=pod

=head1 NAME

CRYPTO_THREAD_lock_new, CRYPTO_THREAD_read_lock, CRYPTO_THREAD_write_lock,
CRYPTO_THREAD_unlock, CRYPTO_THREAD_lock_free, CRYPTO_atomic_add - OpenSSL thread support

=head1 SYNOPSIS

 #include <openssl/crypto.h>

 CRYPTO_RWLOCK *CRYPTO_THREAD_lock_new(void);
 int CRYPTO_THREAD_read_lock(CRYPTO_RWLOCK *lock);
 int CRYPTO_THREAD_write_lock(CRYPTO_RWLOCK *lock);
 int CRYPTO_THREAD_unlock(CRYPTO_RWLOCK *lock);
 void CRYPTO_THREAD_lock_free(CRYPTO_RWLOCK *lock);

 int CRYPTO_atomic_add(int *val, int amount, int *ret, CRYPTO_RWLOCK *lock);

=head1 DESCRIPTION

OpenSSL can be safely used in multi-threaded applications provided that
support for the underlying OS threading API is built-in. Currently, OpenSSL
supports the pthread and Windows APIs. OpenSSL can also be built without
any multi-threading support, for example on platforms that don't provide
any threading support or that provide a threading API that is not yet
supported by OpenSSL.

The following multi-threading function are provided:

=over 4

=item *
CRYPTO_THREAD_lock_new() allocates, initializes and returns a new read/write
lock.

=item *
CRYPTO_THREAD_read_lock() locks the provided B<lock> for reading.

=item *
CRYPTO_THREAD_write_lock() locks the provided B<lock> for writing.

=item *
CRYPTO_THREAD_unlock() unlocks the previously locked B<lock>.

=item *
CRYPTO_THREAD_lock_frees() frees the provided B<lock>.

=item *
CRYPTO_atomic_add() atomically adds B<amount> to B<val> and returns the
result of the operation in B<ret>. B<lock> will be locked, unless atomic
operations are supported on the specific platform. Because of this, if a
variable is modified by CRYPTO_atomic_add() then CRYPTO_atomic_add() must
be the only way that the variable is modified.

=back

=head1 RETURN VALUES

CRYPTO_THREAD_lock_new() returns the allocated lock, or NULL on error.

CRYPTO_THREAD_lock_frees() returns no value.

The other functions return 1 on success or 0 on error.

=head1 NOTES

You can find out if OpenSSL was configured with thread support:

 #define OPENSSL_THREAD_DEFINES
 #include <openssl/opensslconf.h>
 #if defined(OPENSSL_THREADS)
   // thread support enabled
 #else
   // no thread support
 #endif

=head1 SEE ALSO

L<crypto(3)>

=cut