curl_multi_wait(3) libcurl Manual curl_multi_wait(3)
NAME
curl_multi_wait - polls on all easy handles in a multi handle
SYNOPSIS
#include <curl/curl.h>
CURLMcode curl_multi_wait(CURLM *multi_handle,
struct curl_waitfd extra_fds[],
unsigned int extra_nfds,
int timeout_ms,
int *numfds);
DESCRIPTION
curl_multi_wait(3) polls all file descriptors used by the curl easy
handles contained in the given multi handle set. It will block until
activity is detected on at least one of the handles or timeout_ms has
passed. Alternatively, if the multi handle has a pending internal
timeout that has a shorter expiry time than timeout_ms, that shorter
time will be used instead to make sure timeout accuracy is reasonably
kept.
The calling application may pass additional curl_waitfd structures
which are similar to poll(2)'s pollfd structure to be waited on in the
same call.
On completion, if numfds is non-NULL, it will be populated with the to-
tal number of file descriptors on which interesting events occurred.
This number can include both libcurl internal descriptors as well as
descriptors provided in extra_fds.
If no extra file descriptors are provided and libcurl has no file de-
scriptor to offer to wait for, this function will return immediately.
(Try curl_multi_poll(3) instead if you rather avoid this behavior.)
This function is encouraged to be used instead of select(3) when using
the multi interface to allow applications to easier circumvent the com-
mon problem with 1024 maximum file descriptors.
curl_waitfd
struct curl_waitfd {
curl_socket_t fd;
short events;
short revents;
};
CURL_WAIT_POLLIN
Bit flag to curl_waitfd.events indicating the socket should poll
on read events such as new data received.
CURL_WAIT_POLLPRI
Bit flag to curl_waitfd.events indicating the socket should poll
on high priority read events such as out of band data.
CURL_WAIT_POLLOUT
Bit flag to curl_waitfd.events indicating the socket should poll
on write events such as the socket being clear to write without
blocking.
EXAMPLE
CURL *easy_handle;
CURLM *multi_handle;
/* add the individual easy handle */
curl_multi_add_handle(multi_handle, easy_handle);
do {
CURLMcode mc;
int numfds;
mc = curl_multi_perform(multi_handle, &still_running);
if(mc == CURLM_OK ) {
/* wait for activity, timeout or "nothing" */
mc = curl_multi_wait(multi_handle, NULL, 0, 1000, &numfds);
}
if(mc != CURLM_OK) {
fprintf(stderr, "curl_multi failed, code %d.\n", mc);
break;
}
/* 'numfds' being zero means either a timeout or no file descriptors to
wait for. Try timeout on first occurrence, then assume no file
descriptors and no file descriptors to wait for means wait for 100
milliseconds. */
if(!numfds) {
repeats++; /* count number of repeated zero numfds */
if(repeats > 1) {
WAITMS(100); /* sleep 100 milliseconds */
}
}
else
repeats = 0;
} while(still_running);
curl_multi_remove_handle(multi_handle, easy_handle);
AVAILABILITY
This function was added in libcurl 7.28.0.
RETURN VALUE
CURLMcode type, general libcurl multi interface error code. See
libcurl-errors(3)
SEE ALSO
curl_multi_fdset(3), curl_multi_perform(3),curl_multi_poll(3) ,
libcurl 7.81.0 November 26, 2021 curl_multi_wait(3)
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