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Re: CURL Sending FINS without curl_multi_cleanup, and ways to avoid it

From: Daniel Stenberg via curl-library <curl-library_at_cool.haxx.se>
Date: Tue, 13 Aug 2019 17:47:13 +0200 (CEST)

On Tue, 13 Aug 2019, Aravindhan Krishnan via curl-library wrote:

> I have enabled pipeline with pipe-length of 5 (default)

I would advice against enabling pipelining. It had several issues and it has
been removed in later versions.

> and have set CURLMOPT_MAX_TOTAL_CONNECTIONS and
> CURLMOPT_MAX_HOST_CONNECTIONS to 5, just in case if it helps for the
> question below.

Limiting the connection cache and number of parallel connections will not help
curl to do more or better persistent connections.
CURLMOPT_MAX_TOTAL_CONNECTIONS will rather risk capping curl into closing
connections more frequently than otherwise and CURLMOPT_MAX_HOST_CONNECTIONS
risks making curl queue up requests that could otherwise get performed
earlier.

> The client is just an extended version of the sample indicated by
> multi-uv.c, where in I send 20 requests, get the responses, process them and
> repeat the process infinitely. During the entire process I don’t call
> curl_multi_cleanup, but after receiving and processing every response, I
> call curl_multi_remove_handle and curl_easy_cleanup for the completed easy
> handle.

You do 20 parallel requests and has asked libcurl to not keep more than 5 in
the connection cache. 5 is less than 20. There's no room to keep any
connection alive after they're done. They will be closed and discarded as soon
as possible. As requested.

I would suggest you start by simply not setting those options and let libcurl
use its defaults there.

> I was under the impression that there will be no FINs going out of the
> client, and clearly I am wrong.

Correct, libcurl will close connections it could otherwise keep alive - unless
of course there's a reason to. Like keeping the number of connections down or
killing off old ones etc. 

-- 
  / daniel.haxx.se | Get the best commercial curl support there is - from me
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Received on 2019-08-13