c-ares/ares_library_init.3

.\" $Id$
.\"
.\" Copyright 1998 by the Massachusetts Institute of Technology.
.\" Copyright (C) 2004-2009 by Daniel Stenberg
.\"
.\" Permission to use, copy, modify, and distribute this
.\" software and its documentation for any purpose and without
.\" fee is hereby granted, provided that the above copyright
.\" notice appear in all copies and that both that copyright
.\" notice and this permission notice appear in supporting
.\" documentation, and that the name of M.I.T. not be used in
.\" advertising or publicity pertaining to distribution of the
.\" software without specific, written prior permission.
.\" M.I.T. makes no representations about the suitability of
.\" this software for any purpose.  It is provided "as is"
.\" without express or implied warranty.
.\"
.TH ARES_LIBRARY_INIT 3 "19 May 2009"
.SH NAME
ares_library_init \- c-ares library initialization
.SH SYNOPSIS
.nf
.B #include <ares.h>
.PP
.B int ares_library_init(int \fIflags\fP)
.PP
.B cc file.c -lcares
.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 one time 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
call to \fIares_library_cleanup(3)\fP is performed.
.PP
Successive calls to this function do nothing, 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
.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
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.
.TP
.B ARES_LIB_INIT_NONE
Initialize nothing extra. This sets no bit.
.SH 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
\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.
.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 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)
.SH AUTHOR
Yang Tse
.PP
Copyright 1998 by the Massachusetts Institute of Technology.
.br
Copyright (C) 2004-2009 by Daniel Stenberg.