rippled/src/libxrpl/ledger/CachedView.cpp

#include <xrpl/ledger/CachedView.h>

#include <xrpl/basics/CountedObject.h>
#include <xrpl/basics/TaggedCache.ipp>  // IWYU pragma: keep
#include <xrpl/basics/base_uint.h>
#include <xrpl/beast/utility/instrumentation.h>
#include <xrpl/protocol/Keylet.h>
#include <xrpl/protocol/STLedgerEntry.h>

#include <mutex>
#include <optional>

namespace xrpl::detail {

bool
CachedViewImpl::exists(Keylet const& k) const
{
    return read(k) != nullptr;
}

SLE::const_pointer
CachedViewImpl::read(Keylet const& k) const
{
    static CountedObjects::Counter kHits{"CachedView::hit"};
    static CountedObjects::Counter kHitsExpired{"CachedView::hitExpired"};
    static CountedObjects::Counter kMisses{"CachedView::miss"};
    bool cacheHit = false;
    bool baseRead = false;

    auto const digest = [&]() -> std::optional<uint256> {
        {
            std::scoped_lock const lock(mutex_);
            auto const iter = map_.find(k.key);
            if (iter != map_.end())
            {
                cacheHit = true;
                return iter->second;
            }
        }
        return base_.digest(k.key);
    }();
    if (!digest)
        return nullptr;
    auto sle = cache_.fetch(*digest, [&]() {
        baseRead = true;
        return base_.read(k);
    });
    // If the sle is null, then a failure must have occurred in base_.read()
    XRPL_ASSERT(sle || baseRead, "xrpl::CachedView::read : null SLE result from base");
    if (cacheHit && baseRead)
    {
        kHitsExpired.increment();
    }
    else if (cacheHit)
    {
        kHits.increment();
    }
    else
    {
        kMisses.increment();
    }

    if (!cacheHit)
    {
        // Avoid acquiring this lock unless necessary. It is only necessary if
        // the key was not found in the map_. The lock is needed to add the key
        // and digest.
        std::scoped_lock const lock(mutex_);
        map_.emplace(k.key, *digest);
    }
    if (!sle || !k.check(*sle))
        return nullptr;
    return sle;
}

}  // namespace xrpl::detail