curl_multi_poll: a sister to curl_multi_wait() that waits more #4163
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Repeatedly we see problems where using curl_multi_wait() is difficult or just awkward because if it has no file descriptor to wait for internally, it returns immediately and leaves it to the caller to wait for a small amount of time in order to avoid occasional busy-looping. This is often missed or misunderstood, leading to underperforming applications. This change introduces curl_multi_poll() as a replacement drop-in function that accepts the exact same set of arguments. This function works identically to curl_multi_wait() - EXCEPT - for the case when there's nothing to wait for internally, as then this function will by itself wait for a "suitable" short time before it returns. This effectiely avoids all risks of busy-looping and should also make it less likely that apps "over-wait". This also changes the curl tool to use this funtion internally when doing parallel transfers and changes curl_easy_perform() to use it internally.
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Plan: leave this open here for feedback and possible discussions for a week before I land it, should there be no big opposition. Brought up on the mailing list and twitter. |
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For some reason the #4179 clone PR of this seems to have made the CI builds restart in this PR... ? |
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Repeatedly we see problems where using curl_multi_wait() is difficult or
just awkward because if it has no file descriptor to wait for
internally, it returns immediately and leaves it to the caller to wait
for a small amount of time in order to avoid occasional busy-looping.
This is often missed or misunderstood, leading to underperforming
applications.
This change introduces curl_multi_poll() as a replacement drop-in
function that accepts the exact same set of arguments. This function
works identically to curl_multi_wait() - EXCEPT - for the case when
there's nothing to wait for internally, as then this function will by
itself wait for a "suitable" short time before it returns. This
effectiely avoids all risks of busy-looping and should also make it less
likely that apps "over-wait".
This also changes the curl tool to use this funtion internally when
doing parallel transfers and changes curl_easy_perform() to use it
internally.