bionic (3) ares_library_init.3.gz

NAME

       ares_library_init - c-ares library initialization

SYNOPSIS

       #include <ares.h>

       int ares_library_init(int flags)

       int ares_library_init_mem(int flags,
                                 void *(*amalloc)(size_t),
                                 void (*afree)(void *ptr),
                                 void (*arealloc)(void *ptr, size_t size))

DESCRIPTION

       The  ares_library_init  function  performs initializations internally required by the c-ares library that
       must take place before any other function provided by c-ares can be used in a program.

       This function must be called at least once within the life of a  program,  before  the  program  actually
       executes any other c-ares library function.  Initializations done by this function remain effective until
       a number of calls to ares_library_cleanup(3) equal to the number of calls to this function are performed.

       Successive calls to this function do nothing further, only the first call  done  when  c-ares  is  in  an
       uninitialized state is actually effective.

       The  flags  parameter is a bit pattern that tells c-ares exactly which features should be initialized, as
       described below. Set the desired bits by ORing the  values  together.  In  normal  operation  you  should
       specify  ARES_LIB_INIT_ALL.  Don't  use  any  other  value  unless you are familiar with it and trying to
       control some internal c-ares feature.

       The ares_library_init_mem function allows the caller to provide memory management functions that  the  c-
       ares library will be use instead of malloc(3), free(3) and realloc(3).

       This  function  is not thread safe.  You have to call it once the program has started, but this call must
       be done before the program starts any other thread. This is required to avoid potential  race  conditions
       in  library  initialization, and also due to the fact that ares_library_init(3) might call functions from
       other libraries that are thread unsafe, and could conflict with any other thread that  is  already  using
       these other libraries.

       On  Windows  platforms,  the  library  user  should  ensure that WSAStartup() is called before the c-ares
       library is initialized and used.

       Win32/64 application DLLs shall not call ares_library_init(3) from the DllMain function.  Doing  so  will
       produce deadlocks and other problems.

FLAGS

       ARES_LIB_INIT_ALL
            Initialize everything possible. This sets all known bits.

       ARES_LIB_INIT_WIN32
            Initialize Win32/64 specific libraries.

       ARES_LIB_INIT_NONE
            Initialize nothing extra. This sets no bit.

RETURN VALUE

       Upon  successful  completion, ares_library_init() will return 0.  Otherwise, a non-zero error number will
       be returned to indicate the error. Except for ares_strerror(3), you  shall  not  call  any  other  c-ares
       function upon ares_library_init(3) failure.

AVAILABILITY

       This  function  was  first  introduced  in c-ares version 1.7.0 along with the definition of preprocessor
       symbol CARES_HAVE_ARES_LIBRARY_INIT as an indication of the availability of this function. Its  recursive
       behavior,  which  requires  a matching number of calls to ares_library_cleanup() in order to deinitialize
       the library, is present since c-ares version 1.10.0. Earlier versions would deinitialize the  library  on
       the first call to ares_library_cleanup().

       Since  the  introduction  of this function it is absolutely mandatory to call it for any Win32/64 program
       using c-ares.

       Non-Win32/64 systems can still use c-ares version 1.7.0 without calling ares_library_init(3) due  to  the
       fact that currently it is nearly a do-nothing function on non-Win32/64 platforms at this point.

SEE ALSO

       ares_library_cleanup(3), ares_strerror(3)

AUTHOR

       Yang Tse

       Copyright 1998 by the Massachusetts Institute of Technology.
       Copyright (C) 2004-2009 by Daniel Stenberg.

                                                   19 May 2009                              ARES_LIBRARY_INIT(3)