curl_multi_perform(3) libcurl Manual curl_multi_perform(3)
NAME
curl_multi_perform - reads/writes available data from each easy handle
SYNOPSIS
#include <curl/curl.h>
CURLMcode curl_multi_perform(CURLM *multi_handle, int *running_handles);
DESCRIPTION
When the app thinks there's data available for the multi_handle, it should call this function to
read/write whatever there is to read or write right now. curl_multi_perform() returns as soon as the
reads/writes are done. This function does not require that there actually is any data available for
reading or that data can be written, it can be called just in case. It will write the number of han-dles handles
dles that still transfer data in the second argument's integer-pointer.
When you call curl_multi_perform() and the amount of running_handles is changed from the previous
call (or is less than the amount of easy handles you've added to the multi handle), you know that
there is one or more transfers less "running". You can then call curl_multi_info_read(3) to get
information about each individual completed transfer, and that returned info includes CURLcode and
more.
RETURN VALUE
CURLMcode type, general libcurl multi interface error code.
If you receive CURLM_CALL_MULTI_PERFORM, this basically means that you should call curl_multi_perform
again, before you select() on more actions. You don't have to do it immediately, but the return code
means that libcurl may have more data available to return or that there may be more data to send off
before it is "satisfied". Do note that curl_multi_perform(3) will return CURLM_CALL_MULTI_PERFORM
only when it wants to be called again immediately. When things are fine and there are nothing immedi-ate immediate
ate it wants done, it'll return CURLM_OK and you need to wait for "action" and then call this func-tion function
tion again.
NOTE that this only returns errors etc regarding the whole multi stack. There might still have
occurred problems on individual transfers even when this function returns CURLM_OK.
TYPICAL USAGE
Most applications will use curl_multi_fdset(3) to get the multi_handle's file descriptors, then it'll
wait for action on them using select(3) and as soon as one or more of them are ready, curl_multi_per-form(3) curl_multi_perform(3)
form(3) gets called.
SEE ALSO
curl_multi_cleanup(3), curl_multi_init(3), curl_multi_fdset(3), curl_multi_info_read(3), libcurl-errors(3) libcurlerrors(3)
errors(3)
libcurl 7.9.5 1 March 2002 curl_multi_perform(3)
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