NAME

       OPENSSL_INIT_new, OPENSSL_INIT_set_config_appname, OPENSSL_INIT_free, OPENSSL_init_crypto,
       OPENSSL_cleanup, OPENSSL_atexit, OPENSSL_thread_stop - OpenSSL initialisation and deinitialisation
       functions

SYNOPSIS

        #include <openssl/crypto.h>

        void OPENSSL_cleanup(void);
        int OPENSSL_init_crypto(uint64_t opts, const OPENSSL_INIT_SETTINGS *settings);
        int OPENSSL_atexit(void (*handler)(void));
        void OPENSSL_thread_stop(void);

        OPENSSL_INIT_SETTINGS *OPENSSL_INIT_new(void);
        int OPENSSL_INIT_set_config_appname(OPENSSL_INIT_SETTINGS *init,
                                            const char* name);
        void OPENSSL_INIT_free(OPENSSL_INIT_SETTINGS *init);

DESCRIPTION

       During normal operation OpenSSL (libcrypto) will allocate various resources at start up that must,
       subsequently, be freed on close down of the library.  Additionally some resources are allocated on a per
       thread basis (if the application is multi-threaded), and these resources must be freed prior to the
       thread closing.

       As of version 1.1.0 OpenSSL will automatically allocate all resources that it needs so no explicit
       initialisation is required. Similarly it will also automatically deinitialise as required.

       However, there way be situations when explicit initialisation is desirable or needed, for example when
       some non-default initialisation is required. The function OPENSSL_init_crypto() can be used for this
       purpose for libcrypto (see also OPENSSL_init_ssl(3) for the libssl equivalent).

       Numerous internal OpenSSL functions call OPENSSL_init_crypto().  Therefore, in order to perform non-
       default initialisation, OPENSSL_init_crypto() MUST be called by application code prior to any other
       OpenSSL function calls.

       The opts parameter specifies which aspects of libcrypto should be initialised. Valid options are:

       OPENSSL_INIT_NO_LOAD_CRYPTO_STRINGS
           Suppress automatic loading of the libcrypto error strings. This option is not a default option. Once
           selected subsequent calls to OPENSSL_init_crypto() with the option OPENSSL_INIT_LOAD_CRYPTO_STRINGS
           will be ignored.

       OPENSSL_INIT_LOAD_CRYPTO_STRINGS
           Automatic loading of the libcrypto error strings. With this option the library will automatically
           load the libcrypto error strings.  This option is a default option. Once selected subsequent calls to
           OPENSSL_init_crypto() with the option OPENSSL_INIT_NO_LOAD_CRYPTO_STRINGS will be ignored.

       OPENSSL_INIT_ADD_ALL_CIPHERS
           With this option the library will automatically load and make available all libcrypto ciphers. This
           option is a default option. Once selected subsequent calls to OPENSSL_init_crypto() with the option
           OPENSSL_INIT_NO_ADD_ALL_CIPHERS will be ignored.

       OPENSSL_INIT_ADD_ALL_DIGESTS
           With this option the library will automatically load and make available all libcrypto digests. This
           option is a default option. Once selected subsequent calls to OPENSSL_init_crypto() with the option
           OPENSSL_INIT_NO_ADD_ALL_CIPHERS will be ignored.

       OPENSSL_INIT_NO_ADD_ALL_CIPHERS
           With this option the library will suppress automatic loading of libcrypto ciphers. This option is not
           a default option. Once selected subsequent calls to OPENSSL_init_crypto() with the option
           OPENSSL_INIT_ADD_ALL_CIPHERS will be ignored.

       OPENSSL_INIT_NO_ADD_ALL_DIGESTS
           With this option the library will suppress automatic loading of libcrypto digests. This option is not
           a default option. Once selected subsequent calls to OPENSSL_init_crypto() with the option
           OPENSSL_INIT_ADD_ALL_DIGESTS will be ignored.

       OPENSSL_INIT_LOAD_CONFIG
           With this option an OpenSSL configuration file will be automatically loaded and used by calling
           OPENSSL_config(). This is not a default option for libcrypto.  From OpenSSL 1.1.1 this is a default
           option for libssl (see OPENSSL_init_ssl(3) for further details about libssl initialisation). See the
           description of OPENSSL_INIT_new(), below.

       OPENSSL_INIT_NO_LOAD_CONFIG
           With this option the loading of OpenSSL configuration files will be suppressed.  It is the equivalent
           of calling OPENSSL_no_config(). This is not a default option.

       OPENSSL_INIT_ASYNC
           With this option the library with automatically initialise the libcrypto async sub-library (see
           ASYNC_start_job(3)). This is a default option.

       OPENSSL_INIT_ENGINE_RDRAND
           With this option the library will automatically load and initialise the RDRAND engine (if available).
           This not a default option.

       OPENSSL_INIT_ENGINE_DYNAMIC
           With this option the library will automatically load and initialise the dynamic engine. This not a
           default option.

       OPENSSL_INIT_ENGINE_OPENSSL
           With this option the library will automatically load and initialise the openssl engine. This not a
           default option.

       OPENSSL_INIT_ENGINE_CRYPTODEV
           With this option the library will automatically load and initialise the cryptodev engine (if
           available). This not a default option.

       OPENSSL_INIT_ENGINE_CAPI
           With this option the library will automatically load and initialise the CAPI engine (if available).
           This not a default option.

       OPENSSL_INIT_ENGINE_PADLOCK
           With this option the library will automatically load and initialise the padlock engine (if
           available). This not a default option.

       OPENSSL_INIT_ENGINE_AFALG
           With this option the library will automatically load and initialise the AFALG engine. This not a
           default option.

       OPENSSL_INIT_ENGINE_ALL_BUILTIN
           With this option the library will automatically load and initialise all the built in engines listed
           above with the exception of the openssl and afalg engines. This not a default option.

       OPENSSL_INIT_ATFORK
           With this option the library will register its fork handlers.  See OPENSSL_fork_prepare(3) for
           details.

       Multiple options may be combined together in a single call to OPENSSL_init_crypto(). For example:

        OPENSSL_init_crypto(OPENSSL_INIT_NO_ADD_ALL_CIPHERS
                            | OPENSSL_INIT_NO_ADD_ALL_DIGESTS, NULL);

       The OPENSSL_cleanup() function deinitialises OpenSSL (both libcrypto and libssl). All resources allocated
       by OpenSSL are freed. Typically there should be no need to call this function directly as it is initiated
       automatically on application exit. This is done via the standard C library atexit() function. In the
       event that the application will close in a manner that will not call the registered atexit() handlers
       then the application should call OPENSSL_cleanup() directly. Developers of libraries using OpenSSL are
       discouraged from calling this function and should instead, typically, rely on auto-deinitialisation. This
       is to avoid error conditions where both an application and a library it depends on both use OpenSSL, and
       the library deinitialises it before the application has finished using it.

       Once OPENSSL_cleanup() has been called the library cannot be reinitialised.  Attempts to call
       OPENSSL_init_crypto() will fail and an ERR_R_INIT_FAIL error will be added to the error stack. Note that
       because initialisation has failed OpenSSL error strings will not be available, only an error code. This
       code can be put through the openssl errstr command line application to produce a human readable error
       (see errstr(1)).

       The OPENSSL_atexit() function enables the registration of a function to be called during
       OPENSSL_cleanup(). Stop handlers are called after deinitialisation of resources local to a thread, but
       before other process wide resources are freed. In the event that multiple stop handlers are registered,
       no guarantees are made about the order of execution.

       The OPENSSL_thread_stop() function deallocates resources associated with the current thread. Typically
       this function will be called automatically by the library when the thread exits. This should only be
       called directly if resources should be freed at an earlier time, or under the circumstances described in
       the NOTES section below.

       The OPENSSL_INIT_LOAD_CONFIG flag will load a default configuration file. For optional configuration file
       settings, an OPENSSL_INIT_SETTINGS must be created and used.  The routines OPENSSL_init_new() and
       OPENSSL_INIT_set_config_appname() can be used to allocate the object and set the application name, and
       then the object can be released with OPENSSL_INIT_free() when done.

NOTES

       Resources local to a thread are deallocated automatically when the thread exits (e.g. in a pthreads
       environment, when pthread_exit() is called). On Windows platforms this is done in response to a
       DLL_THREAD_DETACH message being sent to the libcrypto32.dll entry point. Some windows functions may cause
       threads to exit without sending this message (for example ExitProcess()). If the application uses such
       functions, then the application must free up OpenSSL resources directly via a call to
       OPENSSL_thread_stop() on each thread. Similarly this message will also not be sent if OpenSSL is linked
       statically, and therefore applications using static linking should also call OPENSSL_thread_stop() on
       each thread. Additionally if OpenSSL is loaded dynamically via LoadLibrary() and the threads are not
       destroyed until after FreeLibrary() is called then each thread should call OPENSSL_thread_stop() prior to
       the FreeLibrary() call.

       On Linux/Unix where OpenSSL has been loaded via dlopen() and the application is multi-threaded and if
       dlclose() is subsequently called prior to the threads being destroyed then OpenSSL will not be able to
       deallocate resources associated with those threads. The application should either call
       OPENSSL_thread_stop() on each thread prior to the dlclose() call, or alternatively the original dlopen()
       call should use the RTLD_NODELETE flag (where available on the platform).

RETURN VALUES

       The functions OPENSSL_init_crypto, OPENSSL_atexit() and OPENSSL_INIT_set_config_appname() return 1 on
       success or 0 on error.

SEE ALSO

       OPENSSL_init_ssl(3)

HISTORY

       The OPENSSL_init_crypto(), OPENSSL_cleanup(), OPENSSL_atexit(), OPENSSL_thread_stop(),
       OPENSSL_INIT_new(), OPENSSL_INIT_set_config_appname() and OPENSSL_INIT_free() functions were added in
       OpenSSL 1.1.0.

COPYRIGHT

       Copyright 2016-2018 The OpenSSL Project Authors. All Rights Reserved.

       Licensed under the OpenSSL license (the "License").  You may not use this file except in compliance with
       the License.  You can obtain a copy in the file LICENSE in the source distribution or at
       <https://www.openssl.org/source/license.html>.