避免商品看板冷快取阻塞

config.py

@@ -320,7 +320,7 @@ YOUTUBE_API_KEY = os.getenv('YOUTUBE_API_KEY', '')
 # ==========================================
 # 系統版本與路徑
 # ==========================================
-SYSTEM_VERSION = "V10.108"
+SYSTEM_VERSION = "V10.109"
 LOG_FILE_PATH = os.path.join(BASE_DIR, 'logs/system.log')
 public_url = PUBLIC_URL  # 用於模板顯示
 

routes/dashboard_routes.py

@@ -11,6 +11,7 @@ import math
 import time
 import hashlib
 import pickle
+import threading
 from datetime import datetime, timezone, timedelta
 from flask import Blueprint, request, render_template
 from sqlalchemy import func, and_, text, bindparam
@@ -699,6 +700,10 @@ class FileLock:
 
 
 _DASHBOARD_STALE_CACHE_MAX_AGE = 86400
+_DASHBOARD_REFRESH_STATE = {
+    'started_at': 0,
+    'running': False,
+}
 
 
 def _new_dashboard_file_lock():
@@ -759,6 +764,38 @@ def _load_stale_full_dashboard_cache(now):
     )
 
 
+def _load_expired_shared_full_dashboard_cache(now):
+    """只讀原 shared cache 檔的過期版本；不讀 clear_cache 後搬走的 stale 檔。"""
+    return _load_dashboard_cache_file(
+        now,
+        _DASHBOARD_SHARED_CACHE_FILE,
+        allow_stale=True,
+        label='過期共享',
+    )
+
+
+def _trigger_dashboard_background_refresh(reason):
+    """使用過期 shared cache 先回首頁時，背景補一次 fresh cache，避免使用者卡 10s。"""
+    now_ts = time.time()
+    if _DASHBOARD_REFRESH_STATE['running']:
+        return
+    if now_ts - _DASHBOARD_REFRESH_STATE['started_at'] < 60:
+        return
+
+    def _refresh():
+        _DASHBOARD_REFRESH_STATE['running'] = True
+        try:
+            warm_full_dashboard_cache(reason=reason, force_rebuild=True)
+        except Exception as exc:
+            sys_log.warning(f"[Dashboard] [Cache] 背景預熱失敗: {exc}")
+        finally:
+            _DASHBOARD_REFRESH_STATE['running'] = False
+
+    _DASHBOARD_REFRESH_STATE['started_at'] = now_ts
+    thread = threading.Thread(target=_refresh, name='dashboard-cache-refresh', daemon=True)
+    thread.start()
+
+
 def _write_shared_full_dashboard_cache(full_data):
     """原子寫入跨 worker 共享的商品看板深度快取。"""
     cache_file = str(_DASHBOARD_SHARED_CACHE_FILE)
@@ -1031,6 +1068,11 @@ def get_full_dashboard_data(force_rebuild=False):
     if shared_full_data:
         return shared_full_data
 
+    expired_shared_data = None if force_rebuild else _load_expired_shared_full_dashboard_cache(now)
+    if expired_shared_data:
+        _trigger_dashboard_background_refresh('expired_shared_cache')
+        return expired_shared_data
+
     # V-Opt: 使用檔案鎖避免多 gunicorn worker 同時計算
     dashboard_lock = _new_dashboard_file_lock()
     lock_acquired = dashboard_lock.acquire(blocking=False)