SOCKET编程第四种完成例程的疑惑

Question

我的疑惑在完成例程的回调函数的参数，WSARecv(lpPerIOData->sClient,
        &lpPerIOData->Buffer,
        1,
        &lpPerIOData->NumberOfBytesRecvd,
        &lpPerIOData->Flags,
        &lpPerIOData->overlap,
        CompletionROUTINE);      
在绑定时，只绑定了lpPerIOData中的overlap，那么在触发的CALLBACK CompletionROUTINE函数中如何将CompletionROUTINE(DWORD, DWORD, LPWSAOVERLAPPED, DWORD);
的第三个参数传递的呢？因为绑定时只绑定了那个结构体中的overlap即lpPerIOData->overlap，并未绑定整个结构体lpPerIOData啊，
#include <WINSOCK2.H>
#include <stdio.h>
#define PORT    5150
#define MSGSIZE 1024
#pragma comment(lib, "ws2_32.lib")
typedef struct
{
 WSAOVERLAPPED overlap;
 WSABUF        Buffer;
  char          szMessage[MSGSIZE];
 DWORD         NumberOfBytesRecvd;
 DWORD         Flags; 
 SOCKET        sClient;
}PER_IO_OPERATION_DATA, *LPPER_IO_OPERATION_DATA;
DWORD WINAPI WorkerThread(LPVOID);
void CALLBACK CompletionROUTINE(DWORD, DWORD, LPWSAOVERLAPPED, DWORD);
SOCKET g_sNewClientConnection;
BOOL   g_bNewConnectionArrived = FALSE;
int main()
{
  WSADATA     wsaData;
  SOCKET      sListen;
  SOCKADDR_IN local, client;
  DWORD       dwThreadId;
  int         iaddrSize = sizeof(SOCKADDR_IN);
  // Initialize Windows Socket library
  WSAStartup(0x0202, &wsaData);
  // Create listening socket
  sListen = socket(AF_INET, SOCK_STREAM, IPPROTO_TCP);
  // Bind
  local.sin_addr.S_un.S_addr = htonl(INADDR_ANY);
 local.sin_family = AF_INET;
 local.sin_port = htons(PORT);
  bind(sListen, (struct sockaddr *)&local, sizeof(SOCKADDR_IN));
  // Listen
  listen(sListen, 3);
  // Create worker thread
  CreateThread(NULL, 0, WorkerThread, NULL, 0, &dwThreadId);
  while (TRUE)
  {
    // Accept a connection
    g_sNewClientConnection = accept(sListen, (struct sockaddr *)&client, &iaddrSize);
    g_bNewConnectionArrived = TRUE;
    printf("Accepted client:%s:%d\n", inet_ntoa(client.sin_addr), ntohs(client.sin_port));
  }
}
DWORD WINAPI WorkerThread(LPVOID lpParam)
{
 LPPER_IO_OPERATION_DATA lpPerIOData = NULL;
  while (TRUE)
  {
    if (g_bNewConnectionArrived)
    {
      // Launch an asynchronous operation for new arrived connection
      lpPerIOData = (LPPER_IO_OPERATION_DATA)HeapAlloc(
        GetProcessHeap(),
        HEAP_ZERO_MEMORY,
        sizeof(PER_IO_OPERATION_DATA));
      lpPerIOData->Buffer.len = MSGSIZE;
      lpPerIOData->Buffer.buf = lpPerIOData->szMessage;
      lpPerIOData->sClient = g_sNewClientConnection;
      
      WSARecv(lpPerIOData->sClient,
        &lpPerIOData->Buffer,
        1,
        &lpPerIOData->NumberOfBytesRecvd,
        &lpPerIOData->Flags,
        &lpPerIOData->overlap,
        CompletionROUTINE);      
      
      g_bNewConnectionArrived = FALSE;
    }
    SleepEx(1000, TRUE);
  }
  return 0;
}
void CALLBACK CompletionROUTINE(DWORD dwError,
                                DWORD cbTransferred,
                                LPWSAOVERLAPPED lpOverlapped,
                                DWORD dwFlags)
{
  LPPER_IO_OPERATION_DATA lpPerIOData = (LPPER_IO_OPERATION_DATA)lpOverlapped;
  
  if (dwError != 0 || cbTransferred == 0)
 {
    // Connection was closed by client
  closesocket(lpPerIOData->sClient);
  HeapFree(GetProcessHeap(), 0, lpPerIOData);
 }
  else
  {
    lpPerIOData->szMessage[cbTransferred] = '\0';
    send(lpPerIOData->sClient, lpPerIOData->szMessage, cbTransferred, 0);
    
    // Launch another asynchronous operation
    memset(&lpPerIOData->overlap, 0, sizeof(WSAOVERLAPPED));
    lpPerIOData->Buffer.len = MSGSIZE;
    lpPerIOData->Buffer.buf = lpPerIOData->szMessage;    
    WSARecv(lpPerIOData->sClient,
      &lpPerIOData->Buffer,
      1,
      &lpPerIOData->NumberOfBytesRecvd,
      &lpPerIOData->Flags,
      &lpPerIOData->overlap,
      CompletionROUTINE);
  }
}

Answer 1

我的理解，完成历程的一个例子：
A线程需要开一个B线程去接收数据，那么需要A线程提前指定一个服务例程，也就是回调，指明要执行的操作步骤，然后B线程就工作，接收到数据之后，调用A线程制定的服务历程去处理数据。这个服务历程在哪里执行呢？在A线程，而不是B在线程内。
服务例程的原型为：
void  CALLBACK CompletionRoution(
    IN DWORD  dwErroe,
    IN DWORD  cbTransferred,
    IN LPWSAOVERLAPPED lpOverlapped,
    IN DWORD  dwFlags
);
OVERLAPPED 结构为：
typedef struct _OVERLAPPED {
    DWORD   Internal;
    DWORD   InternalHigh;
    DWORD   Offset;
    DWORD   OffsetHigh;
    HANDLE  hEvent;
} OVERLAPPED, *LPOVERLAPPED;
WSARecv 的原型为：WSARecv(
    SOCKET s,
    LPWSABUF lpBuffers,
    DWORD dwBufferCount,
    LPDWORD lpNumberOfBytesRecvd,
    LPDWORD lpFlags,
    LPWSAOVERLAPPED lpOverlapped,
    LPWSAOVERLAPPED_COMPLETION_ROUTINE lpCompletionRoutine
    );
看上面的顺序，注意overlapped内部的成员

Answer 2

不管是哪个部分，你把它看作一个内存的指针就可以了，所以lpPerIOData->overlap和lpPerIOData其实是一个值。

Answer 3

经你指点，我又发现，typedef struct
{
  WSAOVERLAPPED overlap;
  WSABUF        Buffer;
  char          szMessage[MSGSIZE];
  DWORD         NumberOfBytesRecvd;
  DWORD         Flags;
}PER_IO_OPERATION_DATA, *LPPER_IO_OPERATION_DATA;
果然是起始地址和WSAOVERLAPPED 是同一个地址，这就是尾随数据吧，多谢。