1CRYPTO_THREAD_RUN_ONCE(3ossl) OpenSSL CRYPTO_THREAD_RUN_ONCE(3ossl)
2
6 CRYPTO_THREAD_run_once, CRYPTO_THREAD_lock_new,
7 CRYPTO_THREAD_read_lock, CRYPTO_THREAD_write_lock,
8 CRYPTO_THREAD_unlock, CRYPTO_THREAD_lock_free, CRYPTO_atomic_add,
9 CRYPTO_atomic_or, CRYPTO_atomic_load - OpenSSL thread support
10
12 #include <openssl/crypto.h>
13 CRYPTO_ONCE CRYPTO_ONCE_STATIC_INIT;
15 int CRYPTO_THREAD_run_once(CRYPTO_ONCE *once, void (*init)(void));
16 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 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
29 OpenSSL can be safely used in multi-threaded applications provided that
30 support for the underlying OS threading API is built-in. Currently,
31 OpenSSL supports the pthread and Windows APIs. OpenSSL can also be
32 built without any multi-threading support, for example on platforms
33 that don't provide any threading support or that provide a threading
34 API that is not yet supported by OpenSSL.
35 The following multi-threading function are provided:
37 • CRYPTO_THREAD_run_once() can be used to perform one-time
39 initialization. The once argument must be a pointer to a static
40 object of type CRYPTO_ONCE that was statically initialized to the
41 value CRYPTO_ONCE_STATIC_INIT. The init argument is a pointer to a
42 function that performs the desired exactly once initialization. In
43 particular, this can be used to allocate locks in a thread-safe
44 manner, which can then be used with the locking functions below.
45 • CRYPTO_THREAD_lock_new() allocates, initializes and returns a new
47 read/write lock.
48 • CRYPTO_THREAD_read_lock() locks the provided lock for reading.
50 • CRYPTO_THREAD_write_lock() locks the provided lock for writing.
52 • CRYPTO_THREAD_unlock() unlocks the previously locked lock.
54 • CRYPTO_THREAD_lock_free() frees the provided lock.
56 • CRYPTO_atomic_add() atomically adds amount to *val and returns the
58 result of the operation in *ret. lock will be locked, unless atomic
59 operations are supported on the specific platform. Because of this,
60 if a variable is modified by CRYPTO_atomic_add() then
61 CRYPTO_atomic_add() must be the only way that the variable is
62 modified. If atomic operations are not supported and lock is NULL,
63 then the function will fail.
64 • CRYPTO_atomic_or() performs an atomic bitwise or of op and *val and
66 stores the result back in *val. It also returns the result of the
67 operation in *ret. lock will be locked, unless atomic operations are
68 supported on the specific platform. Because of this, if a variable is
69 modified by CRYPTO_atomic_or() or read by CRYPTO_atomic_load() then
70 CRYPTO_atomic_or() must be the only way that the variable is
71 modified. If atomic operations are not supported and lock is NULL,
72 then the function will fail.
73 • CRYPTO_atomic_load() atomically loads the contents of *val into *ret.
75 lock will be locked, unless atomic operations are supported on the
76 specific platform. Because of this, if a variable is modified by
77 CRYPTO_atomic_or() or read by CRYPTO_atomic_load() then
78 CRYPTO_atomic_load() must be the only way that the variable is read.
79 If atomic operations are not supported and lock is NULL, then the
80 function will fail.
81
83 CRYPTO_THREAD_run_once() returns 1 on success, or 0 on error.
84 CRYPTO_THREAD_lock_new() returns the allocated lock, or NULL on error.
86 CRYPTO_THREAD_lock_free() returns no value.
88 The other functions return 1 on success, or 0 on error.
90
92 On Windows platforms the CRYPTO_THREAD_* types and functions in the
93 <openssl/crypto.h> header are dependent on some of the types
94 customarily made available by including <windows.h>. The application
95 developer is likely to require control over when the latter is
96 included, commonly as one of the first included headers. Therefore, it
97 is defined as an application developer's responsibility to include
98 <windows.h> prior to <openssl/crypto.h> where use of CRYPTO_THREAD_*
99 types and functions is required.
100
102 You can find out if OpenSSL was configured with thread support:
103 #include <openssl/opensslconf.h>
105 #if defined(OPENSSL_THREADS)
106 /* thread support enabled */
107 #else
108 /* no thread support */
109 #endif
110 This example safely initializes and uses a lock.
112 #ifdef _WIN32
114 # include <windows.h>
115 #endif
116 #include <openssl/crypto.h>
117 static CRYPTO_ONCE once = CRYPTO_ONCE_STATIC_INIT;
119 static CRYPTO_RWLOCK *lock;
120 static void myinit(void)
122 {
123 lock = CRYPTO_THREAD_lock_new();
124 }
125 static int mylock(void)
127 {
128 if (!CRYPTO_THREAD_run_once(&once, void init) || lock == NULL)
129 return 0;
130 return CRYPTO_THREAD_write_lock(lock);
131 }
132 static int myunlock(void)
134 {
135 return CRYPTO_THREAD_unlock(lock);
136 }
137 int serialized(void)
139 {
140 int ret = 0;
141 if (mylock()) {
143 /* Your code here, do not return without releasing the lock! */
144 ret = ... ;
145 }
146 myunlock();
147 return ret;
148 }
149 Finalization of locks is an advanced topic, not covered in this
151 example. This can only be done at process exit or when a dynamically
152 loaded library is no longer in use and is unloaded. The simplest
153 solution is to just "leak" the lock in applications and not repeatedly
154 load/unload shared libraries that allocate locks.
155
157 crypto(7), openssl-threads(7).
158
160 Copyright 2000-2021 The OpenSSL Project Authors. All Rights Reserved.
161 Licensed under the Apache License 2.0 (the "License"). You may not use
163 this file except in compliance with the License. You can obtain a copy
164 in the file LICENSE in the source distribution or at
165 <https://www.openssl.org/source/license.html>.
1663.0.5 2022-07-05 CRYPTO_THREAD_RUN_ONCE(3ossl)