Add a function that purges operator instance cache for an EvalContext. (#6216)

* Add a function that purges operator instance cache for an EvalContext.

---------
Signed-off-by: Michał Zientkiewicz <mzient@gmail.com>

Author: mzient

dali/python/nvidia/dali/experimental/dynamic/_eval_context.py

@@ -169,6 +169,10 @@ def __init__(self, *, num_threads=None, device_id=None, cuda_stream=None):
         self._async_executor = _AsyncExecutor()
         weakref.finalize(self, self._async_executor.shutdown)
 
+    def _purge_operator_cache(self):
+        """Empties the operator instance cache"""
+        self._instance_cache = {}
+
     @property
     def _thread_pool(self):
         if (

dali/test/python/ndd_vs_fn/ndd_vs_fn_test_utils.py

@@ -521,6 +521,8 @@ def run_operator_test(
     batch_size : int, optional
         Max batch size used when building the pipeline.
     """
+    ndd.EvalContext.current()._purge_operator_cache()
+
     if operator_args is None:
         operator_args = {}