Keep track of transaction epoch

nano/store/iterator_impl.hpp

@@ -1,5 +1,8 @@
 #pragma once
 
+#include <nano/lib/utility.hpp>
+#include <nano/store/transaction.hpp>
+
 #include <utility>
 
 namespace nano::store
@@ -8,7 +11,16 @@ template <typename T, typename U>
 class iterator_impl
 {
 public:
-	virtual ~iterator_impl () = default;
+	explicit iterator_impl (nano::store::transaction const & transaction_a) :
+		transaction{ transaction_a },
+		transaction_epoch{ transaction_a.epoch () }
+	{
+	}
+	virtual ~iterator_impl ()
+	{
+		debug_assert (transaction_epoch == transaction.epoch (), "invalid iterator-transaction lifetime detected");
+	}
+
 	virtual iterator_impl<T, U> & operator++ () = 0;
 	virtual iterator_impl<T, U> & operator-- () = 0;
 	virtual bool operator== (iterator_impl<T, U> const & other_a) const = 0;
@@ -23,5 +35,9 @@ public:
 	{
 		return !(*this == other_a);
 	}
+
+protected:
+	nano::store::transaction const & transaction;
+	nano::store::transaction::epoch_t const transaction_epoch;
 };
-} // namespace nano::store
+}

nano/store/lmdb/iterator.hpp

@@ -14,7 +14,8 @@ template <typename T, typename U>
 class iterator : public iterator_impl<T, U>
 {
 public:
-	iterator (store::transaction const & transaction_a, env const & env_a, MDB_dbi db_a, MDB_val const & val_a = MDB_val{}, bool const direction_asc = true)
+	iterator (store::transaction const & transaction_a, env const & env_a, MDB_dbi db_a, MDB_val const & val_a = MDB_val{}, bool const direction_asc = true) :
+		nano::store::iterator_impl<T, U> (transaction_a)
 	{
 		auto status (mdb_cursor_open (env_a.tx (transaction_a), db_a, &cursor));
 		release_assert (status == 0);

nano/store/rocksdb/iterator.hpp

@@ -33,7 +33,8 @@ class iterator : public iterator_impl<T, U>
 public:
 	iterator () = default;
 
-	iterator (::rocksdb::DB * db, store::transaction const & transaction_a, ::rocksdb::ColumnFamilyHandle * handle_a, db_val const * val_a, bool const direction_asc)
+	iterator (::rocksdb::DB * db, store::transaction const & transaction_a, ::rocksdb::ColumnFamilyHandle * handle_a, db_val const * val_a, bool const direction_asc) :
+		nano::store::iterator_impl<T, U> (transaction_a)
 	{
 		// Don't fill the block cache for any blocks read as a result of an iterator
 		if (is_read (transaction_a))

nano/store/transaction.cpp

@@ -29,6 +29,15 @@ nano::store::write_transaction_impl::write_transaction_impl (nano::id_dispenser:
 {
 }
 
+/*
+ * transaction
+ */
+
+auto nano::store::transaction::epoch () const -> epoch_t
+{
+	return current_epoch;
+}
+
 /*
  * read_transaction
  */
@@ -51,11 +60,13 @@ nano::id_dispenser::id_t nano::store::read_transaction::store_id () const
 
 void nano::store::read_transaction::reset ()
 {
+	++current_epoch;
 	impl->reset ();
 }
 
 void nano::store::read_transaction::renew ()
 {
+	++current_epoch;
 	impl->renew ();
 	start = std::chrono::steady_clock::now ();
 }
@@ -102,11 +113,13 @@ nano::id_dispenser::id_t nano::store::write_transaction::store_id () const
 
 void nano::store::write_transaction::commit ()
 {
+	++current_epoch;
 	impl->commit ();
 }
 
 void nano::store::write_transaction::renew ()
 {
+	++current_epoch;
 	impl->renew ();
 	start = std::chrono::steady_clock::now ();
 }

nano/store/transaction.hpp

@@ -36,10 +36,17 @@ public:
 
 class transaction
 {
+public:
+	using epoch_t = size_t;
+
 public:
 	virtual ~transaction () = default;
 	virtual void * get_handle () const = 0;
 	virtual nano::id_dispenser::id_t store_id () const = 0;
+	epoch_t epoch () const;
+
+protected:
+	epoch_t current_epoch{ 0 };
 };
 
 /**