masaori335 commented on code in PR #12735:
URL: https://github.com/apache/trafficserver/pull/12735#discussion_r2596695394
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include/proxy/http/HttpConfig.h:
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@@ -852,6 +856,72 @@ struct HttpConfigParams : public ConfigInfo {
HttpConfigParams &operator=(const HttpConfigParams &) = delete;
};
+/////////////////////////////////////////////////////////////
+//
+// class ParsedConfigCache
+//
+/////////////////////////////////////////////////////////////
+
+/** Cache for pre-parsed string config values.
+ *
+ * Some overridable STRING configs require parsing (e.g., status code lists,
+ * host resolution preferences). Parsing can be non-trivial. This cache stores
+ * parsed results so repeated calls to TSHttpTxnConfigStringSet() with the same
+ * value don't re-parse.
+ *
+ * The static lookup() method handles everything: check cache, parse if needed,
+ * store in cache, and return the result.
+ */
+class ParsedConfigCache
+{
+public:
+ /** Pre-parsed representations for configs that need special parsing. */
+ struct ParsedValue {
+ HostResData host_res_data{};
+ HttpStatusCodeList status_code_list{};
+ HttpForwarded::OptionBitSet forwarded_bitset{};
+ MgmtByte server_session_sharing_match{0};
+ std::string conf_value_storage{}; // Owns the string data.
+ };
+
+ /** Return the parsed value for the configuration.
+ *
+ * On first call for a given (key, value) pair, parses the value and caches
it.
+ * Subsequent calls return the cached result.
+ *
+ * @param key The config key being referenced.
+ * @param value The string value to parse.
+ * @return Reference to the cached parsed value.
+ */
+ static const ParsedValue &lookup(TSOverridableConfigKey key,
std::string_view value);
+
+private:
+ ParsedConfigCache() = default;
+
+ // Enforce singleton pattern.
+ ParsedConfigCache(const ParsedConfigCache &) = delete;
+ ParsedConfigCache &operator=(const ParsedConfigCache &) = delete;
+ ParsedConfigCache(ParsedConfigCache &&) = delete;
+ ParsedConfigCache &operator=(ParsedConfigCache &&) = delete;
+
+ static ParsedConfigCache &instance();
+
+ const ParsedValue &lookup_impl(TSOverridableConfigKey key, std::string_view
value);
+ ParsedValue parse(TSOverridableConfigKey key, std::string_view value);
+
+ // Custom hash for the cache key.
+ struct CacheKeyHash {
+ std::size_t
+ operator()(const std::pair<TSOverridableConfigKey, std::string> &k) const
+ {
+ return std::hash<int>()(static_cast<int>(k.first)) ^
(std::hash<std::string>()(k.second) << 1);
Review Comment:
I guess this 1 bit left-shift is trying to avoid collision. Because If hash
of `k.first` and `k.second` is the same value, it'll be 0, right?
~I'm a bit wondering if we should shift more than 1 bit. The length of
return value of `std::hash` is fixed?~
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