队列(Queue)

队列(Queue)

ACE通过ACE_Unbounded_Queue模板容器，实现队列的数据结构。ACE的队列允许在队列的头部插入元素也允许在队列的尾部插入元素，但是取出都是从头部取出。¹⁾

示例代码

Queues.cpp

此示例演示了分别从栈上和堆上分配空间存储对象元素，并且从头部和尾部分别插入对象元素，以及通过迭代对对象元素进行遍历。

// Queues.cpp,v 1.5 2006/03/30 12:40:48 jwillemsen Exp

#include "ace/OS_Memory.h"

#include "ace/Log_Msg.h"

#include "ace/Containers.h"

#include "DataElement.h"

class QueueExample

{

public:

  // Illustrate the various ACE Queues.

  int run (void);

private:

  // Illustrate the ACE unbounded queue

  // that has copies of the data elements.

  int runStackUnboundedQueue (void);

  // Illustrate the ACE unbounded queue

  // with pointers to elements on the heap.

  int runHeapUnboundedQueue (void);

};

int QueueExample::run (void)

{

  ACE_TRACE (ACE_TEXT ("QueueExample::run"));

  // Illustrate the queue with elements on the stack.

  if (this->runStackUnboundedQueue () != 0)

    {

      return -1;

    }

  ACE_DEBUG ((LM_DEBUG, ACE_TEXT ("/n# of live objects %d/n"),

              DataElement::numOfActiveObjects ()));

  // Illustrate the queue with elements on the heap.

  if (this->runHeapUnboundedQueue () != 0)

    {

      return -1;

    }

  ACE_DEBUG ((LM_DEBUG, ACE_TEXT ("/n# of live objects %d/n"),

              DataElement::numOfActiveObjects ()));

  return 0;

}

// Listing 1 code/ch05

//从栈上分配元素并从队列的头部和尾部分别插入元素，并对数据元素进行遍历

int QueueExample::runStackUnboundedQueue (void)

{

  ACE_TRACE (ACE_TEXT ("QueueExample::runStackUnboundedQueue"));

  ACE_Unbounded_Queue<DataElement> queue;

  DataElement elem1[10];

  int i;

  for (i = 0; i < 10; i++)

    {

      elem1[i].setData (9-i);

      queue.enqueue_head (elem1[i]);

    }

  DataElement elem2[10];

  for (i = 0; i < 10; i++)

    {

      elem2[i].setData (i+10);

      queue.enqueue_tail (elem2[i]);

    }

  for (ACE_Unbounded_Queue_Iterator<DataElement> iter (queue);

       !iter.done ();

       iter.advance ())

    {

      DataElement *elem = 0;

      iter.next (elem);

      ACE_DEBUG ((LM_DEBUG, ACE_TEXT ("%d:"), elem->getData ()));

    }

  return 0;

}

// Listing 1

// Listing 2 code/ch05

//从堆上分配数据元素并进行遍历

int QueueExample::runHeapUnboundedQueue (void)

{

  ACE_TRACE (ACE_TEXT ("QueueExample::runHeapUnboundedQueue"));

  ACE_Unbounded_Queue<DataElement*> queue;

  for (int i = 0; i < 20; i++)

    {

      DataElement *elem;

      ACE_NEW_RETURN(elem, DataElement (i), -1);

      //队列中存储传入指针的副本

      queue.enqueue_head (elem);

    }

  for (ACE_Unbounded_Queue_Iterator<DataElement*> iter

         = queue.begin ();

       !iter.done ();

       iter.advance ())

    {

      DataElement **elem = 0;

      iter.next(elem);

      ACE_DEBUG

        ((LM_DEBUG, ACE_TEXT ("%d:"), (*elem)->getData ()));

     //elem指向的对象元素被释放，可是队列中的指针依然存在，只不过是存储的无效指针。 

     delete (*elem);

    }

  return 0;

}

// Listing 2

int ACE_TMAIN (int, ACE_TCHAR *[])

{

  QueueExample que;

  return que.run ();

}

#if defined (ACE_HAS_EXPLICIT_TEMPLATE_INSTANTIATION)

template class ACE_Node<DataElement>;

template class ACE_Node<DataElement*>;

template class ACE_Unbounded_Queue<DataElement*>;

template class ACE_Unbounded_Queue_Iterator<DataElement*>;

template class ACE_Unbounded_Queue<DataElement>;

template class ACE_Unbounded_Queue_Iterator<DataElement>;

#elif defined (ACE_HAS_TEMPLATE_INSTANTIATION_PRAGMA)

#pragma instantiate ACE_Node<DataElement>

#pragma instantiate ACE_Node<DataElement*>

#pragma instantiate ACE_Unbounded_Queue<DataElement*>

#pragma instantiate ACE_Unbounded_Queue_Iterator<DataElement*>

#pragma instantiate ACE_Unbounded_Queue<DataElement>

#pragma instantiate ACE_Unbounded_Queue_Iterator<DataElement>

#endif /* ACE_HAS_EXPLICIT_TEMPLATE_INSTANTIATION*/

执行结果

D:/project/ACE_wrappers/examples/APG/Containers>Queues

0:1:2:3:4:5:6:7:8:9:10:11:12:13:14:15:16:17:18:19:

# of live objects 0

19:18:17:16:15:14:13:12:11:10:9:8:7:6:5:4:3:2:1:0:

# of live objects 0