我可以在接受服务器上延长TCP握手持续时间吗?

这个问题从为什么在连接（）或Accept（）之前是非块套接字写的？。

以下代码催生了聆听TCP连接的线程。主线程连接到服务器正在收听的地址。

#include <iostream>
#include <sys/socket.h>
#include <arpa/inet.h>
#include <fcntl.h>
#include <unistd.h>
#include <cerrno>
#include <cstring>
#include <pthread.h>
#include <semaphore.h>
class SafeSocket
{
public:
  /** Ctor.
   * Creates a nonblocking socket at the specified IP in the AF_INET family and
   * at a dynamic port.
   */
  SafeSocket( const std::string& ip )
  {
    in_addr_t host_ip = inet_network( ip.c_str() );
    if ( ( socket_ = socket( AF_INET, SOCK_STREAM, 0 ) ) < 0 )
    {
      std::cout << "socket() failed: " << errno << " " << strerror( errno )
                << std::endl;
      socket_ = -1;
    }
    sockaddr_in si;
    memset( &si, 0, sizeof( si ) );
    si.sin_family = AF_INET;
    si.sin_port = 0; // Dynamic port
    si.sin_addr.s_addr = htonl( host_ip );
    if ( bind( socket_, (sockaddr*)&si, sizeof si ) )
    {
      std::cout << "bind() failed: " << errno << " " << strerror( errno )
                << std::endl;
      close( socket_ );
      socket_ = -1;
    }
    // Make the socket do nonblocking connect().
    int flags = fcntl( socket_, F_GETFL, 0 );
    fcntl( socket_, F_SETFL, flags | O_NONBLOCK );
  }
  ~SafeSocket()
  {
    if ( socket_ >= 0 )
    {
      shutdown( socket_, SHUT_RDWR );
      close( socket_ );
    }
  }
  operator int() const
  {
    return socket_;
  }
private:
  int socket_;
};
int connectToClient( const SafeSocket& sock, const std::string& clientIp,
                     const int clientPort )
{
  struct sockaddr_in clientAddr;
  memset( &clientAddr, 0, sizeof clientAddr );
  inet_pton( AF_INET, clientIp.c_str(), &clientAddr.sin_addr );
  clientAddr.sin_family = AF_INET;
  clientAddr.sin_port = htons( clientPort );
  return connect( sock, (sockaddr*)&clientAddr, sizeof clientAddr );
}
std::string serverIp( "127.0.0.200" );
int serverPort = 9099; // Random, hopefully unused.
sem_t listenSem;
/** Entry point to pthread.
 */
void* acceptConnection( void* arg )
{
  int listenSock = socket( PF_INET, SOCK_STREAM, 0 );
  if ( listenSock < 0 )
  {
    std::cout << "socket() failed: " << errno << " " << strerror( errno )
              << std::endl;
    return NULL;
  }
  sockaddr_in si;
  si.sin_family = AF_INET;
  inet_aton( serverIp.c_str(), &si.sin_addr );
  si.sin_port = htons( serverPort );
  int optval = 1;
  setsockopt( listenSock, SOL_SOCKET, SO_REUSEADDR, &optval, sizeof optval);
  int result = bind( listenSock, (sockaddr*)&si, sizeof si );
  if ( result )
  {
    std::cout << "bind() failed: " << errno << " " << strerror( errno )
              << std::endl;
    close( listenSock );
    return NULL;
  }
  std::cout << "listening on socket " << listenSock << std::endl;
  if ( listen( listenSock, 3 ) )
  {
    std::cout << "listen() failed: " << errno << " " << strerror( errno )
              << std::endl;
    close( listenSock );
    return NULL;
  }
  sem_post( &listenSem );
  fd_set readfds;
  FD_ZERO( &readfds );
  FD_SET( listenSock, &readfds );
  struct timeval ts = { 5, 0 };
  if ( -1 != select( listenSock + 1, &readfds, NULL, NULL, &ts ) )
  {
    if ( FD_ISSET( listenSock, &readfds ) )
    {
      sockaddr_in peerSi;
      socklen_t peerAddrLen = sizeof peerSi;
      memset( &peerSi, 0, peerAddrLen );
      sleep( 3 );
      int acceptSock = accept( listenSock, (sockaddr*)&peerSi, &peerAddrLen );
      if ( acceptSock > 0 )
      {
        std::cout << "accepted connection on socket " << acceptSock
                  << std::endl;
        close( acceptSock );
      }
    }
    else
    {
      std::cout << "did not receive a connection to accept." << std::endl;
    }
  }
  close( listenSock );
  return NULL;
}
int main( int argc, char* argv[] )
{
  sem_init( &listenSem, 0, 0 );
  SafeSocket s( "127.0.0.100" );
  std::cout << "Created socket " << s << std::endl;
  pthread_t tid;
  pthread_create( &tid, NULL, acceptConnection, NULL );
  timespec listenTimeout;
  clock_gettime( CLOCK_REALTIME, &listenTimeout );
  listenTimeout.tv_sec += 5;
  sem_timedwait( &listenSem, &listenTimeout );
  fd_set readFds;
  fd_set writeFds;
  FD_ZERO( &readFds );
  FD_ZERO( &writeFds );
  FD_SET( s, &writeFds );
  timeval timeout = { 5, 0 };
  int result = connectToClient( s, serverIp, serverPort );
  std::cout << "connectToClient() returned " << result << " "
            << errno << " " << strerror( errno ) << std::endl;
  if ( -1 == select( s+1, &readFds, &writeFds, NULL, &timeout ) )
  {
    std::cout << "select() failed: " << errno << " " << strerror( errno )
              << std::endl;
  }
  if ( FD_ISSET( s, &writeFds ) )
  {
    std::cout << s << " is writable!" << std::endl;
    int result = -1;
    socklen_t result_len = sizeof result;
    getsockopt( s, SOL_SOCKET, SO_ERROR, &result, &result_len );
    std::cout << "result: " << result << " " << strerror( result ) << std::endl;
  }
  pthread_join( tid, NULL );
  return 0;
}

输出：

>g++ --version
g++ (GCC) 4.8.3 20140911 (Red Hat 4.8.3-7)
Copyright (C) 2013 Free Software Foundation, Inc.
This is free software; see the source for copying conditions.  There is NO
warranty; not even for MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.
>g++ -g main.cpp 
>
>./a.out 
Created socket 3                                             // Immediate
listening on socket 4                                        // Immediate
connectToClient() returned -1 115 Operation now in progress  // Immediate
3 is writable!                                               // Immediate
result: 0 Success                                            // Immediate
accepted connection on socket 5                              // Delayed

ejp在著名的问题上发表了评论，他指出，在这种情况下，只要"目标TCP握手"，select()就会封锁。

那么，是否有一种加长" TCP握手"过程的方法？IE。我想延长select()阻止等待套接字s的时间。可以做到吗？您可能会观察到我试图通过在接受之前添加sleep()来做到这一点，但这不起作用。