=pod

=head1 NAME

OSSL_LIB_CTX, OSSL_LIB_CTX_new, OSSL_LIB_CTX_free, OSSL_LIB_CTX_load_config,
OSSL_LIB_CTX_get0_global_default, OSSL_LIB_CTX_set0_default
- OpenSSL library context

=head1 SYNOPSIS

 #include <openssl/crypto.h>

 typedef struct ossl_lib_ctx_st OSSL_LIB_CTX;

 OSSL_LIB_CTX *OSSL_LIB_CTX_new(void);
 int OSSL_LIB_CTX_load_config(OSSL_LIB_CTX *ctx, const char *config_file);
 void OSSL_LIB_CTX_free(OSSL_LIB_CTX *ctx);
 OSSL_LIB_CTX *OSSL_LIB_CTX_get0_global_default(void);
 OSSL_LIB_CTX *OSSL_LIB_CTX_set0_default(OSSL_LIB_CTX *ctx);

=head1 DESCRIPTION

B<OSSL_LIB_CTX> is an internal OpenSSL library context type.
Applications may allocate their own, but may also use NULL to use
a default context with functions that take an B<OSSL_LIB_CTX>
argument.

When a non default library context is in use care should be taken with
multi-threaded applications to properly clean up thread local resources before
the OSSL_LIB_CTX is freed.
See L<OPENSSL_thread_stop_ex(3)> for more information.

OSSL_LIB_CTX_new() creates a new OpenSSL library context.

OSSL_LIB_CTX_load_config() loads a configuration file using the given C<ctx>.
This can be used to associate a library context with providers that are loaded
from a configuration.

OSSL_LIB_CTX_free() frees the given I<ctx>, unless it happens to be the
default OpenSSL library context.

OSSL_LIB_CTX_get0_global_default() returns a concrete (non NULL) reference to
the global default library context.

OSSL_LIB_CTX_set0_default() sets the default OpenSSL library context to be
I<ctx> in the current thread.  The previous default library context is
returned.  Care should be taken by the caller to restore the previous
default library context with a subsequent call of this function. If I<ctx> is
NULL then no change is made to the default library context, but a pointer to
the current library context is still returned. On a successful call of this
function the returned value will always be a concrete (non NULL) library
context.

Care should be taken when changing the default library context and starting
async jobs (see L<ASYNC_start_job(3)>), as the default library context when
the job is started will be used throughout the lifetime of an async job, no
matter how the calling thread makes further default library context changes
in the mean time.  This means that the calling thread must not free the
library context that was the default at the start of the async job before
that job has finished.

=head1 RETURN VALUES

OSSL_LIB_CTX_new(), OSSL_LIB_CTX_get0_global_default() and
OSSL_LIB_CTX_set0_default() return a library context pointer on success, or NULL
on error.

OSSL_LIB_CTX_free() doesn't return any value.

=head1 HISTORY

OSSL_LIB_CTX, OSSL_LIB_CTX_new(), OSSL_LIB_CTX_load_config(),
OSSL_LIB_CTX_free(), OSSL_LIB_CTX_get0_global_default() and
OSSL_LIB_CTX_set0_default() were added in OpenSSL 3.0.

=head1 COPYRIGHT

Copyright 2019-2021 The OpenSSL Project Authors. All Rights Reserved.

Licensed under the Apache License 2.0 (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
L<https://www.openssl.org/source/license.html>.

=cut
