On 8/2/2017 4:45 AM, Pahome Chen via curl-library wrote:
> Curl version: curl 7.54.0. libcurl/7.54.0 OpenSSL/1.0.2g zlib/1.2.8
>
> I use libcurl to download files from s3 bucket and apply two
> interface: multi_socket and easy.
>
> Both interface download 1MB one time.
>
> Execution order in log is below:
>
> socket callback: s=16 e=0x7f4cb4020230 Adding data: OUT
> socket callback: s=16 e=0x7f4cb4020230 Change action from OUT to IN.
> easy_perform starte. Download 1MB. ->Download finished.
> easy_perform starte. Download 1MB. -> Download finished.
> socket callback: s=16 e=0x7f4cb4020230 Removing.
> multi_socket download done.
>
> In code snippet the two interface use the same curl_easy_setopt() such
> as CURLOPT_WRITEFUNCTION
> CURLOPT_HTTPHEADER
> CURLOPT_URL...etc.
>
> I have questions about that the two interface will affect each other?
> I thought the multi_socket interface will download first that the
> latter easy interface.

You are using multi_socket_action and then in the middle of that you
call easy_perform on some other handles? or (I really hope) is that
happening in a separate thread? In any case if the easy_perform
downloads have finished first any number of factors could contribute to
that. You can only guarantee the order of synchronous downloads because
libcurl would wait for one to finish before going on to the next one. In
other words easy_perform(a); easy_perform(b); easy_perform(c);
guaranteed order because the calls are blocking, a then b then c.
curl_multi_add_handle(multi, a); curl_multi_add_handle(multi, b);
curl_multi_add_handle(multi, c); no guaranteed order. bac, cba, acb, etc

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Received on 2017-08-03