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107 lines
3.3 KiB
C++
107 lines
3.3 KiB
C++
/*
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* Copyright (c) 2024, Oracle and/or its affiliates. All rights reserved.
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* DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
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*
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* This code is free software; you can redistribute it and/or modify it
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* under the terms of the GNU General Public License version 2 only, as
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* published by the Free Software Foundation.
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*
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* This code is distributed in the hope that it will be useful, but WITHOUT
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* ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
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* FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License
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* version 2 for more details (a copy is included in the LICENSE file that
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* accompanied this code).
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*
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* You should have received a copy of the GNU General Public License version
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* 2 along with this work; if not, write to the Free Software Foundation,
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* Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
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*
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* Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
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* or visit www.oracle.com if you need additional information or have any
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* questions.
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*/
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#ifndef SHARE_NMT_ARRAYWITHFREELIST_HPP
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#define SHARE_NMT_ARRAYWITHFREELIST_HPP
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#include "utilities/growableArray.hpp"
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#include <type_traits>
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// A flat array of elements E, backed by C-heap, growing on-demand. It allows for
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// returning arbitrary elements and keeps them in a freelist. Elements can be uniquely
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// identified via array index.
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template<typename E, MemTag MT>
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class ArrayWithFreeList {
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// An E must be trivially copyable and destructible, but it may be constructed
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// however it likes.
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constexpr void static_assert_E_satisfies_type_requirements() const {
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static_assert(std::is_trivially_copyable<E>::value && std::is_trivially_destructible<E>::value, "must be");
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}
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public:
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using I = int32_t;
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static constexpr const I nil = -1;
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private:
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// A free list allocator element is either a link to the next free space
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// or an actual element.
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union BackingElement {
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I link;
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E e;
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};
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GrowableArrayCHeap<BackingElement, MT> _backing_storage;
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I _free_start;
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bool is_in_bounds(I i) {
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return i >= 0 && i < _backing_storage.length();
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}
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public:
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NONCOPYABLE(ArrayWithFreeList);
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ArrayWithFreeList(int initial_capacity = 8)
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: _backing_storage(initial_capacity),
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_free_start(nil) {}
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template<typename... Args>
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I allocate(Args... args) {
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static_assert_E_satisfies_type_requirements();
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BackingElement* be;
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I i;
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if (_free_start != nil) {
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// Must point to already existing index
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be = &_backing_storage.at(_free_start);
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i = _free_start;
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_free_start = be->link;
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} else {
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// There are no free elements, allocate a new one.
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i = _backing_storage.append(BackingElement());
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be = _backing_storage.adr_at(i);
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}
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::new (be) E{args...};
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return i;
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}
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void deallocate(I i) {
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static_assert_E_satisfies_type_requirements();
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assert(i == nil || is_in_bounds(i), "out of bounds free");
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if (i == nil) return;
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BackingElement& be_freed = _backing_storage.at(i);
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be_freed.link = _free_start;
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_free_start = i;
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}
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E& at(I i) {
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static_assert_E_satisfies_type_requirements();
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assert(i != nil, "null pointer dereference");
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assert(is_in_bounds(i), "out of bounds dereference");
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return _backing_storage.at(i).e;
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}
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};
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#endif // SHARE_NMT_ARRAYWITHFREELIST_HPP
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