curl_multi_wait(3)

✨ NAME ✨

curl_multi_wait(3) — straight out of the Library Functions Manual, bestie — is the function that does a poll on all easy handles in a multi handle. She’s the main character when you’ve got a CURLM * and you need to know when something is happening. No cap. 💅

🎀 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 💅

Okay so here’s the tea: 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. Obsessed with the precision, honestly.

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. It’s giving “bring your own fds to the wait party.” 🫶

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. So yes, she counts everyone. 💖

🚨 Real talk, bestie: 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.) Not me warning you before you spin on that. 😭

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. Iconic behavior, fr fr. 🔥

🦋 curl_waitfd 🦋

Here’s the little struct that makes the extra-fd magic happen, bestie:

struct curl_waitfd {
  curl_socket_t fd;
  short events;
  short revents;
};

The flag vibes for events are:

• CURL_WAIT_POLLIN — bit flag to curl_waitfd.events indicating the socket should poll on read events such as new data received. New data incoming? Slay. 💌
• 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. High priority, highkey. 👑
• 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. Clear to write and unbothered. ✨

🌈 PROTOCOLS 🌈

This functionality affects all supported protocols. That’s it. Periodt. 🦋

🍓 EXAMPLE 🍓

This example is literally right here, untouched, because code should stay code:

int main(void)
{
  CURL *easy;
  CURLM *multi = curl_multi_init();
  int still_running;

  easy = curl_easy_init();

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

  do {
    CURLMcode mresult;
    int numfds;

    mresult = curl_multi_perform(multi, &still_running);

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

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

  } while(still_running);

  curl_multi_remove_handle(multi, easy);
}

🧚 AVAILABILITY 🧚

Added in curl 7.28.0. So she’s been around, bestie. 💜

👑 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). Check it and don’t let a non-zero result catch you slippin’. 😌

🌸 SEE ALSO 🌸

• curl_multi_fdset(3)
• curl_multi_perform(3)
• curl_multi_poll(3)

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Okay bye bestie — this page is from libcurl, dated 2026-10-12. curl_multi_wait(3) out. Mwah 💋💖