171 lines
4.3 KiB
C++
171 lines
4.3 KiB
C++
/*
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* Licensed under the Apache License, Version 2.0 (the "License");
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* you may not use this file except in compliance with the License.
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* You may obtain a copy of the License at
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*
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* http://www.apache.org/licenses/LICENSE-2.0
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*
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* Unless required by applicable law or agreed to in writing, software
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* distributed under the License is distributed on an "AS IS" BASIS,
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* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
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* See the License for the specific language governing permissions and
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* limitations under the License.
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*
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* Copyright 2011-2016 Danny Robson <danny@nerdcruft.net>
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*/
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#ifndef CRUFT_UTIL_POOL_HPP
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#define CRUFT_UTIL_POOL_HPP
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#include "nocopy.hpp"
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#include "debug.hpp"
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#include <atomic>
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#include <cstdlib>
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#include <cstdint>
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namespace util {
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/// a simple pre-allocated pool for storage of PODs.
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///
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/// non-POD types can be stored, but there are no guarantees for calling
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/// item destructors at pool destruction time.
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template <typename T>
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class pool {
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protected:
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union node;
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union alignas (T) node {
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std::atomic<node*> next;
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char data[sizeof (T)];
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};
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static_assert (std::atomic<node*>::is_always_lock_free);
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// root address of allocation. used in deletion at destruction time.
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node* m_head;
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// the next available entry in the linked list
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std::atomic<node *> m_next;
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// the total number of items that could be stored
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const size_t m_capacity;
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// the number of items currently stored.
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std::atomic<size_t> m_size;
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public:
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pool (const pool&) = delete;
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pool& operator= (const pool&) = delete;
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pool (pool&&);
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pool& operator= (pool&&);
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explicit
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pool (unsigned int _capacity):
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m_capacity (_capacity),
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m_size (0u)
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{
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// allocate the memory and note the base address for deletion in destructor
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m_next = m_head = new node[m_capacity];
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// build out a complete singly linked list from all the nodes.
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for (size_t i = 0; i < m_capacity - 1; ++i)
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m_next[i].next = m_next + i + 1;
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m_next[m_capacity - 1].next = nullptr;
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}
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~pool ()
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{
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// don't check if everything's been returned as pools are often used
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// for PODs which don't need to be destructed via calling release.
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delete [] m_head;
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}
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// Data management
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[[nodiscard]] T*
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allocate (void)
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{
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// double check we have enough capacity left
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if (!m_next)
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throw std::bad_alloc ();
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CHECK_LT (m_size, m_capacity);
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// unlink the current cursor
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do {
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node* curr = m_next;
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node* soon = curr->next;
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if (m_next.compare_exchange_weak (curr, soon)) {
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++m_size;
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return reinterpret_cast<T*> (curr);
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}
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} while (1);
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}
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void
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deallocate (T *base)
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{
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auto soon = reinterpret_cast<node*> (base);
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do {
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node *curr = m_next;
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soon->next = curr;
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if (m_next.compare_exchange_weak (curr, soon)) {
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--m_size;
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return;
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}
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} while (1);
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}
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template <typename ...Args>
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T*
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construct (Args &&...args)
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{
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auto ptr = allocate ();
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try {
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return new (ptr) T (std::forward<Args> (args)...);
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} catch (...) {
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deallocate (ptr);
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throw;
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}
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}
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void
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destroy (T *ptr)
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{
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ptr->~T ();
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deallocate (ptr);
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}
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size_t capacity (void) const
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{
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return m_capacity;
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}
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size_t size (void) const
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{
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return m_size;
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}
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bool empty (void) const
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{
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return m_size == m_capacity;
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}
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// Indexing
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size_t index (const T*) const;
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T& operator[] (size_t idx) &;
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const T& operator[] (size_t idx) const&;
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};
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}
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#endif
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