volatile_state.hpp

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// SPDX-License-Identifier: BSD-3-Clause
/* Copyright 2019-2020, Intel Corporation */
 
#ifndef LIBPMEMOBJ_CPP_VOLATILE_STATE_HPP
#define LIBPMEMOBJ_CPP_VOLATILE_STATE_HPP
 
#include <cassert>
#include <functional>
#include <memory>
#include <mutex>
#include <shared_mutex>
#include <tuple>
#include <unordered_map>
 
#include <libpmemobj++/detail/common.hpp>
#include <libpmemobj++/detail/life.hpp>
#include <libpmemobj++/pool.hpp>
#include <libpmemobj++/transaction.hpp>
 
namespace pmem
{
 
namespace detail
{
 
class volatile_state {
public:
    template <typename T>
    static T *
    get_if_exists(const PMEMoid &oid)
    {
        auto &map = get_map();
 
        {
            std::shared_lock<rwlock_type> lock(get_rwlock());
            auto it = map.find(oid);
            if (it != map.end())
                return static_cast<T *>(it->second.get());
            else
                return nullptr;
        }
    }
 
    template <typename T>
    static T *
    get(const PMEMoid &oid)
    {
        auto &map = get_map();
 
        auto element = get_if_exists<T>(oid);
        if (element)
            return element;
 
        if (pmemobj_tx_stage() != TX_STAGE_NONE)
            throw pmem::transaction_scope_error(
                "volatile_state::get() cannot be called in a transaction");
 
        {
            std::unique_lock<rwlock_type> lock(get_rwlock());
 
            auto deleter = [](void const *data) {
                T const *p = static_cast<T const *>(data);
                delete p;
            };
 
            auto it = map.find(oid);
            if (it == map.end()) {
                auto ret = map.emplace(
                    std::piecewise_construct,
                    std::forward_as_tuple(oid),
                    std::forward_as_tuple(new T, deleter));
 
                /* emplace could fail only if there is already
                 * an element with the same key which is not
                 * possible */
                assert(ret.second);
 
                it = ret.first;
 
                auto pop = pmemobj_pool_by_oid(oid);
                auto *user_data =
                    static_cast<detail::pool_data *>(
                        pmemobj_get_user_data(pop));
 
                user_data->set_cleanup([oid] {
                    clear_from_pool(oid.pool_uuid_lo);
                });
            }
 
            return static_cast<T *>(it->second.get());
        }
    }
 
    static void
    destroy(const PMEMoid &oid)
    {
        if (pmemobj_tx_stage() == TX_STAGE_WORK) {
            obj::flat_transaction::register_callback(
                obj::flat_transaction::stage::oncommit, [oid] {
                    std::unique_lock<rwlock_type> lock(
                        get_rwlock());
                    get_map().erase(oid);
                });
        } else {
            std::unique_lock<rwlock_type> lock(get_rwlock());
            get_map().erase(oid);
        }
    }
 
private:
    struct pmemoid_hash {
        std::size_t
        operator()(const PMEMoid &oid) const
        {
            return oid.pool_uuid_lo + oid.off;
        }
    };
 
    struct pmemoid_equal_to {
        bool
        operator()(const PMEMoid &lhs, const PMEMoid &rhs) const
        {
            return lhs.pool_uuid_lo == rhs.pool_uuid_lo &&
                lhs.off == rhs.off;
        }
    };
 
    using key_type = PMEMoid;
    using value_type =
        std::unique_ptr<void,
                std::add_pointer<void(const void *)>::type>;
 
    using map_type = std::unordered_map<key_type, value_type, pmemoid_hash,
                        pmemoid_equal_to>;
 
    using rwlock_type = std::shared_timed_mutex;
 
    static void
    clear_from_pool(uint64_t pool_id)
    {
        std::unique_lock<rwlock_type> lock(get_rwlock());
        auto &map = get_map();
 
        for (auto it = map.begin(); it != map.end();) {
            if (it->first.pool_uuid_lo == pool_id)
                it = map.erase(it);
            else
                ++it;
        }
    }
 
    static map_type &
    get_map()
    {
        static map_type map;
        return map;
    }
 
    static rwlock_type &
    get_rwlock()
    {
        static rwlock_type rwlock;
        return rwlock;
    }
};
 
} /* namespace detail */
 
} /* namespace pmem */
 
#endif /* LIBPMEMOBJ_CPP_VOLATILE_STATE_HPP */