Calling curl_easy_pause in CURLOPT_XFERINFOFUNCTION and delay/frequency issue

I have a long-lasting upload where I have to pause the read by returning CURL_READFUNC_PAUSE from the read callback.  Once the data is available, I need to unpause the read. Initially, I was calling curl_easy_pause(curl, CURLPAUSE_SEND_CONT) which was not called from the callback thread but worked fine with the main issue being that unpausing would at times take over a second. I noticed that in the documentation it states that the unpausing should be called from a callback thread. I modified my code to trigger the unpausing from the transfer function (CURLOPT_XFERINFOFUNCTION) but it seems that this function also has a wide variability in the frequency of the call.

I am hoping that my questions can be answered here as I am drawing a blank:

 
What’s the best way to handle the situation when you don’t yet have the bits to submit (NOTE: I can’t block the curl thread as it serves the download)
Can I actually call curl unpause from an unrelated thread (seem to work on all platforms).
In case of directly unpausing from an unrelated thread – how can I make it more prompt as at times I see a delay of over a second?
In case of unpausing from the transfer/progress update callback – how can I make it to be called more frequent so I can unpause in time?
 

Thanks in advance

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Received on 2020-07-15