CURLOPT_PROGRESSFUNCTION is really not a good idea when using the multi

.IP CURLOPT_PROGRESSFUNCTION

Function pointer that should match the \fIcurl_progress_callback\fP prototype

found in \fI<curl/curl.h>\fP. This function gets called by libcurl instead of

its internal equivalent with a frequent interval during data transfer.

Unknown/unused argument values will be set to zero (like if you only download

data, the upload size will remain 0). Returning a non-zero value from this

callback will cause libcurl to abort the transfer and return

\fICURLE_ABORTED_BY_CALLBACK\fP.

its internal equivalent with a frequent interval during data transfer (roughly

once per second).  Unknown/unused argument values pass to the callback will be

set to zero (like if you only download data, the upload size will remain

0). Returning a non-zero value from this callback will cause libcurl to abort

the transfer and return \fICURLE_ABORTED_BY_CALLBACK\fP.

If you transfer data with the multi interface, this function will not be

called during periods of idleness unless you call the appropriate libcurl

function that performs transfers. Usage of the \fBCURLOPT_PROGRESSFUNCTION\fP

callback is not recommended when using the multi interface.

\fICURLOPT_NOPROGRESS\fP must be set to FALSE to make this function actually

get called.