Skip site navigation (1)Skip section navigation (2)

FreeBSD Manual Pages

  
 
  

home | help
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 the read_fd_set argument is not a null pointer, it points to an  ob-
       ject  of	 type fd_set that on returns specifies the file	descriptors to
       be checked for being ready to read.

       If the write_fd_set argument is not a null pointer, it points to	an ob-
       ject of type fd_set that	on return specifies the	file descriptors to be
       checked for being ready to write.

       If the exc_fd_set argument is not a null	pointer, it points to  an  ob-
       ject of type fd_set that	on return specifies the	file descriptors to be
       checked for error conditions pending.

       If no file descriptors are set by libcurl, max_fd will contain -1  when
       this function returns. Otherwise	it will	contain	the highest descriptor
       number libcurl set. When	libcurl	returns	-1 in max_fd,  it  is  because
       libcurl	currently does something that isn't possible for your applica-
       tion to monitor with a socket and unfortunately you can then  not  know
       exactly	when  the current action is completed using select(). You then
       need to wait a while before you proceed and call	 curl_multi_perform(3)
       anyway. How long	to wait? We 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(3) to figure out
       how long	to wait	for action. Call curl_multi_perform(3) even if no  ac-
       tivity has been seen on the fd_sets after the timeout expires as	other-
       wise 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 de-
       scriptor	 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 stor-
       ing it will possibly save you from the crash, but will make  your  pro-
       gram 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_wait(3),
       curl_multi_timeout(3), curl_multi_perform(3), select(2)

libcurl	5.5.5		       February	03, 2016	   curl_multi_fdset(3)

NAME | SYNOPSIS | DESCRIPTION | RETURN VALUE | SEE ALSO

Want to link to this manual page? Use this URL:
<https://www.freebsd.org/cgi/man.cgi?query=curl_multi_fdset&sektion=3&manpath=FreeBSD+12.1-RELEASE+and+Ports>

home | help