1ARES_LIBRARY_INIT(3) Library Functions Manual ARES_LIBRARY_INIT(3)
2
6 ares_library_init - c-ares library initialization
7
9 #include <ares.h>
10 int ares_library_init(int flags)
12 int ares_library_init_mem(int flags,
14 void *(*amalloc)(size_t),
15 void (*afree)(void *ptr),
16 void (*arealloc)(void *ptr, size_t size))
17
19 The ares_library_init function performs initializations internally re‐
20 quired by the c-ares library that must take place before any other
21 function provided by c-ares can be used in a program.
22 This function must be called at least once within the life of a pro‐
24 gram, before the program actually executes any other c-ares library
25 function. Initializations done by this function remain effective until
26 a number of calls to ares_library_cleanup(3) equal to the number of
27 calls to this function are performed.
28 Successive calls to this function do nothing further, only the first
30 call done when c-ares is in an uninitialized state is actually effec‐
31 tive.
32 The flags parameter is a bit pattern that tells c-ares exactly which
34 features should be initialized, as described below. Set the desired
35 bits by ORing the values together. In normal operation you should spec‐
36 ify ARES_LIB_INIT_ALL. Don't use any other value unless you are famil‐
37 iar with it and trying to control some internal c-ares feature.
38 The ares_library_init_mem function allows the caller to provide memory
40 management functions that the c-ares library will be use instead of
41 malloc(3), free(3) and realloc(3).
42 This function is not thread safe. You have to call it once the program
44 has started, but this call must be done before the program starts any
45 other thread. This is required to avoid potential race conditions in
46 library initialization, and also due to the fact that ares_li‐
47 brary_init(3) might call functions from other libraries that are thread
48 unsafe, and could conflict with any other thread that is already using
49 these other libraries.
50 On Windows platforms, the library user should ensure that WSAStartup()
52 is called before the c-ares library is initialized and used.
53 Win32/64 application DLLs shall not call ares_library_init(3) from the
55 DllMain function. Doing so will produce deadlocks and other problems.
56
58 ARES_LIB_INIT_ALL
59 Initialize everything possible. This sets all known bits.
60 ARES_LIB_INIT_WIN32
62 Initialize Win32/64 specific libraries. As of c-ares 1.19.0, this
63 is ignored as there are no currently dynamically loaded libraries.
64 ARES_LIB_INIT_NONE
66 Initialize nothing extra. This sets no bit.
67
69 Upon successful completion, ares_library_init(3) returns 0. Otherwise,
70 a non-zero error number is returned to indicate the error. Except for
71 ares_strerror(3), you shall not call any other c-ares function upon
72 ares_library_init(3) failure.
73
75 This function was first introduced in c-ares version 1.7.0 along with
76 the definition of preprocessor symbol CARES_HAVE_ARES_LIBRARY_INIT as
77 an indication of the availability of this function. Its recursive be‐
78 havior, which requires a matching number of calls to ares_li‐
79 brary_cleanup(3) in order to deinitialize the library, is present since
80 c-ares version 1.10.0. Earlier versions would deinitialize the library
81 on the first call to ares_library_cleanup(3).
82 Since the introduction of this function it is absolutely mandatory to
84 call it for any Win32/64 program using c-ares.
85 Non-Win32/64 systems can still use c-ares version 1.7.0 without calling
87 ares_library_init(3) due to the fact that currently it is nearly a do-
88 nothing function on non-Win32/64 platforms at this point.
89
91 ares_library_cleanup(3), ares_strerror(3)
92
94 Yang Tse
95 Copyright 1998 by the Massachusetts Institute of Technology.
97 Copyright (C) 2004-2009 by Daniel Stenberg.
98 19 May 2009 ARES_LIBRARY_INIT(3)