Squashed 'third_party/immer/' content from commit ad3e3556d

git-subtree-dir: third_party/immer
git-subtree-split: ad3e3556d38bb75966dd24c61a774970a7c7957e

1 files changed, 36 insertions, 0 deletions

diff --git a/immer/detail/ref_count_base.hpp b/immer/detail/ref_count_base.hpp
new file mode 100644
index 000000000000..28f2e46a99f9
--- /dev/null
+++ b/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 */