Add shard thread safety

src/ripple/nodestore/impl/DatabaseShardImp.cpp

@@ -75,9 +75,9 @@ DatabaseShardImp::init()
     using namespace boost::beast::detail;
 
     std::lock_guard lock(m_);
-    auto fail = [this](std::string const& msg)
+    auto fail = [j = j_](std::string const& msg)
     {
-        JLOG(j_.error()) <<
+        JLOG(j.error()) <<
             "[" << ConfigSection::shardDatabase() << "] " << msg;
         return false;
     };
@@ -293,10 +293,9 @@ DatabaseShardImp::prepareShard(std::uint32_t shardIndex)
     std::lock_guard lock(m_);
     assert(init_);
 
-    auto fail = [this, shardIndex](std::string const& msg)
+    auto fail = [j = j_, shardIndex](std::string const& msg)
     {
-        JLOG(j_.error()) <<
-            "shard " << shardIndex << " " << msg;
+        JLOG(j.error()) << "shard " << shardIndex << " " << msg;
         return false;
     };
 
@@ -421,7 +420,6 @@ DatabaseShardImp::importShard(std::uint32_t shardIndex,
         return true;
     };
 
-    {
     std::unique_lock<std::mutex> lock(m_);
     assert(init_);
 
@@ -488,11 +486,10 @@ DatabaseShardImp::importShard(std::uint32_t shardIndex,
     // Add the shard
     complete_.emplace(shardIndex, std::move(shard));
     preShards_.erase(shardIndex);
-    }
 
-    std::lock_guard<std::mutex> lock(m_);
-    setFileStats(lock);
-    updateStatus(lock);
+    std::lock_guard lockg(*lock.release(), std::adopt_lock);
+    setFileStats(lockg);
+    updateStatus(lockg);
     return true;
 }
 
@@ -552,9 +549,9 @@ void
 DatabaseShardImp::setStored(std::shared_ptr<Ledger const> const& ledger)
 {
     auto const shardIndex {seqToShardIndex(ledger->info().seq)};
-    auto fail = [this, shardIndex](std::string const& msg)
+    auto fail = [j = j_, shardIndex](std::string const& msg)
     {
-        JLOG(j_.error()) << "shard " << shardIndex << " " << msg;
+        JLOG(j.error()) << "shard " << shardIndex << " " << msg;
     };
 
     if (ledger->info().hash.isZero())
@@ -622,36 +619,28 @@ DatabaseShardImp::getCompleteShards()
 void
 DatabaseShardImp::validate()
 {
+    std::vector<std::shared_ptr<Shard>> completeShards;
     {
         std::lock_guard lock(m_);
         assert(init_);
 
-        if (complete_.empty() && !incomplete_)
+        if (complete_.empty())
         {
             JLOG(j_.error()) << "no shards found to validate";
             return;
         }
 
-        std::string s {"Found shards "};
-        for (auto const& e : complete_)
-            s += std::to_string(e.second->index()) + ",";
-        if (incomplete_)
-            s += std::to_string(incomplete_->index());
-        else
-            s.pop_back();
-        JLOG(j_.debug()) << s;
+        JLOG(j_.debug()) << "Validating shards " << status_;
+
+        completeShards.reserve(complete_.size());
+        for (auto const& shard : complete_)
+            completeShards.push_back(shard.second);
     }
 
-    for (auto& e : complete_)
-    {
-        app_.shardFamily()->reset();
-        e.second->validate();
-    }
-    if (incomplete_)
-    {
-        app_.shardFamily()->reset();
-        incomplete_->validate();
-    }
+    // Verify each complete stored shard
+    for (auto const& shard : completeShards)
+        shard->validate();
+
     app_.shardFamily()->reset();
 }
 
@@ -1116,29 +1105,15 @@ DatabaseShardImp::setFileStats(std::lock_guard<std::mutex>&)
 void
 DatabaseShardImp::updateStatus(std::lock_guard<std::mutex>&)
 {
+    if (!complete_.empty())
+    {
+        RangeSet<std::uint32_t> rs;
+        for (auto const& e : complete_)
+            rs.insert(e.second->index());
+        status_ = to_string(rs);
+    }
+    else
         status_.clear();
-    status_.reserve(complete_.size() * 8);
-    for (auto it = complete_.begin(); it != complete_.end(); ++it)
-    {
-        if (it == complete_.begin())
-            status_ = std::to_string(it->first);
-        else
-        {
-            if (it->first - std::prev(it)->first > 1)
-            {
-                if (status_.back() == '-')
-                    status_ += std::to_string(std::prev(it)->first);
-                status_ += ',' + std::to_string(it->first);
-            }
-            else
-            {
-                if (status_.back() != '-')
-                    status_ += '-';
-                if (std::next(it) == complete_.end())
-                    status_ += std::to_string(it->first);
-            }
-        }
-    }
 }
 
 std::pair<std::shared_ptr<PCache>, std::shared_ptr<NCache>>

src/ripple/nodestore/impl/DatabaseShardImp.h

@@ -171,7 +171,7 @@ private:
     std::unique_ptr<nudb::context> ctx_;
 
     // Complete shards
-    std::map<std::uint32_t, std::unique_ptr<Shard>> complete_;
+    std::map<std::uint32_t, std::shared_ptr<Shard>> complete_;
 
     // A shard being acquired from the peer network
     std::unique_ptr<Shard> incomplete_;
@@ -226,7 +226,8 @@ private:
     // Finds a random shard index that is not stored
     // Lock must be held
     boost::optional<std::uint32_t>
-    findShardIndexToAdd(std::uint32_t validLedgerSeq,
+    findShardIndexToAdd(
+        std::uint32_t validLedgerSeq,
         std::lock_guard<std::mutex>&);
 
     // Set storage and file descriptor usage stats

src/ripple/nodestore/impl/Shard.cpp

@@ -26,6 +26,8 @@
 #include <ripple/nodestore/Manager.h>
 
 #include <boost/algorithm/string.hpp>
+#include <boost/archive/text_iarchive.hpp>
+#include <boost/archive/text_oarchive.hpp>
 #include <boost/range/adaptor/transformed.hpp>
 
 #include <fstream>
@@ -55,9 +57,8 @@ Shard::Shard(
 bool
 Shard::open(Scheduler& scheduler, nudb::context& ctx)
 {
+    std::lock_guard lock(mutex_);
     assert(!backend_);
-    using namespace boost::filesystem;
-    using namespace boost::beast::detail;
 
     Config const& config {app_.config()};
     Section section {config.section(ConfigSection::shardDatabase())};
@@ -108,7 +109,7 @@ Shard::open(Scheduler& scheduler, nudb::context& ctx)
         if (!preexist)
         {
             // New shard, create a control file
-            if (!saveControl())
+            if (!saveControl(lock))
                 return fail({});
         }
         else if (is_regular_file(control_))
@@ -133,18 +134,20 @@ Shard::open(Scheduler& scheduler, nudb::context& ctx)
                     JLOG(j_.warn()) <<
                         "shard " << index_ <<
                         " has a control file for complete shard";
-                    setComplete();
-                    remove_all(control_);
+                    setComplete(lock);
                 }
             }
         }
         else
-            setComplete();
+            setComplete(lock);
 
-        setCache();
-        if (!initSQLite() || !setFileStats())
+        if (!complete_)
+        {
+            setCache(lock);
+            if (!initSQLite(lock) ||!setFileStats(lock))
                 return fail({});
         }
+    }
     catch (std::exception const& e)
     {
         return fail(std::string("exception ") +
@@ -157,7 +160,9 @@ Shard::open(Scheduler& scheduler, nudb::context& ctx)
 bool
 Shard::setStored(std::shared_ptr<Ledger const> const& ledger)
 {
-    assert(backend_&& !complete_);
+    std::lock_guard lock(mutex_);
+    assert(backend_ && !complete_);
+
     if (boost::icl::contains(storedSeqs_, ledger->info().seq))
     {
         JLOG(j_.debug()) <<
@@ -166,27 +171,16 @@ Shard::setStored(std::shared_ptr<Ledger const> const& ledger)
         return false;
     }
 
-    if (!setSQLiteStored(ledger))
+    if (!setSQLiteStored(ledger, lock))
         return false;
 
     // Check if the shard is complete
     if (boost::icl::length(storedSeqs_) >= maxLedgers_ - 1)
-    {
-        setComplete();
-        if (backend_->backed())
-        {
-            if (!removeAll(control_, j_))
-                return false;
-
-            setCache();
-            if (!initSQLite() || !setFileStats())
-                return false;
-        }
-    }
+        setComplete(lock);
     else
     {
         storedSeqs_.insert(ledger->info().seq);
-        if (backend_->backed() && !saveControl())
+        if (backend_->backed() && !saveControl(lock))
             return false;
     }
 
@@ -202,7 +196,9 @@ Shard::setStored(std::shared_ptr<Ledger const> const& ledger)
 boost::optional<std::uint32_t>
 Shard::prepare()
 {
-    assert(backend_);
+    std::lock_guard lock(mutex_);
+    assert(backend_ && !complete_);
+
     if (storedSeqs_.empty())
          return lastSeq_;
     return prevMissing(storedSeqs_, 1 + lastSeq_, firstSeq_);
@@ -211,33 +207,102 @@ Shard::prepare()
 bool
 Shard::contains(std::uint32_t seq) const
 {
-    assert(backend_);
     if (seq < firstSeq_ || seq > lastSeq_)
         return false;
-    if (complete_)
-        return true;
-    return boost::icl::contains(storedSeqs_, seq);
+
+    std::lock_guard lock(mutex_);
+    assert(backend_);
+
+    return complete_ || boost::icl::contains(storedSeqs_, seq);
 }
 
 void
 Shard::sweep()
 {
-    assert(backend_);
+    std::lock_guard lock(mutex_);
+    assert(pCache_ && nCache_);
+
     pCache_->sweep();
     nCache_->sweep();
 }
 
+std::shared_ptr<Backend> const&
+Shard::getBackend() const
+{
+    std::lock_guard lock(mutex_);
+    assert(backend_);
+
+    return backend_;
+}
+
 bool
-Shard::validate()
+Shard::complete() const
+{
+    std::lock_guard lock(mutex_);
+    assert(backend_);
+
+    return complete_;
+}
+
+std::shared_ptr<PCache>
+Shard::pCache() const
+{
+    std::lock_guard lock(mutex_);
+    assert(pCache_);
+
+    return pCache_;
+}
+
+std::shared_ptr<NCache>
+Shard::nCache() const
+{
+    std::lock_guard lock(mutex_);
+    assert(nCache_);
+
+    return nCache_;
+}
+
+std::uint64_t
+Shard::fileSize() const
+{
+    std::lock_guard lock(mutex_);
+    assert(backend_);
+
+    return fileSz_;
+}
+
+std::uint32_t
+Shard::fdRequired() const
+{
+    std::lock_guard lock(mutex_);
+    assert(backend_);
+
+    return fdRequired_;
+}
+
+std::shared_ptr<Ledger const>
+Shard::lastStored() const
+{
+    std::lock_guard lock(mutex_);
+    assert(backend_);
+
+    return lastStored_;
+}
+
+bool
+Shard::validate() const
 {
     uint256 hash;
-    std::uint32_t seq;
-    std::shared_ptr<Ledger> ledger;
-    auto fail = [this](std::string const& msg)
+    std::uint32_t seq {0};
+    auto fail = [j = j_, index = index_, &hash, &seq](std::string const& msg)
     {
-        JLOG(j_.error()) << "shard " << index_ << " " << msg;
+        JLOG(j.error()) <<
+            "shard " << index << ". " << msg <<
+            (hash.isZero() ? "" : ". Ledger hash " + to_string(hash)) <<
+            (seq == 0 ? "" : ". Ledger sequence " + std::to_string(seq));
         return false;
     };
+    std::shared_ptr<Ledger> ledger;
 
     // Find the hash of the last ledger in this shard
     {
@@ -245,13 +310,13 @@ Shard::validate()
             "WHERE LedgerSeq >= " + std::to_string(lastSeq_) +
             " order by LedgerSeq desc limit 1", app_, false);
         if (!ledger)
-            return fail("is unable to validate due to lacking lookup data");
+            return fail("Unable to validate due to lacking lookup data");
 
         if (seq != lastSeq_)
         {
-            ledger->setImmutable(app_.config());
             boost::optional<uint256> h;
 
+            ledger->setImmutable(app_.config());
             try
             {
                 h = hashOfSeq(*ledger, lastSeq_, j_);
@@ -263,215 +328,92 @@ Shard::validate()
             }
 
             if (!h)
-            {
-                return fail("is missing hash for last ledger sequence " +
-                    std::to_string(lastSeq_));
-            }
+                return fail("Missing hash for last ledger sequence");
             hash = *h;
             seq = lastSeq_;
         }
     }
 
-    JLOG(j_.debug()) <<
-        "shard " << index_ <<
-        " has ledger sequences " << firstSeq_ << "-" << lastSeq_;
-
-    // Use a short age to keep memory consumption low
-    auto const savedAge {pCache_->getTargetAge()};
-    using namespace std::chrono_literals;
-    pCache_->setTargetAge(1s);
-
     // Validate every ledger stored in this shard
     std::shared_ptr<Ledger const> next;
     while (seq >= firstSeq_)
     {
         auto nObj = valFetch(hash);
         if (!nObj)
-            break;
+            return fail("Invalid ledger");
+
         ledger = std::make_shared<Ledger>(
-            InboundLedger::deserializeHeader(makeSlice(nObj->getData()),
-                true), app_.config(), *app_.shardFamily());
+            InboundLedger::deserializeHeader(makeSlice(nObj->getData()), true),
+            app_.config(),
+            *app_.shardFamily());
         if (ledger->info().seq != seq)
-        {
-            fail("encountered invalid ledger sequence " + std::to_string(seq));
-            break;
-        }
+            return fail("Invalid ledger header sequence");
         if (ledger->info().hash != hash)
-        {
-            fail("encountered invalid ledger hash " + to_string(hash) +
-                " on sequence " + std::to_string(seq));
-            break;
-        }
+            return fail("Invalid ledger header hash");
+
         ledger->stateMap().setLedgerSeq(seq);
         ledger->txMap().setLedgerSeq(seq);
         ledger->setImmutable(app_.config());
         if (!ledger->stateMap().fetchRoot(
             SHAMapHash {ledger->info().accountHash}, nullptr))
         {
-            fail("is missing root STATE node on sequence " +
-                std::to_string(seq));
-            break;
+            return fail("Missing root STATE node");
         }
-        if (ledger->info().txHash.isNonZero())
+        if (ledger->info().txHash.isNonZero() &&
+            !ledger->txMap().fetchRoot(
+                SHAMapHash {ledger->info().txHash},
+                nullptr))
         {
-            if (!ledger->txMap().fetchRoot(
-                SHAMapHash {ledger->info().txHash}, nullptr))
-            {
-                fail("is missing root TXN node on sequence " +
-                    std::to_string(seq));
-                break;
-            }
+            return fail("Missing root TXN node");
         }
+
         if (!valLedger(ledger, next))
-            break;
+            return false;
+
         hash = ledger->info().parentHash;
         --seq;
         next = ledger;
-        if (seq % 128 == 0)
-            pCache_->sweep();
     }
 
+    {
+        std::lock_guard lock(mutex_);
         pCache_->reset();
         nCache_->reset();
-    pCache_->setTargetAge(savedAge);
-
-    if (seq >= firstSeq_)
-    {
-        return fail(std::string(" is ") +
-            (complete_ ? "invalid, failed" : "incomplete, stopped") +
-            " on hash " + to_string(hash) + " on sequence " +
-            std::to_string(seq));
     }
 
-    JLOG(j_.debug()) <<
-        "shard " << index_ << " is valid and complete";
+    JLOG(j_.debug()) << "shard " << index_ << " is valid";
     return true;
 }
 
 bool
-Shard::valLedger(std::shared_ptr<Ledger const> const& ledger,
-    std::shared_ptr<Ledger const> const& next)
+Shard::setComplete(std::lock_guard<std::mutex> const& lock)
 {
-    auto fail = [this](std::string const& msg)
-    {
-        JLOG(j_.error()) << "shard " << index_ << " " << msg;
-        return false;
-    };
-
-    if (ledger->info().hash.isZero())
-    {
-        return fail("encountered a zero ledger hash on sequence " +
-            std::to_string(ledger->info().seq));
-    }
-    if (ledger->info().accountHash.isZero())
-    {
-        return fail("encountered a zero account hash on sequence " +
-            std::to_string(ledger->info().seq));
-    }
-
-    bool error {false};
-    auto f = [this, &error](SHAMapAbstractNode& node)
-    {
-        if (!valFetch(node.getNodeHash().as_uint256()))
-            error = true;
-        return !error;
-    };
-
-    // Validate the state map
-    if (ledger->stateMap().getHash().isNonZero())
-    {
-        if (!ledger->stateMap().isValid())
-        {
-            return fail("has an invalid state map on sequence " +
-                std::to_string(ledger->info().seq));
-        }
-
+    // Remove the control file if one exists
     try
     {
-            if (next && next->info().parentHash == ledger->info().hash)
-                ledger->stateMap().visitDifferences(&next->stateMap(), f);
-            else
-                ledger->stateMap().visitNodes(f);
+        using namespace boost::filesystem;
+        if (is_regular_file(control_))
+            remove_all(control_);
+
     }
     catch (std::exception const& e)
     {
-            return fail(std::string("exception ") +
-                e.what() + " in function " + __func__);
-        }
-        if (error)
+        JLOG(j_.error()) <<
+            "shard " << index_ <<
+            " exception " << e.what() <<
+            " in function " << __func__;
         return false;
     }
-    // Validate the transaction map
-    if (ledger->info().txHash.isNonZero())
-    {
-        if (!ledger->txMap().isValid())
-        {
-            return fail("has an invalid transaction map on sequence " +
-                std::to_string(ledger->info().seq));
-        }
 
-        try
-        {
-            ledger->txMap().visitNodes(f);
-        }
-        catch (std::exception const& e)
-        {
-            return fail(std::string("exception ") +
-                e.what() + " in function " + __func__);
-        }
-        if (error)
-            return false;
-    }
-    return true;
-};
-
-std::shared_ptr<NodeObject>
-Shard::valFetch(uint256 const& hash)
-{
-    assert(backend_);
-    std::shared_ptr<NodeObject> nObj;
-    auto fail = [this](std::string const& msg)
-    {
-        JLOG(j_.error()) << "shard " << index_ << " " << msg;
-    };
-
-    try
-    {
-        switch (backend_->fetch(hash.begin(), &nObj))
-        {
-        case ok:
-            break;
-        case notFound:
-        {
-            fail("is missing node object on hash " + to_string(hash));
-            break;
-        }
-        case dataCorrupt:
-        {
-            fail("has a corrupt node object on hash " + to_string(hash));
-            break;
-        }
-        default:
-            fail("encountered unknown error on hash " + to_string(hash));
-        }
-    }
-    catch (std::exception const& e)
-    {
-        fail(std::string("exception ") +
-            e.what() + " in function " + __func__);
-    }
-    return nObj;
-}
-
-void
-Shard::setComplete()
-{
     storedSeqs_.clear();
     complete_ = true;
+
+    setCache(lock);
+    return initSQLite(lock) && setFileStats(lock);
 }
 
 void
-Shard::setCache()
+Shard::setCache(std::lock_guard<std::mutex> const&)
 {
     // complete shards use the smallest cache and
     // fastest expiration to reduce memory consumption.
@@ -503,7 +445,7 @@ Shard::setCache()
 }
 
 bool
-Shard::initSQLite()
+Shard::initSQLite(std::lock_guard<std::mutex> const&)
 {
     Config const& config {app_.config()};
     DatabaseCon::Setup setup;
@@ -515,9 +457,8 @@ Shard::initSQLite()
     {
         if (complete_)
         {
-            using namespace boost::filesystem;
-
             // Remove WAL files if they exist
+            using namespace boost::filesystem;
             for (auto const& d : directory_iterator(dir_))
             {
                 if (is_regular_file(d) &&
@@ -601,7 +542,9 @@ Shard::initSQLite()
 }
 
 bool
-Shard::setSQLiteStored(std::shared_ptr<Ledger const> const& ledger)
+Shard::setSQLiteStored(
+    std::shared_ptr<Ledger const> const& ledger,
+    std::lock_guard<std::mutex> const&)
 {
     auto const seq {ledger->info().seq};
     assert(backend_ && !complete_);
@@ -733,7 +676,7 @@ Shard::setSQLiteStored(std::shared_ptr<Ledger const> const& ledger)
 }
 
 bool
-Shard::setFileStats()
+Shard::setFileStats(std::lock_guard<std::mutex> const&)
 {
     fileSz_ = 0;
     fdRequired_ = 0;
@@ -764,7 +707,7 @@ Shard::setFileStats()
 }
 
 bool
-Shard::saveControl()
+Shard::saveControl(std::lock_guard<std::mutex> const&)
 {
     std::ofstream ofs {control_.string(), std::ios::trunc};
     if (!ofs.is_open())
@@ -779,5 +722,120 @@ Shard::saveControl()
     return true;
 }
 
+bool
+Shard::valLedger(
+    std::shared_ptr<Ledger const> const& ledger,
+    std::shared_ptr<Ledger const> const& next) const
+{
+    auto fail = [j = j_, index = index_, &ledger](std::string const& msg)
+    {
+        JLOG(j.error()) <<
+            "shard " << index << ". " << msg <<
+            (ledger->info().hash.isZero() ?
+                "" : ". Ledger header hash " +
+                to_string(ledger->info().hash)) <<
+            (ledger->info().seq == 0 ?
+                "" : ". Ledger header sequence " +
+                std::to_string(ledger->info().seq));
+        return false;
+    };
+
+    if (ledger->info().hash.isZero())
+        return fail("Invalid ledger header hash");
+    if (ledger->info().accountHash.isZero())
+        return fail("Invalid ledger header account hash");
+
+    bool error {false};
+    auto visit = [this, &error](SHAMapAbstractNode& node)
+    {
+        if (!valFetch(node.getNodeHash().as_uint256()))
+            error = true;
+        return !error;
+    };
+
+    // Validate the state map
+    if (ledger->stateMap().getHash().isNonZero())
+    {
+        if (!ledger->stateMap().isValid())
+            return fail("Invalid state map");
+
+        try
+        {
+            if (next && next->info().parentHash == ledger->info().hash)
+                ledger->stateMap().visitDifferences(&next->stateMap(), visit);
+            else
+                ledger->stateMap().visitNodes(visit);
+        }
+        catch (std::exception const& e)
+        {
+            return fail(std::string("exception ") +
+                e.what() + " in function " + __func__);
+        }
+        if (error)
+            return fail("Invalid state map");
+    }
+
+    // Validate the transaction map
+    if (ledger->info().txHash.isNonZero())
+    {
+        if (!ledger->txMap().isValid())
+            return fail("Invalid transaction map");
+
+        try
+        {
+            ledger->txMap().visitNodes(visit);
+        }
+        catch (std::exception const& e)
+        {
+            return fail(std::string("exception ") +
+                e.what() + " in function " + __func__);
+        }
+        if (error)
+            return fail("Invalid transaction map");
+    }
+    return true;
+};
+
+std::shared_ptr<NodeObject>
+Shard::valFetch(uint256 const& hash) const
+{
+    std::shared_ptr<NodeObject> nObj;
+    auto fail = [j = j_, index = index_, &hash, &nObj](std::string const& msg)
+    {
+        JLOG(j.error()) <<
+            "shard " << index << ". " << msg <<
+            ". Node object hash " << to_string(hash);
+        nObj.reset();
+        return nObj;
+    };
+    Status status;
+
+    try
+    {
+        {
+            std::lock_guard lock(mutex_);
+            status = backend_->fetch(hash.begin(), &nObj);
+        }
+
+        switch (status)
+        {
+        case ok:
+            break;
+        case notFound:
+            return fail("Missing node object");
+        case dataCorrupt:
+            return fail("Corrupt node object");
+        default:
+            return fail("Unknown error");
+        }
+    }
+    catch (std::exception const& e)
+    {
+        return fail(std::string("exception ") +
+            e.what() + " in function " + __func__);
+    }
+    return nObj;
+}
+
 } // NodeStore
 } // ripple

src/ripple/nodestore/impl/Shard.h

@@ -27,11 +27,8 @@
 #include <ripple/nodestore/NodeObject.h>
 #include <ripple/nodestore/Scheduler.h>
 
-#include <nudb/nudb.hpp>
 #include <boost/filesystem.hpp>
-#include <boost/serialization/map.hpp>
-#include <boost/archive/text_oarchive.hpp>
-#include <boost/archive/text_iarchive.hpp>
+#include <nudb/nudb.hpp>
 
 namespace ripple {
 namespace NodeStore {
@@ -63,6 +60,8 @@ class DatabaseShard;
    Shard `i` stores ledgers starting with sequence: `1 + (i * ledgersPerShard)`
    and ending with sequence: `(i + 1) * ledgersPerShard`.
    Once a shard has all its ledgers, it is never written to again.
+
+   Public functions can be called concurrently from any thread.
 */
 class Shard
 {
@@ -88,44 +87,41 @@ public:
     void
     sweep();
 
-    bool
-    validate();
-
     std::uint32_t
-    index() const {return index_;}
-
-    bool
-    complete() const {assert(backend_); return complete_;}
-
-    std::shared_ptr<PCache>&
-    pCache() {assert(backend_); return pCache_;}
-
-    std::shared_ptr<NCache>&
-    nCache() {assert(backend_); return nCache_;}
-
-    std::uint64_t
-    fileSize() const {assert(backend_); return fileSz_;}
-
-    std::uint32_t
-    fdRequired() const {assert(backend_); return fdRequired_;}
-
-    std::shared_ptr<Backend> const&
-    getBackend() const {assert(backend_); return backend_;}
-
-    std::shared_ptr<Ledger const>
-    lastStored() {assert(backend_); return lastStored_;}
-
-private:
-    friend class boost::serialization::access;
-    template<class Archive>
-    void serialize(Archive & ar, const unsigned int version)
+    index() const
     {
-        ar & storedSeqs_;
+        return index_;
     }
 
+    std::shared_ptr<Backend> const&
+    getBackend() const;
+
+    bool
+    complete() const;
+
+    std::shared_ptr<PCache>
+    pCache() const;
+
+    std::shared_ptr<NCache>
+    nCache() const;
+
+    std::uint64_t
+    fileSize() const;
+
+    std::uint32_t
+    fdRequired() const;
+
+    std::shared_ptr<Ledger const>
+    lastStored() const;
+
+    bool
+    validate() const;
+
+private:
     static constexpr auto controlFileName = "control.txt";
 
     Application& app_;
+    mutable std::mutex mutex_;
 
     // Shard Index
     std::uint32_t const index_;
@@ -179,43 +175,52 @@ private:
     // Used as an optimization for visitDifferences
     std::shared_ptr<Ledger const> lastStored_;
 
+    // Marks shard immutable
+    // Lock over mutex_ required
+    bool
+    setComplete(std::lock_guard<std::mutex> const& lock);
+
+    // Set the backend cache
+    // Lock over mutex_ required
+    void
+    setCache(std::lock_guard<std::mutex> const& lock);
+
+    // Open/Create SQLite databases
+    // Lock over mutex_ required
+    bool
+    initSQLite(std::lock_guard<std::mutex> const& lock);
+
+    // Write SQLite entries for a ledger stored in this shard's backend
+    // Lock over mutex_ required
+    bool
+    setSQLiteStored(
+        std::shared_ptr<Ledger const> const& ledger,
+        std::lock_guard<std::mutex> const& lock);
+
+    // Set storage and file descriptor usage stats
+    // Lock over mutex_ required
+    bool
+    setFileStats(std::lock_guard<std::mutex> const& lock);
+
+    // Save the control file for an incomplete shard
+    // Lock over mutex_ required
+    bool
+    saveControl(std::lock_guard<std::mutex> const& lock);
+
     // Validate this ledger by walking its SHAMaps
     // and verifying each merkle tree
     bool
-    valLedger(std::shared_ptr<Ledger const> const& ledger,
-        std::shared_ptr<Ledger const> const& next);
+    valLedger(
+        std::shared_ptr<Ledger const> const& ledger,
+        std::shared_ptr<Ledger const> const& next) const;
 
     // Fetches from the backend and will log
     // errors based on status codes
     std::shared_ptr<NodeObject>
-    valFetch(uint256 const& hash);
-
-    // Marks shard immutable, having stored all of its ledgers
-    void
-    setComplete();
-
-    // Set the backend cache
-    void
-    setCache();
-
-    // Open/Create SQLite databases
-    bool
-    initSQLite();
-
-    // Create SQLite entries for a ledger stored in this shard's backend
-    bool
-    setSQLiteStored(std::shared_ptr<Ledger const> const& ledger);
-
-    // Set storage and file descriptor usage stats
-    bool
-    setFileStats();
-
-    // Save the control file for an incomplete shard
-    bool
-    saveControl();
+    valFetch(uint256 const& hash) const;
 };
 
-} // NodeStore
-} // ripple
+}  // namespace NodeStore
+}  // namespace ripple
 
 #endif