1=pod
2
3=head1 NAME
4
5CRYPTO_set_locking_callback, CRYPTO_set_id_callback, CRYPTO_num_locks,
6CRYPTO_set_dynlock_create_callback, CRYPTO_set_dynlock_lock_callback,
7CRYPTO_set_dynlock_destroy_callback, CRYPTO_get_new_dynlockid,
8CRYPTO_destroy_dynlockid, CRYPTO_lock - OpenSSL thread support
9
10=head1 SYNOPSIS
11
12 #include <openssl/crypto.h>
13
14 void CRYPTO_set_locking_callback(void (*locking_function)(int mode,
15        int n, const char *file, int line));
16
17 void CRYPTO_set_id_callback(unsigned long (*id_function)(void));
18
19 int CRYPTO_num_locks(void);
20
21
22 /* struct CRYPTO_dynlock_value needs to be defined by the user */
23 struct CRYPTO_dynlock_value;
24
25 void CRYPTO_set_dynlock_create_callback(struct CRYPTO_dynlock_value *
26	(*dyn_create_function)(char *file, int line));
27 void CRYPTO_set_dynlock_lock_callback(void (*dyn_lock_function)
28	(int mode, struct CRYPTO_dynlock_value *l,
29	const char *file, int line));
30 void CRYPTO_set_dynlock_destroy_callback(void (*dyn_destroy_function)
31	(struct CRYPTO_dynlock_value *l, const char *file, int line));
32
33 int CRYPTO_get_new_dynlockid(void);
34
35 void CRYPTO_destroy_dynlockid(int i);
36
37 void CRYPTO_lock(int mode, int n, const char *file, int line);
38
39 #define CRYPTO_w_lock(type)	\
40	CRYPTO_lock(CRYPTO_LOCK|CRYPTO_WRITE,type,__FILE__,__LINE__)
41 #define CRYPTO_w_unlock(type)	\
42	CRYPTO_lock(CRYPTO_UNLOCK|CRYPTO_WRITE,type,__FILE__,__LINE__)
43 #define CRYPTO_r_lock(type)	\
44	CRYPTO_lock(CRYPTO_LOCK|CRYPTO_READ,type,__FILE__,__LINE__)
45 #define CRYPTO_r_unlock(type)	\
46	CRYPTO_lock(CRYPTO_UNLOCK|CRYPTO_READ,type,__FILE__,__LINE__)
47 #define CRYPTO_add(addr,amount,type)	\
48	CRYPTO_add_lock(addr,amount,type,__FILE__,__LINE__)
49
50=head1 DESCRIPTION
51
52OpenSSL can safely be used in multi-threaded applications provided
53that at least two callback functions are set.
54
55locking_function(int mode, int n, const char *file, int line) is
56needed to perform locking on shared data structures. 
57(Note that OpenSSL uses a number of global data structures that
58will be implicitly shared whenever multiple threads use OpenSSL.)
59Multi-threaded applications will crash at random if it is not set.
60
61locking_function() must be able to handle up to CRYPTO_num_locks()
62different mutex locks. It sets the B<n>-th lock if B<mode> &
63B<CRYPTO_LOCK>, and releases it otherwise.
64
65B<file> and B<line> are the file number of the function setting the
66lock. They can be useful for debugging.
67
68id_function(void) is a function that returns a thread ID, for example
69pthread_self() if it returns an integer (see NOTES below).  It isn't
70needed on Windows nor on platforms where getpid() returns a different
71ID for each thread (see NOTES below).
72
73Additionally, OpenSSL supports dynamic locks, and sometimes, some parts
74of OpenSSL need it for better performance.  To enable this, the following
75is required:
76
77=over 4
78
79=item *
80Three additional callback function, dyn_create_function, dyn_lock_function
81and dyn_destroy_function.
82
83=item *
84A structure defined with the data that each lock needs to handle.
85
86=back
87
88struct CRYPTO_dynlock_value has to be defined to contain whatever structure
89is needed to handle locks.
90
91dyn_create_function(const char *file, int line) is needed to create a
92lock.  Multi-threaded applications might crash at random if it is not set.
93
94dyn_lock_function(int mode, CRYPTO_dynlock *l, const char *file, int line)
95is needed to perform locking off dynamic lock numbered n. Multi-threaded
96applications might crash at random if it is not set.
97
98dyn_destroy_function(CRYPTO_dynlock *l, const char *file, int line) is
99needed to destroy the lock l. Multi-threaded applications might crash at
100random if it is not set.
101
102CRYPTO_get_new_dynlockid() is used to create locks.  It will call
103dyn_create_function for the actual creation.
104
105CRYPTO_destroy_dynlockid() is used to destroy locks.  It will call
106dyn_destroy_function for the actual destruction.
107
108CRYPTO_lock() is used to lock and unlock the locks.  mode is a bitfield
109describing what should be done with the lock.  n is the number of the
110lock as returned from CRYPTO_get_new_dynlockid().  mode can be combined
111from the following values.  These values are pairwise exclusive, with
112undefined behaviour if misused (for example, CRYPTO_READ and CRYPTO_WRITE
113should not be used together):
114
115	CRYPTO_LOCK	0x01
116	CRYPTO_UNLOCK	0x02
117	CRYPTO_READ	0x04
118	CRYPTO_WRITE	0x08
119
120=head1 RETURN VALUES
121
122CRYPTO_num_locks() returns the required number of locks.
123
124CRYPTO_get_new_dynlockid() returns the index to the newly created lock.
125
126The other functions return no values.
127
128=head1 NOTES
129
130You can find out if OpenSSL was configured with thread support:
131
132 #define OPENSSL_THREAD_DEFINES
133 #include <openssl/opensslconf.h>
134 #if defined(OPENSSL_THREADS)
135   // thread support enabled
136 #else
137   // no thread support
138 #endif
139
140Also, dynamic locks are currently not used internally by OpenSSL, but
141may do so in the future.
142
143Defining id_function(void) has it's own issues.  Generally speaking,
144pthread_self() should be used, even on platforms where getpid() gives
145different answers in each thread, since that may depend on the machine
146the program is run on, not the machine where the program is being
147compiled.  For instance, Red Hat 8 Linux and earlier used
148LinuxThreads, whose getpid() returns a different value for each
149thread.  Red Hat 9 Linux and later use NPTL, which is
150Posix-conformant, and has a getpid() that returns the same value for
151all threads in a process.  A program compiled on Red Hat 8 and run on
152Red Hat 9 will therefore see getpid() returning the same value for
153all threads.
154
155There is still the issue of platforms where pthread_self() returns
156something other than an integer.  This is a bit unusual, and this
157manual has no cookbook solution for that case.
158
159=head1 EXAMPLES
160
161B<crypto/threads/mttest.c> shows examples of the callback functions on
162Solaris, Irix and Win32.
163
164=head1 HISTORY
165
166CRYPTO_set_locking_callback() and CRYPTO_set_id_callback() are
167available in all versions of SSLeay and OpenSSL.
168CRYPTO_num_locks() was added in OpenSSL 0.9.4.
169All functions dealing with dynamic locks were added in OpenSSL 0.9.5b-dev.
170
171=head1 SEE ALSO
172
173L<crypto(3)|crypto(3)>
174
175=cut
176