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, CRYPTO_atomic_store, 9CRYPTO_atomic_load_int, 10OSSL_set_max_threads, OSSL_get_max_threads, 11OSSL_get_thread_support_flags, OSSL_THREAD_SUPPORT_FLAG_THREAD_POOL, 12OSSL_THREAD_SUPPORT_FLAG_DEFAULT_SPAWN - OpenSSL thread support 13 14=head1 SYNOPSIS 15 16 #include <openssl/crypto.h> 17 18 CRYPTO_ONCE CRYPTO_ONCE_STATIC_INIT; 19 int CRYPTO_THREAD_run_once(CRYPTO_ONCE *once, void (*init)(void)); 20 21 CRYPTO_RWLOCK *CRYPTO_THREAD_lock_new(void); 22 int CRYPTO_THREAD_read_lock(CRYPTO_RWLOCK *lock); 23 int CRYPTO_THREAD_write_lock(CRYPTO_RWLOCK *lock); 24 int CRYPTO_THREAD_unlock(CRYPTO_RWLOCK *lock); 25 void CRYPTO_THREAD_lock_free(CRYPTO_RWLOCK *lock); 26 27 int CRYPTO_atomic_add(int *val, int amount, int *ret, CRYPTO_RWLOCK *lock); 28 int CRYPTO_atomic_or(uint64_t *val, uint64_t op, uint64_t *ret, 29 CRYPTO_RWLOCK *lock); 30 int CRYPTO_atomic_load(uint64_t *val, uint64_t *ret, CRYPTO_RWLOCK *lock); 31 int CRYPTO_atomic_store(uint64_t *dst, uint64_t val, CRYPTO_RWLOCK *lock); 32 int CRYPTO_atomic_load_int(int *val, int *ret, CRYPTO_RWLOCK *lock); 33 34 int OSSL_set_max_threads(OSSL_LIB_CTX *ctx, uint64_t max_threads); 35 uint64_t OSSL_get_max_threads(OSSL_LIB_CTX *ctx); 36 uint32_t OSSL_get_thread_support_flags(void); 37 38 #define OSSL_THREAD_SUPPORT_FLAG_THREAD_POOL 39 #define OSSL_THREAD_SUPPORT_FLAG_DEFAULT_SPAWN 40 41=head1 DESCRIPTION 42 43OpenSSL can be safely used in multi-threaded applications provided that 44support for the underlying OS threading API is built-in. Currently, OpenSSL 45supports the pthread and Windows APIs. OpenSSL can also be built without 46any multi-threading support, for example on platforms that don't provide 47any threading support or that provide a threading API that is not yet 48supported by OpenSSL. 49 50The following multi-threading function are provided: 51 52=over 2 53 54=item * 55 56CRYPTO_THREAD_run_once() can be used to perform one-time initialization. 57The I<once> argument must be a pointer to a static object of type 58B<CRYPTO_ONCE> that was statically initialized to the value 59B<CRYPTO_ONCE_STATIC_INIT>. 60The I<init> argument is a pointer to a function that performs the desired 61exactly once initialization. 62In particular, this can be used to allocate locks in a thread-safe manner, 63which can then be used with the locking functions below. 64 65=item * 66 67CRYPTO_THREAD_lock_new() allocates, initializes and returns a new read/write 68lock. 69 70=item * 71 72CRYPTO_THREAD_read_lock() locks the provided I<lock> for reading. 73 74=item * 75 76CRYPTO_THREAD_write_lock() locks the provided I<lock> for writing. 77 78=item * 79 80CRYPTO_THREAD_unlock() unlocks the previously locked I<lock>. 81 82=item * 83 84CRYPTO_THREAD_lock_free() frees the provided I<lock>. 85 86=item * 87 88CRYPTO_atomic_add() atomically adds I<amount> to I<*val> and returns the 89result of the operation in I<*ret>. I<lock> will be locked, unless atomic 90operations are supported on the specific platform. Because of this, if a 91variable is modified by CRYPTO_atomic_add() then CRYPTO_atomic_add() must 92be the only way that the variable is modified. If atomic operations are not 93supported and I<lock> is NULL, then the function will fail. 94 95=item * 96 97CRYPTO_atomic_or() performs an atomic bitwise or of I<op> and I<*val> and stores 98the result back in I<*val>. It also returns the result of the operation in 99I<*ret>. I<lock> will be locked, unless atomic operations are supported on the 100specific platform. Because of this, if a variable is modified by 101CRYPTO_atomic_or() or read by CRYPTO_atomic_load() then CRYPTO_atomic_or() must 102be the only way that the variable is modified. If atomic operations are not 103supported and I<lock> is NULL, then the function will fail. 104 105=item * 106 107CRYPTO_atomic_load() atomically loads the contents of I<*val> into I<*ret>. 108I<lock> will be locked, unless atomic operations are supported on the specific 109platform. Because of this, if a variable is modified by CRYPTO_atomic_or() or 110read by CRYPTO_atomic_load() then CRYPTO_atomic_load() must be the only way that 111the variable is read. If atomic operations are not supported and I<lock> is 112NULL, then the function will fail. 113 114=item * 115 116CRYPTO_atomic_store() atomically stores the contents of I<val> into I<*dst>. 117I<lock> will be locked, unless atomic operations are supported on the specific 118platform. 119 120=item * 121 122CRYPTO_atomic_load_int() works identically to CRYPTO_atomic_load() but operates 123on an I<int> value instead of a I<uint64_t> value. 124 125=item * 126 127OSSL_set_max_threads() sets the maximum number of threads to be used by the 128thread pool. If the argument is 0, thread pooling is disabled. OpenSSL will 129not create any threads and existing threads in the thread pool will be torn 130down. The maximum thread count is a limit, not a target. Threads will not be 131spawned unless (and until) there is demand. Thread polling is disabled by 132default. To enable threading you must call OSSL_set_max_threads() explicitly. 133Under no circumstances is this done for you. 134 135=item * 136 137OSSL_get_thread_support_flags() determines what thread pool functionality 138OpenSSL is compiled with and is able to support in the current run time 139environment. B<OSSL_THREAD_SUPPORT_FLAG_THREAD_POOL> indicates that the base 140thread pool functionality is available, and 141B<OSSL_THREAD_SUPPORT_FLAG_DEFAULT_SPAWN> indicates that the default thread pool 142model is available. The default thread pool model is currently the only model 143available, therefore both of these flags must be set for thread pool 144functionality to be used. 145 146=back 147 148=head1 RETURN VALUES 149 150CRYPTO_THREAD_run_once() returns 1 on success, or 0 on error. 151 152CRYPTO_THREAD_lock_new() returns the allocated lock, or NULL on error. 153 154CRYPTO_THREAD_lock_free() returns no value. 155 156OSSL_set_max_threads() returns 1 on success and 0 on failure. Returns failure 157if OpenSSL-managed thread pooling is not supported (for example, if it is not 158supported on the current platform, or because OpenSSL is not built with the 159necessary support). 160 161OSSL_get_max_threads() returns the maximum number of threads currently allowed 162to be used by the thread pool. If thread pooling is disabled or not available, 163returns 0. 164 165OSSL_get_thread_support_flags() returns zero or more B<OSSL_THREAD_SUPPORT_FLAG> 166values. 167 168The other functions return 1 on success, or 0 on error. 169 170=head1 NOTES 171 172On Windows platforms the CRYPTO_THREAD_* types and functions in the 173F<< <openssl/crypto.h> >> header are dependent on some of the types 174customarily made available by including F<< <windows.h> >>. The application 175developer is likely to require control over when the latter is included, 176commonly as one of the first included headers. Therefore, it is defined as an 177application developer's responsibility to include F<< <windows.h> >> prior to 178F<< <openssl/crypto.h> >> where use of CRYPTO_THREAD_* types and functions is 179required. 180 181=head1 EXAMPLES 182 183You can find out if OpenSSL was configured with thread support: 184 185 #include <openssl/opensslconf.h> 186 #if defined(OPENSSL_THREADS) 187 /* thread support enabled */ 188 #else 189 /* no thread support */ 190 #endif 191 192This example safely initializes and uses a lock. 193 194 #ifdef _WIN32 195 # include <windows.h> 196 #endif 197 #include <openssl/crypto.h> 198 199 static CRYPTO_ONCE once = CRYPTO_ONCE_STATIC_INIT; 200 static CRYPTO_RWLOCK *lock; 201 202 static void myinit(void) 203 { 204 lock = CRYPTO_THREAD_lock_new(); 205 } 206 207 static int mylock(void) 208 { 209 if (!CRYPTO_THREAD_run_once(&once, void init) || lock == NULL) 210 return 0; 211 return CRYPTO_THREAD_write_lock(lock); 212 } 213 214 static int myunlock(void) 215 { 216 return CRYPTO_THREAD_unlock(lock); 217 } 218 219 int serialized(void) 220 { 221 int ret = 0; 222 223 if (mylock()) { 224 /* Your code here, do not return without releasing the lock! */ 225 ret = ... ; 226 } 227 myunlock(); 228 return ret; 229 } 230 231Finalization of locks is an advanced topic, not covered in this example. 232This can only be done at process exit or when a dynamically loaded library is 233no longer in use and is unloaded. 234The simplest solution is to just "leak" the lock in applications and not 235repeatedly load/unload shared libraries that allocate locks. 236 237=head1 SEE ALSO 238 239L<crypto(7)>, L<openssl-threads(7)>. 240 241=head1 HISTORY 242 243CRYPTO_atomic_store() was added in OpenSSL 3.4.0 244 245=head1 COPYRIGHT 246 247Copyright 2000-2023 The OpenSSL Project Authors. All Rights Reserved. 248 249Licensed under the Apache License 2.0 (the "License"). You may not use 250this file except in compliance with the License. You can obtain a copy 251in the file LICENSE in the source distribution or at 252L<https://www.openssl.org/source/license.html>. 253 254=cut 255