1<html> 2<head> 3<meta http-equiv="Content-Type" content="text/html; charset=UTF-8"> 4<title>basic_socket::native_non_blocking (1 of 3 overloads)</title> 5<link rel="stylesheet" href="../../../../../../doc/src/boostbook.css" type="text/css"> 6<meta name="generator" content="DocBook XSL Stylesheets V1.79.1"> 7<link rel="home" href="../../../../boost_asio.html" title="Boost.Asio"> 8<link rel="up" href="../native_non_blocking.html" title="basic_socket::native_non_blocking"> 9<link rel="prev" href="../native_non_blocking.html" title="basic_socket::native_non_blocking"> 10<link rel="next" href="overload2.html" title="basic_socket::native_non_blocking (2 of 3 overloads)"> 11</head> 12<body bgcolor="white" text="black" link="#0000FF" vlink="#840084" alink="#0000FF"> 13<table cellpadding="2" width="100%"><tr> 14<td valign="top"><img alt="Boost C++ Libraries" width="277" height="86" src="../../../../../../boost.png"></td> 15<td align="center"><a href="../../../../../../index.html">Home</a></td> 16<td align="center"><a href="../../../../../../libs/libraries.htm">Libraries</a></td> 17<td align="center"><a href="http://www.boost.org/users/people.html">People</a></td> 18<td align="center"><a href="http://www.boost.org/users/faq.html">FAQ</a></td> 19<td align="center"><a href="../../../../../../more/index.htm">More</a></td> 20</tr></table> 21<hr> 22<div class="spirit-nav"> 23<a accesskey="p" href="../native_non_blocking.html"><img src="../../../../../../doc/src/images/prev.png" alt="Prev"></a><a accesskey="u" href="../native_non_blocking.html"><img src="../../../../../../doc/src/images/up.png" alt="Up"></a><a accesskey="h" href="../../../../boost_asio.html"><img src="../../../../../../doc/src/images/home.png" alt="Home"></a><a accesskey="n" href="overload2.html"><img src="../../../../../../doc/src/images/next.png" alt="Next"></a> 24</div> 25<div class="section"> 26<div class="titlepage"><div><div><h5 class="title"> 27<a name="boost_asio.reference.basic_socket.native_non_blocking.overload1"></a><a class="link" href="overload1.html" title="basic_socket::native_non_blocking (1 of 3 overloads)">basic_socket::native_non_blocking 28 (1 of 3 overloads)</a> 29</h5></div></div></div> 30<p> 31 Gets the non-blocking mode of the native socket implementation. 32 </p> 33<pre class="programlisting">bool native_non_blocking() const; 34</pre> 35<p> 36 This function is used to retrieve the non-blocking mode of the underlying 37 native socket. This mode has no effect on the behaviour of the socket 38 object's synchronous operations. 39 </p> 40<h6> 41<a name="boost_asio.reference.basic_socket.native_non_blocking.overload1.h0"></a> 42 <span class="phrase"><a name="boost_asio.reference.basic_socket.native_non_blocking.overload1.return_value"></a></span><a class="link" href="overload1.html#boost_asio.reference.basic_socket.native_non_blocking.overload1.return_value">Return 43 Value</a> 44 </h6> 45<p> 46 <code class="computeroutput">true</code> if the underlying socket is in non-blocking mode and 47 direct system calls may fail with <code class="computeroutput">boost::asio::error::would_block</code> 48 (or the equivalent system error). 49 </p> 50<h6> 51<a name="boost_asio.reference.basic_socket.native_non_blocking.overload1.h1"></a> 52 <span class="phrase"><a name="boost_asio.reference.basic_socket.native_non_blocking.overload1.remarks"></a></span><a class="link" href="overload1.html#boost_asio.reference.basic_socket.native_non_blocking.overload1.remarks">Remarks</a> 53 </h6> 54<p> 55 The current non-blocking mode is cached by the socket object. Consequently, 56 the return value may be incorrect if the non-blocking mode was set directly 57 on the native socket. 58 </p> 59<h6> 60<a name="boost_asio.reference.basic_socket.native_non_blocking.overload1.h2"></a> 61 <span class="phrase"><a name="boost_asio.reference.basic_socket.native_non_blocking.overload1.example"></a></span><a class="link" href="overload1.html#boost_asio.reference.basic_socket.native_non_blocking.overload1.example">Example</a> 62 </h6> 63<p> 64 This function is intended to allow the encapsulation of arbitrary non-blocking 65 system calls as asynchronous operations, in a way that is transparent 66 to the user of the socket object. The following example illustrates how 67 Linux's <code class="computeroutput">sendfile</code> system call might be encapsulated: 68 </p> 69<pre class="programlisting">template <typename Handler> 70struct sendfile_op 71{ 72 tcp::socket& sock_; 73 int fd_; 74 Handler handler_; 75 off_t offset_; 76 std::size_t total_bytes_transferred_; 77 78 // Function call operator meeting WriteHandler requirements. 79 // Used as the handler for the async_write_some operation. 80 void operator()(boost::system::error_code ec, std::size_t) 81 { 82 // Put the underlying socket into non-blocking mode. 83 if (!ec) 84 if (!sock_.native_non_blocking()) 85 sock_.native_non_blocking(true, ec); 86 87 if (!ec) 88 { 89 for (;;) 90 { 91 // Try the system call. 92 errno = 0; 93 int n = ::sendfile(sock_.native_handle(), fd_, &offset_, 65536); 94 ec = boost::system::error_code(n < 0 ? errno : 0, 95 boost::asio::error::get_system_category()); 96 total_bytes_transferred_ += ec ? 0 : n; 97 98 // Retry operation immediately if interrupted by signal. 99 if (ec == boost::asio::error::interrupted) 100 continue; 101 102 // Check if we need to run the operation again. 103 if (ec == boost::asio::error::would_block 104 || ec == boost::asio::error::try_again) 105 { 106 // We have to wait for the socket to become ready again. 107 sock_.async_wait(tcp::socket::wait_write, *this); 108 return; 109 } 110 111 if (ec || n == 0) 112 { 113 // An error occurred, or we have reached the end of the file. 114 // Either way we must exit the loop so we can call the handler. 115 break; 116 } 117 118 // Loop around to try calling sendfile again. 119 } 120 } 121 122 // Pass result back to user's handler. 123 handler_(ec, total_bytes_transferred_); 124 } 125}; 126 127template <typename Handler> 128void async_sendfile(tcp::socket& sock, int fd, Handler h) 129{ 130 sendfile_op<Handler> op = { sock, fd, h, 0, 0 }; 131 sock.async_wait(tcp::socket::wait_write, op); 132} 133</pre> 134</div> 135<table xmlns:rev="http://www.cs.rpi.edu/~gregod/boost/tools/doc/revision" width="100%"><tr> 136<td align="left"></td> 137<td align="right"><div class="copyright-footer">Copyright © 2003-2020 Christopher M. 138 Kohlhoff<p> 139 Distributed under the Boost Software License, Version 1.0. (See accompanying 140 file LICENSE_1_0.txt or copy at <a href="http://www.boost.org/LICENSE_1_0.txt" target="_top">http://www.boost.org/LICENSE_1_0.txt</a>) 141 </p> 142</div></td> 143</tr></table> 144<hr> 145<div class="spirit-nav"> 146<a accesskey="p" href="../native_non_blocking.html"><img src="../../../../../../doc/src/images/prev.png" alt="Prev"></a><a accesskey="u" href="../native_non_blocking.html"><img src="../../../../../../doc/src/images/up.png" alt="Up"></a><a accesskey="h" href="../../../../boost_asio.html"><img src="../../../../../../doc/src/images/home.png" alt="Home"></a><a accesskey="n" href="overload2.html"><img src="../../../../../../doc/src/images/next.png" alt="Next"></a> 147</div> 148</body> 149</html> 150
