如何将CURLOPT_DNS_CACHE_TIMEOUT与共享DNS缓存一起使用

Question

I'm using my own pool of CURL easy handles reused in multi threaded application - the goal is to reuse TCP connections and DNS lookups. Every time a handle is returned to the pool curl_easy_reset is called on that handle.

At the moment my implementation uses separate local DNS cache for every CURL easy handle. I'm playing with CURL shared interface and shared DNS cache and it seems to work pretty well but I don't understand what is the correct way to set DNS cache timeout?

DNS cache timeout is set on CURL easy handle but the cache is shared. Do I need to set the timeout every time I get a handle from the pool (because of reset called previously) or is cache timeout set only once and remembered until I change it?

Answer 1

The timeout value is actually stored and used per easy handle. Each easy handle thus has its own timeout value, even when the DNS cache is shared. Each easy handle will thus evict a too old entry and re-resolve a name again according to its own value.

When you set the timeout value for an easy handle, that timeout value will "stick" and be used until you set it again to something else. (Like all other options.)

Calling curl_easy_reset() on the handle will of course reset the timeout value for the handle back to its internal default.