CRYPTO_THREAD_run_once, CRYPTO_THREAD_lock_new, CRYPTO_THREAD_read_lock,
CRYPTO_THREAD_write_lock, CRYPTO_THREAD_unlock, CRYPTO_THREAD_lock_free,
CRYPTO_atomic_add - OpenSSL thread support
#include <openssl/crypto.h>
CRYPTO_ONCE CRYPTO_ONCE_STATIC_INIT;
int CRYPTO_THREAD_run_once(CRYPTO_ONCE *once, void (*init)(void));
CRYPTO_RWLOCK *CRYPTO_THREAD_lock_new(void);
int CRYPTO_THREAD_read_lock(CRYPTO_RWLOCK *lock);
int CRYPTO_THREAD_write_lock(CRYPTO_RWLOCK *lock);
int CRYPTO_THREAD_unlock(CRYPTO_RWLOCK *lock);
void CRYPTO_THREAD_lock_free(CRYPTO_RWLOCK *lock);
int CRYPTO_atomic_add(int *val, int amount, int *ret, CRYPTO_RWLOCK *lock);
OpenSSL can be safely used in multi-threaded applications provided that support
for the underlying OS threading API is built-in. Currently, OpenSSL supports
the pthread and Windows APIs. OpenSSL can also be built without any
multi-threading support, for example on platforms that don't provide any
threading support or that provide a threading API that is not yet supported by
OpenSSL.
The following multi-threading function are provided:
- CRYPTO_THREAD_run_once() can be used to perform one-time
initialization. The once argument must be a pointer to a static
object of type CRYPTO_ONCE that was statically initialized to the
value CRYPTO_ONCE_STATIC_INIT. The init argument is a
pointer to a function that performs the desired exactly once
initialization. In particular, this can be used to allocate locks in a
thread-safe manner, which can then be used with the locking functions
below.
- CRYPTO_THREAD_lock_new() allocates, initializes and returns a new
read/write lock.
- CRYPTO_THREAD_read_lock() locks the provided lock for
reading.
- CRYPTO_THREAD_write_lock() locks the provided lock for
writing.
- CRYPTO_THREAD_unlock() unlocks the previously locked
lock.
- CRYPTO_THREAD_lock_free() frees the provided lock.
- CRYPTO_atomic_add() atomically adds amount to val and
returns the result of the operation in ret. lock will be
locked, unless atomic operations are supported on the specific platform.
Because of this, if a variable is modified by CRYPTO_atomic_add()
then CRYPTO_atomic_add() must be the only way that the variable is
modified.
CRYPTO_THREAD_run_once() returns 1 on success, or 0 on error.
CRYPTO_THREAD_lock_new() returns the allocated lock, or
NULL on error.
CRYPTO_THREAD_lock_free() returns no value.
The other functions return 1 on success, or 0 on error.
On Windows platforms the CRYPTO_THREAD_* types and functions in the
openssl/crypto.h header are dependent on some of the types customarily made
available by including windows.h. The application developer is likely to
require control over when the latter is included, commonly as one of the first
included headers. Therefore it is defined as an application developer's
responsibility to include windows.h prior to crypto.h where use of
CRYPTO_THREAD_* types and functions is required.
This example safely initializes and uses a lock.
#ifdef _WIN32
# include <windows.h>
#endif
#include <openssl/crypto.h>
static CRYPTO_ONCE once = CRYPTO_ONCE_STATIC_INIT;
static CRYPTO_RWLOCK *lock;
static void myinit(void)
{
lock = CRYPTO_THREAD_lock_new();
}
static int mylock(void)
{
if (!CRYPTO_THREAD_run_once(&once, void init) || lock == NULL)
return 0;
return CRYPTO_THREAD_write_lock(lock);
}
static int myunlock(void)
{
return CRYPTO_THREAD_unlock(lock);
}
int serialized(void)
{
int ret = 0;
if (mylock()) {
/* Your code here, do not return without releasing the lock! */
ret = ... ;
}
myunlock();
return ret;
}
Finalization of locks is an advanced topic, not covered in this
example. This can only be done at process exit or when a dynamically loaded
library is no longer in use and is unloaded. The simplest solution is to
just "leak" the lock in applications and not repeatedly
load/unload shared libraries that allocate locks.
You can find out if OpenSSL was configured with thread support:
#include <openssl/opensslconf.h>
#if defined(OPENSSL_THREADS)
/* thread support enabled */
#else
/* no thread support */
#endif
Copyright 2000-2018 The OpenSSL Project Authors. All Rights Reserved.
Licensed under the OpenSSL license (the "License"). You
may not use this file except in compliance with the License. You can obtain
a copy in the file LICENSE in the source distribution or at
<https://www.openssl.org/source/license.html>.