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+#
+# __COPYRIGHT__
+#
+# Permission is hereby granted, free of charge, to any person obtaining
+# a copy of this software and associated documentation files (the
+# "Software"), to deal in the Software without restriction, including
+# without limitation the rights to use, copy, modify, merge, publish,
+# distribute, sublicense, and/or sell copies of the Software, and to
+# permit persons to whom the Software is furnished to do so, subject to
+# the following conditions:
+#
+# The above copyright notice and this permission notice shall be included
+# in all copies or substantial portions of the Software.
+#
+# THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY
+# KIND, EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE
+# WARRANTIES OF MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND
+# NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE
+# LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION
+# OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION
+# WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.
+#
+from __future__ import print_function
+
+__revision__ = "__FILE__ __REVISION__ __DATE__ __DEVELOPER__"
+
+__doc__ = """Memoizer
+
+A decorator-based implementation to count hits and misses of the computed
+values that various methods cache in memory.
+
+Use of this modules assumes that wrapped methods be coded to cache their
+values in a consistent way. In particular, it requires that the class uses a
+dictionary named "_memo" to store the cached values.
+
+Here is an example of wrapping a method that returns a computed value,
+with no input parameters::
+
+    @SCons.Memoize.CountMethodCall
+    def foo(self):
+
+        try:                                                    # Memoization
+            return self._memo['foo']                            # Memoization
+        except KeyError:                                        # Memoization
+            pass                                                # Memoization
+
+        result = self.compute_foo_value()
+
+        self._memo['foo'] = result                              # Memoization
+
+        return result
+
+Here is an example of wrapping a method that will return different values
+based on one or more input arguments::
+
+    def _bar_key(self, argument):                               # Memoization
+        return argument                                         # Memoization
+
+    @SCons.Memoize.CountDictCall(_bar_key)
+    def bar(self, argument):
+
+        memo_key = argument                                     # Memoization
+        try:                                                    # Memoization
+            memo_dict = self._memo['bar']                       # Memoization
+        except KeyError:                                        # Memoization
+            memo_dict = {}                                      # Memoization
+            self._memo['dict'] = memo_dict                      # Memoization
+        else:                                                   # Memoization
+            try:                                                # Memoization
+                return memo_dict[memo_key]                      # Memoization
+            except KeyError:                                    # Memoization
+                pass                                            # Memoization
+
+        result = self.compute_bar_value(argument)
+
+        memo_dict[memo_key] = result                            # Memoization
+
+        return result
+
+Deciding what to cache is tricky, because different configurations
+can have radically different performance tradeoffs, and because the
+tradeoffs involved are often so non-obvious.  Consequently, deciding
+whether or not to cache a given method will likely be more of an art than
+a science, but should still be based on available data from this module.
+Here are some VERY GENERAL guidelines about deciding whether or not to
+cache return values from a method that's being called a lot:
+
+    --  The first question to ask is, "Can we change the calling code
+        so this method isn't called so often?"  Sometimes this can be
+        done by changing the algorithm.  Sometimes the *caller* should
+        be memoized, not the method you're looking at.
+
+    --  The memoized function should be timed with multiple configurations
+        to make sure it doesn't inadvertently slow down some other
+        configuration.
+
+    --  When memoizing values based on a dictionary key composed of
+        input arguments, you don't need to use all of the arguments
+        if some of them don't affect the return values.
+
+"""
+
+# A flag controlling whether or not we actually use memoization.
+use_memoizer = None
+
+# Global list of counter objects
+CounterList = {}
+
+class Counter(object):
+    """
+    Base class for counting memoization hits and misses.
+
+    We expect that the initialization in a matching decorator will
+    fill in the correct class name and method name that represents
+    the name of the function being counted.
+    """
+    def __init__(self, cls_name, method_name):
+        """
+        """
+        self.cls_name = cls_name
+        self.method_name = method_name
+        self.hit = 0
+        self.miss = 0
+    def key(self):
+        return self.cls_name+'.'+self.method_name
+    def display(self):
+        print("    {:7d} hits {:7d} misses    {}()".format(self.hit, self.miss, self.key()))
+    def __eq__(self, other):
+        try:
+            return self.key() == other.key()
+        except AttributeError:
+            return True
+
+class CountValue(Counter):
+    """
+    A counter class for simple, atomic memoized values.
+
+    A CountValue object should be instantiated in a decorator for each of
+    the class's methods that memoizes its return value by simply storing
+    the return value in its _memo dictionary.
+    """
+    def count(self, *args, **kw):
+        """ Counts whether the memoized value has already been
+            set (a hit) or not (a miss).
+        """
+        obj = args[0]
+        if self.method_name in obj._memo:
+            self.hit = self.hit + 1
+        else:
+            self.miss = self.miss + 1
+
+class CountDict(Counter):
+    """
+    A counter class for memoized values stored in a dictionary, with
+    keys based on the method's input arguments.
+
+    A CountDict object is instantiated in a decorator for each of the
+    class's methods that memoizes its return value in a dictionary,
+    indexed by some key that can be computed from one or more of
+    its input arguments.
+    """
+    def __init__(self, cls_name, method_name, keymaker):
+        """
+        """
+        Counter.__init__(self, cls_name, method_name)
+        self.keymaker = keymaker
+    def count(self, *args, **kw):
+        """ Counts whether the computed key value is already present
+           in the memoization dictionary (a hit) or not (a miss).
+        """
+        obj = args[0]
+        try:
+            memo_dict = obj._memo[self.method_name]
+        except KeyError:
+            self.miss = self.miss + 1
+        else:
+            key = self.keymaker(*args, **kw)
+            if key in memo_dict:
+                self.hit = self.hit + 1
+            else:
+                self.miss = self.miss + 1
+
+def Dump(title=None):
+    """ Dump the hit/miss count for all the counters
+        collected so far.
+    """
+    if title:
+        print(title)
+    for counter in sorted(CounterList):
+        CounterList[counter].display()
+
+def EnableMemoization():
+    global use_memoizer
+    use_memoizer = 1
+
+def CountMethodCall(fn):
+    """ Decorator for counting memoizer hits/misses while retrieving
+        a simple value in a class method. It wraps the given method
+        fn and uses a CountValue object to keep track of the
+        caching statistics.
+        Wrapping gets enabled by calling EnableMemoization().
+    """
+    if use_memoizer:
+        def wrapper(self, *args, **kwargs):
+            global CounterList
+            key = self.__class__.__name__+'.'+fn.__name__
+            if key not in CounterList:
+                CounterList[key] = CountValue(self.__class__.__name__, fn.__name__)
+            CounterList[key].count(self, *args, **kwargs)
+            return fn(self, *args, **kwargs)
+        wrapper.__name__= fn.__name__
+        return wrapper
+    else:
+        return fn
+
+def CountDictCall(keyfunc):
+    """ Decorator for counting memoizer hits/misses while accessing
+        dictionary values with a key-generating function. Like
+        CountMethodCall above, it wraps the given method
+        fn and uses a CountDict object to keep track of the
+        caching statistics. The dict-key function keyfunc has to
+        get passed in the decorator call and gets stored in the
+        CountDict instance.
+        Wrapping gets enabled by calling EnableMemoization().
+    """
+    def decorator(fn):
+        if use_memoizer:
+            def wrapper(self, *args, **kwargs):
+                global CounterList
+                key = self.__class__.__name__+'.'+fn.__name__
+                if key not in CounterList:
+                    CounterList[key] = CountDict(self.__class__.__name__, fn.__name__, keyfunc)
+                CounterList[key].count(self, *args, **kwargs)
+                return fn(self, *args, **kwargs)
+            wrapper.__name__= fn.__name__
+            return wrapper
+        else:
+            return fn
+    return decorator
+
+# Local Variables:
+# tab-width:4
+# indent-tabs-mode:nil
+# End:
+# vim: set expandtab tabstop=4 shiftwidth=4: