ARES_LIBRARY_CLEANUP(3) Introduction to Library Functions

NAME

ares_library_cleanup - c-ares library deinitialization

SYNOPSIS

#include <ares.h>

void ares_library_cleanup(void)

DESCRIPTION

The ares_library_cleanup function uninitializes the c-ares library,
freeing all resources previously acquired by ares_library_init(3)
when the library was initialized, provided there was only one single
previous call to ares_library_init(3). If there was more than one
previous call to ares_library_init(3), this function uninitializes
the c-ares library only if it is the call matching the call to
ares_library_init(3) which initialized the library (usually the very
first call to ares_library_init(3)). Other calls to
ares_library_cleanup(3) have no effect other than decrementing an
internal counter.

This function must be called when the program using c-ares will no
longer need any c-ares function. Once the program has called
ares_library_cleanup(3) sufficiently often such that the library is
uninitialised, it shall not make any further call to any c-ares
function.

This function does not cancel any pending c-ares lookups or requests
previously done. Program must use ares_cancel(3) for this purpose.

This function is not thread safe. You have to call it once the
program is about to terminate, but this call must be done once the
program has terminated every single thread that it could have
initiated. This is required to avoid potential race conditions in
library deinitialization, and also due to the fact that
ares_library_cleanup(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.

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

AVAILABILITY

This function was first introduced in c-ares version 1.7.0 along with
the definition of preprocessor symbol CARES_HAVE_ARES_LIBRARY_CLEANUP
as an indication of the availability of this function. Reference
counting in ares_library_init(3) and ares_library_cleanup(3), which
requires calls to the former function to match calls to the latter,
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_cleanup(3) due to the fact that currently it is
nearly a do-nothing function on non-Win32/64 platforms.

SEE ALSO

ares_library_init(3), ares_cancel(3)

19 May 2009 ARES_LIBRARY_CLEANUP(3)