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curl_multi_fdset(3)                            libcurl Manual                            curl_multi_fdset(3)



NAME
       curl_multi_fdset - extracts file descriptor information from a multi handle

SYNOPSIS
       #include <curl/curl.h>

       CURLMcode curl_multi_fdset(CURLM *multi_handle,
                                  fd_set *read_fd_set,
                                  fd_set *write_fd_set,
                                  fd_set *exc_fd_set,
                                  int *max_fd);

DESCRIPTION
       This  function  extracts  file descriptor information from a given multi_handle.  libcurl returns its
       fd_set sets. The application can use these to select() on, but be sure to FD_ZERO them before calling
       this  function  as  curl_multi_fdset(3)  only  adds its own descriptors, it doesn't zero or otherwise
       remove any others. The curl_multi_perform(3) function should be called as soon  as  one  of  them  is
       ready to be read from or written to.

       If  no file descriptors are set by libcurl, max_fd will contain -1 when this function returns. Other-wise Otherwise
       wise it will contain the higher descriptor number libcurl set. When libcurl returns -1 in max_fd,  it
       is  because libcurl currently does something that isn't possible for your application to monitor with
       a socket and unfortunately you can then not know exactly when the current action is  completed  using
       select().  When  max_fd  returns  with  -1,  you  need  to  wait  a  while  and then proceed and call
       curl_multi_perform anyway. How long to wait? I would suggest 100 milliseconds at least, but  you  may
       want to test it out in your own particular conditions to find a suitable value.

       When  doing  select(),  you  should use curl_multi_timeout to figure out how long to wait for action.
       Call curl_multi_perform even if no activity has been seen on the fd_sets after the timeout expires as
       otherwise internal retries and timeouts may not work as you'd think and want.

       If  one  of the sockets used by libcurl happens to be larger than what can be set in an fd_set, which
       on POSIX systems means that the file descriptor is larger than FD_SETSIZE, then libcurl will  try  to
       not set it. Setting a too large file descriptor in an fd_set implies an out of bounds write which can
       cause crashes, or worse. The effect of NOT storing it will possibly save you from the crash, but will
       make your program NOT wait for sockets it should wait for...

RETURN VALUE
       CURLMcode type, general libcurl multi interface error code. See libcurl-errors(3)

SEE ALSO
       curl_multi_cleanup(3), curl_multi_init(3), curl_multi_timeout(3), curl_multi_perform(3)



libcurl 7.16.0                                   2 Jan 2006                              curl_multi_fdset(3)