[IMP] core: rebuild LRU on OrderedDict

That's pretty much the entire point of OrderedDict's existence.

Also removed the iteration methods: they're not used and they're not
thread-safe, since they're written as generators they "return"
instantaneously when called immediately unlocking, then the iteration
itself is unprotected, so the entire thing is useless.

They could be reimplemented with explicit locking (a `with self._lock`
internally) if there's ever a use case for it, but that doesn't seem
to be the case at the moment.

closes odoo/odoo#46061

Signed-off-by: Xavier Morel (xmo) <xmo@odoo.com>

odoo/tools/lru.py

@@ -1,31 +1,21 @@
 # -*- coding: utf-8 -*-
-# taken from http://code.activestate.com/recipes/252524-length-limited-o1-lru-cache-implementation/
+import collections
 import threading
 
 from .func import synchronized
 
 __all__ = ['LRU']
 
-class LRUNode(object):
-    __slots__ = ['prev', 'next', 'me']
-    def __init__(self, prev, me):
-        self.prev = prev
-        self.me = me
-        self.next = None
-
 class LRU(object):
     """
-    Implementation of a length-limited O(1) LRU queue.
-    Built for and used by PyPE:
-    http://pype.sourceforge.net
-    Copyright 2003 Josiah Carlson.
+    Implementation of a length-limited O(1) LRU map.
+
+    Original Copyright 2003 Josiah Carlson, later rebuilt on OrderedDict.
     """
-    def __init__(self, count, pairs=[]):
+    def __init__(self, count, pairs=()):
         self._lock = threading.RLock()
         self.count = max(count, 1)
-        self.d = {}
-        self.first = None
-        self.last = None
+        self.d = collections.OrderedDict()
         for key, value in pairs:
             self[key] = value
 
@@ -41,88 +31,29 @@ class LRU(object):
 
     @synchronized()
     def __getitem__(self, obj):
-        a = self.d[obj].me
-        self[a[0]] = a[1]
-        return a[1]
+        a = self.d[obj]
+        self.d.move_to_end(obj, last=False)
+        return a
 
     @synchronized()
     def __setitem__(self, obj, val):
-        if obj in self.d:
-            del self[obj]
-        nobj = LRUNode(self.last, (obj, val))
-        if self.first is None:
-            self.first = nobj
-        if self.last:
-            self.last.next = nobj
-        self.last = nobj
-        self.d[obj] = nobj
-        if len(self.d) > self.count:
-            if self.first == self.last:
-                self.first = None
-                self.last = None
-                return
-            a = self.first
-            a.next.prev = None
-            self.first = a.next
-            a.next = None
-            del self.d[a.me[0]]
-            del a
+        self.d[obj] = val
+        self.d.move_to_end(obj, last=False)
+        while len(self.d) > self.count:
+            self.d.popitem(last=True)
 
     @synchronized()
     def __delitem__(self, obj):
-        nobj = self.d[obj]
-        if nobj.prev:
-            nobj.prev.next = nobj.next
-        else:
-            self.first = nobj.next
-        if nobj.next:
-            nobj.next.prev = nobj.prev
-        else:
-            self.last = nobj.prev
         del self.d[obj]
 
-    @synchronized()
-    def __iter__(self):
-        cur = self.first
-        while cur is not None:
-            cur2 = cur.next
-            yield cur.me[1]
-            cur = cur2
-
     @synchronized()
     def __len__(self):
         return len(self.d)
 
-    # FIXME: should this have a P2 and a P3 version or something?
-    @synchronized()
-    def iteritems(self):
-        cur = self.first
-        while cur is not None:
-            cur2 = cur.next
-            yield cur.me
-            cur = cur2
-    items = iteritems
-
-    @synchronized()
-    def iterkeys(self):
-        return iter(self.d)
-
-    @synchronized()
-    def itervalues(self):
-        return iter(self.d.values())
-
-    @synchronized()
-    def keys(self):
-        return list(self.d)
-
     @synchronized()
     def pop(self,key):
-        v=self[key]
-        del self[key]
-        return v
+        return self.d.pop(key)
 
     @synchronized()
     def clear(self):
-        self.d = {}
-        self.first = None
-        self.last = None
+        self.d.clear()