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>. 72If the argument is NULL, nothing is done. 73 74=item * 75 76CRYPTO_atomic_add() atomically adds I<amount> to I<*val> and returns the 77result of the operation in I<*ret>. I<lock> will be locked, unless atomic 78operations are supported on the specific platform. Because of this, if a 79variable is modified by CRYPTO_atomic_add() then CRYPTO_atomic_add() must 80be the only way that the variable is modified. If atomic operations are not 81supported and I<lock> is NULL, then the function will fail. 82 83=item * 84 85CRYPTO_atomic_or() performs an atomic bitwise or of I<op> and I<*val> and stores 86the result back in I<*val>. It also returns the result of the operation in 87I<*ret>. I<lock> will be locked, unless atomic operations are supported on the 88specific platform. Because of this, if a variable is modified by 89CRYPTO_atomic_or() or read by CRYPTO_atomic_load() then CRYPTO_atomic_or() must 90be the only way that the variable is modified. If atomic operations are not 91supported and I<lock> is NULL, then the function will fail. 92 93=item * 94 95CRYPTO_atomic_load() atomically loads the contents of I<*val> into I<*ret>. 96I<lock> will be locked, unless atomic operations are supported on the specific 97platform. Because of this, if a variable is modified by CRYPTO_atomic_or() or 98read by CRYPTO_atomic_load() then CRYPTO_atomic_load() must be the only way that 99the variable is read. If atomic operations are not supported and I<lock> is 100NULL, then the function will fail. 101 102=back 103 104=head1 RETURN VALUES 105 106CRYPTO_THREAD_run_once() returns 1 on success, or 0 on error. 107 108CRYPTO_THREAD_lock_new() returns the allocated lock, or NULL on error. 109 110CRYPTO_THREAD_lock_free() returns no value. 111 112The other functions return 1 on success, or 0 on error. 113 114=head1 NOTES 115 116On Windows platforms the CRYPTO_THREAD_* types and functions in the 117F<< <openssl/crypto.h> >> header are dependent on some of the types 118customarily made available by including F<< <windows.h> >>. The application 119developer is likely to require control over when the latter is included, 120commonly as one of the first included headers. Therefore, it is defined as an 121application developer's responsibility to include F<< <windows.h> >> prior to 122F<< <openssl/crypto.h> >> where use of CRYPTO_THREAD_* types and functions is 123required. 124 125=head1 EXAMPLES 126 127You can find out if OpenSSL was configured with thread support: 128 129 #include <openssl/opensslconf.h> 130 #if defined(OPENSSL_THREADS) 131 /* thread support enabled */ 132 #else 133 /* no thread support */ 134 #endif 135 136This example safely initializes and uses a lock. 137 138 #ifdef _WIN32 139 # include <windows.h> 140 #endif 141 #include <openssl/crypto.h> 142 143 static CRYPTO_ONCE once = CRYPTO_ONCE_STATIC_INIT; 144 static CRYPTO_RWLOCK *lock; 145 146 static void myinit(void) 147 { 148 lock = CRYPTO_THREAD_lock_new(); 149 } 150 151 static int mylock(void) 152 { 153 if (!CRYPTO_THREAD_run_once(&once, void init) || lock == NULL) 154 return 0; 155 return CRYPTO_THREAD_write_lock(lock); 156 } 157 158 static int myunlock(void) 159 { 160 return CRYPTO_THREAD_unlock(lock); 161 } 162 163 int serialized(void) 164 { 165 int ret = 0; 166 167 if (!mylock()) { 168 /* Do not unlock unless the lock was successfully acquired. */ 169 return 0; 170 } 171 172 /* Your code here, do not return without releasing the lock! */ 173 ret = ... ; 174 myunlock(); 175 return ret; 176 } 177 178Finalization of locks is an advanced topic, not covered in this example. 179This can only be done at process exit or when a dynamically loaded library is 180no longer in use and is unloaded. 181The simplest solution is to just "leak" the lock in applications and not 182repeatedly load/unload shared libraries that allocate locks. 183 184=head1 SEE ALSO 185 186L<crypto(7)>, L<openssl-threads(7)>. 187 188=head1 COPYRIGHT 189 190Copyright 2000-2024 The OpenSSL Project Authors. All Rights Reserved. 191 192Licensed under the Apache License 2.0 (the "License"). You may not use 193this file except in compliance with the License. You can obtain a copy 194in the file LICENSE in the source distribution or at 195L<https://www.openssl.org/source/license.html>. 196 197=cut 198