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, CRYPTO_atomic_add - OpenSSL thread support
11 #include <openssl/crypto.h>
13 CRYPTO_ONCE CRYPTO_ONCE_STATIC_INIT;
14 int CRYPTO_THREAD_run_once(CRYPTO_ONCE *once, void (*init)(void));
16 CRYPTO_RWLOCK *CRYPTO_THREAD_lock_new(void);
17 int CRYPTO_THREAD_read_lock(CRYPTO_RWLOCK *lock);
18 int CRYPTO_THREAD_write_lock(CRYPTO_RWLOCK *lock);
19 int CRYPTO_THREAD_unlock(CRYPTO_RWLOCK *lock);
20 void CRYPTO_THREAD_lock_free(CRYPTO_RWLOCK *lock);
22 int CRYPTO_atomic_add(int *val, int amount, int *ret, CRYPTO_RWLOCK *lock);
26 OpenSSL can be safely used in multi-threaded applications provided that
27 support for the underlying OS threading API is built-in. Currently, OpenSSL
28 supports the pthread and Windows APIs. OpenSSL can also be built without
29 any multi-threading support, for example on platforms that don't provide
30 any threading support or that provide a threading API that is not yet
33 The following multi-threading function are provided:
38 CRYPTO_THREAD_run_once() can be used to perform one-time initialization.
39 The B<once> argument must be a pointer to a static object of type
40 B<CRYPTO_ONCE> that was statically initialized to the value
41 B<CRYPTO_ONCE_STATIC_INIT>.
42 The B<init> argument is a pointer to a function that performs the desired
43 exactly once initialization.
44 In particular, this can be used to allocate locks in a thread-safe manner,
45 which can then be used with the locking functions below.
48 CRYPTO_THREAD_lock_new() allocates, initializes and returns a new read/write
52 CRYPTO_THREAD_read_lock() locks the provided B<lock> for reading.
55 CRYPTO_THREAD_write_lock() locks the provided B<lock> for writing.
58 CRYPTO_THREAD_unlock() unlocks the previously locked B<lock>.
61 CRYPTO_THREAD_lock_frees() frees the provided B<lock>.
64 CRYPTO_atomic_add() atomically adds B<amount> to B<val> and returns the
65 result of the operation in B<ret>. B<lock> will be locked, unless atomic
66 operations are supported on the specific platform. Because of this, if a
67 variable is modified by CRYPTO_atomic_add() then CRYPTO_atomic_add() must
68 be the only way that the variable is modified.
74 CRYPTO_THREAD_run_once() returns 1 on success, or 0 on error.
76 CRYPTO_THREAD_lock_new() returns the allocated lock, or NULL on error.
78 CRYPTO_THREAD_lock_frees() returns no value.
80 The other functions return 1 on success or 0 on error.
84 This example safely initializes and uses a lock.
86 #include <openssl/crypto.h>
88 static CRYPTO_ONCE once = CRYPTO_ONCE_STATIC_INIT;
89 static CRYPTO_RWLOCK *lock;
91 static void myinit(void)
93 lock = CRYPTO_THREAD_lock_new();
96 static int mylock(void)
98 if (!CRYPTO_THREAD_run_once(&once, void init) || lock == NULL)
100 return CRYPTO_THREAD_write_lock(lock);
103 static int myunlock(void)
105 return CRYPTO_THREAD_unlock(lock);
113 /* Your code here, do not return without releasing the lock! */
120 Finalization of locks is an advanced topic, not covered in this example.
121 This can only be done at process exit or when a dynamically loaded library is
122 no longer in use and is unloaded.
123 The simplest solution is to just "leak" the lock in applications and not
124 repeatedly load/unload shared libraries that allocate locks.
128 You can find out if OpenSSL was configured with thread support:
130 #include <openssl/opensslconf.h>
131 #if defined(OPENSSL_THREADS)
132 // thread support enabled
145 Copyright 2000-2016 The OpenSSL Project Authors. All Rights Reserved.
147 Licensed under the OpenSSL license (the "License"). You may not use
148 this file except in compliance with the License. You can obtain a copy
149 in the file LICENSE in the source distribution or at
150 L<https://www.openssl.org/source/license.html>.