Add garbage collection at the end of each round in cyclic controller

nvflare/app_common/workflows/cyclic_ctl.py

@@ -12,6 +12,7 @@
 # See the License for the specific language governing permissions and
 # limitations under the License.
 
+import gc
 import random
 
 from nvflare.apis.client import Client
@@ -205,7 +206,8 @@ def control_flow(self, abort_signal: Signal, fl_ctx: FLContext):
                     # Call the self._engine to persist the snapshot of all the FLComponents
                     self._engine.persist_components(fl_ctx, completed=False)
 
-                self.log_info(fl_ctx, "Ending current round={}.".format(self._current_round))
+                self.log_debug(fl_ctx, "Ending current round={}.".format(self._current_round))
+                gc.collect()
 
             self.log_debug(fl_ctx, "Cyclic ended.")
         except Exception as e: