Go to main content

man pages section 3: Library Interfaces and Headers

Exit Print View

Updated: Thursday, June 13, 2019

curl_multi_socket (3)


curl_multi_socket - reads/writes available data


#include <curl/curl.h>
CURLMcode curl_multi_socket(CURLM * multi_handle, curl_socket_t sockfd,
int *running_handles);

CURLMcode curl_multi_socket_all(CURLM *multi_handle,
int *running_handles);


curl_multi_socket(3)            libcurl Manual            curl_multi_socket(3)

       curl_multi_socket - reads/writes available data

       #include <curl/curl.h>
       CURLMcode curl_multi_socket(CURLM * multi_handle, curl_socket_t sockfd,
                                   int *running_handles);

       CURLMcode curl_multi_socket_all(CURLM *multi_handle,
                                       int *running_handles);

       These     functions     are     deprecated.    Do    not    use!    See
       curl_multi_socket_action(3) instead!

       At return, the integer running_handles points to will contain the  num-
       ber  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_action(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)
       to figure out which easy handle that completed.

       The curl_multi_socket_action(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  CURL-
       MOPT_SOCKETFUNCTION(3)  option to 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)  option
       with  curl_multi_setopt(3).  Your application will then get 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) function with
       the sockfd argument set to CURL_SOCKET_TIMEOUT. You can  also  use  the
       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.

       Usage  of  curl_multi_socket(3)  is deprecated, whereas the function is
       equivalent to curl_multi_socket_action(3) with ev_bitmask set to 0.

       Force libcurl to (re-)check all  its  internal  sockets  and  transfers
       instead  of just a single one by calling curl_multi_socket_all(3). Note
       that there should not be any reason to use this function!

       The socket callback function uses a prototype like this

         int curl_socket_callback(CURL *easy,      /* easy handle */
                                  curl_socket_t s, /* socket */
                                  int action,      /* see values below */
                                  void *userp,    /* private callback pointer */
                                  void *socketp); /* private socket pointer */

       The callback MUST return 0.

       The easy argument is a pointer to the easy handle that deals with  this
       particular  socket.  Note  that  a  single handle may work with several
       sockets simultaneously.

       The s argument is the actual socket value as you  use  it  within  your

       The action argument to the callback has one of five values:

              CURL_POLL_NONE (0)
                     register, not interested in readiness (yet)

              CURL_POLL_IN (1)
                     register, interested in read readiness

              CURL_POLL_OUT (2)
                     register, interested in write readiness

              CURL_POLL_INOUT (3)
                     register, interested in both read and write readiness

              CURL_POLL_REMOVE (4)

       The  socketp argument is a private pointer you have previously set with
       curl_multi_assign(3) to be associated with the s socket. If no  pointer
       has  been  set, socketp will be NULL. This argument is of course a ser-
       vice to applications that want to keep certain data or structs that are
       strictly associated to the given socket.

       The  userp  argument  is a private pointer you have previously set with
       curl_multi_setopt(3) and the CURLMOPT_SOCKETDATA(3) option.

       CURLMcode type, general libcurl multi interface error code.

       Legacy: If you receive CURLM_CALL_MULTI_PERFORM, this  basically  means
       that  you  should  call curl_multi_socket(3) again, before you wait for
       more actions on libcurl's sockets. You don't have to do it immediately,
       but  the return code means that libcurl may have more data available to
       return or that there may be more data to send off before it is  "satis-

       should not be returned and no application needs to care about them.

       NOTE that 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.

       1. Create a multi handle

       2. Set the socket callback with CURLMOPT_SOCKETFUNCTION(3)

       3. Set the timeout callback with CURLMOPT_TIMERFUNCTION(3), to  get  to
       know what timeout value to use when waiting for socket activities.

       4. Add easy handles with curl_multi_add_handle()

       5.  Provide  some  means to manage the sockets libcurl is using, so you
       can check them for activity. This can be done through your  application
       code, or by way of an external library such as libevent or glib.

       6. Wait for activity on any of libcurl's sockets, use the timeout value
       your callback has been told

       7, When activity is detected, call curl_multi_socket_action()  for  the
       socket(s)  that  got action. If no activity is detected and the timeout
       expires, call curl_multi_socket_action(3) with CURL_SOCKET_TIMEOUT

       8. Go back to step 6.

       This function was added in libcurl 7.15.4, and is deemed  stable  since

       curl_multi_socket(3)  is  deprecated,  use  curl_multi_socket_action(3)

       See attributes(7) for descriptions of the following attributes:

       |Availability   | web/curl         |
       |Stability      | Uncommitted      |
       curl_multi_cleanup(3),     curl_multi_init(3),     curl_multi_fdset(3),
       curl_multi_info_read(3), the hiperfifo.c example

       This     software     was    built    from    source    available    at
       https://github.com/oracle/solaris-userland.   The  original   community
       source    was    downloaded    from    https://github.com/curl/curl/ar-

       Further information about this software can be found on the open source
       community website at http://curl.haxx.se/.

libcurl 7.16.0                    9 Jul 2006              curl_multi_socket(3)