openssl/doc/crypto/OPENSSL_init_crypto.pod

=pod

=head1 NAME

OPENSSL_init_crypto, OPENSSL_cleanup,
OPENSSL_atexit, OPENSSL_thread_stop - OpenSSL
initialisation and deinitialisation functions

=head1 SYNOPSIS

 #include <openssl/crypto.h>

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

=head1 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 L<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 B<opts> parameter specifies which aspects of libcrypto should be
initialised. Valid options are:

=over 4

=item 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
B<OPENSSL_INIT_LOAD_CRYPTO_STRINGS> will be ignored.

=item 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
B<OPENSSL_INIT_NO_LOAD_CRYPTO_STRINGS> will be ignored.

=item 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
B<OPENSSL_INIT_NO_ADD_ALL_CIPHERS> will be ignored.

=item 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
B<OPENSSL_INIT_NO_ADD_ALL_CIPHERS> will be ignored.

=item 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
B<OPENSSL_INIT_ADD_ALL_CIPHERS> will be ignored.

=item 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
B<OPENSSL_INIT_ADD_ALL_DIGESTS> will be ignored.

=item 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.

=item 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.

=item OPENSSL_INIT_ASYNC

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

=item OPENSSL_INIT_ENGINE_RDRAND

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

=item OPENSSL_INIT_ENGINE_DYNAMIC

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

=item OPENSSL_INIT_ENGINE_OPENSSL

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

=item OPENSSL_INIT_ENGINE_CRYPTODEV

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

=item OPENSSL_INIT_ENGINE_CAPI

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

=item OPENSSL_INIT_ENGINE_PADLOCK

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

=item OPENSSL_INIT_ENGINE_DASYNC

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

=item 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 dasync
engines. This not a default option.

=back

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

 OPENSSL_INIT_start_library(OPENSSL_INIT_NO_ADD_ALL_CIPHERS
                            | OPENSSL_INIT_NO_ADD_ALL_DIGESTS, NULL);


The B<settings> parameter to OPENSSL_INIT_start_library() may be used to
provide optional settings values to an option. Currently the only option this
applies to is OPENSSL_INIT_LOAD_CONFIG. This provides the optional
OPENSSL_INIT_SET_CONF_FILENAME parameter to provide a filename to load
configuration from. If no filename is provided then the system default
configuration file is assumed. For example

 const OPENSSL_INIT_SETTINGS settings[2] = {
     { OPENSSL_INIT_SET_CONF_FILENAME, .value.type_string = "myconf.cnf" },
     { OPENSSL_INIT_SET_END, .value.type_int = 0 }
 };
 OPENSSL_init_crypto(OPENSSL_INIT_LOAD_CONFIG, settings);

The B<settings> parameter must be an array of OPENSSL_INIT_SETTINGS values
terminated with an OPENSSL_INIT_SET_END entry.

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
L<atexit(3)> 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.

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.

=head1 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 libeay32.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(). 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().

=head1 RETURN VALUES

The function OPENSSL_atexit() returns 1 on success or 0 on
error.

=head1 SEE ALSO

L<OPENSSL_init_ssl(3)>

=head1 HISTORY

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

=cut