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// Copyright Yahoo. Licensed under the terms of the Apache 2.0 license. See LICENSE in the project root.
#pragma once
#include "atomic_entry_ref.h"
#include <atomic>
#include <vespa/vespalib/util/generationholder.h>
#include <functional>
namespace vespalib { class MemoryUsage; }
namespace vespalib::datastore {
class EntryComparator;
class EntryRefFilter;
class FixedSizeHashMap;
struct ICompactable;
/*
* Hash map over keys in data store, meant to support a faster
* dictionary for unique store with relation to lookups.
*
* Currently hardcoded key and data types, where key references an entry
* in a UniqueStore and value references a posting list
* (cf. search::attribute::PostingStore).
*
* This structure supports one writer and many readers.
*
* A reader must own an appropriate GenerationHandler::Guard to ensure
* that memory is held while it can be accessed by reader.
*
* The writer must update generation and call assign_generation and
* reclaim_memory as needed to free up memory no longer needed by any
* readers.
*/
class ShardedHashMap {
public:
using KvType = std::pair<AtomicEntryRef, AtomicEntryRef>;
using generation_t = GenerationHandler::generation_t;
using sgeneration_t = GenerationHandler::sgeneration_t;
private:
GenerationHolder _gen_holder;
static constexpr size_t num_shards = 3;
std::atomic<FixedSizeHashMap *> _maps[num_shards];
std::unique_ptr<const EntryComparator> _comp;
void alloc_shard(size_t shard_idx);
void hold_shard(std::unique_ptr<const FixedSizeHashMap> map);
public:
ShardedHashMap(std::unique_ptr<const EntryComparator> comp);
~ShardedHashMap();
KvType& add(const EntryComparator& comp, EntryRef key_ref, std::function<EntryRef(void)> &insert_entry);
KvType* remove(const EntryComparator& comp, EntryRef key_ref);
KvType* find(const EntryComparator& comp, EntryRef key_ref);
const KvType* find(const EntryComparator& comp, EntryRef key_ref) const;
void assign_generation(generation_t current_gen);
void reclaim_memory(generation_t oldest_used_gen);
size_t size() const noexcept;
const EntryComparator &get_default_comparator() const noexcept { return *_comp; }
MemoryUsage get_memory_usage() const;
void foreach_key(std::function<void(EntryRef)> callback) const;
void move_keys_on_compact(ICompactable& compactable, const EntryRefFilter& compacting_buffers);
bool normalize_values(std::function<EntryRef(EntryRef)> normalize);
bool normalize_values(std::function<void(std::vector<EntryRef>&)> normalize, const EntryRefFilter& filter);
void foreach_value(std::function<void(const std::vector<EntryRef>&)> callback, const EntryRefFilter& filter);
bool has_held_buffers() const;
void compact_worst_shard();
};
}
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