Tribblix: manual page: curl_multi

curl_multi_perform(3) Introduction to Library Functions

NAME

curl_multi_perform - run all transfers until it would block

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 is 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 stores 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.

PROTOCOLS

This functionality affects all supported protocols

EXAMPLE

int main(void)
{
int still_running;
CURLM *multi = curl_multi_init();
CURL *curl = curl_easy_init();
if(curl) {
curl_multi_add_handle(multi, curl);
do {
CURLMcode mc = curl_multi_perform(multi, &still_running);

if(!mc && still_running)
/* wait for activity, timeout or "nothing" */
mc = curl_multi_poll(multi, 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 curl 7.9.6

RETURN VALUE

This function returns a CURLMcode indicating success or error.

CURLM_OK (0) means everything was OK, non-zero means an error
occurred, see libcurl-errors(3).

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 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).