mdbx++: добавление txn::commit_embark_read().

mdbx.h++

@@ -4318,6 +4318,10 @@ public:
   /// \brief Commit all the operations of a transaction into the database.
   void commit();
 
+  /// \brief Commit all the operations of a transaction into the database
+  /// and then start read transaction.
+  void commit_embark_read();
+
   using commit_latency = MDBX_commit_latency;
 
   /// \brief Commit all the operations of a transaction into the database

src/mdbx.c++

@@ -1555,6 +1555,13 @@ void txn_managed::commit(commit_latency *latency) {
     MDBX_CXX20_UNLIKELY err.throw_exception();
 }
 
+void txn_managed::commit_embark_read() {
+  auto env = this->env();
+  commit();
+  error::success_or_throw(
+      ::mdbx_txn_begin(env, nullptr, MDBX_TXN_RDONLY, &handle_));
+}
+
 //------------------------------------------------------------------------------
 
 bool txn::drop_map(const char *name, bool throw_if_absent) {