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8252588: HotSpot Style Guide should permit uniform initialization

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Reviewed-by: jrose, dholmes, dcubed, tschatzl, kvn
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Kim Barrett 2020-11-17 03:16:10 +00:00
parent c35e1a284b
commit 537b40e013
2 changed files with 29 additions and 0 deletions
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12
doc/hotspot-style.html
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@ -49,6 +49,7 @@
<li><a href="#thread_local">thread_local</a></li>
<li><a href="#nullptr">nullptr</a></li>
<li><a href="#atomic">&lt;atomic&gt;</a></li>
<li><a href="#uniform-initialization">Uniform Initialization</a></li>
<li><a href="#additional-permitted-features">Additional Permitted Features</a></li>
<li><a href="#excluded-features">Excluded Features</a></li>
<li><a href="#undecided-features">Undecided Features</a></li>
@ -275,6 +276,17 @@ while ( test_foo(args...) ) { // No, excess spaces around control</code></pre></
<p>Do not use facilities provided by the <code>&lt;atomic&gt;</code> header (<a href="http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2007/n2427.html">n2427</a>), (<a href="http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2008/n2752.htm">n2752</a>); instead, use the HotSpot <code>Atomic</code> class and related facilities.</p>
<p>Atomic operations in HotSpot code must have semantics which are consistent with those provided by the JDK's compilers for Java. There are platform-specific implementation choices that a C++ compiler might make or change that are outside the scope of the C++ Standard, and might differ from what the Java compilers implement.</p>
<p>In addition, HotSpot <code>Atomic</code> has a concept of &quot;conservative&quot; memory ordering, which may differ from (may be stronger than) sequentially consistent. There are algorithms in HotSpot that are believed to rely on that ordering.</p>
<h3 id="uniform-initialization">Uniform Initialization</h3>
<p>The use of <em>uniform initialization</em> (<a href="http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2008/n2672.htm">n2672</a>), also known as <em>brace initialization</em>, is permitted.</p>
<p>Some relevant sections from cppreference.com:</p>
<ul>
<li><a href="https://en.cppreference.com/w/cpp/language/initialization">initialization</a></li>
<li><a href="https://en.cppreference.com/w/cpp/language/value_initialization">value initialization</a></li>
<li><a href="https://en.cppreference.com/w/cpp/language/direct_initialization">direct initialization</a></li>
<li><a href="https://en.cppreference.com/w/cpp/language/list_initialization">list initialization</a></li>
<li><a href="https://en.cppreference.com/w/cpp/language/aggregate_initialization">aggregate initialization</a></li>
</ul>
<p>Although related, the use of <code>std::initializer_list</code> remains forbidden, as part of the avoidance of the C++ Standard Library in HotSpot code.</p>
<h3 id="additional-permitted-features">Additional Permitted Features</h3>
<ul>
<li><p><code>constexpr</code> (<a href="http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2007/n2235.pdf">n2235</a>) (<a href="https://isocpp.org/files/papers/N3652.html">n3652</a>)</p></li>

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doc/hotspot-style.md
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@ -681,6 +681,23 @@ ordering, which may differ from (may be stronger than) sequentially
consistent. There are algorithms in HotSpot that are believed to rely
on that ordering.
### Uniform Initialization
The use of _uniform initialization_
([n2672](http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2008/n2672.htm)),
also known as _brace initialization_, is permitted.
Some relevant sections from cppreference.com:
* [initialization](https://en.cppreference.com/w/cpp/language/initialization)
* [value initialization](https://en.cppreference.com/w/cpp/language/value_initialization)
* [direct initialization](https://en.cppreference.com/w/cpp/language/direct_initialization)
* [list initialization](https://en.cppreference.com/w/cpp/language/list_initialization)
* [aggregate initialization](https://en.cppreference.com/w/cpp/language/aggregate_initialization)
Although related, the use of `std::initializer_list` remains forbidden, as
part of the avoidance of the C++ Standard Library in HotSpot code.
### Additional Permitted Features
* `constexpr`