ACE_Mesaage_Block,ACE_InputCdr,ACE_OutputCdr的使用

The ACE_Message_Block class enables efficient manipulation of fixed- and variable-sized messages. ACE_Message_Block implements the Composite pattern [GHJV95] and provides the following capabilities:

• Each ACE_Message_Block contains a pointer to a reference-counted ACE_Data_Block, which in turn points to the actual data associated with a message. This design allows flexible and efficient sharing of data and minimizes excessive memory copying overhead.

• It allows multiple messages to be chained together into a singly linked list to support composite messages, which can be used for polymorphic lists and for layered protocol stacks that require headers/trailers to be inserted/removed efficiently.

• It allows multiple messages to be joined together in a doubly linked list that forms the basis of the ACE_Message_Queue class outlined on page 228 and described in [SH].

• It treats synchronization and memory management properties as aspects [Kic97, CE00] that applications can vary without changing the underlying ACE_Message_Block implementation.

• The ACE_Message_Block Class Diagram

• 
  照片名稱：Two Kinds of ACE_Message_Block

•  ACE_Message_Block  一般和 ACE_InputCdr,ACE_outputCdr 結合使用，以下是使用的一些方法：

• //mb = new ACE_Message_Block();
   //ACE_CDR::mb_align(mb);
   /*ACE_OutputCDR cdr(mb->wr_ptr(),ACE_CDR::MAX_ALIGNMENT+8);*/ //這種方法不對
   ACE_OutputCDR cdr(ACE_CDR::MAX_ALIGNMENT+8);
   size_t length1 = cdr.length();
•  ACE_Message_Block * mb = NULL;
   mb = new ACE_Message_Block(cdr.begin()->rd_ptr(),cdr.begin()->total_length());
   ACE_ASSERT(cdr.begin()->rd_ptr() == cdr.begin()->wr_ptr() );
   cdr << ACE_CDR::Long(22);
   cdr << ACE_CDR::Long(22);
•  size_t length2 = cdr.length();
•  /*mb->wr_ptr((cdr.begin())->total_length());*/
•  mb->wr_ptr(length2 - length1); // wr_ptr指針要往前移動 length2 - length1個字節，ACE_OutputCDR 不會去更新wr_ptr，只能手工更新
   ACE_Message_Block * payload = NULL;  
   payload = new ACE_Message_Block("11111");  //申請另外一個 ACE_Message_Block
   payload->rd_ptr(5);
•  payload->wr_ptr(10);
•  mb->cont(payload);  //形成ACE_Message_Block鏈表
   
  ACE_InputCDR 的使用
  
• ACE_Message_Block * mb = new ACE_Message_Block (ACE_DEFAULT_CDR_BUFSIZE);
   if(sock_.recv_n(mb->wr_ptr(),8) == 8)
   {
    mb->wr_ptr(8);
    
    ACE_InputCDR cdr(mb);
•   ACE_CDR::Long Type,Type1;
    cdr >> Type;
•   cdr >>Type1;
•   if(sock_.recv_n(mb->wr_ptr(),3) > 0)
    {
     mb->wr_ptr(3);
    }
  關於ACE_Message_block ,ACE_Inputcdr,ACE_OutputCdr的使用的注意事項還有很多，需要一步一步發掘。