我是寫Linux后端的（golang、c++、py），后端緩存算法通常是指的是內存里面的lru、或diskqueue，都是獨立使用。 很少有用內存lru與disklru結合的場景需求。近段時間研究android開發，里面有一些設計思想值得后端學習。

寫這篇文章的原因：
看到了android開發里面的一個片段

于是在畫板里面手繪下圖：

為了簡化測試，用Python編程語言實現

import tkinter as tk
from tkinter import ttk, messagebox
from PIL import Image, ImageTk, ImageOps
import requests
from io import BytesIO
import threading
import queue
from functools import lru_cache
from diskcache import Cache
import os# 配置緩存
CACHE_DIR = "image_cache"
os.makedirs(CACHE_DIR, exist_ok=True)
disk_cache = Cache(CACHE_DIR)  # 磁盤緩存（自動管理容量）@lru_cache(maxsize=5)  # LRU緩存（僅記錄URL）
def get_from_lru(url):passclass ImageLoader:def __init__(self):self.queue = queue.Queue()self.thread = threading.Thread(target=self._worker, daemon=True)self.thread.start()def load(self, url, callback):self.queue.put((url, callback))def _worker(self):while True:url, callback = self.queue.get()data = Nonecache_type = "error"# 檢查LRUif get_from_lru.cache_info().currsize > 0:data = disk_cache.get(url)if data:cache_type = "lru"# 檢查磁盤if not data:data = disk_cache.get(url)if data:cache_type = "disk"get_from_lru(url)  # 更新LRU標記# 網絡加載if not data:try:res = requests.get(url, timeout=10)res.raise_for_status()data = res.contentcache_type = "network"disk_cache.set(url, data)  # 自動處理容量限制get_from_lru(url)except Exception as e:callback(None, cache_type)continue# 返回結果try:img = Image.open(BytesIO(data))callback(img, cache_type)except:callback(None, "error")class ImageViewerApp:def __init__(self, root):self.root = rootself.root.title("圖片查看器")self.urls = [f"https://picsum.photos/seed/img{i}/800/600" for i in range(1, 11)]self.current = 0self.loader = ImageLoader()self._create_widgets()def _create_widgets(self):frame = ttk.Frame(self.root, padding=10)frame.pack(fill=tk.BOTH, expand=True)# 圖片顯示區域self.img_label = ttk.Label(frame)self.img_label.pack(fill=tk.BOTH, expand=True, padx=10, pady=10)# 導航按鈕btn_frame = ttk.Frame(frame)btn_frame.pack(fill=tk.X, pady=5)self.prev_btn = ttk.Button(btn_frame, text="? 上一張", command=self.prev_image)self.prev_btn.pack(side=tk.LEFT, padx=5)self.next_btn = ttk.Button(btn_frame, text="下一張 ?", command=self.next_image)self.next_btn.pack(side=tk.RIGHT, padx=5)# 緩存狀態self.status_label = ttk.Label(frame, text="緩存狀態: LRU(0/5), 磁盤(0/8)")self.status_label.pack(fill=tk.X, pady=2)# 加載指示器self.loading = ttk.Label(self.img_label, text="加載中...", font=("SimHei", 12))def _load_image(self, index):self.current = indexurl = self.urls[index]self.status_label.config(text="加載中...")self.loading.place(relx=0.5, rely=0.5, anchor="center")self.prev_btn.config(state=tk.DISABLED)self.next_btn.config(state=tk.DISABLED)self.loader.load(url, self._on_loaded)def _on_loaded(self, img, cache_type):self.root.after(0, lambda: self._update_display(img, cache_type))def _update_display(self, img, cache_type):self.loading.place_forget()self.prev_btn.config(state=tk.NORMAL)self.next_btn.config(state=tk.NORMAL)if img:# 調整圖片大小max_w = self.img_label.winfo_width() - 20max_h = self.img_label.winfo_height() - 20img = ImageOps.contain(img, (max_w or 500, max_h or 400))self.photo = ImageTk.PhotoImage(img)self.img_label.config(image=self.photo)# 更新緩存狀態lru = get_from_lru.cache_info().currsizedisk = len(disk_cache)self.status_label.config(text=f"緩存狀態: LRU({lru}/5) [{cache_type.upper()}], 磁盤({disk}/8)")else:messagebox.showerror("錯誤", "無法加載圖片")def prev_image(self):self._load_image((self.current - 1) % 10)def next_image(self):self._load_image((self.current + 1) % 10)if __name__ == "__main__":root = tk.Tk()root.geometry("800x600")app = ImageViewerApp(root)app._load_image(0)root.mainloop()

測試效果：
經過緩存的圖片從內存或文件加載，速度快了很多。 用空間換時間^_