fix null reference in SnapshotRegistry (#46123)

Co-authored-by: Kirill Vasilenko <[email protected]>

5 files changed, 52 insertions, 3 deletions

diff --git a/ydb/core/tx/columnshard/scan_snapshot_guard.cpp b/ydb/core/tx/columnshard/scan_snapshot_guard.cpp
index 461032766fd..a1383fb27d7 100644
--- a/ydb/core/tx/columnshard/scan_snapshot_guard.cpp
+++ b/ydb/core/tx/columnshard/scan_snapshot_guard.cpp
@@ -166,9 +166,10 @@ std::unique_ptr<IScanSnapshotGuard> CreateScanSnapshotGuard(ui64 passedStep, ui6
     }
 
     if (const auto holder = AppDataVerified().SnapshotRegistryHolder) {
-        if (const auto registry = holder->Get()) {
+        auto registry = holder->Get();
+        if (registry.get()) {
             return CreateRegistryScanSnapshotGuard(
-                passedStep, schemeShardId, lastCleanupSnapshot, pathIdTranslator, registry, AppDataVerified().LongTxServiceConfig);
+                passedStep, schemeShardId, lastCleanupSnapshot, pathIdTranslator, std::move(registry), AppDataVerified().LongTxServiceConfig);
         }
     }
 
diff --git a/ydb/core/tx/long_tx_service/public/snapshot_registry.cpp b/ydb/core/tx/long_tx_service/public/snapshot_registry.cpp
index 1640353c92f..97cdfeb2c43 100644
--- a/ydb/core/tx/long_tx_service/public/snapshot_registry.cpp
+++ b/ydb/core/tx/long_tx_service/public/snapshot_registry.cpp
@@ -90,7 +90,10 @@ namespace {
         }
 
         void Set(std::unique_ptr<IImmutableSnapshotRegistry>&& registry) override {
-            TTrueAtomicSharedPtr<IImmutableSnapshotRegistry> newRegistry(registry.release());
+            TTrueAtomicSharedPtr<IImmutableSnapshotRegistry> newRegistry;
+            if (registry) {
+                newRegistry = TTrueAtomicSharedPtr<IImmutableSnapshotRegistry>(registry.release());
+            }
             Registry.swap(newRegistry);
         }
     private:
diff --git a/ydb/core/tx/long_tx_service/public/ut/snapshot_registry_ut.cpp b/ydb/core/tx/long_tx_service/public/ut/snapshot_registry_ut.cpp
new file mode 100644
index 00000000000..e4927bb6c28
--- /dev/null
+++ b/ydb/core/tx/long_tx_service/public/ut/snapshot_registry_ut.cpp
@@ -0,0 +1,43 @@
+#include <ydb/core/tx/long_tx_service/public/snapshot_registry.h>
+
+#include <library/cpp/testing/unittest/registar.h>
+
+namespace NKikimr {
+
+Y_UNIT_TEST_SUITE(TImmutableSnapshotRegistryHolderTest) {
+    std::unique_ptr<IImmutableSnapshotRegistry> BuildRegistry() {
+        auto builder = CreateImmutableSnapshotRegistryBuilder();
+        builder->SetSnapshotBorder(TRowVersion(100, 0));
+        builder->SetOldestCollectionTime(TInstant::MilliSeconds(50));
+        return std::move(*builder).Build();
+    }
+
+    Y_UNIT_TEST(EmptyByDefault) {
+        auto holder = CreateImmutableSnapshotRegistryHolder();
+        const auto& registry = holder->Get();
+        UNIT_ASSERT(!registry);
+        UNIT_ASSERT(registry.get() == nullptr);
+    }
+
+    Y_UNIT_TEST(SetAndGet) {
+        auto holder = CreateImmutableSnapshotRegistryHolder();
+        holder->Set(BuildRegistry());
+        const auto& registry = holder->Get();
+        UNIT_ASSERT(registry);
+        UNIT_ASSERT(registry.get() != nullptr);
+        UNIT_ASSERT_VALUES_EQUAL(registry->GetBorder(), TRowVersion(100, 0));
+    }
+
+    Y_UNIT_TEST(SetNullClearsRegistry) {
+        auto holder = CreateImmutableSnapshotRegistryHolder();
+        holder->Set(BuildRegistry());
+        UNIT_ASSERT(holder->Get());
+
+        holder->Set(nullptr);
+        const auto& registry = holder->Get();
+        UNIT_ASSERT(!registry);
+        UNIT_ASSERT(registry.get() == nullptr);
+    }
+}
+
+} // namespace NKikimr
diff --git a/ydb/core/tx/long_tx_service/public/ut/ya.make b/ydb/core/tx/long_tx_service/public/ut/ya.make
index e14b1dec683..02cc6bb8f1f 100644
--- a/ydb/core/tx/long_tx_service/public/ut/ya.make
+++ b/ydb/core/tx/long_tx_service/public/ut/ya.make
@@ -1,6 +1,7 @@
 UNITTEST_FOR(ydb/core/tx/long_tx_service/public)
 
 SRCS(
+    snapshot_registry_ut.cpp
     types_ut.cpp
 )
 
diff --git a/ydb/core/tx/long_tx_service/public/ya.make b/ydb/core/tx/long_tx_service/public/ya.make
index dba07d5ccac..1602fbae88b 100644
--- a/ydb/core/tx/long_tx_service/public/ya.make
+++ b/ydb/core/tx/long_tx_service/public/ya.make
@@ -14,6 +14,7 @@ PEERDIR(
     library/cpp/uri
     ydb/core/base
     ydb/core/protos
+    ydb/core/scheme
     ydb/core/util
     yql/essentials/public/issue
 )