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