D1765R0.bs

<pre class='metadata'>
Title: Make native handles usable in the library
Shortname: D1765
Status: D
Revision: 0
Group: WG21
URL: https://wg21.link/D1765R0
!Audience: LEWGI
!Source: <a href="https://github.com/eliaskosunen/wg21/blob/master/D1765R0.bs">github.com/eliaskosunen/wg21: D1765R0</a>
Editor: Elias Kosunen, isocpp@eliaskosunen.com, https://eliaskosunen.com
Date: 2019-08-18
Abstract: This paper proposes unifying the rest of the native handles in the library with [[!P1759]].
Repository: https://github.com/eliaskosunen/wg21
Markup Shorthands: markdown yes
</pre>

Revision History {#history}
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Revision 0 {#r0}
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Initial revision

Introduction {#intro}
=====================

During the feedback session for [[!P1759]] in LEWGI in Cologne (July 2019),
it became apparent that the native handle facilities in `std::thread` and `std::mutex`
are difficult to depend on.
The reason for this is in how it is specified: the presence of these facilities is implementation-defined
(from [[N4800]] [**thread.req.native**]:

<blockquote>
Several classes described in this Clause have members <code>native_handle_type</code> and <code>native_handle</code>.
<b>The presence of these members</b> and their semantics <b>is implementation-defined.</b>
[ <i>Note:</i> These members allow implementations to provide access to implementation details.
Their names are specified to facilitate portable compile-time detection.
Actual use of these members is inherently non-portable.
&mdash; <i>end note</i> ]
</blockquote>

The same situation is present in the Networking TS (from [[N4734]] [**socket.reqmts.native**]):

<blockquote>
Several classes described in this document have a member type
<code>native_handle_type</code>, a member function <code>native_handle</code>,
and member functions that return or accept arguments of type <code>native_handle_type</code>.
<b>The presence of these members</b> and their semantics <b>is implementation-defined.</b>

When an operation has its effects specified as if by passing the result of <code>native_handle()</code>
to a POSIX function the effect is as if <code>native_handle_type</code> is the type <code>int</code>.

[ <i>Note:</i> These members allow implementations to provide access to their implementation details.
Their names are specified to facilitate portable compile-time detection.
Actual use of these members is inherently non-portable.
For operating systems that are based on POSIX, implementations can define the <code>native_handle_type</code>
for sockets as <code>int</code>, representing the native file descriptor associated with the socket.
&mdash; <i>end note</i> ]
</blockquote>



<pre class="biblio">
{
    "P1759": {
        "title": "Native handle from file streams",
        "href": "https://wg21.link/p1759",
        "authors": [
            "Elias Kosunen"
        ],
        "publisher": "WG21"
    }
}
</pre>