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#ifndef Pegasus_MessageQueue_h
#define Pegasus_MessageQueue_h

#include <Pegasus/Common/Config.h>
#include <Pegasus/Common/Message.h>
#include <Pegasus/Common/Mutex.h>
#include <Pegasus/Common/List.h>
#include <Pegasus/Common/Linkage.h>

PEGASUS_NAMESPACE_BEGIN

/** The MessageQueue class represents a queue abstraction and is used by
    modules to exchange messages. Methods are provided for enqueuing,
    dequeuing, removing, iterating messages. Some methods are virtual and
    may be overriden by subclasses to modify the behavior.

    <h1>A Word about using the find() Methods</h1>

    There are two find() methods. One that takes a queue id and one that
    takes a name. The time complexity of the former is O(1); whereas, the
    time complexity of the latter is O(n). Therefore, use the queue id form
    since it is more efficient.
*/
class PEGASUS_COMMON_LINKAGE MessageQueue
{
public:

    /** This constructor places this object on a queue table which is
    maintained by this class. Each message queue has a queue-id (which
    may be obtained by calling getQueueId()). The queue-id may be passed
    to lookupQueue() to obtain a pointer to the corresponding queue).
    */
    MessageQueue(const char *name);

    /** Removes this queue from the queue table. */
    virtual ~MessageQueue();

    /** Enques a message (places it at the back of the queue).
    @param message pointer to message to be enqueued.
    @exception  NullPointer exception if message parameter is null.
    */
    virtual void enqueue(Message* message);

    /** Dequeues a message (removes it from the front of the queue).
    @return pointer to message or zero if queue is empty.
    */
    virtual Message* dequeue();

    /**
        This function will indicate whether the MessageQueue is active or not. 
        By default this function will return true and do nothing else.
    */
    virtual Boolean isActive();

    /** Returns true if there are no messages on the queue. */
    Boolean isEmpty() const { return  (Boolean) _messageList.is_empty(); }

    /** Returns the number of messages on the queue. */
    Uint32 getCount() const {  return (Uint32) _messageList.size(); }

    /** Retrieve the queue id for this queue. */
    Uint32 getQueueId() const throw() { return _queueId; }

    /** Provide a string name for this queue to be used by the print method.
     */
    const char* getQueueName() const;

    /** This method is called after a message has been enqueued. This default
    implementation does nothing. Derived classes may override this to
    take some action each time a message is enqueued (for example, this
    method could handle the incoming message in the thread of the caller
    of enqueue()).
    */
    virtual void handleEnqueue() ;

    /** Lookup a message queue from a queue id. Note this is an O(1) operation.
     */
    static MessageQueue* lookup(Uint32 queueId);

    /** Lookup a message given a queue name. NOte this is an O(N) operation.
     */
    static MessageQueue* lookup(const char *name);

    /** Get the next available queue id. It always returns a non-zero
    queue id an monotonically increases and finally wraps (to one)
    after reaching the maximum unsigned 32 bit integer.
    */
    static Uint32 getNextQueueId();

    /** Put the queue id into the stack.
    */
    static void putQueueId(Uint32 queueId);

protected:
    Uint32 _queueId;
    char *_name;

private:
    List<Message, Mutex> _messageList;
};

PEGASUS_NAMESPACE_END

#endif /* Pegasus_MessageQueue_h */