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我正在探索 boost asio 产品

客户端发送一个 1 字节的标头，指示后面的字节长度。

相关服务器代码：

  enum {max_length=1};     

  void handle_read(const boost::system::error_code & error, const size_t & bytes_transferred){
if (! error){
  ++ctr;
  std::string inc_data_str(this->inc_data.begin(),this->inc_data.end());
  std::cout<<"received string: "<<inc_data_str<<" with size "<<inc_data_str.size()
           <<" bytes_transferred: "<<bytes_transferred<<" ctr: "<<ctr<<std::endl;
  int size_inc_next = boost::lexical_cast<int>(inc_data_str);
  int offset = 0;
  //std::cout<<"incoming integer of size "<<size_inc_next<<" processed from string: "<<inc_data_str<<std::endl;                    
  std::vector<char> next_inc_data(size_inc_next+offset);
  boost::asio::read(this->socket,boost::asio::buffer(next_inc_data),boost::asio::transfer_exactly(size_inc_next+offset));
  std::string int_recvd(next_inc_data.begin(),next_inc_data.begin()+size_inc_next);
  //std::cout<<boost::posix_time::microsec_clock::local_time()<<std::endl;                                                         
  //std::cout<<"received integer: "<<int_recvd<<" from string "<<int_recvd<<" of size "<<int_recvd.size()<<std::endl;              
  this->process_connection();
 } // ! error
} // handle_read

void process_connection(){
                                                   boost::asio::async_read(this->socket,boost::asio::buffer(this->inc_data),boost::asio::transfer_exactly(max_length),
                    boost::bind(&Connection::handle_read,shared_from_this(),boost::asio::placeholders::error,
                                    boost::asio::placeholders::bytes_transferred));
}

相关客户代码：

  void on_write(const boost::system::error_code & error_code){
if (! error_code){
  std::string transfer_data("15");
  std::vector<char> v_td(transfer_data.begin(),transfer_data.end());
  ++ctr;
  for (std::vector<char>::iterator iter = v_td.begin(); iter != v_td.end(); ++iter) std::cout<<*iter;
  std::cout<<" ctr: "<<ctr;
  std::endl(std::cout);
        boost::asio::async_write(this->socket,boost::asio::buffer(v_td),boost::asio::transfer_exactly(2),
                           boost::bind(&Client::on_write,shared_from_this(),
                                       boost::asio::placeholders::error));
  }
 }

服务器进程的预期示例打印输出：

  received string: 1 with size 1 bytes_transferred: 1 ctr: 159685

客户端进程的预期示例打印输出：

  15 ctr: 356293

这样的预期输出会产生一段时间，但是在说 356293 客户端迭代之后（这个 ctr 数字对于肉眼来说是不确定的，因为重复的过程试验），服务器中断并出现以下错误：

 received string:  with size 1 bytes_transferred: 1 ctr: 159686
 terminate called after throwing an instance of 'boost::exception_detail::clone_impl<boost::exception_detail::error_info_injector<boost::bad_lexical_cast> >'
 what():  bad lexical cast: source type value could not be interpreted as target

中止（核心转储）

请注意，接收到的字符串是“空白”。有时它也会与替代消息中断：

 received string: X with size 1 bytes_transferred: 1 ctr: 159686

这里发生了什么，为什么以及如何解决？

strace 之后的进一步编辑：

客户端跟踪：

 sendmsg(6, {msg_name(0)=NULL, msg_iov(1)=[{"15", 2}], msg_controllen=0, msg_flags=0}, MSG_NOSIGNAL) = 2
 epoll_wait(4, {}, 128, 0)               = 0
 write(1, "15 ctr: 204441\n", 1515 ctr: 204441)        = 15
 sendmsg(6, {msg_name(0)=NULL, msg_iov(1)=[{"15", 2}], msg_controllen=0, msg_flags=0},    MSG_NOSIGNAL) = 2
 epoll_wait(4, {}, 128, 0)               = 0
 write(1, "15 ctr: 204442\n", 1515 ctr: 204442)        = 15
 sendmsg(6, {msg_name(0)=NULL, msg_iov(1)=[{"15", 2}], msg_controllen=0, msg_flags=0}, MSG_NOSIGNAL) = -1 EAGAIN (Resource temporarily \
 unavailable)
 epoll_wait(4, {{EPOLLOUT, {u32=167539936, u64=167539936}}}, 128, -1) = 1
 sendmsg(6, {msg_name(0)=NULL, msg_iov(1)=[{"\0\0", 2}], msg_controllen=0,   msg_flags=0}, MSG_NOSIGNAL) = 2
 write(1, "15 ctr: 204443\n", 1515 ctr: 204443)        = 15
 sendmsg(6, {msg_name(0)=NULL, msg_iov(1)=[{"15", 2}], msg_controllen=0, msg_flags=0},     MSG_NOSIGNAL) = 2
 epoll_wait(4, {}, 128, 0)               = 0
 write(1, "15 ctr: 204444\n", 1515 ctr: 204444)        = 15
 sendmsg(6, {msg_name(0)=NULL, msg_iov(1)=[{"15", 2}], msg_controllen=0, msg_flags=0}, MSG_NOSIGNAL) = 2
 epoll_wait(4, {}, 128, 0)               = 0
 write(1, "15 ctr: 204445\n", 1515 ctr: 204445)        = 15

服务器跟踪：

 write(1, "received string: 1 with size 1 b"..., 64received string: 1 with size 1   bytes_transferred: 1 ctr: 204441) = 64
 write(1, "incoming integer of size 1 proce"..., 52incoming integer of size 1 processed from string: 1) = 52
 recvmsg(7, {msg_name(0)=NULL, msg_iov(1)=[{"5", 1}], msg_controllen=0, msg_flags=0},0) = 1
 write(1, "received integer: 5 from string "..., 44received integer: 5 from string 5 of size 1) = 44
 recvmsg(7, {msg_name(0)=NULL, msg_iov(1)=[{"1", 1}], msg_controllen=0, msg_flags=0},0) = 1
 epoll_wait(4, {}, 128, 0)               = 0
 write(1, "received string: 1 with size 1 b"..., 64received string: 1 with size 1 bytes_transferred: 1 ctr: 204442) = 64
 write(1, "incoming integer of size 1 proce"..., 52incoming integer of size 1 processed from string: 1) = 52
 recvmsg(7, {msg_name(0)=NULL, msg_iov(1)=[{"5", 1}], msg_controllen=0, msg_flags=0}, 0) = 1
 write(1, "received integer: 5 from string "..., 44received integer: 5 from string 5 of size 1) = 44
 recvmsg(7, {msg_name(0)=NULL, msg_iov(1)=[{"\0", 1}], msg_controllen=0, msg_flags=0}, 0) = 1
 epoll_wait(4, {}, 128, 0)               = 0
 write(1, "received string: \0 with size 1 b"..., 64received string: ^@ with size 1 bytes_transferred: 1 ctr: 204443) = 64
 futex(0xb76640fc, FUTEX_WAKE_PRIVATE, 2147483647) = 0
 write(1, "inc_data_str\n", 13inc_data_str)          = 13

对于客户端进程，错误的“\0\0”发送之前的 epoll_wait 与其他 epoll_wait 调用不同（u32=....，u64=....）......不知道这是什么意思尽管

总结一下令人困惑的部分，strace 表示正在传输空值，但下一行的 strace 表示使用文字“15”对标准输出进行写入系统调用，这意味着这就是 transfer_data 向量中的内容

重新编辑：

最后我插入了一个

  boost::this_thread::sleep(boost::posix_time::microseconds(200));

就在客户端 on_write 函数中的 write 语句之前。

有了这个，没有遇到任何问题。那么这可能与 asio 对象有关吗？是插座吗？

4

2 回答 2

4

您的客户端因缓冲区寿命而损坏

void 
on_write(
    const boost::system::error_code& error_code
)
{
    if ( !error_code ) {
        std::string transfer_data("15");
        std::vector<char> v_td(transfer_data.begin(), transfer_data.end());
        //                 ^
        //                  \------ goes out of scope before async_write() returns

        boost::asio::async_write(
            this->socket,
            boost::asio::buffer(v_td),
            boost::asio::transfer_exactly(2),
            boost::bind( 
                &Client::on_write,
                shared_from_this(),
                boost::asio::placeholders::error
            )
        );
     }
 }

您需要确保给定的缓冲区async_write()在调用完成处理程序之前保持有效：

buffers一个或多个包含要写入的数据的缓冲区。尽管缓冲区对象可以根据需要被复制，但底层内存块的所有权由调用者保留，它必须保证它们在调用处理程序之前保持有效。处理程序

于 2013-04-26T16:43:29.453 回答
0

好吧，异常消息说，有一个不好的词法转换。我在您的服务器代码中看到了一个：

int size_inc_next = boost::lexical_cast<int>(inc_data_str);

也许你应该在那里放一个断点并调试。当你收到消息

接收到的字符串：X，大小为 1 bytes_transferred：1 ctr：159686

这显然是 . 之前的行的输出lexical_cast。然后inc_data_str似乎是“X” - 并将其转换为 int 应该会触发错误的转换异常。

为什么我不知道连接的另一端有一个“X”。

于 2013-04-26T06:24:24.683 回答