curl\_multi\_socket(3) Library Functions Manual curl\_multi\_socket(3)

# [NAME](#NAME)

curl\_multi\_socket - read/write available data

# [SYNOPSIS](#SYNOPSIS)

```
#include <curl/curl.h>
CURLMcode curl_multi_socket(CURLM *multi_handle, curl_socket_t sockfd,


                            int *running_handles);
```

# [DESCRIPTION](#DESCRIPTION)

This function is deprecated. Use [*curl\_multi\_socket\_action(3)*](/man/os/curl/curl_multi_socket_action.3) instead with **ev\_bitmask** set to 0.

At return, the integer **running\_handles** points to contains the number of still running easy handles within the multi handle. When this number reaches zero, all transfers are complete/done. Note that when you call [*curl\_multi\_socket(3)*](/man/os/curl/curl_multi_socket.3) on a specific socket and the counter decreases by one, it DOES NOT necessarily mean that this exact socket/transfer is the one that completed. Use [*curl\_multi\_info\_read(3)*](/man/os/curl/curl_multi_info_read.3) to figure out which easy handle that completed.

The [*curl\_multi\_socket(3)*](/man/os/curl/curl_multi_socket.3) functions inform the application about updates in the socket (file descriptor) status by doing none, one, or multiple calls to the socket callback function set with the [*CURLMOPT\_SOCKETFUNCTION(3)*](/man/os/curl/CURLMOPT_SOCKETFUNCTION.3) option to [*curl\_multi\_setopt(3)*](/man/os/curl/curl_multi_setopt.3). They update the status with changes since the previous time the callback was called.

Get the timeout time by setting the [*CURLMOPT\_TIMERFUNCTION(3)*](/man/os/curl/CURLMOPT_TIMERFUNCTION.3) option with [*curl\_multi\_setopt(3)*](/man/os/curl/curl_multi_setopt.3). Your application then gets called with information on how long to wait for socket actions at most before doing the timeout action: call the [*curl\_multi\_socket\_action(3)*](/man/os/curl/curl_multi_socket_action.3) function with the **sockfd** argument set to CURL\_SOCKET\_TIMEOUT. You can also use the [*curl\_multi\_timeout(3)*](/man/os/curl/curl_multi_timeout.3) function to poll the value at any given time, but for an event-based system using the callback is far better than relying on polling the timeout value.

# [PROTOCOLS](#PROTOCOLS)

This functionality affects all supported protocols

# [EXAMPLE](#EXAMPLE)

```
int main(void)
{


  /* the event-library gets told when there activity on the socket 'fd',


     which we translate to a call to curl_multi_socket_action() */


  int running;


  int rc;


  int fd = 2;


  CURLM *multi = curl_multi_init();


  rc = curl_multi_socket(multi, fd, &running);
}
```

# [DEPRECATED](#DEPRECATED)

[*curl\_multi\_socket(3)*](/man/os/curl/curl_multi_socket.3) is deprecated, use [*curl\_multi\_socket\_action(3)*](/man/os/curl/curl_multi_socket_action.3) instead.

# [AVAILABILITY](#AVAILABILITY)

Added in curl 7.15.4

# [RETURN VALUE](#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)*](/man/os/curl/libcurl-errors.3).

The return code is for the whole multi stack. Problems still might have occurred on individual transfers even when one of these functions return OK.

# [SEE ALSO](#SEE_ALSO)

[**curl\_multi\_cleanup**(3)](/man/os/curl/curl_multi_cleanup.3), [**curl\_multi\_fdset**(3)](/man/os/curl/curl_multi_fdset.3), [**curl\_multi\_info\_read**(3)](/man/os/curl/curl_multi_info_read.3), [**curl\_multi\_init**(3)](/man/os/curl/curl_multi_init.3), **the**hiperfifo.c**example**

2026-10-14 libcurl

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Document: curl_multi_socket(3) from curl 8.23.0-r0 (Chainguard OS)
Source: https://github.com/curl/curl.git