introduce @lru_cache decorator from python 3.2

1 files changed, 168 insertions, 0 deletions

diff --git a/psutil/_compat.py b/psutil/_compat.py
index 5c68f745..9c9684ec 100644
--- a/psutil/_compat.py
+++ b/psutil/_compat.py
@@ -272,3 +272,171 @@ except ImportError:
                             getattr(original, attribute).copy())
             return fn
         return inner
+
+
+# py 2.5 functools.update_wrapper
+try:
+    from functools import update_wrapper
+except ImportError:
+    WRAPPER_ASSIGNMENTS = ('__module__', '__name__', '__doc__')
+    WRAPPER_UPDATES = ('__dict__',)
+
+    def update_wrapper(wrapper, wrapped, assigned=WRAPPER_ASSIGNMENTS,
+                       updated=WRAPPER_UPDATES):
+        """Update a wrapper function to look like the wrapped function, see:
+        http://docs.python.org/library/functools.html#functools.update_wrapper
+        """
+        for attr in assigned:
+            setattr(wrapper, attr, getattr(wrapped, attr))
+        for attr in updated:
+            getattr(wrapper, attr).update(getattr(wrapped, attr, {}))
+        return wrapper
+
+
+# py 3.2 functools.lru_cache
+# Taken from: http://code.activestate.com/recipes/578078
+# Credit: Raymond Hettinger
+try:
+    from functools import lru_cache
+except ImportError:
+    try:
+        from threading import RLock
+    except ImportError:
+        from dummy_threading import RLock
+
+    _CacheInfo = namedtuple("CacheInfo",
+                            ["hits", "misses", "maxsize", "currsize"])
+
+    class _HashedSeq(list):
+        __slots__ = 'hashvalue'
+
+        def __init__(self, tup, hash=hash):
+            self[:] = tup
+            self.hashvalue = hash(tup)
+
+        def __hash__(self):
+            return self.hashvalue
+
+    def _make_key(args, kwds, typed,
+                  kwd_mark=(object(), ),
+                  fasttypes=set((int, str, frozenset, type(None))),
+                  sorted=sorted, tuple=tuple, type=type, len=len):
+        'Make a cache key from optionally typed positional and keyword arguments'
+        key = args
+        if kwds:
+            sorted_items = sorted(kwds.items())
+            key += kwd_mark
+            for item in sorted_items:
+                key += item
+        if typed:
+            key += tuple(type(v) for v in args)
+            if kwds:
+                key += tuple(type(v) for k, v in sorted_items)
+        elif len(key) == 1 and type(key[0]) in fasttypes:
+            return key[0]
+        return _HashedSeq(key)
+
+    def lru_cache(maxsize=100, typed=False):
+        """Least-recently-used cache decorator, see:
+        http://docs.python.org/3/library/functools.html#functools.lru_cache
+        """
+        def decorating_function(user_function):
+            cache = dict()
+            stats = [0, 0]
+            HITS, MISSES = 0, 1
+            make_key = _make_key
+            cache_get = cache.get
+            _len = len
+            lock = RLock()
+            root = []
+            root[:] = [root, root, None, None]
+            nonlocal_root = [root]
+            PREV, NEXT, KEY, RESULT = 0, 1, 2, 3
+            if maxsize == 0:
+                def wrapper(*args, **kwds):
+                    result = user_function(*args, **kwds)
+                    stats[MISSES] += 1
+                    return result
+            elif maxsize is None:
+                def wrapper(*args, **kwds):
+                    key = make_key(args, kwds, typed)
+                    result = cache_get(key, root)
+                    if result is not root:
+                        stats[HITS] += 1
+                        return result
+                    result = user_function(*args, **kwds)
+                    cache[key] = result
+                    stats[MISSES] += 1
+                    return result
+            else:
+                def wrapper(*args, **kwds):
+                    if kwds or typed:
+                        key = make_key(args, kwds, typed)
+                    else:
+                        key = args
+                    lock.acquire()
+                    try:
+                        link = cache_get(key)
+                        if link is not None:
+                            root, = nonlocal_root
+                            link_prev, link_next, key, result = link
+                            link_prev[NEXT] = link_next
+                            link_next[PREV] = link_prev
+                            last = root[PREV]
+                            last[NEXT] = root[PREV] = link
+                            link[PREV] = last
+                            link[NEXT] = root
+                            stats[HITS] += 1
+                            return result
+                    finally:
+                        lock.release()
+                    result = user_function(*args, **kwds)
+                    lock.acquire()
+                    try:
+                        root, = nonlocal_root
+                        if key in cache:
+                            pass
+                        elif _len(cache) >= maxsize:
+                            oldroot = root
+                            oldroot[KEY] = key
+                            oldroot[RESULT] = result
+                            root = nonlocal_root[0] = oldroot[NEXT]
+                            oldkey = root[KEY]
+                            root[KEY] = root[RESULT] = None
+                            del cache[oldkey]
+                            cache[key] = oldroot
+                        else:
+                            last = root[PREV]
+                            link = [last, root, key, result]
+                            last[NEXT] = root[PREV] = cache[key] = link
+                        stats[MISSES] += 1
+                    finally:
+                        lock.release()
+                    return result
+
+            def cache_info():
+                """Report cache statistics"""
+                lock.acquire()
+                try:
+                    return _CacheInfo(stats[HITS], stats[MISSES], maxsize,
+                                      len(cache))
+                finally:
+                    lock.release()
+
+            def cache_clear():
+                """Clear the cache and cache statistics"""
+                lock.acquire()
+                try:
+                    cache.clear()
+                    root = nonlocal_root[0]
+                    root[:] = [root, root, None, None]
+                    stats[:] = [0, 0]
+                finally:
+                    lock.release()
+
+            wrapper.__wrapped__ = user_function
+            wrapper.cache_info = cache_info
+            wrapper.cache_clear = cache_clear
+            return update_wrapper(wrapper, user_function)
+
+        return decorating_function