语法: ok, err = ngx.shared.DICT:safe_set(key, value, exptime?, flags?)
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.*
类似 set 方法，但当共享内存区块存储空间不足时，不覆盖 (最近最少使用的) 有效的项 (非过期项)。此时，它将返回 nil 和字符串 "no memory" (内存不足)。
此方法最早出现在 0.7.18 版本中。
更多功能请参考 ngx.shared.DICT。
English Source
syntax: ok, err = ngx.shared.DICT:safe_set(key, value, exptime?, flags?)
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.*
Similar to the set method, but never overrides the (least recently used) unexpired items in the store when running out of storage in the shared memory zone. In this case, it will immediately return nil and the string "no memory".
This feature was first introduced in the v0.7.18 release.
See also ngx.shared.DICT.