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<a href="https://github.com/tarantool/tarantool/commit/<a class=hub.com/tarantool/tarantool/commit/1a7476e6b082b7a53a58045b1acfb59aaee68365">1a7476e6b<a href="https://github.com/tarantool/tarantool/commit/1a7476e6b082b7a53a58045b1acfb59aaee68365">&quot;&gt;httpc: fix zero timeout handling

When libcurl is built with --enable-threaded-resolver (which is default)
and the version of the library is 7.60 or above, libcurl calls a timer
callback with exponentially increasing timeout_ms value during DNS
resolving.

This behaviour was introduced in curl-7_59_0-36-g67636222f (see [1],
[2]). During first ten milliseconds the library sets a timer to a passed
time divided by three (see Curl_resolver_getsock()). It is possible that
passed time is zero during at least several thousands of iterations.

Before this commit we didn&amp;#39;t set a libev timer in curl_multi_timer_cb()
when a timeout_ms value is zero, but call curl_multi_process()
immediately. Libcurl however can call curl_multi_timer_cb() again and
here we&amp;#39;re going into a recursion that stops only when timeous_ms
becomes positive. Often we generate several thousands of stack frames
within this recursion and exceed 512KiB of a fiber stack size.

The fix is easy: set a libev timer to call curl_multi_process() even
when a timeout_ms value is zero.

The reason why we did the call to curl_multi_process() immediately is
the unclear wording in the CURLMOPT_TIMERFUNCTION option documentation.
This documentation page was fixed in curl-7_64_0-88-g47e540df8 (see [3],
[4], [5]).

There is also the related change in curl-7_60_0-121-g3ef67c686 (see [6],
[7]): after this commit libcurl calls a timer callback with zero
timeout_ms during a first three milliseconds of asynchronous DNS
resolving.

Fixes #4179.

[1]: https://github.com/curl/curl/pull/2419
[2]: https://github.com/curl/curl/commit/</a><a class="double-link" href="https://github.com/tarantool/tarantool/commit/<a class="double-link" href="https://github.com/tarantool/tarantool/commit/67636222f42b7db146b963deb577a981b4fcdfa2">67636222f</a>">67636222f</a><a href="https://github.com/tarantool/tarantool/commit/1a7476e6b082b7a53a58045b1acfb59aaee68365">
[3]: https://github.com/curl/curl/issues/3537
[4]: https:... (continued)

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