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=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
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