So I wanted to see how libcurl deals with dropped connections and I did a small test.

Consider the following setup:

(computer) -> (hub) -> (adsl modem)

I arranged it that way so the computer NIC would not be factor in the test.

I wrote a small program that simply downloads a file and while the download was in progress, I turned off the modem.
Interestingly, the program was stuck on the event loop (epoll_wait) indefinitely.
After doing some debugging it turned out that once my timer call back calls: curl_multi_socket_action(curl_m_handle, CURL_SOCKET_TIMEOUT, 0, &running_handles); when the timeout elapses Libcurl doesn’t call my socket_callback to notify me that I need to unregister from the eventloop (CURL_POLL_REMOVE). More specifically Curl_splaygetbest identified the timeout socket and in turn called multi_runsingle and singlesocket() but the remove_sock_from_hash block was not entered. BTW, I tested this both on Windows and Linux – same behavior.

Any idea why?

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Received on 2016-01-27