diff --git a/src/hiopbbpy/utils/evaluation_manager.py b/src/hiopbbpy/utils/evaluation_manager.py
index 444a57795..465ddb327 100644
--- a/src/hiopbbpy/utils/evaluation_manager.py
+++ b/src/hiopbbpy/utils/evaluation_manager.py
@@ -6,6 +6,7 @@
             Weslley S Pereira <wdasilv@nrel.gov>
 """
 
+import threading
 import logging
 import copy
 import os
@@ -71,6 +72,7 @@ def __init__(
     cpu_executor=None,
     mpi_executor=None) -> None:
     self._queue = deque([])
+    self._queue_lock = threading.Lock()
     self.logger = logging.getLogger(self.__class__.__name__)
 
     self.executors = {
@@ -100,7 +102,7 @@ def sync(self) -> None:
     future_objs = [queue_obj[1] for queue_obj in self._queue]
     wait(future_objs)
 
-  def submit_tasks(self, fn, X, execute_at="cpu", *args, **kwargs) -> None:
+  def submit_tasks(self, fn, X, execute_at="cpu", **kwargs) -> None:
     """Submits tasks to the specified executor.
 
     :param fn: The function to be executed.
@@ -108,16 +110,15 @@ def submit_tasks(self, fn, X, execute_at="cpu", *args, **kwargs) -> None:
     :param execute_at: The executor to use for task submission. It can be
         "cpu" for intra-node parallelism or "mpi" for inter-node
         parallelism.
-    :param args: Additional positional arguments to be passed to the
-        function.
     :param kwargs: Additional keyword arguments to be passed to the
         function.
     """
     key = execute_at.lower()
-    for x in X:
-      future_obj = self.executors[key].submit(fn, x, *args, **kwargs)
-      self._queue.append([copy.deepcopy(x), future_obj])
-      self.logger.info(f"Submitted f({x})")
+    with self._queue_lock:
+      for x in X:
+        future_obj = self.executors[key].submit(fn, x, **kwargs)
+        self._queue.append([copy.deepcopy(x), future_obj])
+        self.logger.info(f"Submitted f({x})")
 
   def retrieve_results(self) -> tuple[list, list]:
     """Retrieves the results of completed tasks.
@@ -127,33 +128,31 @@ def retrieve_results(self) -> tuple[list, list]:
     """
     X = deque([])
     F = deque([])
-    Idxs = deque([])
-    new_queue = deque([])
-    for i, item in enumerate(self._queue):
-      x = item[0]
-      future = item[1]
-      if future.done():
-        # Try to get result
-        try:
-          fx = future.result()
-          Idxs.append(i)
-        except CancelledError:
-          self.logger.warning(f"The execution of x={x} was cancelled.")
-          continue
-
-        # Add result to the output
-        X.append(x)
-        F.append(fx)
-        self.logger.info(f"Completed: f({x}) = {fx}")
-      else:
-        # Keep the future in the queue
-        new_queue.append(item)
-
-    # Remove completed tasks from the queue
-    self._queue = new_queue
-
-    X = [X[Idxs[i]] for i in range(len(Idxs))]
-    F = [F[Idxs[i]] for i in range(len(Idxs))]
+
+    with self._queue_lock:
+      new_queue = deque([])
+      for item in self._queue:
+        x = item[0]
+        future = item[1]
+        if future.done():
+          # Try to get result
+          try:
+            fx = future.result()
+          except CancelledError:
+            self.logger.warning(f"The execution of x={x} was cancelled.")
+            continue
+
+          # Add result to the output
+          X.append(x)
+          F.append(fx)
+          self.logger.info(f"Completed: f({x}) = {fx}")
+        else:
+          # Keep the future in the queue
+          new_queue.append(item)
+
+      # Remove completed tasks from the queue
+      self._queue = new_queue
+
     return list(X), list(F)