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>.