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curl_multi_perform(3)               libcurl              curl_multi_perform(3)


NAME

       curl_multi_perform - reads/writes available data from easy handles


SYNOPSIS

       #include <curl/curl.h>

       CURLMcode curl_multi_perform(CURLM *multi_handle, int *running_handles);


DESCRIPTION

       This function performs transfers on all the added handles that need
       attention in a non-blocking fashion. The easy handles have previously
       been added to the multi handle with curl_multi_add_handle(3).

       When an application has found out there's data available for the
       multi_handle or a timeout has elapsed, the application should call this
       function to read/write whatever there is to read or write right now
       etc.  curl_multi_perform(3) 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 store the number of handles that still transfer
       data in the second argument's integer-pointer.

       If the amount of running_handles is changed from the previous call (or
       is less than the amount of easy handles you have 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. If an added handle fails quickly, it may never be counted as
       a running_handle. You could use curl_multi_info_read(3) to track actual
       status of the added handles in that case.

       When running_handles is set to zero (0) on the return of this function,
       there is no longer any transfers in progress.

       When this function returns error, the state of all transfers are
       uncertain and they cannot be continued. curl_multi_perform(3) should
       not be called again on the same multi handle after an error has been
       returned, unless first removing all the handles and adding new ones.


EXAMPLE

       int still_running;
       do {
         CURLMcode mc = curl_multi_perform(multi_handle, &still_running);

         if(!mc && still_running)
           /* wait for activity, timeout or "nothing" */
           mc = curl_multi_poll(multi_handle, NULL, 0, 1000, NULL);

         if(mc) {
           fprintf(stderr, "curl_multi_poll() failed, code %d.\n", (int)mc);
           break;
         }

       /* if there are still transfers, loop! */
       } while(still_running);


AVAILABILITY

       Added in 7.9.6


RETURN VALUE

       CURLMcode type, general libcurl multi interface error code.

       This function returns errors regarding the whole multi stack. Problems
       on individual transfers may have occurred even when this function
       returns CURLM_OK. Use curl_multi_info_read(3) to figure out how
       individual transfers did.


TYPICAL USAGE

       Most applications will use curl_multi_poll(3) to make libcurl wait for
       activity on any of the ongoing transfers. As soon as one or more file
       descriptor has activity or the function times out, the application
       calls curl_multi_perform(3).


SEE ALSO

       curl_multi_cleanup(3), curl_multi_init(3),  curl_multi_wait(3),
       curl_multi_add_handle(3),  curl_multi_fdset(3),
       curl_multi_info_read(3),  libcurl-errors(3)

libcurl 8.1.2                   April 26, 2023           curl_multi_perform(3)

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