CRYPTO_set_locking_callback(3)
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 generally be used safely in multi-threaded applications
provided that at least two callback functions are set, the lock-
ing_function and threadid_func. Note that OpenSSL is not completely
thread-safe, and unfortunately not all global resources have the neces-
sary locks. Further, the thread-safety does not extend to things like
multiple threads using the same SSL object at the same time.
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 when-
ever 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() dif-
ferent 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 call-
back should not fill in id directly, but should use CRYPTO_THREA-
DID_set_numeric() if thread IDs are numeric, or CRYPTO_THREA-
DID_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 imple-
mentation 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 follow-
ing 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 func-
tions 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_call-
back(), CRYPTO_get_id_callback(), and CRYPTO_thread_id() functions
which assumed thread IDs to always be represented by 'unsigned long'.
SEE ALSO
crypto(3)
1.0.2t 2019-09-10 threads(3)
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