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>. 72 73=item * 74 75CRYPTO_atomic_add() atomically adds I<amount> to I<*val> and returns the 76result of the operation in I<*ret>. I<lock> will be locked, unless atomic 77operations are supported on the specific platform. Because of this, if a 78variable is modified by CRYPTO_atomic_add() then CRYPTO_atomic_add() must 79be the only way that the variable is modified. If atomic operations are not 80supported and I<lock> is NULL, then the function will fail. 81 82=item * 83 84CRYPTO_atomic_or() performs an atomic bitwise or of I<op> and I<*val> and stores 85the result back in I<*val>. It also returns the result of the operation in 86I<*ret>. I<lock> will be locked, unless atomic operations are supported on the 87specific platform. Because of this, if a variable is modified by 88CRYPTO_atomic_or() or read by CRYPTO_atomic_load() then CRYPTO_atomic_or() must 89be the only way that the variable is modified. If atomic operations are not 90supported and I<lock> is NULL, then the function will fail. 91 92=item * 93 94CRYPTO_atomic_load() atomically loads the contents of I<*val> into I<*ret>. 95I<lock> will be locked, unless atomic operations are supported on the specific 96platform. Because of this, if a variable is modified by CRYPTO_atomic_or() or 97read by CRYPTO_atomic_load() then CRYPTO_atomic_load() must be the only way that 98the variable is read. If atomic operations are not supported and I<lock> is 99NULL, then the function will fail. 100 101=back 102 103=head1 RETURN VALUES 104 105CRYPTO_THREAD_run_once() returns 1 on success, or 0 on error. 106 107CRYPTO_THREAD_lock_new() returns the allocated lock, or NULL on error. 108 109CRYPTO_THREAD_lock_free() returns no value. 110 111The other functions return 1 on success, or 0 on error. 112 113=head1 NOTES 114 115On Windows platforms the CRYPTO_THREAD_* types and functions in the 116F<< <openssl/crypto.h> >> header are dependent on some of the types 117customarily made available by including F<< <windows.h> >>. The application 118developer is likely to require control over when the latter is included, 119commonly as one of the first included headers. Therefore, it is defined as an 120application developer's responsibility to include F<< <windows.h> >> prior to 121F<< <openssl/crypto.h> >> where use of CRYPTO_THREAD_* types and functions is 122required. 123 124=head1 EXAMPLES 125 126You can find out if OpenSSL was configured with thread support: 127 128 #include <openssl/opensslconf.h> 129 #if defined(OPENSSL_THREADS) 130 /* thread support enabled */ 131 #else 132 /* no thread support */ 133 #endif 134 135This example safely initializes and uses a lock. 136 137 #ifdef _WIN32 138 # include <windows.h> 139 #endif 140 #include <openssl/crypto.h> 141 142 static CRYPTO_ONCE once = CRYPTO_ONCE_STATIC_INIT; 143 static CRYPTO_RWLOCK *lock; 144 145 static void myinit(void) 146 { 147 lock = CRYPTO_THREAD_lock_new(); 148 } 149 150 static int mylock(void) 151 { 152 if (!CRYPTO_THREAD_run_once(&once, void init) || lock == NULL) 153 return 0; 154 return CRYPTO_THREAD_write_lock(lock); 155 } 156 157 static int myunlock(void) 158 { 159 return CRYPTO_THREAD_unlock(lock); 160 } 161 162 int serialized(void) 163 { 164 int ret = 0; 165 166 if (mylock()) { 167 /* Your code here, do not return without releasing the lock! */ 168 ret = ... ; 169 } 170 myunlock(); 171 return ret; 172 } 173 174Finalization of locks is an advanced topic, not covered in this example. 175This can only be done at process exit or when a dynamically loaded library is 176no longer in use and is unloaded. 177The simplest solution is to just "leak" the lock in applications and not 178repeatedly load/unload shared libraries that allocate locks. 179 180=head1 SEE ALSO 181 182L<crypto(7)>, L<openssl-threads(7)>. 183 184=head1 COPYRIGHT 185 186Copyright 2000-2021 The OpenSSL Project Authors. All Rights Reserved. 187 188Licensed under the Apache License 2.0 (the "License"). You may not use 189this file except in compliance with the License. You can obtain a copy 190in the file LICENSE in the source distribution or at 191L<https://www.openssl.org/source/license.html>. 192 193=cut 194