xref: /freebsd/crypto/openssl/doc/man3/CRYPTO_THREAD_run_once.pod (revision f81cdf24ba5436367377f7c8e8f51f6df2a75ca7) 
1=pod
2
3=head1 NAME
4
5CRYPTO_THREAD_run_once,
6CRYPTO_THREAD_lock_new, CRYPTO_THREAD_read_lock, CRYPTO_THREAD_write_lock,
7CRYPTO_THREAD_unlock, CRYPTO_THREAD_lock_free,
8CRYPTO_atomic_add, CRYPTO_atomic_or, CRYPTO_atomic_load - OpenSSL thread support
9
10=head1 SYNOPSIS
11
12 #include <openssl/crypto.h>
13
14 CRYPTO_ONCE CRYPTO_ONCE_STATIC_INIT;
15 int CRYPTO_THREAD_run_once(CRYPTO_ONCE *once, void (*init)(void));
16
17 CRYPTO_RWLOCK *CRYPTO_THREAD_lock_new(void);
18 int CRYPTO_THREAD_read_lock(CRYPTO_RWLOCK *lock);
19 int CRYPTO_THREAD_write_lock(CRYPTO_RWLOCK *lock);
20 int CRYPTO_THREAD_unlock(CRYPTO_RWLOCK *lock);
21 void CRYPTO_THREAD_lock_free(CRYPTO_RWLOCK *lock);
22
23 int CRYPTO_atomic_add(int *val, int amount, int *ret, CRYPTO_RWLOCK *lock);
24 int CRYPTO_atomic_or(uint64_t *val, uint64_t op, uint64_t *ret,
25                      CRYPTO_RWLOCK *lock);
26 int CRYPTO_atomic_load(uint64_t *val, uint64_t *ret, CRYPTO_RWLOCK *lock);
27
28=head1 DESCRIPTION
29
30OpenSSL can be safely used in multi-threaded applications provided that
31support for the underlying OS threading API is built-in. Currently, OpenSSL
32supports the pthread and Windows APIs. OpenSSL can also be built without
33any multi-threading support, for example on platforms that don't provide
34any threading support or that provide a threading API that is not yet
35supported by OpenSSL.
36
37The following multi-threading function are provided:
38
39=over 2
40
41=item *
42
43CRYPTO_THREAD_run_once() can be used to perform one-time initialization.
44The I<once> argument must be a pointer to a static object of type
45B<CRYPTO_ONCE> that was statically initialized to the value
46B<CRYPTO_ONCE_STATIC_INIT>.
47The I<init> argument is a pointer to a function that performs the desired
48exactly once initialization.
49In particular, this can be used to allocate locks in a thread-safe manner,
50which can then be used with the locking functions below.
51
52=item *
53
54CRYPTO_THREAD_lock_new() allocates, initializes and returns a new read/write
55lock.
56
57=item *
58
59CRYPTO_THREAD_read_lock() locks the provided I<lock> for reading.
60
61=item *
62
63CRYPTO_THREAD_write_lock() locks the provided I<lock> for writing.
64
65=item *
66
67CRYPTO_THREAD_unlock() unlocks the previously locked I<lock>.
68
69=item *
70
71CRYPTO_THREAD_lock_free() frees the provided I<lock>.
72
73=item *
74
75CRYPTO_atomic_add() atomically adds I<amount> to I<*val> and returns the
76result of the operation in I<*ret>. I<lock> will be locked, unless atomic
77operations are supported on the specific platform. Because of this, if a
78variable is modified by CRYPTO_atomic_add() then CRYPTO_atomic_add() must
79be the only way that the variable is modified. If atomic operations are not
80supported and I<lock> is NULL, then the function will fail.
81
82=item *
83
84CRYPTO_atomic_or() performs an atomic bitwise or of I<op> and I<*val> and stores
85the result back in I<*val>. It also returns the result of the operation in
86I<*ret>. I<lock> will be locked, unless atomic operations are supported on the
87specific platform. Because of this, if a variable is modified by
88CRYPTO_atomic_or() or read by CRYPTO_atomic_load() then CRYPTO_atomic_or() must
89be the only way that the variable is modified. If atomic operations are not
90supported and I<lock> is NULL, then the function will fail.
91
92=item *
93
94CRYPTO_atomic_load() atomically loads the contents of I<*val> into I<*ret>.
95I<lock> will be locked, unless atomic operations are supported on the specific
96platform. Because of this, if a variable is modified by CRYPTO_atomic_or() or
97read by CRYPTO_atomic_load() then CRYPTO_atomic_load() must be the only way that
98the variable is read. If atomic operations are not supported and I<lock> is
99NULL, then the function will fail.
100
101=back
102
103=head1 RETURN VALUES
104
105CRYPTO_THREAD_run_once() returns 1 on success, or 0 on error.
106
107CRYPTO_THREAD_lock_new() returns the allocated lock, or NULL on error.
108
109CRYPTO_THREAD_lock_free() returns no value.
110
111The other functions return 1 on success, or 0 on error.
112
113=head1 NOTES
114
115On Windows platforms the CRYPTO_THREAD_* types and functions in the
116F<< <openssl/crypto.h> >> header are dependent on some of the types
117customarily made available by including F<< <windows.h> >>. The application
118developer is likely to require control over when the latter is included,
119commonly as one of the first included headers. Therefore, it is defined as an
120application developer's responsibility to include F<< <windows.h> >> prior to
121F<< <openssl/crypto.h> >> where use of CRYPTO_THREAD_* types and functions is
122required.
123
124=head1 EXAMPLES
125
126You can find out if OpenSSL was configured with thread support:
127
128 #include <openssl/opensslconf.h>
129 #if defined(OPENSSL_THREADS)
130     /* thread support enabled */
131 #else
132     /* no thread support */
133 #endif
134
135This example safely initializes and uses a lock.
136
137 #ifdef _WIN32
138 # include <windows.h>
139 #endif
140 #include <openssl/crypto.h>
141
142 static CRYPTO_ONCE once = CRYPTO_ONCE_STATIC_INIT;
143 static CRYPTO_RWLOCK *lock;
144
145 static void myinit(void)
146 {
147     lock = CRYPTO_THREAD_lock_new();
148 }
149
150 static int mylock(void)
151 {
152     if (!CRYPTO_THREAD_run_once(&once, void init) || lock == NULL)
153         return 0;
154     return CRYPTO_THREAD_write_lock(lock);
155 }
156
157 static int myunlock(void)
158 {
159     return CRYPTO_THREAD_unlock(lock);
160 }
161
162 int serialized(void)
163 {
164     int ret = 0;
165
166     if (mylock()) {
167         /* Your code here, do not return without releasing the lock! */
168         ret = ... ;
169     }
170     myunlock();
171     return ret;
172 }
173
174Finalization of locks is an advanced topic, not covered in this example.
175This can only be done at process exit or when a dynamically loaded library is
176no longer in use and is unloaded.
177The simplest solution is to just "leak" the lock in applications and not
178repeatedly load/unload shared libraries that allocate locks.
179
180=head1 SEE ALSO
181
182L<crypto(7)>, L<openssl-threads(7)>.
183
184=head1 COPYRIGHT
185
186Copyright 2000-2021 The OpenSSL Project Authors. All Rights Reserved.
187
188Licensed under the Apache License 2.0 (the "License").  You may not use
189this file except in compliance with the License.  You can obtain a copy
190in the file LICENSE in the source distribution or at
191L<https://www.openssl.org/source/license.html>.
192
193=cut
194