lrucache.py

"""
TkinterWeb v3.24
This is a wrapper for the Tkhtml3 widget from http://tkhtml.tcl.tk/tkhtml.html, 
which displays styled HTML documents in Tkinter.

Copyright (c) 2024 Andereoo

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 _thread import RLock
from functools import _make_key, update_wrapper


def _lru_cache_wrapper(user_function):
    """This function is a modified version of the one that comes built-in with functools
    It only adds to the cache if the data is not None.
    This means that if a page load is stopped, re-loading the page will not cause the page to be blank."""
    sentinel = object()
    make_key = _make_key
    PREV, NEXT, KEY, RESULT = 0, 1, 2, 3

    cache = {}
    hits = misses = 0
    maxsize = 128
    typed = False
    full = False
    cache_get = cache.get
    cache_len = cache.__len__
    lock = RLock()
    root = []
    root[:] = [root, root, None, None]

    def wrapper(*args, **kwds):
        nonlocal root, hits, misses, full
        key = make_key(args, kwds, typed)
        with lock:
            link = cache_get(key)
            if link is not None:
                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
                hits += 1
                return result
            misses += 1
        result = user_function(*args, **kwds)
        if result[0]:
            with lock:
                if key in cache:
                    pass
                elif full:
                    oldroot = root
                    oldroot[KEY] = key
                    oldroot[RESULT] = result
                    root = oldroot[NEXT]
                    oldkey = root[KEY]
                    oldresult = root[RESULT]
                    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
                    full = cache_len() >= maxsize
        return result
    return wrapper


def lru_cache():
    def decorator(func):
        wrapper = _lru_cache_wrapper(func)
        return update_wrapper(wrapper, func)
    return decorator