[libcxx-commits] [libcxx] [libcxx] Implementation of non lock-free atomic shared_ptr (PR #194215)

[Hristo Hristov via libcxx-commits]

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@@ -0,0 +1,491 @@
+// -*- C++ -*-
+//===----------------------------------------------------------------------===//
+//
+// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
+// See https://llvm.org/LICENSE.txt for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+//===----------------------------------------------------------------------===//
+
+#ifndef _LIBCPP___MEMORY_ATOMIC_SHARED_PTR_H
+#define _LIBCPP___MEMORY_ATOMIC_SHARED_PTR_H
+
+#include <__atomic/atomic_sync_lite.h>
+#include <__atomic/check_memory_order.h>
+#include <__atomic/memory_order.h>
+#include <__atomic/support.h>
+#include <__config>
+#include <__cstddef/nullptr_t.h>
+#include <__memory/shared_count.h>
+#include <__utility/move.h>
+
+#include <cstdint>
+
+#if !defined(_LIBCPP_HAS_NO_PRAGMA_SYSTEM_HEADER)
+#  pragma GCC system_header
+#endif
+
+#if defined(__SANITIZE_THREAD__) || (defined(__has_feature) && __has_feature(thread_sanitizer))
+#  if __has_include(<sanitizer/tsan_interface.h>)
+#    include <sanitizer/tsan_interface.h>
+#    define _LIBCPP_ATOMIC_SHARED_PTR_TSAN 1
+#  endif
+#endif
+
+_LIBCPP_PUSH_MACROS
+#include <__undef_macros>
+
+// TSAN annotations model the lock-bit protocol on __ctrl_.
+#if defined(_LIBCPP_ATOMIC_SHARED_PTR_TSAN)
+#  define _LIBCPP_ATOMIC_SP_TSAN_PRE_LOCK(addr)                                                                        \
+    ::__tsan_mutex_pre_lock(reinterpret_cast<void*>(const_cast<__cxx_atomic_impl<uintptr_t>*>(addr)), 0)
+#  define _LIBCPP_ATOMIC_SP_TSAN_POST_LOCK(addr)                                                                       \
+    ::__tsan_mutex_post_lock(reinterpret_cast<void*>(const_cast<__cxx_atomic_impl<uintptr_t>*>(addr)), 0, 0)
+#  define _LIBCPP_ATOMIC_SP_TSAN_PRE_UNLOCK(addr)                                                                      \
+    ::__tsan_mutex_pre_unlock(reinterpret_cast<void*>(const_cast<__cxx_atomic_impl<uintptr_t>*>(addr)), 0)
+#  define _LIBCPP_ATOMIC_SP_TSAN_POST_UNLOCK(addr)                                                                     \
+    ::__tsan_mutex_post_unlock(reinterpret_cast<void*>(const_cast<__cxx_atomic_impl<uintptr_t>*>(addr)), 0)
+#else
+#  define _LIBCPP_ATOMIC_SP_TSAN_PRE_LOCK(addr) ((void)(addr))
+#  define _LIBCPP_ATOMIC_SP_TSAN_POST_LOCK(addr) ((void)(addr))
+#  define _LIBCPP_ATOMIC_SP_TSAN_PRE_UNLOCK(addr) ((void)(addr))
+#  define _LIBCPP_ATOMIC_SP_TSAN_POST_UNLOCK(addr) ((void)(addr))
+#endif
+
+_LIBCPP_BEGIN_NAMESPACE_STD
+
+#if _LIBCPP_STD_VER >= 20 && _LIBCPP_HAS_THREADS && _LIBCPP_HAS_ATOMIC_HEADER
+
+template <class _Tp>
+class shared_ptr;
+
+template <class _Tp>
+class weak_ptr;
+
+template <class _Tp>
+struct atomic;
+
+// Split state into pointer word and control word.
+// The control word stores control-block pointer plus lock/notify bits.
+struct __atomic_smart_ptr_storage {
+  static constexpr uintptr_t __lock_bit_   = uintptr_t{1};
+  static constexpr uintptr_t __notify_bit_ = uintptr_t{2};
+  static constexpr uintptr_t __ptr_mask_   = ~(__lock_bit_ | __notify_bit_);
+
+  _LIBCPP_HIDE_FROM_ABI static uintptr_t __encode(__shared_weak_count* __ctrl, uintptr_t __bits) _NOEXCEPT {
----------------
H-G-Hristov wrote:

```suggestion
  _LIBCPP_HIDE_FROM_ABI static uintptr_t __encode(__shared_weak_count* __ctrl, uintptr_t __bits) noexcept {
```

And below...

https://github.com/llvm/llvm-project/pull/194215