Fix LWG Issue 2078. Make std::async(policy,...) try multiple policies until one succeeds.

llvm-svn: 193960

2 files changed, 19 insertions, 7 deletions

diff --git a/libcxx/include/future b/libcxx/include/future
index ff8e59b17a9..7561d190f41 100644
--- a/libcxx/include/future
+++ b/libcxx/include/future
@@ -2331,20 +2331,32 @@ private:
     }
 };
 
+bool __does_policy_contain(launch __policy, launch __value )
+{ return (int(__policy) & int(__value)) != 0; }
+
 template <class _Fp, class... _Args>
 future<typename __invoke_of<typename decay<_Fp>::type, typename decay<_Args>::type...>::type>
 async(launch __policy, _Fp&& __f, _Args&&... __args)
 {
     typedef __async_func<typename decay<_Fp>::type, typename decay<_Args>::type...> _BF;
     typedef typename _BF::_Rp _Rp;
-    future<_Rp> __r;
-    if (int(__policy) & int(launch::async))
-        __r = _VSTD::__make_async_assoc_state<_Rp>(_BF(__decay_copy(_VSTD::forward<_Fp>(__f)),
+
+#ifndef _LIBCPP_NO_EXCEPTIONS
+    try
+    {
+#endif
+        if (__does_policy_contain(__policy, launch::async))
+        return _VSTD::__make_async_assoc_state<_Rp>(_BF(__decay_copy(_VSTD::forward<_Fp>(__f)),
                                                      __decay_copy(_VSTD::forward<_Args>(__args))...));
-    else if (int(__policy) & int(launch::deferred))
-        __r = _VSTD::__make_deferred_assoc_state<_Rp>(_BF(__decay_copy(_VSTD::forward<_Fp>(__f)),
+#ifndef _LIBCPP_NO_EXCEPTIONS
+    }
+    catch ( ... ) { if (__policy == launch::async) throw ; }
+#endif
+
+    if (__does_policy_contain(__policy, launch::deferred))
+        return _VSTD::__make_deferred_assoc_state<_Rp>(_BF(__decay_copy(_VSTD::forward<_Fp>(__f)),
                                                         __decay_copy(_VSTD::forward<_Args>(__args))...));
-    return __r;
+    return future<_Rp>{};
 }
 
 template <class _Fp, class... _Args>
diff --git a/libcxx/www/cxx1y_status.html b/libcxx/www/cxx1y_status.html
index 87e65f748d2..15515fd5695 100644
--- a/libcxx/www/cxx1y_status.html
+++ b/libcxx/www/cxx1y_status.html
@@ -196,7 +196,7 @@
 	<tr><td><a href="http://www.open-std.org/jtc1/sc22/wg21/docs/lwg-defects.html#2194">2194</a></td><td>Impossible container requirements for adaptor types</td><td>Chicago</td><td>Complete</td></tr>
 	<tr><td><a href="http://www.open-std.org/jtc1/sc22/wg21/docs/lwg-defects.html#2013">2013</a></td><td>Do library implementers have the freedom to add constexpr?</td><td>Chicago</td><td>Complete</td></tr>
 	<tr><td><a href="http://www.open-std.org/jtc1/sc22/wg21/docs/lwg-defects.html#2018">2018</a></td><td>regex_traits::isctype Returns clause is wrong</td><td>Chicago</td><td>Complete</td></tr>
-	<tr><td><a href="http://www.open-std.org/jtc1/sc22/wg21/docs/lwg-defects.html#2078">2078</a></td><td>Throw specification of async() incomplete</td><td>Chicago</td><td></td></tr>
+	<tr><td><a href="http://www.open-std.org/jtc1/sc22/wg21/docs/lwg-defects.html#2078">2078</a></td><td>Throw specification of async() incomplete</td><td>Chicago</td><td>Complete</td></tr>
 	<tr><td><a href="http://www.open-std.org/jtc1/sc22/wg21/docs/lwg-defects.html#2097">2097</a></td><td>packaged_task constructors should be constrained</td><td>Chicago</td><td>Complete</td></tr>
 	<tr><td><a href="http://www.open-std.org/jtc1/sc22/wg21/docs/lwg-defects.html#2100">2100</a></td><td>Timed waiting functions cannot timeout if launch::async policy used</td><td>Chicago</td><td>Complete</td></tr>
 	<tr><td><a href="http://www.open-std.org/jtc1/sc22/wg21/docs/lwg-defects.html#2120">2120</a></td><td>What should async do if neither 'async' nor 'deferred' is set in policy?</td><td>Chicago</td><td>Complete</td></tr>