curl_multi_socket_action(3libcurl Manuacurl_multi_socket_action(3)


     curl_multi_socket_action - reads/writes available data given
     an action


     #include <curl/curl.h>

     CURLMcode curl_multi_socket_action(CURLM * multi_handle,
                                        curl_socket_t sockfd,
                                        int ev_bitmask,
                                        int *running_handles);


     When the application has detected action on a socket handled
     by  libcurl, it should call curl_multi_socket_action(3) with
     the sockfd argument set to the socket with the action.  When
     the  events  on a socket are known, they can be passed as an
     events bitmask ev_bitmask by first setting ev_bitmask to  0,
     and  then  adding  using  bitwise  OR (|) any combination of
     events to be chosen from  CURL_CSELECT_IN,  CURL_CSELECT_OUT
     or  CURL_CSELECT_ERR.  When  the  events  on  a  socket  are
     unknown, pass 0 instead, and libcurl will test the  descrip-
     tor   internally.   It   is   also   permissible   to   pass
     CURL_SOCKET_TIMEOUT to the sockfd parameter in order to ini-
     tiate the whole process or when a timeout occurs.

     At return, running_handles points to the number  of  running
     easy  handles  within  the  multi  handle.  When this number
     reaches zero, all transfers are complete/done. 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

     The curl_multi_socket_action(3) functions inform the  appli-
     cation  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) 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)  func-
     tion  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.

libcurl 7.58.0     Last change: June 07, 2016                   1

curl_multi_socket_action(3libcurl Manuacurl_multi_socket_action(3)


     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,
                                                   NULL if not
                                                   previously assigned with
                                                   curl_multi_assign(3) */

     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 system.

     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 readi-

          CURL_POLL_REMOVE (4)

     The socketp argument is a private pointer  you  have  previ-
     ously  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 service 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


     CURLMcode type, general libcurl multi interface error code.

libcurl 7.58.0     Last change: June 07, 2016                   2

curl_multi_socket_action(3libcurl Manuacurl_multi_socket_action(3)

     Before     version     7.20.0:      If      you      receive
     CURLM_CALL_MULTI_PERFORM,  this  basically  means  that  you
     should call  curl_multi_socket_action(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 "satisfied".

     The return code from this function 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. Set the timeout callback with CURLMOPT_TIMERFUNCTION,  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. Call  curl_multi_socket_action(...,  CURL_SOCKET_TIMEOUT,
     0,  ...)   to kickstart everything. To get one or more call-
     backs called.

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

     8,      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.


     This function was added in libcurl  7.15.4,  and  is  deemed
     stable since 7.16.0.


     curl_multi_cleanup(3),                   curl_multi_init(3),
     curl_multi_fdset(3),       curl_multi_info_read(3),      the
     hiperfifo.c example

libcurl 7.58.0     Last change: June 07, 2016                   3

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