Tribblix: manual page: curl_multi

curl_multi_poll(3) Introduction to Library Functions 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

extern void handle_fd(int);

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

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).