windows 套接字子进程继承

网络编程模式中，有一种是多进程模式，主进程侦听，收到连接后，启动子进程处理请求，每个连接一个子进程。

在linux中通过fork很容易实现，因为fork时子进程继承父进程的文件描述符，套接字也是一种文件描述符。

在windows句柄也能够继承，但是必须通过外部方法告诉子进程句柄值，可以通过命令行参数或者环境变量的方式传递。

怎么获取套接字的句柄呢？其实套接字本身就是一个句柄，只是平常使用recv、send来操作套接字，没觉得它是一个句柄。

 需要注意的是，在win 9x中，套接字句柄默认是不继承的，需要使用复制句柄（DuplicateHandle）函数复制一个可继承的句柄。

主进程代码片段：

   // This is a Winsock server that is listening on a port.   // When a client connects, the server spawns a child process and   // passes the socket handle to the child.   // The child can use this socket handle to interact with the   // client and the parent is free to go back to waiting for   // other clients to connect.   OrigSock=accept(listen_socket,(struct sockaddr *)&from,&fromlen);   if (OrigSock == INVALID_SOCKET)  {      fprintf(stderr,"accept failed %d\n",GetLastError());      return -1;   }   {      STARTUPINFO si;      PROCESS_INFORMATION pi;      char argbuf[256];      memset(&si,0,sizeof(si));      //       // Duplicate the socket OrigSock to create an inheritable copy.      //       if (!DuplicateHandle(GetCurrentProcess(),            (HANDLE)OrigSock,            GetCurrentProcess(),            (HANDLE*)&DuplicateSock,            0,            TRUE, // Inheritable            DUPLICATE_SAME_ACCESS)) {         fprintf(stderr,"dup error %d\n",GetLastError());         return -1;      }      //       // Spawn the child process.      // The first command line argument (argv[1]) is the socket handle.      //       wsprintf(argbuf,"child.exe %d",DuplicateSock);      if (!CreateProcess(NULL,argbuf,NULL,NULL,               TRUE, // inherit handles               0,NULL,NULL,&si,&pi) ){         fprintf(stderr,"createprocess failed %d\n",GetLastError());         return -1;      }      //       // On Windows 95, the parent needs to wait until the child      // is done with the duplicated handle before closing it.      //       WaitForSingleObject(pi.hProcess, INFINITE);   }   //    // The duplicated socket handle must be closed by the owner   // process--the parent. Otherwise, socket handle leakage   // occurs. On the other hand, closing the handle prematurely   // would make the duplicated handle invalid in the child. In this   // sample, we use WaitForSingleObject(pi.hProcess, INFINITE) to   // wait for the child.   //    closesocket(OrigSock);   closesocket(DuplicateSock);

子进程代码片段： 

   main(int argc, char *argv[]){      SOCKET Sock;      /* WSAStartup etc. */       if (2 == argc){         Sock = atoi(argv[1]);   // use Sock      }   }