ares_library_init3

Usage

#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))

Overview

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.