Update atomic Design A spec with reference C++ implementations for the purpose of documeting the semantics of each atomic operation.

git-svn-id: https://llvm.org/svn/llvm-project/libcxx/trunk@116713 91177308-0d34-0410-b5e6-96231b3b80d8

www/atomic_design_a.html

@@ -71,7 +71,7 @@ type __atomic_load(const type* atomic_obj, int mem_ord);
 
 <font color="#C80000">// type must be trivially copyable</font>
 <font color="#C80000">// Behavior is defined for mem_ord = 0, 3, 5</font>
-type __atomic_store(type* atomic_obj, type desired, int mem_ord);
+void __atomic_store(type* atomic_obj, type desired, int mem_ord);
 
 <font color="#C80000">// type must be trivially copyable</font>
 <font color="#C80000">// Behavior is defined for mem_ord = [0 ... 5]</font>
@@ -160,6 +160,150 @@ translate_memory_order(int o)
     return o;
 }
 </pre></blockquote>
+
+<p>
+Below are representative C++ implementations of all of the operations.  Their
+purpose is to document the desired semantics of each operation, assuming
+<tt>memory_order_seq_cst</tt>.  This is essentially the code that will be called
+if the front end calls out to compiler-rt.
+</p>
+
+<blockquote><pre>
+template &lt;class T&gt;
+T
+__atomic_load(T const volatile* obj)
+{
+    unique_lock&lt;mutex&gt; _(some_mutex);
+    return *obj;
+}
+
+template &lt;class T&gt;
+void
+__atomic_store(T volatile* obj, T desr)
+{
+    unique_lock&lt;mutex&gt; _(some_mutex);
+    *obj = desr;
+}
+
+template &lt;class T&gt;
+T
+__atomic_exchange(T volatile* obj, T desr)
+{
+    unique_lock&lt;mutex&gt; _(some_mutex);
+    T r = *obj;
+    *obj = desr;
+    return r;
+}
+
+template &lt;class T&gt;
+bool
+__atomic_compare_exchange_strong(T volatile* obj, T* exp, T desr)
+{
+    unique_lock&lt;mutex&gt; _(some_mutex);
+    if (std::memcmp(const_cast&lt;T*&gt;(obj), exp, sizeof(T)) == 0) <font color="#C80000">// if (*obj == *exp)</font>
+    {
+        std::memcpy(const_cast&lt;T*&gt;(obj), &amp;desr, sizeof(T)); <font color="#C80000">// *obj = desr;</font>
+        return true;
+    }
+    std::memcpy(exp, const_cast&lt;T*&gt;(obj), sizeof(T)); <font color="#C80000">// *exp = *obj;</font>
+    return false;
+}
+
+<font color="#C80000">// May spuriously return false (even if *obj == *exp)</font>
+template &lt;class T&gt;
+bool
+__atomic_compare_exchange_weak(T volatile* obj, T* exp, T desr)
+{
+    unique_lock&lt;mutex&gt; _(some_mutex);
+    if (std::memcmp(const_cast&lt;T*&gt;(obj), exp, sizeof(T)) == 0) <font color="#C80000">// if (*obj == *exp)</font>
+    {
+        std::memcpy(const_cast&lt;T*&gt;(obj), &amp;desr, sizeof(T)); <font color="#C80000">// *obj = desr;</font>
+        return true;
+    }
+    std::memcpy(exp, const_cast&lt;T*&gt;(obj), sizeof(T)); <font color="#C80000">// *exp = *obj;</font>
+    return false;
+}
+
+template &lt;class T&gt;
+T
+__atomic_fetch_add(T volatile* obj, T operand)
+{
+    unique_lock&lt;mutex&gt; _(some_mutex);
+    T r = *obj;
+    *obj += operand;
+    return r;
+}
+
+template &lt;class T&gt;
+T
+__atomic_fetch_sub(T volatile* obj, T operand)
+{
+    unique_lock&lt;mutex&gt; _(some_mutex);
+    T r = *obj;
+    *obj -= operand;
+    return r;
+}
+
+template &lt;class T&gt;
+T
+__atomic_fetch_and(T volatile* obj, T operand)
+{
+    unique_lock&lt;mutex&gt; _(some_mutex);
+    T r = *obj;
+    *obj &amp;= operand;
+    return r;
+}
+
+template &lt;class T&gt;
+T
+__atomic_fetch_or(T volatile* obj, T operand)
+{
+    unique_lock&lt;mutex&gt; _(some_mutex);
+    T r = *obj;
+    *obj |= operand;
+    return r;
+}
+
+template &lt;class T&gt;
+T
+__atomic_fetch_xor(T volatile* obj, T operand)
+{
+    unique_lock&lt;mutex&gt; _(some_mutex);
+    T r = *obj;
+    *obj ^= operand;
+    return r;
+}
+
+void*
+__atomic_fetch_add(void* volatile* obj, ptrdiff_t operand)
+{
+    unique_lock&lt;mutex&gt; _(some_mutex);
+    void* r = *obj;
+    (char*&amp;)(*obj) += operand;
+    return r;
+}
+
+void*
+__atomic_fetch_sub(void* volatile* obj, ptrdiff_t operand)
+{
+    unique_lock&lt;mutex&gt; _(some_mutex);
+    void* r = *obj;
+    (char*&amp;)(*obj) -= operand;
+    return r;
+}
+
+void __atomic_thread_fence()
+{
+    unique_lock&lt;mutex&gt; _(some_mutex);
+}
+
+void __atomic_signal_fence()
+{
+    unique_lock&lt;mutex&gt; _(some_mutex);
+}
+</pre></blockquote>
+
+
 </div>
 </body>
 </html>