Revert commit removing allocator support from packaged_task. Will investigate further

llvm-svn: 319091
Cr-Mirrored-From: sso://chromium.googlesource.com/_direct/external/github.com/llvm/llvm-project
Cr-Mirrored-Commit: a2f3c63282330be0226158cdfdc27c4c2aef9cdc
diff --git a/include/future b/include/future
index 1bc4799..a7c28a4 100644
--- a/include/future
+++ b/include/future
@@ -328,6 +328,8 @@
     packaged_task() noexcept;
     template <class F>
         explicit packaged_task(F&& f);
+    template <class F, class Allocator>
+        packaged_task(allocator_arg_t, const Allocator& a, F&& f);
     ~packaged_task();
 
     // no copy
@@ -354,6 +356,8 @@
 template <class R>
   void swap(packaged_task<R(ArgTypes...)&, packaged_task<R(ArgTypes...)>&) noexcept;
 
+template <class R, class Alloc> struct uses_allocator<packaged_task<R>, Alloc>;
+
 }  // std
 
 */
@@ -2024,6 +2028,19 @@
              >
         _LIBCPP_INLINE_VISIBILITY
         explicit packaged_task(_Fp&& __f) : __f_(_VSTD::forward<_Fp>(__f)) {}
+    template <class _Fp, class _Allocator,
+              class = typename enable_if
+              <
+                  !is_same<
+                      typename decay<_Fp>::type, 
+                      packaged_task
+                      >::value
+                  >::type
+              >
+        _LIBCPP_INLINE_VISIBILITY
+        packaged_task(allocator_arg_t, const _Allocator& __a, _Fp&& __f)
+             : __f_(allocator_arg, __a, _VSTD::forward<_Fp>(__f)),
+               __p_(allocator_arg, __a) {}
     // ~packaged_task() = default;
 
     // no copy
@@ -2140,6 +2157,19 @@
               >
         _LIBCPP_INLINE_VISIBILITY
         explicit packaged_task(_Fp&& __f) : __f_(_VSTD::forward<_Fp>(__f)) {}
+    template <class _Fp, class _Allocator,
+              class = typename enable_if
+              <
+                  !is_same<
+                      typename decay<_Fp>::type, 
+                      packaged_task
+                      >::value
+                  >::type
+              >    
+        _LIBCPP_INLINE_VISIBILITY
+        packaged_task(allocator_arg_t, const _Allocator& __a, _Fp&& __f)
+             : __f_(allocator_arg, __a, _VSTD::forward<_Fp>(__f)),
+               __p_(allocator_arg, __a) {}
     // ~packaged_task() = default;
 
     // no copy
@@ -2241,6 +2271,10 @@
     __x.swap(__y);
 }
 
+template <class _Callable, class _Alloc>
+struct _LIBCPP_TEMPLATE_VIS uses_allocator<packaged_task<_Callable>, _Alloc>
+    : public true_type {};
+
 template <class _Rp, class _Fp>
 future<_Rp>
 #ifndef _LIBCPP_HAS_NO_RVALUE_REFERENCES