NAME

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, CRYPTO_atomic_or, CRYPTO_atomic_load, CRYPTO_atomic_load_int, OSSL_set_max_threads, OSSL_get_max_threads, OSSL_get_thread_support_flags, OSSL_THREAD_SUPPORT_FLAG_THREAD_POOL, OSSL_THREAD_SUPPORT_FLAG_DEFAULT_SPAWN - OpenSSL thread support

SYNOPSIS

 #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);
 int CRYPTO_atomic_or(uint64_t *val, uint64_t op, uint64_t *ret,
                      CRYPTO_RWLOCK *lock);
 int CRYPTO_atomic_load(uint64_t *val, uint64_t *ret, CRYPTO_RWLOCK *lock);
 int CRYPTO_atomic_load_int(int *val, int *ret, CRYPTO_RWLOCK *lock);

 int OSSL_set_max_threads(OSSL_LIB_CTX *ctx, uint64_t max_threads);
 uint64_t OSSL_get_max_threads(OSSL_LIB_CTX *ctx);
 uint32_t OSSL_get_thread_support_flags(void);

 #define OSSL_THREAD_SUPPORT_FLAG_THREAD_POOL
 #define OSSL_THREAD_SUPPORT_FLAG_DEFAULT_SPAWN

DESCRIPTION

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:

RETURN VALUES

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.

OSSL_set_max_threads() returns 1 on success and 0 on failure. Returns failure if OpenSSL-managed thread pooling is not supported (for example, if it is not supported on the current platform, or because OpenSSL is not built with the necessary support).

OSSL_get_max_threads() returns the maximum number of threads currently allowed to be used by the thread pool. If thread pooling is disabled or not available, returns 0.

OSSL_get_thread_support_flags() returns zero or more OSSL_THREAD_SUPPORT_FLAG values.

The other functions return 1 on success, or 0 on error.

NOTES

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 <openssl/crypto.h> where use of CRYPTO_THREAD_* types and functions is required.

EXAMPLES

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

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.

SEE ALSO

crypto(7), openssl-threads(7).

COPYRIGHT

Copyright 2000-2023 The OpenSSL Project Authors. All Rights Reserved.

Licensed under the Apache License 2.0 (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.