Add read snapshot class for unique store dictionary.

5 files changed, 59 insertions, 24 deletions

diff --git a/vespalib/src/vespa/vespalib/datastore/unique_store_dictionary.h b/vespalib/src/vespa/vespalib/datastore/unique_store_dictionary.h
index cbc681b96e3..becd1fd4450 100644
--- a/vespalib/src/vespa/vespalib/datastore/unique_store_dictionary.h
+++ b/vespalib/src/vespa/vespalib/datastore/unique_store_dictionary.h
@@ -13,13 +13,24 @@ class EntryComparatorWrapper;
  * A dictionary for unique store. Mostly accessed via base class.
  */
 template <typename DictionaryT, typename ParentT = UniqueStoreDictionaryBase>
-class UniqueStoreDictionary : public ParentT
-{
+class UniqueStoreDictionary : public ParentT {
 protected:
     using DictionaryType = DictionaryT;
     using DataType = typename DictionaryType::DataType;
+    using FrozenView = typename DictionaryType::FrozenView;
+    using ReadSnapshot = typename ParentT::ReadSnapshot;
     using generation_t = typename ParentT::generation_t;
 
+    class ReadSnapshotImpl : public ReadSnapshot {
+    private:
+        FrozenView _frozen_view;
+
+    public:
+        ReadSnapshotImpl(FrozenView frozen_view);
+        EntryRef get_frozen_root() const override { return _frozen_view.getRoot(); }
+        void foreach_key(std::function<void(EntryRef)> callback) const override;
+    };
+
     DictionaryType _dict;
 
 public:
@@ -35,8 +46,8 @@ public:
     uint32_t get_num_uniques() const override;
     vespalib::MemoryUsage get_memory_usage() const override;
     void build(const std::vector<EntryRef> &refs, const std::vector<uint32_t> &ref_counts, std::function<void(EntryRef)> hold) override;
+    std::unique_ptr<ReadSnapshot> get_read_snapshot() const override;
     EntryRef get_frozen_root() const override;
-    void foreach_key(EntryRef root, std::function<void(EntryRef)> callback) const override;
 };
 
 }
diff --git a/vespalib/src/vespa/vespalib/datastore/unique_store_dictionary.hpp b/vespalib/src/vespa/vespalib/datastore/unique_store_dictionary.hpp
index 6e40b0b7c97..49ffc337206 100644
--- a/vespalib/src/vespa/vespalib/datastore/unique_store_dictionary.hpp
+++ b/vespalib/src/vespa/vespalib/datastore/unique_store_dictionary.hpp
@@ -17,6 +17,21 @@
 namespace search::datastore {
 
 template <typename DictionaryT, typename ParentT>
+UniqueStoreDictionary<DictionaryT, ParentT>::
+ReadSnapshotImpl::ReadSnapshotImpl(FrozenView frozen_view)
+    : _frozen_view(frozen_view)
+{
+}
+
+template <typename DictionaryT, typename ParentT>
+void
+UniqueStoreDictionary<DictionaryT, ParentT>::
+ReadSnapshotImpl::foreach_key(std::function<void(EntryRef)> callback) const
+{
+    _frozen_view.foreach_key(callback);
+}
+
+template <typename DictionaryT, typename ParentT>
 UniqueStoreDictionary<DictionaryT, ParentT>::UniqueStoreDictionary()
     : ParentT(),
       _dict()
@@ -135,18 +150,17 @@ UniqueStoreDictionary<DictionaryT, ParentT>::build(const std::vector<EntryRef> &
 }
 
 template <typename DictionaryT, typename ParentT>
-EntryRef
-UniqueStoreDictionary<DictionaryT, ParentT>::get_frozen_root() const
+std::unique_ptr<typename ParentT::ReadSnapshot>
+UniqueStoreDictionary<DictionaryT, ParentT>::get_read_snapshot() const
 {
-    return _dict.getFrozenView().getRoot();
+    return std::make_unique<ReadSnapshotImpl>(_dict.getFrozenView());
 }
 
 template <typename DictionaryT, typename ParentT>
-void
-UniqueStoreDictionary<DictionaryT, ParentT>::foreach_key(EntryRef root,
-                                                         std::function<void(EntryRef)> callback) const
+EntryRef
+UniqueStoreDictionary<DictionaryT, ParentT>::get_frozen_root() const
 {
-    _dict.getAllocator().getNodeStore().foreach_key(root, callback);
+    return _dict.getFrozenView().getRoot();
 }
 
 }
diff --git a/vespalib/src/vespa/vespalib/datastore/unique_store_dictionary_base.h b/vespalib/src/vespa/vespalib/datastore/unique_store_dictionary_base.h
index 82c8687513a..be1b6c8b5a6 100644
--- a/vespalib/src/vespa/vespalib/datastore/unique_store_dictionary_base.h
+++ b/vespalib/src/vespa/vespalib/datastore/unique_store_dictionary_base.h
@@ -12,12 +12,25 @@ class EntryComparator;
 struct ICompactable;
 class UniqueStoreAddResult;
 
-/*
- * Interface class for unique store dictonary.
+/**
+ * Interface class for unique store dictionary.
  */
-class UniqueStoreDictionaryBase
-{
+class UniqueStoreDictionaryBase {
 public:
+    /**
+     * Class that provides a read snapshot of the dictionary.
+     *
+     * A generation guard that must be taken and held while the snapshot is considered valid.
+     */
+    class ReadSnapshot {
+    public:
+        using UP = std::unique_ptr<ReadSnapshot>;
+        virtual ~ReadSnapshot() = default;
+        // TODO: Remove when all relevant functions have been migrated to this API.
+        virtual EntryRef get_frozen_root() const = 0;
+        virtual void foreach_key(std::function<void(EntryRef)> callback) const = 0;
+    };
+
     using generation_t = vespalib::GenerationHandler::generation_t;
     virtual ~UniqueStoreDictionaryBase() = default;
     virtual void freeze() = 0;
@@ -30,8 +43,8 @@ public:
     virtual uint32_t get_num_uniques() const = 0;
     virtual vespalib::MemoryUsage get_memory_usage() const = 0;
     virtual void build(const std::vector<EntryRef> &refs, const std::vector<uint32_t> &ref_counts, std::function<void(EntryRef)> hold) = 0;
+    virtual std::unique_ptr<ReadSnapshot> get_read_snapshot() const = 0;
     virtual EntryRef get_frozen_root() const = 0;
-    virtual void foreach_key(EntryRef root, std::function<void(EntryRef)> callback) const = 0;
 };
 
 }
diff --git a/vespalib/src/vespa/vespalib/datastore/unique_store_enumerator.h b/vespalib/src/vespa/vespalib/datastore/unique_store_enumerator.h
index a2e626c6b20..3f260bfbc15 100644
--- a/vespalib/src/vespa/vespalib/datastore/unique_store_enumerator.h
+++ b/vespalib/src/vespa/vespalib/datastore/unique_store_enumerator.h
@@ -19,24 +19,22 @@ public:
     using EnumValues = std::vector<std::vector<uint32_t>>;
 
 private:
-    const UniqueStoreDictionaryBase &_dict;
-    EntryRef _frozen_root;
+    UniqueStoreDictionaryBase::ReadSnapshot::UP _dict_snapshot;
     const DataStoreBase &_store;
     EnumValues _enumValues;
     uint32_t _next_enum_val;
 public:
     UniqueStoreEnumerator(const UniqueStoreDictionaryBase &dict, const DataStoreBase &store);
     ~UniqueStoreEnumerator();
-    EntryRef get_frozen_root() const { return _frozen_root; }
+    EntryRef get_frozen_root() const { return _dict_snapshot->get_frozen_root(); }
     void enumerateValue(EntryRef ref);
     void enumerateValues();
     void clear();
 
     template <typename Function>
     void
-    foreach_key(Function &&func) const
-    {
-        _dict.foreach_key(_frozen_root, func);
+    foreach_key(Function &&func) const {
+        _dict_snapshot->foreach_key(func);
     }
 
     uint32_t mapEntryRefToEnumValue(EntryRef ref) const {
diff --git a/vespalib/src/vespa/vespalib/datastore/unique_store_enumerator.hpp b/vespalib/src/vespa/vespalib/datastore/unique_store_enumerator.hpp
index a6053d4f64e..10ca0944519 100644
--- a/vespalib/src/vespa/vespalib/datastore/unique_store_enumerator.hpp
+++ b/vespalib/src/vespa/vespalib/datastore/unique_store_enumerator.hpp
@@ -8,8 +8,7 @@ namespace search::datastore {
 
 template <typename RefT>
 UniqueStoreEnumerator<RefT>::UniqueStoreEnumerator(const UniqueStoreDictionaryBase &dict, const DataStoreBase &store)
-    : _dict(dict),
-      _frozen_root(_dict.get_frozen_root()),
+    : _dict_snapshot(dict.get_read_snapshot()),
       _store(store),
       _enumValues(),
       _next_enum_val(1)
@@ -46,7 +45,7 @@ UniqueStoreEnumerator<RefT>::enumerateValues()
         }
     }
     _next_enum_val = 1;
-    _dict.foreach_key(_frozen_root, [this](EntryRef ref) { enumerateValue(ref); });
+    _dict_snapshot->foreach_key([this](EntryRef ref) { enumerateValue(ref); });
 }
 
 template <typename RefT>