
    case *RESET{*}_ACTION:
      return *reset{*}Action(cob, callbackID, descIn, value, completion, descOut);
    default:
      return reqDestroy;
    \}
\}
\\
\\
The implementation of the functions we defined in the previous method:
\\

1. 
   

   Wiki Markup
   /* ------------------ \[ Action implementations \] ----------------- */

   
   

2. /// implementation of async. on() method
3. ActionRequest
4. PowerSupply::onAction(BACIComponent* cob, const int& callbackID,
5. const CBDescIn& descIn, BACIValue* value,
6. Completion& completion, CBDescOut& descOut)
7. {
8. ACS_DEBUG_PARAM("::PowerSupply::onAction", "%s", getComponent()->getName());
9. ...........
10. completion = ACSErrTypeOK::ACSErrOKCompletion();
11. // complete action requesting done invokation,
12. // otherwise return reqInvokeWorking and set descOut.estimated_timeout
13. return reqInvokeDone;
14. }

...

\\
The offAction() and resetAction() functions are based on the same rule - just replace the name and the part where the device server actually does something.
\\
\\
We have to describe the device server's actions (like on(), off(), reset()). These are asynchronous (usually they take some time and we do not want to block a client while executing) so we have to register the action to the Activator that will then do the rest of the procedure.  For example, calling on() will just register that action inside a queue until Activator calls PowerSupply::invokeAction which will in turn, call onAction().
\\
The client must provide a pointer to it's implementation of callbacks and the structure of type CBDescIn (that identifies the callback) as an argument of the registerAction() method. Our device server sends these parameters to Activator and also adds a pointer to itself and a description of an action (integer - ON_ACTION will be replaced with 1, OFF_ACTION with 2 and so on).
\\
Your job is to write one block of a code for each action and change only the last argument of the method registerAction - an integer which is later sent back to the device server, to the method invokeAction(). First argument of registerAction() method - in this case BACIValue::type_null - is a callback type.
\\
void
*PowerSupply::on* (ACS::CBvoid_ptr cb, const ACS::CBDescIn & desc)
  throw(CORBA::SystemException)
\{
  getComponent()->registerAction(BACIValue::type_null, cb, desc, this, *ON{*}_ACTION);
\}
\\
void
*PowerSupply::off* (ACS::CBvoid_ptr cb, const ACS::CBDescIn & desc)
  throw(CORBA::SystemException)
\{
  getComponent()->registerAction(BACIValue::type_null, cb, desc, this, *OFF{*}_ACTION);
\}
\\
void
*PowerSupply::reset* (ACS::CBvoid_ptr cb, const ACS::CBDescIn & desc)
  throw(CORBA::SystemException)
\{
  getComponent()->registerAction(BACIValue::type_null, cb, desc, this, *RESET{*}_ACTION);
\}
\\
throw(...) defines what kind of exceptions are available.
\\
\\
If a client wants to do something with current, readback, and other properties, it must get a reference to these properties. This is done in following code:
\\
ACS::{*}RWdouble{*}_ptr
*PowerSupply::current{*}()
    throw(CORBA::SystemException)
\{
    if (m_current_sp==0)
        return ACS::{*}RWdouble{*}::_nil();
\\
    ACS::{*}RWdouble{*}_var prop = ACS::{*}RWdouble{*}::_narrow(m_current_sp->getCORBAReference());
    return prop._retn();
\}
\\
ACS::{*}ROdouble{*}_ptr
*PowerSupply::readback{*}()
    throw(CORBA::SystemException)
\{
    if (m_readback_p==0)
        return ACS::{*}ROdouble{*}::_nil();
\\
   ACS::{*}ROdouble{*}_var prop = ACS::{*}ROdouble{*}::_narrow(m_readback_sp->getCORBAReference());
    return prop._retn();
\}
\\
ACS::{*}ROpattern{*}_ptr
*PowerSupply::status{*}()
    throw(CORBA::SystemException)
\{
    if (m_status_p==0)
        return ACS::{*}ROpattern{*}::_nil();
\\
   ACS::{*}ROpattern{*}_var prop = ACS::{*}ROpattern{*}::_narrow(m_status_sp->getCORBAReference());
    return prop._retn();
\}
\\
One must write accessors for every property, changing the name of a property (current), variable (m_current_sp) and type of a property (replace all fields where RWdouble appears with ROdouble or ROpattern).
\\
Now we are really near the end. We have to add MACI DLL support functions. For this purpose we use the macro MACI_DLL_SUPPORT_FUNCTIONS(class_name):
\\
/* --------------- \[ MACI DLL support functions \] -----------------*/
\\
#include <maciACSComponentDefines.h>
MACI_DLL_SUPPORT_FUNCTIONS ({*}PowerSupply{*})
\\
/* ----------------------------------------------------------------*/
\\
As we said at the beginning of the paragraph, it is possible to use the properties without smart pointers even if we discourage this implementation. We briefly describe herein the changes in the previous code if smart pointers were not used.
In the include file each property is defined without the templetized smart pointer type and, of course, the baciSmartPropertyPointer.h is not needed. Note that the names of the variables terminate with _p and not with _sp to highlight that we are now using pointers instead of smart pointers. 
\\
*ROdouble* m_readback_p* 
*ROdouble* m_readback_p;* 
*RWdouble*  m_current_p;*
\\
In the constructor these pointers are first initialized to 0 then each property is created in the same way they are created with smart pointers. The CHARACTERISTIC_COMPONENT_PROPERTY macro must be implemented for each BACI property.  The macro performs error checking and generates a description of the property. This macro must not be used with smart pointers because they take care of all the initializations automatically.
\\
The following is the constructor without using smart pointers for the properties.
\\
*PowerSupply{*}::{*}PowerSupply{*}(const ACE_CString& name,
  maci::ContainerServices * containerServices):
 CharacteristicComponentImpl(name,containerServices),
 *m_readback_p({*}0{*}),*
 *m_current_p({*}0{*}),*
 *m_status_p({*}0{*}) \{*
 m_readback_p = new *ROdouble{*}(name+":{*}readback{*}", getComponent());
 CHARACTERISTIC_COMPONENT_PROPERTY(readback, m_readback_p);
\\
 m_current_p  = new *RWdouble{*}(name+":{*}current{*}", getComponent());
 CHARACTERISTIC_COMPONENT_PROPERTY (current, m_current_p);
\\
 m_status_p = new *ROpattern{*}(name+":{*}status{*}", getComponent());
 CHARACTERISTIC_COMPONENT_PROPERTY(status, m_status_p);
*\}*
\\
Another difference is in the destructor because for each property we must call the destroy method but not the delete. 
\\
*PowerSupply{*}::~{*}PowerSupply{*}() \{
 ...
 (m_readback_p) \{ m_readback_p->destroy(); m_readback_p = 0; \}
 (m_current_p) \{ m_current_p->destroy(); m_current_p = 0; \}
 if (m_status_p) \{ m_status_p->destroy(); m_status_p = 0; \}
\}The rest of the code remains the same apart for the renaming of the variables.
\\
\\
\\
\\

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The ContainerServices

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Logging and debugging

ACS_TRACE("::PowerSupply::~PowerSupply");
\\
ACS_DEBUG("::PowerSupply::~PowerSupply", "COB destroyed");
\\
ACS_LOG(LM_RUNTIME_CONTEXT, "PowerSupply/DLLOpen", 
       (LM_ERROR, "Failed to create Component - constructor returned 0!"));
Find out more about this in Logging and Archiving (\[R04\]). 

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Compiling

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