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include/asio/detail/object_pool.hpp

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+//
+// detail/object_pool.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_DETAIL_OBJECT_POOL_HPP
+#define ASIO_DETAIL_OBJECT_POOL_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/memory.hpp"
+
+#include "asio/detail/push_options.hpp"
+
+namespace asio {
+namespace detail {
+
+template <typename Object, typename Allocator>
+class object_pool
+{
+public:
+  // Constructor.
+  template <typename... Args>
+  object_pool(const Allocator& allocator,
+      unsigned int preallocated, Args... args)
+    : allocator_(allocator),
+      live_list_(0),
+      free_list_(0)
+  {
+    while (preallocated > 0)
+    {
+      Object* o = allocate_object<Object>(allocator_, args...);
+      o->next_ = free_list_;
+      o->prev_ = 0;
+      free_list_ = o;
+      --preallocated;
+    }
+  }
+
+  // Destructor destroys all objects.
+  ~object_pool()
+  {
+    destroy_list(live_list_);
+    destroy_list(free_list_);
+  }
+
+  // Get the object at the start of the live list.
+  Object* first()
+  {
+    return live_list_;
+  }
+
+  // Allocate a new object with an argument.
+  template <typename... Args>
+  Object* alloc(Args... args)
+  {
+    Object* o = free_list_;
+    if (o)
+      free_list_ = free_list_->next_;
+    else
+      o = allocate_object<Object>(allocator_, args...);
+
+    o->next_ = live_list_;
+    o->prev_ = 0;
+    if (live_list_)
+      live_list_->prev_ = o;
+    live_list_ = o;
+
+    return o;
+  }
+
+  // Free an object. Moves it to the free list. No destructors are run.
+  void free(Object* o)
+  {
+    if (live_list_ == o)
+      live_list_ = o->next_;
+
+    if (o->prev_)
+      o->prev_->next_ = o->next_;
+
+    if (o->next_)
+      o->next_->prev_ = o->prev_;
+
+    o->next_ = free_list_;
+    o->prev_ = 0;
+    free_list_ = o;
+  }
+
+private:
+  object_pool(const object_pool&) = delete;
+  object_pool& operator=(const object_pool&) = delete;
+
+  // Helper function to destroy all elements in a list.
+  void destroy_list(Object* list)
+  {
+    while (list)
+    {
+      Object* o = list;
+      list = o->next_;
+      deallocate_object(allocator_, o);
+    }
+  }
+
+  // The execution_context allocator used to manage pooled object memory.
+  Allocator allocator_;
+
+  // The list of live objects.
+  Object* live_list_;
+
+  // The free list.
+  Object* free_list_;
+};
+
+} // namespace detail
+} // namespace asio
+
+#include "asio/detail/pop_options.hpp"
+
+#endif // ASIO_DETAIL_OBJECT_POOL_HPP