MemStore.h

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/*
 * Copyright (C) 1996-2025 The Squid Software Foundation and contributors
 *
 * Squid software is distributed under GPLv2+ license and includes
 * contributions from numerous individuals and organizations.
 * Please see the COPYING and CONTRIBUTORS files for details.
 */
 
#ifndef SQUID_SRC_MEMSTORE_H
#define SQUID_SRC_MEMSTORE_H
 
#include "ipc/mem/Page.h"
#include "ipc/mem/PageStack.h"
#include "ipc/StoreMap.h"
#include "Store.h"
#include "store/Controlled.h"
 
// StoreEntry restoration info not already stored by Ipc::StoreMap
struct MemStoreMapExtraItem {
    Ipc::Mem::PageId page; 
};
typedef Ipc::StoreMapItems<MemStoreMapExtraItem> MemStoreMapExtras;
typedef Ipc::StoreMap MemStoreMap;
 
class ShmWriter;
 
class MemStore: public Store::Controlled, public Ipc::StoreMapCleaner
{
public:
    MemStore();
    ~MemStore() override;
 
    bool keepInLocalMemory(const StoreEntry &e) const;
 
    void write(StoreEntry &e);
 
    void completeWriting(StoreEntry &e);
 
    void disconnect(StoreEntry &e);
 
    /* Storage API */
    void create() override {}
    void init() override;
    StoreEntry *get(const cache_key *) override;
    uint64_t maxSize() const override;
    uint64_t minSize() const override;
    uint64_t currentSize() const override;
    uint64_t currentCount() const override;
    int64_t maxObjectSize() const override;
    void getStats(StoreInfoStats &stats) const override;
    void stat(StoreEntry &e) const override;
    void reference(StoreEntry &e) override;
    bool dereference(StoreEntry &e) override;
    void updateHeaders(StoreEntry *e) override;
    void maintain() override;
    bool anchorToCache(StoreEntry &) override;
    bool updateAnchored(StoreEntry &) override;
    void evictCached(StoreEntry &) override;
    void evictIfFound(const cache_key *) override;
 
    static bool Enabled() { return EntryLimit() > 0; }
    static int64_t EntryLimit();
    static bool Requested();
 
protected:
    friend ShmWriter;
 
    bool shouldCache(StoreEntry &e) const;
    bool startCaching(StoreEntry &e);
 
    void copyToShm(StoreEntry &e);
    void copyToShmSlice(StoreEntry &e, Ipc::StoreMapAnchor &anchor, Ipc::StoreMap::Slice &slice);
    bool copyFromShm(StoreEntry &e, const sfileno index, const Ipc::StoreMapAnchor &anchor);
    void copyFromShmSlice(StoreEntry &, const StoreIOBuffer &);
 
    void updateHeadersOrThrow(Ipc::StoreMapUpdate &update);
 
    void anchorEntry(StoreEntry &e, const sfileno index, const Ipc::StoreMapAnchor &anchor);
    bool updateAnchoredWith(StoreEntry &, const sfileno, const Ipc::StoreMapAnchor &);
 
    Ipc::Mem::PageId pageForSlice(Ipc::StoreMapSliceId sliceId);
    Ipc::StoreMap::Slice &nextAppendableSlice(const sfileno entryIndex, sfileno &sliceOffset);
    sfileno reserveSapForWriting(Ipc::Mem::PageId &page);
 
    // Ipc::StoreMapCleaner API
    void noteFreeMapSlice(const Ipc::StoreMapSliceId sliceId) override;
 
private:
    // TODO: move freeSlots into map
    Ipc::Mem::Pointer<Ipc::Mem::PageStack> freeSlots; 
    MemStoreMap *map; 
 
    typedef MemStoreMapExtras Extras;
    Ipc::Mem::Pointer<Extras> extras; 
 
    sfileno lastWritingSlice;
 
    class SlotAndPage
    {
    public:
        SlotAndPage(): slot(nullptr), page(nullptr) {}
        bool operator !() const { return !slot && !page; }
        Ipc::Mem::PageId *slot; 
        Ipc::Mem::PageId *page; 
    };
    SlotAndPage waitingFor; 
};
 
// Why use Store as a base? MemStore and SwapDir are both "caches".
 
// Why not just use a SwapDir API? That would not help much because Store has
// to check/update memory cache separately from the disk cache. And same API
// would hurt because we can support synchronous get/put, unlike the disks.
 
#endif /* SQUID_SRC_MEMSTORE_H */