c-ares/docs/ares_library_init.3

.\"
.\" Copyright 1998 by the Massachusetts Institute of Technology.
.\" Copyright (C) 2004-2009 by Daniel Stenberg
.\" SPDX-License-Identifier: MIT
.\"
.TH ARES_LIBRARY_INIT 3 "19 May 2009"
.SH NAME
ares_library_init \- c-ares library initialization
.SH SYNOPSIS
.nf
#include <ares.h>

int ares_library_init(int \fIflags\fP)

int ares_library_init_mem(int \fIflags\fP,
                          void *(*\fIamalloc\fP)(size_t),
                          void (*\fIafree\fP)(void *ptr),
                          void (*\fIarealloc\fP)(void *ptr, size_t size))
.fi
.SH DESCRIPTION
.PP
The
.B 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.
.PP
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 \fIares_library_cleanup(3)\fP equal to the number of calls to
this function are performed.
.PP
Successive calls to this function do nothing further, only the first
call done when c-ares is in an uninitialized state is actually
effective.
.PP
The
.I 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
\fIARES_LIB_INIT_ALL\fP. Don't use any other value unless you are
familiar with it and trying to control some internal c-ares feature.
.PP
The
.B ares_library_init_mem
function allows the caller to provide memory management functions that the
c-ares library will be use instead of \fImalloc(3)\fP, \fIfree(3)\fP and
\fIrealloc(3)\fP.
.PP
.B 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 \fIares_library_init(3)\fP might call functions from other libraries that
are thread unsafe, and could conflict with any other thread that is already
using these other libraries.
.PP
On Windows platforms, the library user should ensure that \fIWSAStartup()\fP
is called before the c-ares library is initialized and used.
.PP
Win32/64 application DLLs shall not call \fIares_library_init(3)\fP from the
DllMain function. Doing so will produce deadlocks and other problems.
.SH FLAGS
.TP 5
.B ARES_LIB_INIT_ALL
Initialize everything possible. This sets all known bits.
.TP
.B 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.
.TP
.B ARES_LIB_INIT_NONE
Initialize nothing extra. This sets no bit.
.SH RETURN VALUE
Upon successful completion, \fIares_library_init(3)\fP returns 0.  Otherwise,
a non-zero error number is returned to indicate the error. Except for
\fIares_strerror(3)\fP, you shall not call any other c-ares function upon
\fIares_library_init(3)\fP failure.
.SH AVAILABILITY
This function was first introduced in c-ares version 1.7.0 along with the
definition of preprocessor symbol \fICARES_HAVE_ARES_LIBRARY_INIT\fP as an
indication of the availability of this function. Its recursive behavior, which
requires a matching number of calls to \fIares_library_cleanup(3)\fP 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
\fIares_library_cleanup(3)\fP.
.PP
Since the introduction of this function it is absolutely mandatory to
call it for any Win32/64 program using c-ares.
.PP
Non-Win32/64 systems can still use c-ares version 1.7.0 without calling
\fIares_library_init(3)\fP due to the fact that \fIcurrently\fP it is nearly
a do-nothing function on non-Win32/64 platforms at this point.
.SH SEE ALSO
.BR ares_library_cleanup (3),
.BR ares_strerror (3)