forked from OSchip/llvm-project
92 lines
2.5 KiB
HTML
92 lines
2.5 KiB
HTML
<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01//EN"
|
|
"http://www.w3.org/TR/html4/strict.dtd">
|
|
<!-- Material used from: HTML 4.01 specs: http://www.w3.org/TR/html401/ -->
|
|
<html>
|
|
<head>
|
|
<META http-equiv="Content-Type" content="text/html; charset=ISO-8859-1">
|
|
<title><atomic> design</title>
|
|
<link type="text/css" rel="stylesheet" href="menu.css">
|
|
<link type="text/css" rel="stylesheet" href="content.css">
|
|
</head>
|
|
|
|
<body>
|
|
<div id="menu">
|
|
<div>
|
|
<a href="https://llvm.org/">LLVM Home</a>
|
|
</div>
|
|
|
|
<div class="submenu">
|
|
<label>libc++ Info</label>
|
|
<a href="/index.html">About</a>
|
|
</div>
|
|
|
|
<div class="submenu">
|
|
<label>Quick Links</label>
|
|
<a href="https://lists.llvm.org/mailman/listinfo/cfe-dev">cfe-dev</a>
|
|
<a href="https://lists.llvm.org/mailman/listinfo/cfe-commits">cfe-commits</a>
|
|
<a href="https://bugs.llvm.org/">Bug Reports</a>
|
|
<a href="https://github.com/llvm/llvm-project/tree/master/libcxx/">Browse Sources</a>
|
|
</div>
|
|
</div>
|
|
|
|
<div id="content">
|
|
<!--*********************************************************************-->
|
|
<h1><atomic> design</h1>
|
|
<!--*********************************************************************-->
|
|
|
|
<p>
|
|
There are currently 3 designs under consideration. They differ in where most
|
|
of the implementation work is done. The functionality exposed to the customer
|
|
should be identical (and conforming) for all three designs.
|
|
</p>
|
|
|
|
<ol type="A">
|
|
<li>
|
|
<a href="atomic_design_a.html">Minimal work for the library</a>
|
|
</li>
|
|
<li>
|
|
<a href="atomic_design_b.html">Something in between</a>
|
|
</li>
|
|
<li>
|
|
<a href="atomic_design_c.html">Minimal work for the front end</a>
|
|
</li>
|
|
</ol>
|
|
|
|
<p>
|
|
With any design, the (back end) compiler writer should note:
|
|
</p>
|
|
|
|
<blockquote>
|
|
<p>
|
|
The decision to implement lock-free operations on any given type (or not) is an
|
|
ABI-binding decision. One can not change from treating a type as not lock free,
|
|
to lock free (or vice-versa) without breaking your ABI.
|
|
</p>
|
|
|
|
<p>
|
|
Example:
|
|
</p>
|
|
|
|
<blockquote><pre>
|
|
TU1.cc
|
|
-----------
|
|
extern atomic<long long> A;
|
|
int foo() { return A.compare_exchange_strong(w, x); }
|
|
|
|
TU2.cc
|
|
-----------
|
|
extern atomic<long long> A;
|
|
void bar() { return A.compare_exchange_strong(y, z); }
|
|
</pre></blockquote>
|
|
</blockquote>
|
|
|
|
<p>
|
|
If only <em>one</em> of these calls to <tt>compare_exchange_strong</tt> is
|
|
implemented with mutex-locked code, then that mutex-locked code will not be
|
|
executed mutually exclusively of the one implemented in a lock-free manner.
|
|
</p>
|
|
|
|
</div>
|
|
</body>
|
|
</html>
|