[libc++] Split __shared_count out of <__memory/shared_ptr.h> (#115943)

`__shared_count` is used in a few places where `shared_ptr` isn't. This
avoids a bunch of transitive includes needed for the implementation of
`shared_ptr` in these places.

Author: philnik777

libcxx/include/CMakeLists.txt

@@ -557,6 +557,7 @@ set(files
   __memory/ranges_construct_at.h
   __memory/ranges_uninitialized_algorithms.h
   __memory/raw_storage_iterator.h
+  __memory/shared_count.h
   __memory/shared_ptr.h
   __memory/swap_allocator.h
   __memory/temp_value.h

libcxx/include/__locale

@@ -12,7 +12,7 @@
 
 #include <__config>
 #include <__locale_dir/locale_base_api.h>
-#include <__memory/shared_ptr.h> // __shared_count
+#include <__memory/shared_count.h>
 #include <__mutex/once_flag.h>
 #include <__type_traits/make_unsigned.h>
 #include <__utility/no_destroy.h>

libcxx/include/__memory/shared_count.h

@@ -0,0 +1,136 @@
+//===----------------------------------------------------------------------===//
+//
+// 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_SHARED_COUNT_H
+#define _LIBCPP___MEMORY_SHARED_COUNT_H
+
+#include <__config>
+#include <typeinfo>
+
+#if !defined(_LIBCPP_HAS_NO_PRAGMA_SYSTEM_HEADER)
+#  pragma GCC system_header
+#endif
+
+_LIBCPP_BEGIN_NAMESPACE_STD
+
+// NOTE: Relaxed and acq/rel atomics (for increment and decrement respectively)
+// should be sufficient for thread safety.
+// See https://llvm.org/PR22803
+#if (defined(__clang__) && __has_builtin(__atomic_add_fetch) && defined(__ATOMIC_RELAXED) &&                           \
+     defined(__ATOMIC_ACQ_REL)) ||                                                                                     \
+    defined(_LIBCPP_COMPILER_GCC)
+#  define _LIBCPP_HAS_BUILTIN_ATOMIC_SUPPORT 1
+#else
+#  define _LIBCPP_HAS_BUILTIN_ATOMIC_SUPPORT 0
+#endif
+
+template <class _ValueType>
+inline _LIBCPP_HIDE_FROM_ABI _ValueType __libcpp_relaxed_load(_ValueType const* __value) {
+#if _LIBCPP_HAS_THREADS && defined(__ATOMIC_RELAXED) &&                                                                \
+    (__has_builtin(__atomic_load_n) || defined(_LIBCPP_COMPILER_GCC))
+  return __atomic_load_n(__value, __ATOMIC_RELAXED);
+#else
+  return *__value;
+#endif
+}
+
+template <class _ValueType>
+inline _LIBCPP_HIDE_FROM_ABI _ValueType __libcpp_acquire_load(_ValueType const* __value) {
+#if _LIBCPP_HAS_THREADS && defined(__ATOMIC_ACQUIRE) &&                                                                \
+    (__has_builtin(__atomic_load_n) || defined(_LIBCPP_COMPILER_GCC))
+  return __atomic_load_n(__value, __ATOMIC_ACQUIRE);
+#else
+  return *__value;
+#endif
+}
+
+template <class _Tp>
+inline _LIBCPP_HIDE_FROM_ABI _Tp __libcpp_atomic_refcount_increment(_Tp& __t) _NOEXCEPT {
+#if _LIBCPP_HAS_BUILTIN_ATOMIC_SUPPORT && _LIBCPP_HAS_THREADS
+  return __atomic_add_fetch(&__t, 1, __ATOMIC_RELAXED);
+#else
+  return __t += 1;
+#endif
+}
+
+template <class _Tp>
+inline _LIBCPP_HIDE_FROM_ABI _Tp __libcpp_atomic_refcount_decrement(_Tp& __t) _NOEXCEPT {
+#if _LIBCPP_HAS_BUILTIN_ATOMIC_SUPPORT && _LIBCPP_HAS_THREADS
+  return __atomic_add_fetch(&__t, -1, __ATOMIC_ACQ_REL);
+#else
+  return __t -= 1;
+#endif
+}
+
+class _LIBCPP_EXPORTED_FROM_ABI __shared_count {
+  __shared_count(const __shared_count&);
+  __shared_count& operator=(const __shared_count&);
+
+protected:
+  long __shared_owners_;
+  virtual ~__shared_count();
+
+private:
+  virtual void __on_zero_shared() _NOEXCEPT = 0;
+
+public:
+  _LIBCPP_HIDE_FROM_ABI explicit __shared_count(long __refs = 0) _NOEXCEPT : __shared_owners_(__refs) {}
+
+#if defined(_LIBCPP_SHARED_PTR_DEFINE_LEGACY_INLINE_FUNCTIONS)
+  void __add_shared() noexcept;
+  bool __release_shared() noexcept;
+#else
+  _LIBCPP_HIDE_FROM_ABI void __add_shared() _NOEXCEPT { __libcpp_atomic_refcount_increment(__shared_owners_); }
+  _LIBCPP_HIDE_FROM_ABI bool __release_shared() _NOEXCEPT {
+    if (__libcpp_atomic_refcount_decrement(__shared_owners_) == -1) {
+      __on_zero_shared();
+      return true;
+    }
+    return false;
+  }
+#endif
+  _LIBCPP_HIDE_FROM_ABI long use_count() const _NOEXCEPT { return __libcpp_relaxed_load(&__shared_owners_) + 1; }
+};
+
+class _LIBCPP_EXPORTED_FROM_ABI __shared_weak_count : private __shared_count {
+  long __shared_weak_owners_;
+
+public:
+  _LIBCPP_HIDE_FROM_ABI explicit __shared_weak_count(long __refs = 0) _NOEXCEPT
+      : __shared_count(__refs),
+        __shared_weak_owners_(__refs) {}
+
+protected:
+  ~__shared_weak_count() override;
+
+public:
+#if defined(_LIBCPP_SHARED_PTR_DEFINE_LEGACY_INLINE_FUNCTIONS)
+  void __add_shared() noexcept;
+  void __add_weak() noexcept;
+  void __release_shared() noexcept;
+#else
+  _LIBCPP_HIDE_FROM_ABI void __add_shared() _NOEXCEPT { __shared_count::__add_shared(); }
+  _LIBCPP_HIDE_FROM_ABI void __add_weak() _NOEXCEPT { __libcpp_atomic_refcount_increment(__shared_weak_owners_); }
+  _LIBCPP_HIDE_FROM_ABI void __release_shared() _NOEXCEPT {
+    if (__shared_count::__release_shared())
+      __release_weak();
+  }
+#endif
+  void __release_weak() _NOEXCEPT;
+  _LIBCPP_HIDE_FROM_ABI long use_count() const _NOEXCEPT { return __shared_count::use_count(); }
+  __shared_weak_count* lock() _NOEXCEPT;
+
+  virtual const void* __get_deleter(const type_info&) const _NOEXCEPT;
+
+private:
+  virtual void __on_zero_shared_weak() _NOEXCEPT = 0;
+};
+
+_LIBCPP_END_NAMESPACE_STD
+
+#endif // _LIBCPP___MEMORY_SHARED_COUNT_H

libcxx/include/__memory/shared_ptr.h

@@ -30,6 +30,7 @@
 #include <__memory/compressed_pair.h>
 #include <__memory/construct_at.h>
 #include <__memory/pointer_traits.h>
+#include <__memory/shared_count.h>
 #include <__memory/uninitialized_algorithms.h>
 #include <__memory/unique_ptr.h>
 #include <__type_traits/add_lvalue_reference.h>
@@ -70,55 +71,6 @@ _LIBCPP_PUSH_MACROS
 
 _LIBCPP_BEGIN_NAMESPACE_STD
 
-// NOTE: Relaxed and acq/rel atomics (for increment and decrement respectively)
-// should be sufficient for thread safety.
-// See https://llvm.org/PR22803
-#if (defined(__clang__) && __has_builtin(__atomic_add_fetch) && defined(__ATOMIC_RELAXED) &&                           \
-     defined(__ATOMIC_ACQ_REL)) ||                                                                                     \
-    defined(_LIBCPP_COMPILER_GCC)
-#  define _LIBCPP_HAS_BUILTIN_ATOMIC_SUPPORT 1
-#else
-#  define _LIBCPP_HAS_BUILTIN_ATOMIC_SUPPORT 0
-#endif
-
-template <class _ValueType>
-inline _LIBCPP_HIDE_FROM_ABI _ValueType __libcpp_relaxed_load(_ValueType const* __value) {
-#if _LIBCPP_HAS_THREADS && defined(__ATOMIC_RELAXED) &&                                                                \
-    (__has_builtin(__atomic_load_n) || defined(_LIBCPP_COMPILER_GCC))
-  return __atomic_load_n(__value, __ATOMIC_RELAXED);
-#else
-  return *__value;
-#endif
-}
-
-template <class _ValueType>
-inline _LIBCPP_HIDE_FROM_ABI _ValueType __libcpp_acquire_load(_ValueType const* __value) {
-#if _LIBCPP_HAS_THREADS && defined(__ATOMIC_ACQUIRE) &&                                                                \
-    (__has_builtin(__atomic_load_n) || defined(_LIBCPP_COMPILER_GCC))
-  return __atomic_load_n(__value, __ATOMIC_ACQUIRE);
-#else
-  return *__value;
-#endif
-}
-
-template <class _Tp>
-inline _LIBCPP_HIDE_FROM_ABI _Tp __libcpp_atomic_refcount_increment(_Tp& __t) _NOEXCEPT {
-#if _LIBCPP_HAS_BUILTIN_ATOMIC_SUPPORT && _LIBCPP_HAS_THREADS
-  return __atomic_add_fetch(&__t, 1, __ATOMIC_RELAXED);
-#else
-  return __t += 1;
-#endif
-}
-
-template <class _Tp>
-inline _LIBCPP_HIDE_FROM_ABI _Tp __libcpp_atomic_refcount_decrement(_Tp& __t) _NOEXCEPT {
-#if _LIBCPP_HAS_BUILTIN_ATOMIC_SUPPORT && _LIBCPP_HAS_THREADS
-  return __atomic_add_fetch(&__t, -1, __ATOMIC_ACQ_REL);
-#else
-  return __t -= 1;
-#endif
-}
-
 class _LIBCPP_EXPORTED_FROM_ABI bad_weak_ptr : public std::exception {
 public:
   _LIBCPP_HIDE_FROM_ABI bad_weak_ptr() _NOEXCEPT                               = default;
@@ -139,70 +91,6 @@ class _LIBCPP_EXPORTED_FROM_ABI bad_weak_ptr : public std::exception {
 template <class _Tp>
 class _LIBCPP_TEMPLATE_VIS weak_ptr;
 
-class _LIBCPP_EXPORTED_FROM_ABI __shared_count {
-  __shared_count(const __shared_count&);
-  __shared_count& operator=(const __shared_count&);
-
-protected:
-  long __shared_owners_;
-  virtual ~__shared_count();
-
-private:
-  virtual void __on_zero_shared() _NOEXCEPT = 0;
-
-public:
-  _LIBCPP_HIDE_FROM_ABI explicit __shared_count(long __refs = 0) _NOEXCEPT : __shared_owners_(__refs) {}
-
-#if defined(_LIBCPP_SHARED_PTR_DEFINE_LEGACY_INLINE_FUNCTIONS)
-  void __add_shared() noexcept;
-  bool __release_shared() noexcept;
-#else
-  _LIBCPP_HIDE_FROM_ABI void __add_shared() _NOEXCEPT { __libcpp_atomic_refcount_increment(__shared_owners_); }
-  _LIBCPP_HIDE_FROM_ABI bool __release_shared() _NOEXCEPT {
-    if (__libcpp_atomic_refcount_decrement(__shared_owners_) == -1) {
-      __on_zero_shared();
-      return true;
-    }
-    return false;
-  }
-#endif
-  _LIBCPP_HIDE_FROM_ABI long use_count() const _NOEXCEPT { return __libcpp_relaxed_load(&__shared_owners_) + 1; }
-};
-
-class _LIBCPP_EXPORTED_FROM_ABI __shared_weak_count : private __shared_count {
-  long __shared_weak_owners_;
-
-public:
-  _LIBCPP_HIDE_FROM_ABI explicit __shared_weak_count(long __refs = 0) _NOEXCEPT
-      : __shared_count(__refs),
-        __shared_weak_owners_(__refs) {}
-
-protected:
-  ~__shared_weak_count() override;
-
-public:
-#if defined(_LIBCPP_SHARED_PTR_DEFINE_LEGACY_INLINE_FUNCTIONS)
-  void __add_shared() noexcept;
-  void __add_weak() noexcept;
-  void __release_shared() noexcept;
-#else
-  _LIBCPP_HIDE_FROM_ABI void __add_shared() _NOEXCEPT { __shared_count::__add_shared(); }
-  _LIBCPP_HIDE_FROM_ABI void __add_weak() _NOEXCEPT { __libcpp_atomic_refcount_increment(__shared_weak_owners_); }
-  _LIBCPP_HIDE_FROM_ABI void __release_shared() _NOEXCEPT {
-    if (__shared_count::__release_shared())
-      __release_weak();
-  }
-#endif
-  void __release_weak() _NOEXCEPT;
-  _LIBCPP_HIDE_FROM_ABI long use_count() const _NOEXCEPT { return __shared_count::use_count(); }
-  __shared_weak_count* lock() _NOEXCEPT;
-
-  virtual const void* __get_deleter(const type_info&) const _NOEXCEPT;
-
-private:
-  virtual void __on_zero_shared_weak() _NOEXCEPT = 0;
-};
-
 template <class _Tp, class _Dp, class _Alloc>
 class __shared_ptr_pointer : public __shared_weak_count {
   _LIBCPP_COMPRESSED_TRIPLE(_Tp, __ptr_, _Dp, __deleter_, _Alloc, __alloc_);

libcxx/include/__mutex/once_flag.h

@@ -11,7 +11,7 @@
 
 #include <__config>
 #include <__functional/invoke.h>
-#include <__memory/shared_ptr.h> // __libcpp_acquire_load
+#include <__memory/shared_count.h> // __libcpp_acquire_load
 #include <__tuple/tuple_indices.h>
 #include <__tuple/tuple_size.h>
 #include <__utility/forward.h>

libcxx/include/future

@@ -378,7 +378,7 @@ template <class R, class Alloc> struct uses_allocator<packaged_task<R>, Alloc>;
 #  include <__memory/allocator_traits.h>
 #  include <__memory/compressed_pair.h>
 #  include <__memory/pointer_traits.h>
-#  include <__memory/shared_ptr.h>
+#  include <__memory/shared_count.h>
 #  include <__memory/unique_ptr.h>
 #  include <__memory/uses_allocator.h>
 #  include <__system_error/error_category.h>

libcxx/include/module.modulemap

@@ -1542,6 +1542,7 @@ module std [system] {
       export std.algorithm.in_out_result
     }
     module raw_storage_iterator               { header "__memory/raw_storage_iterator.h" }
+    module shared_count                       { header "__memory/shared_count.h" }
     module shared_ptr                         { header "__memory/shared_ptr.h" }
     module swap_allocator                     { header "__memory/swap_allocator.h" }
     module temp_value                         { header "__memory/temp_value.h" }

libcxx/include/mutex

@@ -190,7 +190,6 @@ template<class Callable, class ...Args>
 #include <__chrono/time_point.h>
 #include <__condition_variable/condition_variable.h>
 #include <__config>
-#include <__memory/shared_ptr.h>
 #include <__mutex/lock_guard.h>
 #include <__mutex/mutex.h>
 #include <__mutex/once_flag.h>