IOCP multithreaded server and reference counted class

问题

I work on IOCP Server (Overlapped I/O , 4 threads, CreateIoCompletionPort, GetQueuedCompletionStatus, WSASend etc). And my goal is to send single reference counted buffer too all connected sockets.(I followed Len Holgate's suggestion from this post WSAsend to all connected socket in multithreaded iocp server) . After sending buffer to all connected clients it should be deleted.

this is class with buffer to be send

class refbuf
{
 private:
  int m_nLength;
  int m_wsk;
  char *m_pnData; // buffer to send
  mutable int mRefCount;

  public:
  ...

  void grab() const 
   {
          ++mRefCount;
   }

  void release() const
 {
    if(mRefCount > 0);
    --mRefCount;

    if(mRefCount == 0) {delete (refbuf *)this;}
 }  

    ...

char* bufadr() { return m_pnData;}


};

sending buffer to all socket

refbuf *refb = new refbuf(4);
...
EnterCriticalSection(&g_CriticalSection);
pTmp1 = g_pCtxtList; // start of linked list with sockets
   while( pTmp1 ) 
   {  
     pTmp2 = pTmp1->pCtxtBack;
     ovl=TakeOvl();     // ovl -struct containing WSAOVERLAPPED 
     ovl->wsabuf.buf=refb->bufadr();// adress m_pnData from refbuf 
     ovl->rcb=refb;  //when GQCS get notification rcb is used to decrease mRefCount
     ovl->wsabuf.len=4;
     refb->grab();     // mRefCount ++
     WSASend(pTmp1->Socket, &(ovl->wsabuf),1,&dwSendNumBytes,0,&(ovl->Overlapped),   NULL);    
     pTmp1 = pTmp2;
  }
   LeaveCriticalSection(&g_CriticalSection);

and 1 of 4 threads

 GetQueuedCompletionStatus(hIOCP, &dwIoSize,(PDWORD_PTR)&lpPerSocketContext, (LPOVERLAPPED *)&lpOverlapped, INFINITE);
 ... 
 lpIOContext = (PPER_IO_CONTEXT)lpOverlapped;
 lpIOContext->rcb->release();  //mRefCount --,if mRefCount reach 0, delete object

i check this with 5 connected clients and it seems to work. When GQCS receives all notifaction, mRefCount reachs 0 and delete is executed.

And my questions: is that approach appropriate? What if there will be for example 100 or more clients? Is situation avoided when one thread can delete object before another still use it? How to implement atomic reference count in this scernario? Thanks in advance.

回答1:

Obvious issues; in order of importance...

Your refbuf class doesn't use thread safe ref count manipulation. Use InterlockedIncrement() etc.
I assume that TakeOvl() obtains a new OVERLAPPED and WSABUF structure per operation.
Your naming could be better, why grab() rather than AddRef(), what does TakeOvl() take from? Those Tmp variables are something and the least important something is that they're 'temporary' so name them after a more important something. Go Read Code Complete.

来源：https://stackoverflow.com/questions/20597582/iocp-multithreaded-server-and-reference-counted-class

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multithreading

reference

iocp