279 lines
9.0 KiB
C++
279 lines
9.0 KiB
C++
/*
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* This Source Code Form is subject to the terms of the Mozilla Public
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* License, v. 2.0. If a copy of the MPL was not distributed with this
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* file, You can obtain one at http://mozilla.org/MPL/2.0/.
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*
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* Copyright 2011-2019 Danny Robson <danny@nerdcruft.net>
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*/
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#pragma once
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#include "cast.hpp"
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#include "debug/assert.hpp"
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#include "debug/panic.hpp"
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#include "parallel/stack.hpp"
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#include "view.hpp"
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#include <atomic>
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#include <new>
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#include <cstddef>
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#include <cstdint>
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namespace cruft {
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/// A simple, thread safe, pre-allocated pool allocator.
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template <typename T>
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class pool {
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private:
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/// A collection of all unallocated slots.
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parallel::stack<void*> m_available;
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/// A pointer to the start of the allocated region.
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void *m_store;
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/// The total number of items for which storage has been allocated.
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std::size_t m_capacity;
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// We used to use std::aligned_storage_t and arrays/vectors proper for
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// data storage. But this requires that the user has already defined
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// ValueT ahead of time (given we need to call sizeof outside a deduced
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// context).
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//
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// We tried a strategy where nodes were a union of ValueT and a
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// linked-list. However this proved heinously expensive to traverse to
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// find allocated objects that need to be destroyed when our destructor
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// is called.
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public:
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///////////////////////////////////////////////////////////////////////
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pool (const pool&) = delete;
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pool& operator= (const pool&) = delete;
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//---------------------------------------------------------------------
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pool (pool &&rhs) noexcept
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: m_available (0)
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, m_store (nullptr)
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, m_capacity (0)
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{
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std::swap (m_available, rhs.m_available);
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std::swap (m_store, rhs.m_store);
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std::swap (m_capacity, rhs.m_capacity);
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}
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//---------------------------------------------------------------------
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pool& operator= (pool &&rhs) noexcept
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{
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std::swap (m_available, rhs.m_available);
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std::swap (m_store, rhs.m_store);
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std::swap (m_capacity, rhs.m_capacity);
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return *this;
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}
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//---------------------------------------------------------------------
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pool clone (void) const
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{
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pool res (m_capacity);
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memcpy (res.m_store, m_store, sizeof (T) * m_capacity);
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res.m_available = m_available.clone ();
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// Rebase the pointers to available data so they point into the
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// cloned object.
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auto offset = reinterpret_cast<uintptr_t> (res.m_store) - reinterpret_cast<uintptr_t> (m_store);
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auto data = res.m_available.store (
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decltype(res.m_available)::contract::I_HAVE_LOCKED_THIS_STRUCTURE
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);
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for (auto &ptr: data)
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ptr = reinterpret_cast<void*> (reinterpret_cast<uintptr_t> (ptr) + offset);
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return res;
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}
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//---------------------------------------------------------------------
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explicit
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pool (std::size_t _capacity)
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: m_available (_capacity)
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, m_store (::operator new[] (_capacity * sizeof (T), std::align_val_t {alignof (T)}))
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, m_capacity (_capacity)
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{
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if (!m_store)
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throw std::bad_alloc ();
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reindex ();
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}
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//---------------------------------------------------------------------
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~pool ()
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{
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clear ();
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::operator delete[] (
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m_store,
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m_capacity * sizeof (T),
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std::align_val_t {alignof (T)}
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);
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}
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///////////////////////////////////////////////////////////////////////
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[[nodiscard]] T*
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allocate [[gnu::malloc]] [[gnu::returns_nonnull]] (void)
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{
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void *raw;
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if (!m_available.pop (&raw))
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throw std::bad_alloc ();
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return reinterpret_cast<T*> (raw);
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}
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//---------------------------------------------------------------------
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void
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deallocate (T *cooked)
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{
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void *raw = reinterpret_cast<void*> (cooked);
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if (unlikely (!m_available.push (raw)))
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panic (__FUNCTION__);
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}
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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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//---------------------------------------------------------------------
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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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//---------------------------------------------------------------------
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void destroy (size_t idx)
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{
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return destroy (&(*this)[idx]);
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}
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///////////////////////////////////////////////////////////////////////
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auto capacity (void) const { return m_capacity; }
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size_t size (void) const { return capacity () - m_available.size (); }
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ssize_t ssize (void) const { return capacity () - m_available.size (); }
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bool empty (void) const { return size () == 0; }
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bool full (void) const { return size () == capacity (); }
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/// Destroys all objects that have been allocated, frees the
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/// associated memory, and then rebuilds the free node list ready for
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/// allocations again.
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///
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/// NOTE: All bets are off if any object throws an exception out of
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/// their destructor. We provide no exception guarantees.
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///
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/// This call is NOT thread safe. No users should be accessing this
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/// object for the duration of this call.
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void clear (void)
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{
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auto const valid_queue = m_available.store (
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decltype(m_available)::contract::I_HAVE_LOCKED_THIS_STRUCTURE
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);
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std::sort (valid_queue.begin (), valid_queue.end ());
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// Now that we've ordered the nodes we can walk the list from
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// start to finish and find nodes that aren't in the free list.
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// Call the destructors on the data contained in these.
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auto node_cursor = valid_queue.begin ();
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auto data_cursor = reinterpret_cast<T*> (m_store);
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auto const data_end = data_cursor + m_capacity;
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while (node_cursor != valid_queue.end ()) {
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while (&*data_cursor < *node_cursor) {
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reinterpret_cast<T*> (&*data_cursor)->~T ();
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++data_cursor;
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}
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++node_cursor;
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++data_cursor;
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}
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while (data_cursor != data_end) {
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reinterpret_cast<T*> (&*data_cursor)->~T ();
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++data_cursor;
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}
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reindex ();
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}
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///////////////////////////////////////////////////////////////////////
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size_t index (T const *ptr) const
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{
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CHECK_GE (ptr, reinterpret_cast<T*> (m_store));
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CHECK_LT (ptr, reinterpret_cast<T*> (m_store) + capacity ());
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return ptr - reinterpret_cast<T*> (m_store);
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}
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/// returns the base address of the allocation.
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///
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/// guaranteed to point to the first _possible_ allocated value;
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/// however it may not be _live_ at any given moment.
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///
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/// DO NOT use this pointer for indexing as you _may_ be unable to
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/// account for internal node sizes, alignment, or padding. This is
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/// why the return type is void.
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///
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/// We may be using one particular representation at the moment but
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/// stability is not guaranteed at this point.
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void * base (void) & { return m_store; }
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void const* base (void) const& { return m_store; }
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///////////////////////////////////////////////////////////////////////
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T& operator[] (size_t idx) &
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{
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return reinterpret_cast<T*> (m_store) [idx];
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}
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//---------------------------------------------------------------------
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T const& operator[] (size_t idx) const&
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{
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return reinterpret_cast<T*> (m_store) [idx];
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}
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private:
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void reindex (void)
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{
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m_available.clear ();
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T* elements = reinterpret_cast<T*> (m_store);
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for (size_t i = m_capacity; i--; )
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// The available indices _should_ have enough capacity at all
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// times as we've presumably allocated it at construction time,
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// but it's worthwhile checking anyway.
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if (!m_available.push (elements + i)) [[unlikely]]
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throw std::bad_alloc ();
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}
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};
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}
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