7f19d64164
git-subtree-dir: third_party/immer git-subtree-split: ad3e3556d38bb75966dd24c61a774970a7c7957e
110 lines
2.9 KiB
C++
110 lines
2.9 KiB
C++
//
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// immer: immutable data structures for C++
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// Copyright (C) 2016, 2017, 2018 Juan Pedro Bolivar Puente
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//
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// This software is distributed under the Boost Software License, Version 1.0.
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// See accompanying file LICENSE or copy at http://boost.org/LICENSE_1_0.txt
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//
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#pragma once
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#include <immer/heap/tags.hpp>
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#include <atomic>
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#include <memory>
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#include <utility>
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namespace immer {
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/*!
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* Provides transience ownership tracking when a *tracing garbage
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* collector* is used instead of reference counting.
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*
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* @rst
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*
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* .. warning:: Using this policy without an allocation scheme that
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* includes automatic tracing garbage collection may cause memory
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* leaks.
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*
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* @endrst
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*/
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struct gc_transience_policy
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{
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template <typename HeapPolicy>
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struct apply
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{
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struct type
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{
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using heap_ = typename HeapPolicy::type;
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struct edit
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{
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void* v;
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edit() = delete;
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bool operator==(edit x) const { return v == x.v; }
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bool operator!=(edit x) const { return v != x.v; }
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};
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struct owner
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{
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void* make_token_()
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{
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return heap_::allocate(1, norefs_tag{});
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};
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mutable std::atomic<void*> token_;
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operator edit() { return {token_}; }
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owner()
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: token_{make_token_()}
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{}
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owner(const owner& o)
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: token_{make_token_()}
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{
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o.token_ = make_token_();
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}
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owner(owner&& o) noexcept
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: token_{o.token_.load()}
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{}
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owner& operator=(const owner& o)
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{
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o.token_ = make_token_();
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token_ = make_token_();
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return *this;
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}
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owner& operator=(owner&& o) noexcept
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{
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token_ = o.token_.load();
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return *this;
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}
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};
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struct ownee
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{
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edit token_{nullptr};
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ownee& operator=(edit e)
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{
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assert(e != noone);
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// This would be a nice safety plug but it sadly
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// does not hold during transient concatenation.
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// assert(token_ == e || token_ == edit{nullptr});
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token_ = e;
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return *this;
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}
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bool can_mutate(edit t) const { return token_ == t; }
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bool owned() const { return token_ != edit{nullptr}; }
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};
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static owner noone;
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};
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};
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};
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template <typename HP>
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typename gc_transience_policy::apply<HP>::type::owner
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gc_transience_policy::apply<HP>::type::noone = {};
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} // namespace immer
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