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include/asio/recycling_allocator.hpp

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+//
+// recycling_allocator.hpp
+// ~~~~~~~~~~~~~~~~~~~~~~~
+//
+// Copyright (c) 2003-2025 Christopher M. Kohlhoff (chris at kohlhoff dot com)
+//
+// Distributed under the Boost Software License, Version 1.0. (See accompanying
+// file LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt)
+//
+
+#ifndef ASIO_RECYCLING_ALLOCATOR_HPP
+#define ASIO_RECYCLING_ALLOCATOR_HPP
+
+#if defined(_MSC_VER) && (_MSC_VER >= 1200)
+# pragma once
+#endif // defined(_MSC_VER) && (_MSC_VER >= 1200)
+
+#include "asio/detail/config.hpp"
+#include "asio/detail/recycling_allocator.hpp"
+
+#include "asio/detail/push_options.hpp"
+
+namespace asio {
+
+/// An allocator that caches memory blocks in thread-local storage for reuse.
+/**
+ * The @recycling_allocator uses a simple strategy where a limited number of
+ * small memory blocks are cached in thread-local storage, if the current
+ * thread is running an @c io_context or is part of a @c thread_pool.
+ */
+template <typename T>
+class recycling_allocator
+{
+public:
+  /// The type of object allocated by the recycling allocator.
+  typedef T value_type;
+
+  /// Rebind the allocator to another value_type.
+  template <typename U>
+  struct rebind
+  {
+    /// The rebound @c allocator type.
+    typedef recycling_allocator<U> other;
+  };
+
+  /// Default constructor.
+  constexpr recycling_allocator() noexcept
+  {
+  }
+
+  /// Converting constructor.
+  template <typename U>
+  constexpr recycling_allocator(
+      const recycling_allocator<U>&) noexcept
+  {
+  }
+
+  /// Equality operator. Always returns true.
+  constexpr bool operator==(
+      const recycling_allocator&) const noexcept
+  {
+    return true;
+  }
+
+  /// Inequality operator. Always returns false.
+  constexpr bool operator!=(
+      const recycling_allocator&) const noexcept
+  {
+    return false;
+  }
+
+  /// Allocate memory for the specified number of values.
+  T* allocate(std::size_t n)
+  {
+    return detail::recycling_allocator<T>().allocate(n);
+  }
+
+  /// Deallocate memory for the specified number of values.
+  void deallocate(T* p, std::size_t n)
+  {
+    detail::recycling_allocator<T>().deallocate(p, n);
+  }
+};
+
+/// A proto-allocator that caches memory blocks in thread-local storage for
+/// reuse.
+/**
+ * The @recycling_allocator uses a simple strategy where a limited number of
+ * small memory blocks are cached in thread-local storage, if the current
+ * thread is running an @c io_context or is part of a @c thread_pool.
+ */
+template <>
+class recycling_allocator<void>
+{
+public:
+  /// No values are allocated by a proto-allocator.
+  typedef void value_type;
+
+  /// Rebind the allocator to another value_type.
+  template <typename U>
+  struct rebind
+  {
+    /// The rebound @c allocator type.
+    typedef recycling_allocator<U> other;
+  };
+
+  /// Default constructor.
+  constexpr recycling_allocator() noexcept
+  {
+  }
+
+  /// Converting constructor.
+  template <typename U>
+  constexpr recycling_allocator(
+      const recycling_allocator<U>&) noexcept
+  {
+  }
+
+  /// Equality operator. Always returns true.
+  constexpr bool operator==(
+      const recycling_allocator&) const noexcept
+  {
+    return true;
+  }
+
+  /// Inequality operator. Always returns false.
+  constexpr bool operator!=(
+      const recycling_allocator&) const noexcept
+  {
+    return false;
+  }
+};
+
+} // namespace asio
+
+#include "asio/detail/pop_options.hpp"
+
+#endif // ASIO_RECYCLING_ALLOCATOR_HPP