Provided by: libssl-doc_1.0.1f-1ubuntu2.27_all 
NAME
CRYPTO_THREADID_set_callback, CRYPTO_THREADID_get_callback, CRYPTO_THREADID_current,
CRYPTO_THREADID_cmp, CRYPTO_THREADID_cpy, CRYPTO_THREADID_hash,
CRYPTO_set_locking_callback, CRYPTO_num_locks, CRYPTO_set_dynlock_create_callback,
CRYPTO_set_dynlock_lock_callback, CRYPTO_set_dynlock_destroy_callback,
CRYPTO_get_new_dynlockid, CRYPTO_destroy_dynlockid, CRYPTO_lock - OpenSSL thread support
SYNOPSIS
#include <openssl/crypto.h>
/* Don't use this structure directly. */
typedef struct crypto_threadid_st
{
void *ptr;
unsigned long val;
} CRYPTO_THREADID;
/* Only use CRYPTO_THREADID_set_[numeric|pointer]() within callbacks */
void CRYPTO_THREADID_set_numeric(CRYPTO_THREADID *id, unsigned long val);
void CRYPTO_THREADID_set_pointer(CRYPTO_THREADID *id, void *ptr);
int CRYPTO_THREADID_set_callback(void (*threadid_func)(CRYPTO_THREADID *));
void (*CRYPTO_THREADID_get_callback(void))(CRYPTO_THREADID *);
void CRYPTO_THREADID_current(CRYPTO_THREADID *id);
int CRYPTO_THREADID_cmp(const CRYPTO_THREADID *a,
const CRYPTO_THREADID *b);
void CRYPTO_THREADID_cpy(CRYPTO_THREADID *dest,
const CRYPTO_THREADID *src);
unsigned long CRYPTO_THREADID_hash(const CRYPTO_THREADID *id);
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_dynlock_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, locking_function and threadid_func.
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
applications will crash at random if it is not set.
locking_function() must be able to handle up to CRYPTO_num_locks() different mutex locks.
It sets the n-th lock if mode & CRYPTO_LOCK, and releases it otherwise.
file and line are the file number of the function setting the lock. They can be useful for
debugging.
threadid_func(CRYPTO_THREADID *id) is needed to record the currently-executing thread's
identifier into id. The implementation of this callback should not fill in id directly,
but should use CRYPTO_THREADID_set_numeric() if thread IDs are numeric, or
CRYPTO_THREADID_set_pointer() if they are pointer-based. If the application does not
register such a callback using CRYPTO_THREADID_set_callback(), then a default
implementation is used - on Windows and BeOS this uses the system's default thread
identifying APIs, and on all other platforms it uses the address of errno. The latter is
satisfactory for thread-safety if and only if the platform has a thread-local error number
facility.
Once threadid_func() is registered, or if the built-in default implementation is to be
used;
• CRYPTO_THREADID_current() records the currently-executing thread ID into the given id
object.
• CRYPTO_THREADID_cmp() compares two thread IDs (returning zero for equality, ie. the
same semantics as memcmp()).
• CRYPTO_THREADID_cpy() duplicates a thread ID value,
• CRYPTO_THREADID_hash() returns a numeric value usable as a hash-table key. This is
usually the exact numeric or pointer-based thread ID used internally, however this
also handles the unusual case where pointers are larger than 'long' variables and the
platform's thread IDs are pointer-based - in this case, mixing is done to attempt to
produce a unique numeric value even though it is not as wide as the platform's true
thread IDs.
Additionally, OpenSSL supports dynamic locks, and sometimes, some parts of OpenSSL need it
for better performance. To enable this, the following is required:
• Three additional callback function, dyn_create_function, dyn_lock_function and
dyn_destroy_function.
• A structure defined with the data that each lock needs to handle.
struct CRYPTO_dynlock_value has to be defined to contain whatever structure is needed to
handle locks.
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.
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.
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.
CRYPTO_get_new_dynlockid() is used to create locks. It will call dyn_create_function for
the actual creation.
CRYPTO_destroy_dynlockid() is used to destroy locks. It will call dyn_destroy_function
for the actual destruction.
CRYPTO_lock() is used to lock and unlock the locks. mode is a bitfield describing what
should be done with the lock. n is the number of the lock as returned from
CRYPTO_get_new_dynlockid(). mode can be combined from the following values. These values
are pairwise exclusive, with undefined behaviour 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
CRYPTO_num_locks() returns the required number of locks.
CRYPTO_get_new_dynlockid() returns the index to the newly created lock.
The other functions return no values.
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
Also, dynamic locks are currently not used internally by OpenSSL, but may do so in the
future.
EXAMPLES
crypto/threads/mttest.c shows examples of the callback functions on Solaris, Irix and
Win32.
HISTORY
CRYPTO_set_locking_callback() is available in all versions of SSLeay and OpenSSL.
CRYPTO_num_locks() was added in OpenSSL 0.9.4. All functions dealing with dynamic locks
were added in OpenSSL 0.9.5b-dev. CRYPTO_THREADID and associated functions were
introduced in OpenSSL 1.0.0 to replace (actually, deprecate) the previous
CRYPTO_set_id_callback(), CRYPTO_get_id_callback(), and CRYPTO_thread_id() functions which
assumed thread IDs to always be represented by 'unsigned long'.
SEE ALSO
crypto(3)