Merge pull request #494 from alexandrehassan/remove-pysingleton

Create a metaclass for Singleton's and remove pysingleton

Author: fliiiix

radish/customtyperegistry.py

@@ -4,13 +4,12 @@
 
 # Keep for backwards compat:
 from parse_type import TypeBuilder  # noqa: F401
-from singleton import singleton
 
 from .exceptions import RadishError
+from .utils import Singleton
 
 
-@singleton()
-class CustomTypeRegistry:
+class CustomTypeRegistry(metaclass=Singleton):
     """
     Registry for all custom argument expressions
     """

radish/extensionregistry.py

@@ -2,11 +2,10 @@
 Provide plugin interface for radish extensions
 """
 
-from singleton import singleton
+from .utils import Singleton
 
 
-@singleton()
-class ExtensionRegistry:
+class ExtensionRegistry(metaclass=Singleton):
     """
     Registers all extensions
     """

radish/hookregistry.py

@@ -3,14 +3,13 @@
 """
 
 import tagexpressions
-from singleton import singleton
 
 from . import utils
 from .exceptions import HookError
+from .utils import Singleton
 
 
-@singleton()
-class HookRegistry:
+class HookRegistry(metaclass=Singleton):
     """
     Represents an object with all registered hooks
     """

radish/stepregistry.py

@@ -5,13 +5,11 @@
 import inspect
 import re
 
-from singleton import singleton
-
 from .exceptions import RadishError, SameStepError, StepRegexError
+from .utils import Singleton
 
 
-@singleton()
-class StepRegistry:
+class StepRegistry(metaclass=Singleton):
     """
     Represents the step registry
     """

radish/utils.py

@@ -12,6 +12,7 @@
 import traceback
 import warnings
 from datetime import datetime, timedelta, timezone
+from threading import Lock
 
 
 class Failure:
@@ -230,3 +231,35 @@ def split_unescape(s, delim, escape="\\", unescape=True):
             current.append(ch)
     ret.append("".join(current))
     return ret
+
+
+class Singleton(type):
+    """
+    Metaclass for singleton classes. To create a singleton class use this metaclass:
+
+    class MySingletonClass(metaclass=Singleton):
+        pass
+
+    Now Singleton will ensure that only one instance of MySingletonClass is created.
+    """
+
+    _instances = {}
+    _lock = Lock()
+
+    def __call__(cls, *args, **kwargs):
+        """
+        Called when you create a new instance of a class with this metaclass.
+
+        It ensures that only one instance of the class is created (singleton pattern).
+
+        When you call `MySingletonClass(args, kwargs)`, python calls
+        `Singleton.__call__(MySingletonClass, args, kwargs)`.
+
+        This method in turn check if an instance of `MySingletonClass` already exists.
+        If not, it creates one and stores it in the `_instances` dictionary.
+        """
+        if cls not in cls._instances:  # Only grab the lock if the instance is not in the dict
+            with cls._lock:  # Ensure thread-safety
+                if cls not in cls._instances:  # in case instance was added while waiting for lock
+                    cls._instances[cls] = super(Singleton, cls).__call__(*args, **kwargs)
+        return cls._instances[cls]

requirements.txt

@@ -1,4 +1,3 @@
-pysingleton==0.2.1
 colorful==0.5.8
 docopt==0.6.2
 ipython==7.34.0

setup.py

@@ -37,7 +37,6 @@ def get_meta(name):
 # mandatory requirements for the radish base features
 requirements = [
     "docopt",
-    "pysingleton",
     "colorful>=0.3.11",
     "tag-expressions>=2.0.0",
     "parse_type>0.4.0",

tests/unit/test_utils.py

@@ -8,6 +8,7 @@
 """
 
 from datetime import datetime, timezone
+from threading import Lock, Thread
 
 import pytest
 from freezegun import freeze_time
@@ -67,3 +68,46 @@ def test_make_unique_obj_list():
     value_list.sort()
 
     assert value_list == ["1", "2"]
+
+
+def test_singleton_behavior():
+    """Test that Singleton metaclass enforces singleton behavior"""
+
+    class MySingletonClass(metaclass=utils.Singleton):
+        def __init__(self):
+            self.value = 42
+
+    instance1 = MySingletonClass()
+    instance1.value = 100  # Modify value to test singleton behavior
+    instance2 = MySingletonClass()
+
+    assert instance1 is instance2  # They should be the same instance
+    assert instance1.value == instance2.value  # Value should be the same changed value
+
+
+def test_singleton_thread_safety():
+    """
+    Test that Singleton metaclass is thread-safe by creating multiple instances in parallel threads
+    """
+
+    class MyThreadSafeSingleton(metaclass=utils.Singleton):
+        def __init__(self):
+            self.value = 0
+
+    instances = []
+    lock = Lock()
+
+    def create_instance():
+        instance = MyThreadSafeSingleton()
+        with lock:  # Ensure thread-safe appending
+            instances.append(instance)
+
+    threads = [Thread(target=create_instance) for _ in range(10)]
+    for thread in threads:
+        thread.start()
+    for thread in threads:
+        thread.join()
+
+    first_instance = instances[0]
+    for instance in instances:
+        assert instance is first_instance