threads(3)threads(3)NAME
threads, CRYPTO_set_locking_callback, CRYPTO_set_id_callback,
CRYPTO_num_locks, CRYPTO_set_dynlock_create_callback, CRYPTO_set_dyn‐
lock_lock_callback, CRYPTO_set_dynlock_destroy_callback,
CRYPTO_get_new_dynlockid, CRYPTO_destroy_dynlockid, CRYPTO_lock -
OpenSSL thread support
SYNOPSIS
#include <openssl/crypto.h>
void CRYPTO_set_locking_callback(
void (*locking_function)(int mode, int n, const char *file, int
line) ); void CRYPTO_set_id_callback(
unsigned long (*id_function)(void) ); int CRYPTO_num_locks(
void );
/* struct CRYPTO_dynlock_value needs to be defined by the user */
struct CRYPTO_dynlock_value;
void CRYPTO_set_dynlock_create_callback(
struct CRYPTO_dynlock_value * (*dyn_create_function)(char
*file, int line) ); void CRYPTO_set_dynlock_lock_callback(
void (*dyn_lock_function)(int mode, struct CRYPTO_dynlock_value
*l, const char *file, int line) ); void CRYPTO_set_dyn‐
lock_destroy_callback(
void (*dyn_destroy_function)(struct CRYPTO_dynlock_value *l,
const char *file, int line) ); int CRYPTO_get_new_dynlockid(
void ); void CRYPTO_destroy_dynlockid(
int i ); void CRYPTO_lock(
int mode,
int n,
const char *file,
int line );
#define CRYPTO_w_lock(type) \
CRYPTO_lock(CRYPTO_LOCK|CRYPTO_WRITE,type,__FILE__,__LINE__)
#define CRYPTO_w_unlock(type) \
CRYPTO_lock(CRYPTO_UNLOCK|CRYPTO_WRITE,type,__FILE__,__LINE__)
#define CRYPTO_r_lock(type) \
CRYPTO_lock(CRYPTO_LOCK|CRYPTO_READ,type,__FILE__,__LINE__)
#define CRYPTO_r_unlock(type) \
CRYPTO_lock(CRYPTO_UNLOCK|CRYPTO_READ,type,__FILE__,__LINE__)
#define CRYPTO_add(addr,amount,type) \
CRYPTO_add_lock(addr,amount,type,__FILE__,__LINE__)
DESCRIPTION
OpenSSL can safely be used in multi-threaded applications provided that
at least two callback functions are set.
The locking_function(int mode, int n, const char *file, int line) is
needed to perform locking on shared data structures. Multi-threaded
applications will crash at random if it is not set.
The locking_function() (int mode, int n, const char *file, int line) is
needed to perform locking on shared data structures. (Note that
OpenSSL uses a number of global data structures that will be implicitly
shared whenever multiple threads use OpenSSL.) Multi-threaded applica‐
tions will crash at random if it is not set.
The file and line are the file number of the function setting the lock.
They can be useful for debugging.
The id_function(void) function returns a thread ID. It is not needed
on Windows nor on platforms where getpid() returns a different ID for
each thread (most notably Linux).
Additionally, OpenSSL supports dynamic locks, and some parts of OpenSSL
need it for better performance. To enable this, the following is
required: Three additional callback functions: dyn_create_function,
dyn_lock_function and dyn_destroy_function. A structure defined with
the data that each lock needs to handle.
The struct CRYPTO_dynlock_value has to be defined to contain whatever
structure is needed to handle locks.
The dyn_create_function(const char *file, int line) is needed to create
a lock. Multi-threaded applications might crash at random if it is not
set.
The dyn_lock_function(int mode, CRYPTO_dynlock *l, const char *file,
int line) is needed to perform locking off dynamic lock numbered n.
Multi-threaded applications might crash at random if it is not set.
The dyn_destroy_function(CRYPTO_dynlock *l, const char *file, int line)
is needed to destroy the lock
l. Multi-threaded applications might crash at random if it is not set.
The CRYPTO_get_new_dynlockid() function is used to create locks. It
will call dyn_create_function for the actual creation.
The CRYPTO_destroy_dynlockid() function is used to destroy locks. It
will call dyn_destroy_function for the actual destruction.
The CRYPTO_lock() function is used to lock and unlock the locks. The
mode is a bitfield describing what should be done with the lock. The
value of n is the number of the lock as returned from the
CRYPTO_get_new_dynlockid() function. The mode can be combined from the
following values. These values are pairwise exclusive, with undefined
behavior if misused. For example, CRYPTO_READ and CRYPTO_WRITE should
not be used together: CRYPTO_LOCK 0x01 CRYPTO_UNLOCK 0x02
CRYPTO_READ 0x04 CRYPTO_WRITE 0x08
RETURN VALUES
The CRYPTO_num_locks() function returns the required number of locks.
CRYPTO_get_new_dynlockid() function returns the index to the newly cre‐
ated lock.
The other functions return no values.
NOTES
You can determine if OpenSSL was configured with thread support:
#define OPENSSL_THREAD_DEFINES #include <openssl/opensslconf.h> #if
defined(THREADS)
// thread support enabled #else
// no thread support #endif
Also, dynamic locks are not used internally by OpenSSL.
HISTORY
The CRYPTO_set_locking_callback() and CRYPTO_set_id_callback() func‐
tions are available in all versions of SSLeay and OpenSSL. The
CRYPTO_num_locks() function was added in OpenSSL 0.9.4. All functions
dealing with dynamic locks were added in OpenSSL 0.9.5b-dev.
SEE ALSO
Functions: crypto(3)threads(3)
