xref: /aosp_15_r20/external/curl/docs/libcurl/curl_multi_wait.md (revision 6236dae45794135f37c4eb022389c904c8b0090d)

---
c: Copyright (C) Daniel Stenberg, <[email protected]>, et al.
SPDX-License-Identifier: curl
Title: curl_multi_wait
Section: 3
Source: libcurl
See-also:
  - curl_multi_fdset (3)
  - curl_multi_perform (3)
  - curl_multi_poll (3)
Protocol:
  - All
Added-in: 7.28.0
---

# NAME

curl_multi_wait - poll on all easy handles in a multi handle

# SYNOPSIS

~~~c
#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 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 being 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*.

If no extra file descriptors are provided and libcurl has no file descriptor
to offer to wait for, this function returns immediately. (Consider using
curl_multi_poll(3) to 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 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
int main(void)
{
  CURL *easy;
  CURLM *multi = curl_multi_init();
  int still_running;

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

  do {
    CURLMcode mc;
    int numfds;

    mc = curl_multi_perform(multi, &still_running);

    if(mc == CURLM_OK) {
      /* wait for activity, timeout or "nothing" */
      mc = curl_multi_wait(multi, NULL, 0, 1000, &numfds);
    }

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

  } while(still_running);

  curl_multi_remove_handle(multi, easy);
}
~~~

# %AVAILABILITY%

# RETURN VALUE

CURLMcode type, general libcurl multi interface error code. See
libcurl-errors(3)