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LocalStatusPublisher Class Reference

Collaboration diagram for LocalStatusPublisher:

Detailed Description

While developing embedded system, one frequently encounters a situation where many entities are interested in occurrence of a particular event. This introduces a strong coupling between the publisher and subscriber of this event change notification. Thus whenever a new entity needs the information, code for the publisher of the information also needs to be modified to accommodate the new request.

The Publish-Subscribe Pattern solves the tight coupling problem. Here the coupling is removed by the publisher of information supporting a generic interface for subscribers. Entities interested in the information subscribe to the publisher by registering for the information. With this interface, the publisher code does not need to be modified every time a subscriber is introduced.

This class can be used as a helper class when this generic subscribe-publish interface is desired. The following important public methods are supported:

• PublishStatus: Invoke this method to inform all registered subscribers about status change.
• Register: Invoke this method to register an object for the status change notification.
• Deregister: Invoke this method to deregister an object. The object will not receive any notifications of status change after it deregisters.

See also:

Publish Subscribe Design Pattern

RemoteStatusPublisher

Definition at line 34 of file Local_Status_Publisher.h.

Public Types
enum	OperationStatus
	Status of an operation.
Public Member Functions
void	PublishStatus (int unitId, int status)
	PublishStatus() notifies subscribers about status change.
OperationStatus	Register (Subscriber *pSubscriber)
	Register() is invoked by objects inheriting from Subscriber.
OperationStatus	Deregister (Subscriber *pSubscriber)
	Deregister() removes a subscriber.
Private Types
enum	{ NOT_FOUND = -1, MAX_SUBSCRIBERS = 100 }
Private Member Functions
int	Find (Subscriber *pSubscriber) const
	This method searches for an entry that matches the pointer.
Private Attributes
Subscriber *	m_pSubscriber [MAX_SUBSCRIBERS]
	Subscribers being tracked by the publisher. The entire list should be scanned for non NULL subscriber pointers.

Member Enumeration Documentation

anonymous enum [private]

Enumeration values: NOT_FOUND  Return when an entry is not found. MAX_SUBSCRIBERS  Maximum number of subscribers. Definition at line 36 of file Local_Status_Publisher.h. 00036 { 00038 NOT_FOUND = -1, 00039 00041 MAX_SUBSCRIBERS = 100 00042 };

Member Function Documentation

int LocalStatusPublisher::Find (  Subscriber *  pSubscriber  )  const [inline, private]

This method searches for an entry that matches the pointer. It returns the index of the entry. If the entry is not found, it returns NOT_FOUND. Parameters: pSubscriber  Pointer to the subscriber to be found. See also: Publish Subscribe Design Patterns Definition at line 57 of file Local_Status_Publisher.h. 00058 { 00059 int index = NOT_FOUND; 00060 for (int i=0; i < MAX_SUBSCRIBERS; i++) 00061 { 00062 if (m_pSubscriber[i] == pSubscriber) 00063 { 00064 index = i; 00065 break; 00066 } 00067 } 00068 return index; 00069 }

void LocalStatusPublisher::PublishStatus (  int  unitId, int  status )  [inline]

PublishStatus() notifies subscribers about status change. Invoke this method whenever you need to update the status to all the subscribers of the status information. Parameters: unitId  Id of the unit that needs a status publication. status  The status that needs to be published. See also: Publish Subscribe Design Patterns Definition at line 85 of file Local_Status_Publisher.h. 00086 { 00087 for (int i=0; i < MAX_SUBSCRIBERS; i++) 00088 { 00089 // A valid subscriber exists only when the pointer is non NULL 00090 if (m_pSubscriber[i]) 00091 { 00092 m_pSubscriber[i]->HandleStatusChange(unitId, status); 00093 } 00094 } 00095 }

OperationStatus LocalStatusPublisher::Register (  Subscriber *  pSubscriber  )  [inline]

Register() is invoked by objects inheriting from Subscriber. Once registered, the object is notified whenever status change is detected. The method returns FAILURE in the following cases: Duplicate Request Subscriber Table is full Parameters: pSubscriber  Subscriber being registered for the service. See also: Publish Subscribe Design Patterns Definition at line 108 of file Local_Status_Publisher.h. 00109 { 00110 OperationStatus status = FAILURE; 00111 // First check if the subscriber is already present 00112 // in the list 00113 int index = Find(pSubscriber); 00114 00115 if (index == NOT_FOUND) 00116 { 00117 // Subscriber was not found, so this is not a duplicate request 00118 // Now look for a free entry by finding NULL 00119 index = Find(NULL); 00120 if (index != NOT_FOUND) 00121 { 00122 // A free entry has been found 00123 m_pSubscriber[index] = pSubscriber; 00124 status = SUCCESS; 00125 } 00126 } 00127 return status; 00128 }

OperationStatus LocalStatusPublisher::Deregister (  Subscriber *  pSubscriber  )  [inline]

Deregister() removes a subscriber. Returns FAILURE if the subscriber was not registered in the first place. Parameters: pSubscriber  Pointer to the subscriber that needs to be deregistered. See also: Publish Subscribe Design Patterns Definition at line 138 of file Local_Status_Publisher.h. 00139 { 00140 OperationStatus status = FAILURE; 00141 // Search for the entry 00142 int index = Find(pSubscriber); 00143 if (index != NOT_FOUND) 00144 { 00145 // Free the entry by marking as NULL 00146 m_pSubscriber[index] = NULL; 00147 status = SUCCESS; 00148 } 00149 return SUCCESS; 00150 }

• Local_Status_Publisher.h

Generated on Sun Feb 13 21:30:33 2005 for Object Oriented Design Examples by 1.3.4

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