1CRYPTO_THREAD_RUN_ONCE(3) OpenSSL CRYPTO_THREAD_RUN_ONCE(3)
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 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
26 OpenSSL can be safely used in multi-threaded applications provided that
27 support for the underlying OS threading API is built-in. Currently,
28 OpenSSL supports the pthread and Windows APIs. OpenSSL can also be
29 built without any multi-threading support, for example on platforms
30 that don't provide any threading support or that provide a threading
31 API that is not yet supported by OpenSSL.
32 The following multi-threading function are provided:
34 · CRYPTO_THREAD_run_once() can be used to perform one-time
36 initialization. The once argument must be a pointer to a static
37 object of type CRYPTO_ONCE that was statically initialized to the
38 value CRYPTO_ONCE_STATIC_INIT. The init argument is a pointer to a
39 function that performs the desired exactly once initialization. In
40 particular, this can be used to allocate locks in a thread-safe
41 manner, which can then be used with the locking functions below.
42 · CRYPTO_THREAD_lock_new() allocates, initializes and returns a new
44 read/write lock.
45 · CRYPTO_THREAD_read_lock() locks the provided lock for reading.
47 · CRYPTO_THREAD_write_lock() locks the provided lock for writing.
49 · CRYPTO_THREAD_unlock() unlocks the previously locked lock.
51 · CRYPTO_THREAD_lock_free() frees the provided lock.
53 · CRYPTO_atomic_add() atomically adds amount to val and returns the
55 result of the operation in ret. lock will be locked, unless atomic
56 operations are supported on the specific platform. Because of this,
57 if a variable is modified by CRYPTO_atomic_add() then
58 CRYPTO_atomic_add() must be the only way that the variable is
59 modified.
60
62 CRYPTO_THREAD_run_once() returns 1 on success, or 0 on error.
63 CRYPTO_THREAD_lock_new() returns the allocated lock, or NULL on error.
65 CRYPTO_THREAD_lock_free() returns no value.
67 The other functions return 1 on success, or 0 on error.
69
71 On Windows platforms the CRYPTO_THREAD_* types and functions in the
72 openssl/crypto.h header are dependent on some of the types customarily
73 made available by including windows.h. The application developer is
74 likely to require control over when the latter is included, commonly as
75 one of the first included headers. Therefore, it is defined as an
76 application developer's responsibility to include windows.h prior to
77 crypto.h where use of CRYPTO_THREAD_* types and functions is required.
78
80 This example safely initializes and uses a lock.
81 #ifdef _WIN32
83 # include <windows.h>
84 #endif
85 #include <openssl/crypto.h>
86 static CRYPTO_ONCE once = CRYPTO_ONCE_STATIC_INIT;
88 static CRYPTO_RWLOCK *lock;
89 static void myinit(void)
91 {
92 lock = CRYPTO_THREAD_lock_new();
93 }
94 static int mylock(void)
96 {
97 if (!CRYPTO_THREAD_run_once(&once, void init) || lock == NULL)
98 return 0;
99 return CRYPTO_THREAD_write_lock(lock);
100 }
101 static int myunlock(void)
103 {
104 return CRYPTO_THREAD_unlock(lock);
105 }
106 int serialized(void)
108 {
109 int ret = 0;
110 if (mylock()) {
112 /* Your code here, do not return without releasing the lock! */
113 ret = ... ;
114 }
115 myunlock();
116 return ret;
117 }
118 Finalization of locks is an advanced topic, not covered in this
120 example. This can only be done at process exit or when a dynamically
121 loaded library is no longer in use and is unloaded. The simplest
122 solution is to just "leak" the lock in applications and not repeatedly
123 load/unload shared libraries that allocate locks.
124
126 You can find out if OpenSSL was configured with thread support:
127 #include <openssl/opensslconf.h>
129 #if defined(OPENSSL_THREADS)
130 /* thread support enabled */
131 #else
132 /* no thread support */
133 #endif
134
136 crypto(7)
137
139 Copyright 2000-2020 The OpenSSL Project Authors. All Rights Reserved.
140 Licensed under the OpenSSL license (the "License"). You may not use
142 this file except in compliance with the License. You can obtain a copy
143 in the file LICENSE in the source distribution or at
144 <https://www.openssl.org/source/license.html>.
1451.1.1k 2021-03-26 CRYPTO_THREAD_RUN_ONCE(3)