TaggedCache.h

#pragma once
 
#include <xrpl/basics/IntrusivePointer.h>
#include <xrpl/basics/Log.h>
#include <xrpl/basics/SharedWeakCachePointer.ipp>
#include <xrpl/basics/UnorderedContainers.h>
#include <xrpl/basics/hardened_hash.h>
#include <xrpl/beast/clock/abstract_clock.h>
#include <xrpl/beast/insight/Insight.h>
 
#include <atomic>
#include <functional>
#include <mutex>
#include <thread>
#include <type_traits>
#include <vector>
 
namespace xrpl {
 
template <
    class Key,
    class T,
    bool IsKeyCache = false,
    class SharedWeakUnionPointerType = SharedWeakCachePointer<T>,
    class SharedPointerType = std::shared_ptr<T>,
    class Hash = hardened_hash<>,
    class KeyEqual = std::equal_to<Key>,
    class Mutex = std::recursive_mutex>
class TaggedCache
{
public:
    using mutex_type = Mutex;
    using key_type = Key;
    using mapped_type = T;
    using clock_type = beast::abstract_clock<std::chrono::steady_clock>;
    using shared_weak_combo_pointer_type = SharedWeakUnionPointerType;
    using shared_pointer_type = SharedPointerType;
 
public:
    TaggedCache(
        std::string const& name,
        int size,
        clock_type::duration expiration,
        clock_type& clock,
        beast::Journal journal,
        beast::insight::Collector::ptr const& collector = beast::insight::NullCollector::New());
 
public:
    clock_type&
    clock();
 
    std::size_t
    size() const;
 
    int
    getCacheSize() const;
 
    int
    getTrackSize() const;
 
    float
    getHitRate();
 
    void
    clear();
 
    void
    reset();
 
    template <class KeyComparable>
    bool
    touch_if_exists(KeyComparable const& key);
 
    using SweptPointersVector = std::vector<SharedWeakUnionPointerType>;
 
    void
    sweep();
 
    bool
    del(key_type const& key, bool valid);
 
public:
    template <class R>
    bool
    canonicalize(key_type const& key, SharedPointerType& data, R&& replaceCallback);
 
    bool
    canonicalize_replace_cache(key_type const& key, SharedPointerType const& data);
 
    bool
    canonicalize_replace_client(key_type const& key, SharedPointerType& data);
 
    SharedPointerType
    fetch(key_type const& key);
 
    template <class ReturnType = bool>
    auto
    insert(key_type const& key, T const& value) -> std::enable_if_t<!IsKeyCache, ReturnType>;
 
    template <class ReturnType = bool>
    auto
    insert(key_type const& key) -> std::enable_if_t<IsKeyCache, ReturnType>;
 
    // VFALCO NOTE It looks like this returns a copy of the data in
    //             the output parameter 'data'. This could be expensive.
    //             Perhaps it should work like standard containers, which
    //             simply return an iterator.
    //
    bool
    retrieve(key_type const& key, T& data);
 
    mutex_type&
    peekMutex();
 
    std::vector<key_type>
    getKeys() const;
 
    // CachedSLEs functions.
    double
    rate() const;
 
    template <class Handler>
    SharedPointerType
    fetch(key_type const& digest, Handler const& h);
    // End CachedSLEs functions.
 
private:
    SharedPointerType
    initialFetch(key_type const& key, std::lock_guard<mutex_type> const& l);
 
    void
    collect_metrics();
 
private:
    struct Stats
    {
        template <class Handler>
        Stats(std::string const& prefix, Handler const& handler, beast::insight::Collector::ptr const& collector)
            : hook(collector->make_hook(handler))
            , size(collector->make_gauge(prefix, "size"))
            , hit_rate(collector->make_gauge(prefix, "hit_rate"))
            , hits(0)
            , misses(0)
        {
        }
 
        beast::insight::Hook hook;
        beast::insight::Gauge size;
        beast::insight::Gauge hit_rate;
 
        std::size_t hits;
        std::size_t misses;
    };
 
    class KeyOnlyEntry
    {
    public:
        clock_type::time_point last_access;
 
        explicit KeyOnlyEntry(clock_type::time_point const& last_access_) : last_access(last_access_)
        {
        }
 
        void
        touch(clock_type::time_point const& now)
        {
            last_access = now;
        }
    };
 
    class ValueEntry
    {
    public:
        shared_weak_combo_pointer_type ptr;
        clock_type::time_point last_access;
 
        ValueEntry(clock_type::time_point const& last_access_, shared_pointer_type const& ptr_)
            : ptr(ptr_), last_access(last_access_)
        {
        }
 
        bool
        isWeak() const
        {
            if (!ptr)
                return true;
            return ptr.isWeak();
        }
        bool
        isCached() const
        {
            return ptr && ptr.isStrong();
        }
        bool
        isExpired() const
        {
            return ptr.expired();
        }
        SharedPointerType
        lock()
        {
            return ptr.lock();
        }
        void
        touch(clock_type::time_point const& now)
        {
            last_access = now;
        }
    };
 
    typedef typename std::conditional<IsKeyCache, KeyOnlyEntry, ValueEntry>::type Entry;
 
    using KeyOnlyCacheType = hardened_partitioned_hash_map<key_type, KeyOnlyEntry, Hash, KeyEqual>;
 
    using KeyValueCacheType = hardened_partitioned_hash_map<key_type, ValueEntry, Hash, KeyEqual>;
 
    using cache_type = hardened_partitioned_hash_map<key_type, Entry, Hash, KeyEqual>;
 
    [[nodiscard]] std::thread
    sweepHelper(
        clock_type::time_point const& when_expire,
        [[maybe_unused]] clock_type::time_point const& now,
        typename KeyValueCacheType::map_type& partition,
        SweptPointersVector& stuffToSweep,
        std::atomic<int>& allRemovals,
        std::lock_guard<std::recursive_mutex> const&);
 
    [[nodiscard]] std::thread
    sweepHelper(
        clock_type::time_point const& when_expire,
        clock_type::time_point const& now,
        typename KeyOnlyCacheType::map_type& partition,
        SweptPointersVector&,
        std::atomic<int>& allRemovals,
        std::lock_guard<std::recursive_mutex> const&);
 
    beast::Journal m_journal;
    clock_type& m_clock;
    Stats m_stats;
 
    mutex_type mutable m_mutex;
 
    // Used for logging
    std::string m_name;
 
    // Desired number of cache entries (0 = ignore)
    int const m_target_size;
 
    // Desired maximum cache age
    clock_type::duration const m_target_age;
 
    // Number of items cached
    int m_cache_count;
    cache_type m_cache;  // Hold strong reference to recent objects
    std::uint64_t m_hits;
    std::uint64_t m_misses;
};
 
}  // namespace xrpl