ARES_LIBRARY_INIT(3) Introduction to Library Functions ARES_LIBRARY_INIT(3)

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. As of c-ares 1.19.0,
this is ignored as there are no currently dynamically loaded
libraries.

ARES_LIB_INIT_NONE
Initialize nothing extra. This sets no bit.

RETURN VALUE

Upon successful completion, ares_library_init(3) returns 0.
Otherwise, a non-zero error number is 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(3) 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(3).

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)

19 May 2009 ARES_LIBRARY_INIT(3)