---
c: Copyright (C) Daniel Stenberg, <daniel@haxx.se>, et al.
SPDX-License-Identifier: curl
Title: curl_multi_poll
Section: 3
Source: libcurl
See-also:
  - curl_multi_fdset (3)
  - curl_multi_perform (3)
  - curl_multi_wait (3)
  - curl_multi_wakeup (3)
Protocol:
  - All
Added-in: 7.66.0
---

# NAME

curl_multi_poll - poll on all easy handles in a multi handle

# SYNOPSIS

~~~c
#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

~~~c
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%

# EXAMPLE

~~~c
extern void handle_fd(int);

int main(void)
{
  CURL *easy_handle;
  CURLM *multi_handle;
  int still_running = 0;
  int myfd = 2; /* this is our own file descriptor */

  multi_handle = curl_multi_init();
  easy_handle = curl_easy_init();

  /* add the individual easy handle */
  curl_multi_add_handle(multi_handle, easy_handle);

  do {
    CURLMcode mresult;
    int numfds;

    mresult = curl_multi_perform(multi_handle, &still_running);

    if(mresult == 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 */
      mresult = curl_multi_poll(multi_handle, &myown, 1, 1000, &numfds);

      if(myown.revents) {
        /* did our descriptor receive an event? */
        handle_fd(myfd);
      }
    }

    if(mresult != CURLM_OK) {
      fprintf(stderr, "curl_multi failed, code %d.\n", mresult);
      break;
    }

  } while(still_running);

  curl_multi_remove_handle(multi_handle, easy_handle);
}
~~~

# %AVAILABILITY%

# 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).
