...one of the most highly
regarded and expertly designed C++ library projects in the
world.
— Herb Sutter and Andrei
Alexandrescu, C++
Coding Standards
Gets the non-blocking mode of the native socket implementation.
bool native_non_blocking() const;
This function is used to retrieve the non-blocking mode of the underlying native socket. This mode has no effect on the behaviour of the socket object's synchronous operations.
true
if the underlying socket
is in non-blocking mode and direct system calls may fail with boost::asio::error::would_block
(or the equivalent system
error).
The current non-blocking mode is cached by the socket object. Consequently, the return value may be incorrect if the non-blocking mode was set directly on the native socket.
This function is intended to allow the encapsulation of arbitrary non-blocking
system calls as asynchronous operations, in a way that is transparent
to the user of the socket object. The following example illustrates how
Linux's sendfile
system
call might be encapsulated:
template <typename Handler> struct sendfile_op { tcp::socket& sock_; int fd_; Handler handler_; off_t offset_; std::size_t total_bytes_transferred_; // Function call operator meeting WriteHandler requirements. // Used as the handler for the async_write_some operation. void operator()(boost::system::error_code ec, std::size_t) { // Put the underlying socket into non-blocking mode. if (!ec) if (!sock_.native_non_blocking()) sock_.native_non_blocking(true, ec); if (!ec) { for (;;) { // Try the system call. errno = 0; int n = ::sendfile(sock_.native_handle(), fd_, &offset_, 65536); ec = boost::system::error_code(n < 0 ? errno : 0, boost::asio::error::get_system_category()); total_bytes_transferred_ += ec ? 0 : n; // Retry operation immediately if interrupted by signal. if (ec == boost::asio::error::interrupted) continue; // Check if we need to run the operation again. if (ec == boost::asio::error::would_block || ec == boost::asio::error::try_again) { // We have to wait for the socket to become ready again. sock_.async_write_some(boost::asio::null_buffers(), *this); return; } if (ec || n == 0) { // An error occurred, or we have reached the end of the file. // Either way we must exit the loop so we can call the handler. break; } // Loop around to try calling sendfile again. } } // Pass result back to user's handler. handler_(ec, total_bytes_transferred_); } }; template <typename Handler> void async_sendfile(tcp::socket& sock, int fd, Handler h) { sendfile_op<Handler> op = { sock, fd, h, 0, 0 }; sock.async_write_some(boost::asio::null_buffers(), op); }