语法: flushed = ngx.shared.DICT:flush_expired(max_count?)
环境: init_by_lua*, set_by_lua*, rewrite_by_lua*, access_by_lua*, content_by_lua*, header_filter_by_lua*, body_filter_by_lua*, log_by_lua*, ngx.timer.*
清除字典中已过期的的内容，最多清除可选参数 max_count (最大数量) 个。当参数 max_count 值为 0 或者未指定时，意为无数量限制。返回值为实际清除的数量。
与 flush_all 方法不同，此方法释放删除掉的已过期内容占用的内存。
这个功能最早出现在 v0.6.3 版本中。
更多功能请参考 ngx.shared.DICT.flush_all 和 ngx.shared.DICT。
English Source
syntax: flushed = ngx.shared.DICT:flush_expired(max_count?)
context: init_by_lua*, set_by_lua*, rewrite_by_lua*, access_by_lua*, content_by_lua*, header_filter_by_lua*, body_filter_by_lua*, log_by_lua*, ngx.timer.*
Flushes out the expired items in the dictionary, up to the maximal number specified by the optional max_count argument. When the max_count argument is given 0 or not given at all, then it means unlimited. Returns the number of items that have actually been flushed.
Unlike the flush_all method, this method actually free up the memory used by the expired items.
This feature was first introduced in the v0.6.3 release.
See also ngx.shared.DICT.flush_all and ngx.shared.DICT.