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Re: curl_multi_fdset alternatives

From: Daniel Stenberg <>
Date: Sun, 11 Sep 2005 15:41:12 +0200 (CEST)

On Sun, 11 Sep 2005, Alexander Lazic wrote:

> Ok i try to make a little pseudo prog:

Not quite. Here's my take on a pseudo prog as I imagine the API. I'll keep
this around for future documentation, so if you have questions or improvements
on this please let me know.

struct apps {
   int fd; /* the socket of the handler */
   CURL *easy_h; /* the curl easy handler */
   int what; /* what to check for in this socket */
   int timeout; /* when to timeout */

int nsockets; /* simple-minded but here to show */

CURLM *multi_h;

/* this callback might very well be called multiple times for a single easy
    handle. Both to change the state if the 'what' but also to make it deal
    with more than one socket. */
int curl_socket_callback(CURL *easy, /* easy handle */
                          curl_socket_t s, /* socket */
                          int what, /* Why i was called */
                          long ms, /* timeout for wait */
                          void *userp); /* "private" pointer */
   struct apps *my_s =(struct apps *)userp;

   /* note that this is blatantly assuming that we haven't got info about this
      particular socket before. a real implemenation would need to do this
      better and differently */
   my_s[nsockets].fd = s;
   my_s[nsockets].what = what;
   my_s[nsockets].timeout = ms;
   my_s[nsockets].easy_h = easy;


   return 0;

} /* end of callback */

#define NSOCKETS 1000 /* suitable number, or make code that can realloc this to
                          a larger number should the need arise */

#define NEASYHANDLES 200 /* the number of simultaneous transfers we support */

void main(int argc, char **argv)

   struct apps my_s[NSOCKETS];

   /* setup all easy handles */

   easyh[0] = curl_easy_init();
   easyh[1] = curl_easy_init();
   easyh[2] = curl_easy_init();

   /* get a multi handle */
   multi_h = curl_multi_init();

   /* add all easy handles */
   for(i=0; i <= NEASYHANDLES; i++)
     curl_multi_add_handle(multi_h, easy_h[i]);

   /* open up your own sockets, pipes, file handles and whatever you want to
      use in your app */

   /* start the transfers */
                         my_s); /* pass our array to the callback */

   /* at this point, you should have got to know about a fair amount of
      sockets from libcurl and you have your own set, wait for action */

   for(i=0; i<nsockets; i++) {
     /* Set up structs to enable waiting on action on sockets. This could
        involve setting fd_sets for select(), or filling in pollfd structs for
        poll() or other things depending on what underlying function/system you
        intend to use */


   do {

     /* Wait for action(s) on sockets or timeout. The action can be on your own
        sockets or on libcurl's sockets. */


     /* If the function returned and there is action to be done on a libcurl
        socket, you figure out what socket it was and what the related easy
        handle for it is, and you call curl_multi_socket() telling libcurl.
        You point out a callback and userp again since libcurl may very well
        update the state of its sockets for us.*/

     curl_multi_socket(multi_h, thissocket, thiseasyh
                       curl_socket_callback, my_s);

   } while(!done);


   return 0; /* success! */

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Received on 2005-09-11