merge(3p/immer): Subtree merge at 'ad3e3556d' as 'third_party/immer' r/1299

Change-Id: I9636a41ad44b4218293833fd3e9456d9b07c731b

1 files changed, 36 insertions, 0 deletions

diff --git a/third_party/immer/immer/detail/ref_count_base.hpp b/third_party/immer/immer/detail/ref_count_base.hpp
new file mode 100644
index 000000000000..28f2e46a99f9
--- /dev/null
+++ b/third_party/immer/immer/detail/ref_count_base.hpp
@@ -0,0 +1,36 @@
+//
+// immer: immutable data structures for C++
+// Copyright (C) 2016, 2017, 2018 Juan Pedro Bolivar Puente
+//
+// This software is distributed under the Boost Software License, Version 1.0.
+// See accompanying file LICENSE or copy at http://boost.org/LICENSE_1_0.txt
+//
+
+#pragma once
+
+#include <atomic>
+
+namespace immer {
+namespace detail {
+
+template <typename Deriv>
+struct ref_count_base
+{
+    mutable std::atomic<int> ref_count{0};
+
+    friend void intrusive_ptr_add_ref(const Deriv* x)
+    {
+        x->ref_count.fetch_add(1, std::memory_order_relaxed);
+    }
+
+    friend void intrusive_ptr_release(const Deriv* x)
+    {
+        if (x->ref_count.fetch_sub(1, std::memory_order_release) == 1) {
+            std::atomic_thread_fence(std::memory_order_acquire);
+            delete x;
+        }
+    }
+};
+
+} /* namespace detail */
+} /* namespace immer */