diff --git a/README.rst b/README.rst
index 15da61a..c6f0e20 100644
--- a/README.rst
+++ b/README.rst
@@ -245,6 +245,12 @@ Run a single test example for debugging with verbose and immediate stdout output
 Changelog
 ---------
 
+Changes in Version 0.11.1 (2025-08-27)
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+
+- Fix a bug where automatic port assignment would give the same port to two
+  different mongodb servers leading to errors such as ``Found two member configurations with same host field``.
+
 Changes in Version 0.11.0 (2024-12-30)
 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
 
diff --git a/mongo_orchestration/_version.py b/mongo_orchestration/_version.py
index 0deb0e3..cb73775 100644
--- a/mongo_orchestration/_version.py
+++ b/mongo_orchestration/_version.py
@@ -1 +1 @@
-__version__ = "0.12.0.dev0"
\ No newline at end of file
+__version__ = "0.11.1"
\ No newline at end of file
diff --git a/mongo_orchestration/process.py b/mongo_orchestration/process.py
index d58dad8..dd7b542 100644
--- a/mongo_orchestration/process.py
+++ b/mongo_orchestration/process.py
@@ -53,9 +53,10 @@ def __init__(self, min_port=1025, max_port=2000, port_sequence=None):
             max_port - max port number  (ignoring if 'port_sequence' is not None)
             port_sequence - iterate sequence which contains numbers of ports
         """
-        if not self.__id:  # singleton checker
-            self.__id = id(self)
-            self.__init_range(min_port, max_port, port_sequence)
+        with self._lock:
+            if not self.__id:  # singleton checker
+                self.__id = id(self)
+                self.__init_range(min_port, max_port, port_sequence)
 
     def __init_range(self, min_port=1025, max_port=2000, port_sequence=None):
         if port_sequence:
@@ -87,21 +88,21 @@ def release_port(self, port):
     def port(self, check=False):
         """return next opened port
         Args:
-          check - check is port realy free
+          check - check is port really free
         """
-        if not self.__ports:  # refresh ports if sequence is empty
-            self.refresh()
+        with self._lock:
+            if not self.__ports:  # refresh ports if sequence is empty
+                self.refresh()
 
-        try:
-            port = self.__ports.pop()
-            if check:
-                while not self.__check_port(port):
-                    self.release_port(port)
+            try:
+                while True:
                     port = self.__ports.pop()
-        except (IndexError, KeyError):
-            raise IndexError("Could not find a free port,\nclosed ports: {closed}".format(closed=self.__closed))
-        self.__closed.add(port)
-        return port
+                    self.__closed.add(port)
+                    if check and not self.__check_port(port):
+                        continue
+                    return port
+            except (IndexError, KeyError):
+                raise IndexError("Could not find a free port,\nclosed ports: {closed}".format(closed=self.__closed))
 
     def refresh(self, only_closed=False):
         """refresh ports status
diff --git a/mongo_orchestration/singleton.py b/mongo_orchestration/singleton.py
index bec04be..034f1c5 100644
--- a/mongo_orchestration/singleton.py
+++ b/mongo_orchestration/singleton.py
@@ -1,6 +1,6 @@
 #!/usr/bin/python
 # coding=utf-8
-# Copyright 2012-2014 MongoDB, Inc.
+# Copyright 2012-2025 MongoDB, Inc.
 #
 # Licensed under the Apache License, Version 2.0 (the "License");
 # you may not use this file except in compliance with the License.
@@ -13,12 +13,14 @@
 # WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 # See the License for the specific language governing permissions and
 # limitations under the License.
-
+import threading
 
 class Singleton(object):
     _instances = {}
+    _lock = threading.Lock()
 
     def __new__(class_, *args, **kwargs):
-        if class_ not in class_._instances:
-            class_._instances[class_] = super(Singleton, class_).__new__(class_, *args, **kwargs)
-        return class_._instances[class_]
+        with class_._lock:
+            if class_ not in class_._instances:
+                class_._instances[class_] = super(Singleton, class_).__new__(class_, *args, **kwargs)
+            return class_._instances[class_]