5 CRYPTO_THREAD_run_once,
6 CRYPTO_THREAD_lock_new, CRYPTO_THREAD_read_lock, CRYPTO_THREAD_write_lock,
7 CRYPTO_THREAD_unlock, CRYPTO_THREAD_lock_free,
8 CRYPTO_atomic_add, CRYPTO_atomic_or, CRYPTO_atomic_load,
9 OSSL_set_max_threads, OSSL_get_max_threads,
10 OSSL_get_thread_support_flags - OpenSSL thread support
14 #include <openssl/crypto.h>
16 CRYPTO_ONCE CRYPTO_ONCE_STATIC_INIT;
17 int CRYPTO_THREAD_run_once(CRYPTO_ONCE *once, void (*init)(void));
19 CRYPTO_RWLOCK *CRYPTO_THREAD_lock_new(void);
20 int CRYPTO_THREAD_read_lock(CRYPTO_RWLOCK *lock);
21 int CRYPTO_THREAD_write_lock(CRYPTO_RWLOCK *lock);
22 int CRYPTO_THREAD_unlock(CRYPTO_RWLOCK *lock);
23 void CRYPTO_THREAD_lock_free(CRYPTO_RWLOCK *lock);
25 int CRYPTO_atomic_add(int *val, int amount, int *ret, CRYPTO_RWLOCK *lock);
26 int CRYPTO_atomic_or(uint64_t *val, uint64_t op, uint64_t *ret,
28 int CRYPTO_atomic_load(uint64_t *val, uint64_t *ret, CRYPTO_RWLOCK *lock);
30 int OSSL_set_max_threads(OSSL_LIB_CTX *ctx, uint64_t max_threads);
31 uint64_t OSSL_get_max_threads(OSSL_LIB_CTX *ctx);
32 uint32_t OSSL_get_thread_support_flags(void);
36 OpenSSL can be safely used in multi-threaded applications provided that
37 support for the underlying OS threading API is built-in. Currently, OpenSSL
38 supports the pthread and Windows APIs. OpenSSL can also be built without
39 any multi-threading support, for example on platforms that don't provide
40 any threading support or that provide a threading API that is not yet
43 The following multi-threading function are provided:
49 CRYPTO_THREAD_run_once() can be used to perform one-time initialization.
50 The I<once> argument must be a pointer to a static object of type
51 B<CRYPTO_ONCE> that was statically initialized to the value
52 B<CRYPTO_ONCE_STATIC_INIT>.
53 The I<init> argument is a pointer to a function that performs the desired
54 exactly once initialization.
55 In particular, this can be used to allocate locks in a thread-safe manner,
56 which can then be used with the locking functions below.
60 CRYPTO_THREAD_lock_new() allocates, initializes and returns a new read/write
65 CRYPTO_THREAD_read_lock() locks the provided I<lock> for reading.
69 CRYPTO_THREAD_write_lock() locks the provided I<lock> for writing.
73 CRYPTO_THREAD_unlock() unlocks the previously locked I<lock>.
77 CRYPTO_THREAD_lock_free() frees the provided I<lock>.
81 CRYPTO_atomic_add() atomically adds I<amount> to I<*val> and returns the
82 result of the operation in I<*ret>. I<lock> will be locked, unless atomic
83 operations are supported on the specific platform. Because of this, if a
84 variable is modified by CRYPTO_atomic_add() then CRYPTO_atomic_add() must
85 be the only way that the variable is modified. If atomic operations are not
86 supported and I<lock> is NULL, then the function will fail.
90 CRYPTO_atomic_or() performs an atomic bitwise or of I<op> and I<*val> and stores
91 the result back in I<*val>. It also returns the result of the operation in
92 I<*ret>. I<lock> will be locked, unless atomic operations are supported on the
93 specific platform. Because of this, if a variable is modified by
94 CRYPTO_atomic_or() or read by CRYPTO_atomic_load() then CRYPTO_atomic_or() must
95 be the only way that the variable is modified. If atomic operations are not
96 supported and I<lock> is NULL, then the function will fail.
100 CRYPTO_atomic_load() atomically loads the contents of I<*val> into I<*ret>.
101 I<lock> will be locked, unless atomic operations are supported on the specific
102 platform. Because of this, if a variable is modified by CRYPTO_atomic_or() or
103 read by CRYPTO_atomic_load() then CRYPTO_atomic_load() must be the only way that
104 the variable is read. If atomic operations are not supported and I<lock> is
105 NULL, then the function will fail.
109 OSSL_set_max_threads() sets the maximum number of threads to be used by the
110 thread pool. If the argument is 0, thread pooling is disabled. OpenSSL will
111 not create any threads and existing threads in the thread pool will be torn
112 down. The maximum thread count is a limit, not a target. Threads will not be
113 spawned unless (and until) there is demand. Thread polling is disabled by
114 default. To enable threading you must call OSSL_set_max_threads() explicitly.
115 Under no circumstances is this done for you.
121 CRYPTO_THREAD_run_once() returns 1 on success, or 0 on error.
123 CRYPTO_THREAD_lock_new() returns the allocated lock, or NULL on error.
125 CRYPTO_THREAD_lock_free() returns no value.
127 OSSL_set_max_threads() returns 1 on success and 0 on failure. Returns failure
128 if OpenSSL-managed thread pooling is not supported (for example, if it is not
129 supported on the current platform, or because OpenSSL is not built with the
132 OSSL_get_max_threads() returns the maximum number of threads currently allowed
133 to be used by the thread pool. If thread pooling is disabled or not available,
136 The other functions return 1 on success, or 0 on error.
140 On Windows platforms the CRYPTO_THREAD_* types and functions in the
141 F<< <openssl/crypto.h> >> header are dependent on some of the types
142 customarily made available by including F<< <windows.h> >>. The application
143 developer is likely to require control over when the latter is included,
144 commonly as one of the first included headers. Therefore, it is defined as an
145 application developer's responsibility to include F<< <windows.h> >> prior to
146 F<< <openssl/crypto.h> >> where use of CRYPTO_THREAD_* types and functions is
151 You can find out if OpenSSL was configured with thread support:
153 #include <openssl/opensslconf.h>
154 #if defined(OPENSSL_THREADS)
155 /* thread support enabled */
157 /* no thread support */
160 This example safely initializes and uses a lock.
163 # include <windows.h>
165 #include <openssl/crypto.h>
167 static CRYPTO_ONCE once = CRYPTO_ONCE_STATIC_INIT;
168 static CRYPTO_RWLOCK *lock;
170 static void myinit(void)
172 lock = CRYPTO_THREAD_lock_new();
175 static int mylock(void)
177 if (!CRYPTO_THREAD_run_once(&once, void init) || lock == NULL)
179 return CRYPTO_THREAD_write_lock(lock);
182 static int myunlock(void)
184 return CRYPTO_THREAD_unlock(lock);
192 /* Your code here, do not return without releasing the lock! */
199 Finalization of locks is an advanced topic, not covered in this example.
200 This can only be done at process exit or when a dynamically loaded library is
201 no longer in use and is unloaded.
202 The simplest solution is to just "leak" the lock in applications and not
203 repeatedly load/unload shared libraries that allocate locks.
207 L<crypto(7)>, L<openssl-threads(7)>.
211 Copyright 2000-2021 The OpenSSL Project Authors. All Rights Reserved.
213 Licensed under the Apache License 2.0 (the "License"). You may not use
214 this file except in compliance with the License. You can obtain a copy
215 in the file LICENSE in the source distribution or at
216 L<https://www.openssl.org/source/license.html>.