.Dd $Mdocdate: March 26 2016 $
.Dt CRYPTO_SET_LOCKING_CALLBACK 3
.Os
.Sh NAME
.Nm CRYPTO_THREADID_set_callback ,
.Nm CRYPTO_THREADID_get_callback ,
.Nm CRYPTO_THREADID_current ,
.Nm CRYPTO_THREADID_cmp ,
.Nm CRYPTO_THREADID_cpy ,
.Nm CRYPTO_THREADID_hash ,
.Nm CRYPTO_set_locking_callback ,
.Nm CRYPTO_num_locks ,
.Nm CRYPTO_set_dynlock_create_callback ,
.Nm CRYPTO_set_dynlock_lock_callback ,
.Nm CRYPTO_set_dynlock_destroy_callback ,
.Nm CRYPTO_get_new_dynlockid ,
.Nm CRYPTO_destroy_dynlockid ,
.Nm CRYPTO_lock ,
.Nm CRYPTO_w_lock ,
.Nm CRYPTO_w_unlock ,
.Nm CRYPTO_r_lock ,
.Nm CRYPTO_r_unlock ,
.Nm CRYPTO_add ,
.Nm CRYPTO_add_lock ,
.Nm CRYPTO_set_id_callback
.Nd OpenSSL thread support
.Sh SYNOPSIS
.In openssl/crypto.h
.Bd -literal
/* 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 */
.Ed
.Pp
.Ft void
.Fo CRYPTO_THREADID_set_numeric
.Fa "CRYPTO_THREADID *id"
.Fa "unsigned long val"
.Fc
.Ft void
.Fo CRYPTO_THREADID_set_pointer
.Fa "CRYPTO_THREADID *id"
.Fa "void *ptr"
.Fc
.Ft int
.Fo CRYPTO_THREADID_set_callback
.Fa "void (*threadid_func)(CRYPTO_THREADID *)"
.Fc
.Ft void
.Fo "(*CRYPTO_THREADID_get_callback(void))"
.Fa "CRYPTO_THREADID *"
.Fc
.Ft void
.Fo CRYPTO_THREADID_current
.Fa "CRYPTO_THREADID *id"
.Fc
.Ft int
.Fo CRYPTO_THREADID_cmp
.Fa "const CRYPTO_THREADID *a"
.Fa "const CRYPTO_THREADID *b"
.Fc
.Ft void
.Fo CRYPTO_THREADID_cpy
.Fa "CRYPTO_THREADID *dest"
.Fa "const CRYPTO_THREADID *src"
.Fc
.Ft unsigned long
.Fo CRYPTO_THREADID_hash
.Fa "const CRYPTO_THREADID *id"
.Fc
.Ft int
.Fo CRYPTO_num_locks
.Fa void
.Fc
.Bd -literal
/* struct CRYPTO_dynlock_value needs to be defined by the user */
struct CRYPTO_dynlock_value;
.Ed
.Pp
.Ft void
.Fo CRYPTO_set_dynlock_create_callback
.Fa "struct CRYPTO_dynlock_value *"
.Fa "(*dyn_create_function)(char *file, int line)"
.Fc
.Ft void
.Fo CRYPTO_set_dynlock_lock_callback
.Fa "void (*dyn_lock_function)(int mode, struct CRYPTO_dynlock_value *l,\
 const char *file, int line)"
.Fc
.Ft void
.Fo CRYPTO_set_dynlock_destroy_callback
.Fa "void (*dyn_destroy_function)(struct CRYPTO_dynlock_value *l,\
 const char *file, int line)"
.Fc
.Ft int
.Fo CRYPTO_get_new_dynlockid
.Fa void
.Fc
.Ft void
.Fo CRYPTO_destroy_dynlockid
.Fa "int i"
.Fc
.Ft void
.Fo CRYPTO_lock
.Fa "int mode"
.Fa "int n"
.Fa "const char *file"
.Fa "int line"
.Fc
.Bd -literal
#define	CRYPTO_w_lock(type) \e
	CRYPTO_lock(CRYPTO_LOCK|CRYPTO_WRITE, type, __FILE__, __LINE__)
#define	CRYPTO_w_unlock(type) \e
	CRYPTO_lock(CRYPTO_UNLOCK|CRYPTO_WRITE, type, __FILE__, __LINE__)
#define	CRYPTO_r_lock(type) \e
	CRYPTO_lock(CRYPTO_LOCK|CRYPTO_READ, type, __FILE__, __LINE__)
#define	CRYPTO_r_unlock(type) \e
	CRYPTO_lock(CRYPTO_UNLOCK|CRYPTO_READ, type, __FILE__, __LINE__)
#define	CRYPTO_add(addr,amount,type) \e
	CRYPTO_add_lock(addr, amount, type, __FILE__, __LINE__)
.Ed
.Sh DESCRIPTION
OpenSSL can safely be used in multi-threaded applications provided that
at least two callback functions are set,
.Fn locking_function
and
.Fn threadid_func .
.Pp
.Fo locking_function
.Fa "int mode"
.Fa "int n"
.Fa "const char *file"
.Fa "int line"
.Fc
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.
.Pp
.Fn locking_function
must be able to handle up to
.Fn CRYPTO_num_locks
different mutex locks.
It sets the
.Fa n Ns -th
lock if
.Fa mode
includes
.Dv CRYPTO_LOCK ,
and releases it otherwise.
.Pp
.Fa file
and
.Fa line
are the file number of the function setting the lock.
They can be useful for debugging.
.Pp
.Fo threadid_func
.Fa "CRYPTO_THREADID *id"
.Fc
is needed to record the currently-executing thread's identifier into
.Fa id .
The implementation of this callback should not fill in
.Fa id
directly, but should use
.Fn CRYPTO_THREADID_set_numeric
if thread IDs are numeric, or
.Fn CRYPTO_THREADID_set_pointer
if they are pointer-based.
If the application does not register such a callback using
.Fn 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
.Va errno .
The latter is satisfactory for thread-safety if and only if the platform
has a thread-local error number facility.
.Pp
Once
.Fn threadid_func
is registered, or if the built-in default implementation is to be used,
.Bl -bullet
.It
.Fn CRYPTO_THREADID_current
records the currently-executing thread ID into the given
.Fa id
object.
.It
.Fn CRYPTO_THREADID_cmp
compares two thread IDs (returning zero for equality, i.e. the same
semantics as
.Xr memcmp 3 ) .
.It
.Fn CRYPTO_THREADID_cpy
duplicates a thread ID value.
.It
.Fn 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
.Vt long
variables and the platform's thread IDs are pointer-based \(em 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.
.El
.Pp
Additionally, OpenSSL supports dynamic locks, and sometimes, some parts
of OpenSSL need it for better performance.
To enable this, the following is required:
.Bl -bullet
.It
Three additional callback functions,
.Fn dyn_create_function ,
.Fn dyn_lock_function ,
and
.Fn dyn_destroy_function .
.It
A structure defined with the data that each lock needs to handle.
.El
.Pp
.Vt struct CRYPTO_dynlock_value
has to be defined to contain whatever structure is needed to handle locks.
.Pp
.Fo dyn_create_function
.Fa "const char *file"
.Fa "int line"
.Fc
is needed to create a lock.
Multi-threaded applications might crash at random if it is not set.
.Pp
.Fo dyn_lock_function
.Fa "int mode"
.Fa "CRYPTO_dynlock *l"
.Fa "const char *file"
.Fa "int line"
.Fc
is needed to perform locking off dynamic lock numbered n.
Multi-threaded applications might crash at random if it is not set.
.Pp
.Fo dyn_destroy_function
.Fa "CRYPTO_dynlock *l"
.Fa "const char *file"
.Fa "int line"
.Fc
is needed to destroy the lock
.Fa l .
Multi-threaded applications might crash at random if it is not set.
.Pp
.Fn CRYPTO_get_new_dynlockid
is used to create locks.
It will call
.Fn dyn_create_function
for the actual creation.
.Pp
.Fn CRYPTO_destroy_dynlockid
is used to destroy locks.
It will call
.Fn dyn_destroy_function
for the actual destruction.
.Pp
.Fn CRYPTO_lock
is used to lock and unlock the locks.
.Fa mode
is a bitfield describing what should be done with the lock.
.Fa n
is the number of the lock as returned from
.Fn CRYPTO_get_new_dynlockid .
.Fa mode
can be combined from the following values.
These values are pairwise exclusive, with undefined behaviour if misused
(for example,
.Dv CRYPTO_READ
and
.Dv CRYPTO_WRITE
should not be used together):
.Bd -literal -offset indent
CRYPTO_LOCK	0x01
CRYPTO_UNLOCK	0x02
CRYPTO_READ	0x04
CRYPTO_WRITE	0x08
.Ed
.Sh RETURN VALUES
.Fn CRYPTO_num_locks
returns the required number of locks.
.Pp
.Fn CRYPTO_get_new_dynlockid
returns the index to the newly created lock.
.Pp
The other functions return no values.
.Sh NOTES
You can find out if OpenSSL was configured with thread support:
.Bd -literal -offset indent
#define OPENSSL_THREAD_DEFINES
#include <openssl/opensslconf.h>
#if defined(OPENSSL_THREADS)
	/* thread support enabled */
#else
	/* no thread support */
#endif
.Ed
.Pp
Also, dynamic locks are currently not used internally by OpenSSL, but
may do so in the future.
.Sh EXAMPLES
.Pa crypto/threads/mttest.c
shows examples of the callback functions on Solaris, Irix and Win32.
.Sh SEE ALSO
.Xr crypto 3
.Sh HISTORY
.Fn CRYPTO_set_locking_callback
is available in all versions of SSLeay and OpenSSL.
.Fn CRYPTO_num_locks
was added in OpenSSL 0.9.4.
All functions dealing with dynamic locks were added in OpenSSL 0.9.5b-dev.
.Vt CRYPTO_THREADID
and associated functions were introduced in OpenSSL 1.0.0 to replace
(actually, deprecate) the previous
.Fn CRYPTO_set_id_callback ,
.Fn CRYPTO_get_id_callback ,
and
.Fn CRYPTO_thread_id
functions which assumed thread IDs to always be represented by
.Vt unsigned long .