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casacore::Queue< T > Class Template Reference

A First-In-First-Out (FIFO) data structure. More...

#include <Queue.h>

Public Member Functions

 Queue ()
 Create a Queue with no elements. More...
 
 Queue (const Queue< T > &other)
 Create a queue which is a copy of other. More...
 
 ~Queue ()
 
Queue< T > & operator= (const Queue< T > &other)
 Create a queue which is a copy of other. More...
 
void enqueue (const T &value)
 Place an element in the queue. More...
 
void operator() (const T &value)
 Short-hand for enqueue();. More...
 
void dequeue (T &value)
 Remove an element from the head of the queue and decrease nelements() by one. More...
 
operator() ()
 Short-hand for dequeue. More...
 
void clear ()
 Delete all the elements from the queue, and free up any resources. More...
 
void compress ()
 Leave this queue logically unchanged, but remove unused storage. More...
 
uInt nelements () const
 How many elements are in the queue? More...
 

Private Attributes

Int first_p
 
Int next_p
 
Block< T > data_p
 

Detailed Description

template<class T>
class casacore::Queue< T >

A First-In-First-Out (FIFO) data structure.

Review Status

Reviewed By:
Gareth Hunt
Date Reviewed:
94Jan06
Test programs:
tQueue

Synopsis

A Queue as implemented here is a simple container which can grow with time, and which returns its elements (only) in the order they are inserted. That is, the fundamental operations are to insert an element in the queue (at the "back") and retrieve an element (from the "front").

Queue<Int> queue;
Int x;
queue(1); // enqueue
queue.enqueue(2); // enqueue
queue(3); // enqueue
queue(4); // enqueue
queue.dequeue(x); // dequeue
cout << x << endl;
..\.
while (queue.nelements() > 0)
cout << queue() << " "; // dequeue
cout << endl;

Presently the implementation is rather simple. It stores the elements in a Block<T> which resizes (exponentially to avoid quadratic behaviour) when necessary. New elements are added to the end of the block, old elements are pulled off the front of the Block. The positions at the beginning are only reclaimed when the queue is empty or the compress() member is called. This implementation is reasonably time efficient, but not necessarily space efficient. A more sophisticated implementation may be necessary eventually.

To be used in a Queue, a class must have a default constructor, assignment operator, and copy constructor.

Motivation

This class was written for an application which thought it needed to queue up some Glish events while it processed other Glish events. In fact that application (Clean) was simplified so that it doesn't presently operate that way.

To Do

Definition at line 96 of file Queue.h.

Constructor & Destructor Documentation

template<class T>
casacore::Queue< T >::Queue ( )

Create a Queue with no elements.

template<class T>
casacore::Queue< T >::Queue ( const Queue< T > &  other)

Create a queue which is a copy of other.

Compresses unused heap storage.

template<class T>
casacore::Queue< T >::~Queue ( )

Member Function Documentation

template<class T>
void casacore::Queue< T >::clear ( )

Delete all the elements from the queue, and free up any resources.

template<class T>
void casacore::Queue< T >::compress ( )

Leave this queue logically unchanged, but remove unused storage.

With the present Block<T> based implementation, removes the unused entries at the beginning of the block.

template<class T>
void casacore::Queue< T >::dequeue ( T &  value)

Remove an element from the head of the queue and decrease nelements() by one.

If called when nelements() is zero, an exception is thrown.

template<class T>
void casacore::Queue< T >::enqueue ( const T &  value)

Place an element in the queue.

After calling this, nelements() is increaed by one.

template<class T>
uInt casacore::Queue< T >::nelements ( ) const
inline

How many elements are in the queue?

Definition at line 136 of file Queue.h.

References casacore::Queue< T >::first_p, and casacore::Queue< T >::next_p.

template<class T>
void casacore::Queue< T >::operator() ( const T &  value)

Short-hand for enqueue();.

template<class T>
T casacore::Queue< T >::operator() ( )

Short-hand for dequeue.

template<class T>
Queue<T>& casacore::Queue< T >::operator= ( const Queue< T > &  other)

Create a queue which is a copy of other.

Compresses unused heap storage.

Member Data Documentation

template<class T>
Block<T> casacore::Queue< T >::data_p
private

Definition at line 140 of file Queue.h.

template<class T>
Int casacore::Queue< T >::first_p
private

Definition at line 138 of file Queue.h.

Referenced by casacore::Queue< T >::nelements().

template<class T>
Int casacore::Queue< T >::next_p
private

Definition at line 139 of file Queue.h.

Referenced by casacore::Queue< T >::nelements().


The documentation for this class was generated from the following file: