curl_multi_poll(3) Library Functions Manual curl_multi_poll(3)
NAME
curl_multi_poll - poll on all easy handles in a multi handle
SYNOPSIS
#include <curl/curl.h>
CURLMcode curl_multi_poll(CURLM *multi_handle,
struct curl_waitfd extra_fds[],
unsigned int extra_nfds,
int timeout_ms,
int *numfds);
DESCRIPTION
curl_multi_poll(3) polls all file descriptors used by the curl easy
handles contained in the given multi handle set. It blocks 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 is 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 gets populated with the total
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.
The curl_multi_wakeup(3) function can be used from another thread to
wake up this function and return faster. This is one of the details
that makes this function different than curl_multi_wait(3) which cannot
be woken up this way.
If no extra file descriptors are provided and libcurl has no file
descriptor to offer to wait for, this function instead waits during
timeout_ms milliseconds (or shorter if an internal timer indicates so).
This is the other detail that makes this function different than
curl_multi_wait(3).
This function is encouraged to be used instead of select(3) when using
the multi interface to allow applications to easier circumvent the
common 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.
PROTOCOLS
This functionality affects all supported protocols
EXAMPLE
int main(void)
{
CURL *easy_handle;
CURLM *multi_handle;
int still_running = 0;
int myfd; /* this is our own file descriptor */
/* 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) {
struct curl_waitfd myown;
myown.fd = myfd;
myown.events = CURL_WAIT_POLLIN; /* wait for input */
myown.revents = 0; /* clear it */
/* wait for activity on curl's descriptors or on our own,
or timeout */
mc = curl_multi_poll(multi_handle, &myown, 1, 1000, &numfds);
if(myown.revents) {
/* did our descriptor receive an event? */
handle_fd(myfd);
}
}
if(mc != CURLM_OK) {
fprintf(stderr, "curl_multi failed, code %d.\n", mc);
break;
}
} while(still_running);
curl_multi_remove_handle(multi_handle, easy_handle);
}
AVAILABILITY
Added in curl 7.66.0
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_wait(3),
curl_multi_wakeup(3)
libcurl 2024-08-05 curl_multi_poll(3)
curl 8.9.1 - Generated Wed Aug 7 11:01:26 CDT 2024