From 2952ab6dee669e198bb3e535788a3f05b0de98a7 Mon Sep 17 00:00:00 2001
From: Sinisa Veseli <sveseli@aps.anl.gov>
Date: Tue, 14 Apr 2015 13:19:20 +0000
Subject: [PATCH] reordered initialization call, added some test code
---
src/python/dm/common/utility/singleton.py | 29 +++++++++++++++++++----
1 file changed, 25 insertions(+), 4 deletions(-)
diff --git a/src/python/dm/common/utility/singleton.py b/src/python/dm/common/utility/singleton.py
index 8325b6bc..00c0f215 100755
--- a/src/python/dm/common/utility/singleton.py
+++ b/src/python/dm/common/utility/singleton.py
@@ -4,12 +4,16 @@ class Singleton(object):
__instance = None
+ # This class will behave properly as long as getInstance() is called.
+ # If object is constructed using constructor, __init__() will be called
+ # multiple times in the derived class (i.e., one needs protection
+ # against multiple initializations in the derived class)
def __new__(cls, *args, **kwargs):
# Allow subclasses to create their own instances.
if cls.__instance is None or cls != type(cls.__instance):
instance = object.__new__(cls, *args, **kwargs)
- cls.__instance = instance
instance.__init__(*args, **kwargs)
+ cls.__instance = instance
return cls.__instance
@classmethod
@@ -18,12 +22,13 @@ class Singleton(object):
def __init__(self, *args, **kwargs):
# Only initialize once.
- if Singleton.__instance is not None:
+ if self.__class__.__instance is not None:
return
####################################################################
# Testing
if __name__ == '__main__':
+ print 'Testing Singleton class'
s1 = Singleton.getInstance()
s2 = Singleton()
s3 = Singleton.getInstance()
@@ -33,8 +38,11 @@ if __name__ == '__main__':
print 'S3: ', s3
print 'S4: ', s4
class A(Singleton):
+ __instance = None
def __init__(self, x):
- self.x = x
+ if self.__class__.__instance is None:
+ print 'in A.__init__()'
+ self.x = x
class B(Singleton):
def __init__(self, x):
self.x = x
@@ -42,18 +50,31 @@ if __name__ == '__main__':
def __init__(self):
self.x = 14
+ print
+ print 'Testing Class A'
+ print 'Init A(3)'
a1 = A(3)
+ print 'Init A(4)'
a2 = A(4)
+ print 'A.getInstance()'
+ a3 = A.getInstance()
+ print 'A.getInstance()'
+ a4 = A.getInstance()
print a1
print a2
- print a2.x, a1.x
+ print a3
+ print a3.x, a2.x, a1.x
+ print
+ print 'Testing Class B'
b1 = B(6)
b2 = B(5)
print b1
print b2
print b2.x, b1.x
+ print
+ print 'Testing Class C'
c1 = C()
c2 = C()
print c1
--
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