我正在探索提升asio产品
客户端发送1字节的标头，指示要遵循的字节长度。
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
客户端流程的预期示例打印输出：
15 ctr: 356293
这样的预期输出产生了一段时间，但是说在356293客户端迭代之后（这个ctr数对于过程的重复试验肉眼是不确定的），服务器中断了以下错误：
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（核心倾销）
请注意，收到的字符串为“空白”。 有时它也会打破替代信息：
received string: X with size 1 bytes_transferred: 1 ctr: 159686
这里发生了什么以及为什么以及如何解决这个问题？
strace后进一步编辑：
客户跟踪：
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 = ....）...不知道这意味着什么
总结一下令人困惑的部分，strace指示空值被传输，但是下一行的strace指示写入系统调用标准输出，文字“15”表示这是transfer_data向量中的内容
重新编辑：
最后我插了一个
boost::this_thread::sleep(boost::posix_time::microseconds(200));
就在客户端on_write函数的write语句之前。
有了这个，没有遇到任何问题。那么asio对象会出现什么样的并发问题呢？是插座吗？
答案 0 :(得分：4)
由于缓冲生存期，您的客户端已损坏
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
)
);
}
}
在调用完成处理程序之前，您需要确保给async_write()的缓冲区保持有效：
缓冲区包含要写入的数据的一个或多个缓冲区。虽然可以根据需要复制buffers对象，但是所有权 必须通过调用者保留底层内存块 保证它们在调用处理程序之前保持有效。处理
答案 1 :(得分：0)
嗯，异常消息说，有一个糟糕的词汇演员。我在你的服务器代码中看到一个：
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进行调试。当你收到消息时
收到字符串：X，大小为1 bytes_transferred：1 ctr：159686
显然是lexical_cast之前的行的输出。然后inc_data_str似乎是“X” - 并将其转换为int应触发该错误的强制转换异常。
为什么有一个“X”来自连接的另一端我无法分辨。