1cb7eff45b
Reviewed-by: Richard Levitte <levitte@openssl.org> (Merged from https://github.com/openssl/openssl/pull/9847)
171 lines
4.7 KiB
Text
171 lines
4.7 KiB
Text
=pod
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=head1 NAME
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CRYPTO_THREAD_run_once,
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CRYPTO_THREAD_lock_new, CRYPTO_THREAD_read_lock, CRYPTO_THREAD_write_lock,
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CRYPTO_THREAD_unlock, CRYPTO_THREAD_lock_free,
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CRYPTO_atomic_add - OpenSSL thread support
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=head1 SYNOPSIS
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#include <openssl/crypto.h>
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CRYPTO_ONCE CRYPTO_ONCE_STATIC_INIT;
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int CRYPTO_THREAD_run_once(CRYPTO_ONCE *once, void (*init)(void));
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CRYPTO_RWLOCK *CRYPTO_THREAD_lock_new(void);
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int CRYPTO_THREAD_read_lock(CRYPTO_RWLOCK *lock);
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int CRYPTO_THREAD_write_lock(CRYPTO_RWLOCK *lock);
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int CRYPTO_THREAD_unlock(CRYPTO_RWLOCK *lock);
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void CRYPTO_THREAD_lock_free(CRYPTO_RWLOCK *lock);
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int CRYPTO_atomic_add(int *val, int amount, int *ret, CRYPTO_RWLOCK *lock);
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=head1 DESCRIPTION
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OpenSSL can be safely used in multi-threaded applications provided that
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support for the underlying OS threading API is built-in. Currently, OpenSSL
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supports the pthread and Windows APIs. OpenSSL can also be built without
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any multi-threading support, for example on platforms that don't provide
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any threading support or that provide a threading API that is not yet
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supported by OpenSSL.
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The following multi-threading function are provided:
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=over 2
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=item *
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CRYPTO_THREAD_run_once() can be used to perform one-time initialization.
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The B<once> argument must be a pointer to a static object of type
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B<CRYPTO_ONCE> that was statically initialized to the value
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B<CRYPTO_ONCE_STATIC_INIT>.
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The B<init> argument is a pointer to a function that performs the desired
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exactly once initialization.
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In particular, this can be used to allocate locks in a thread-safe manner,
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which can then be used with the locking functions below.
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=item *
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CRYPTO_THREAD_lock_new() allocates, initializes and returns a new read/write
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lock.
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=item *
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CRYPTO_THREAD_read_lock() locks the provided B<lock> for reading.
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=item *
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CRYPTO_THREAD_write_lock() locks the provided B<lock> for writing.
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=item *
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CRYPTO_THREAD_unlock() unlocks the previously locked B<lock>.
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=item *
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CRYPTO_THREAD_lock_free() frees the provided B<lock>.
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=item *
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CRYPTO_atomic_add() atomically adds B<amount> to B<val> and returns the
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result of the operation in B<ret>. B<lock> will be locked, unless atomic
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operations are supported on the specific platform. Because of this, if a
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variable is modified by CRYPTO_atomic_add() then CRYPTO_atomic_add() must
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be the only way that the variable is modified.
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=back
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=head1 RETURN VALUES
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CRYPTO_THREAD_run_once() returns 1 on success, or 0 on error.
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CRYPTO_THREAD_lock_new() returns the allocated lock, or NULL on error.
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CRYPTO_THREAD_lock_free() returns no value.
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The other functions return 1 on success, or 0 on error.
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=head1 NOTES
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On Windows platforms the CRYPTO_THREAD_* types and functions in the
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openssl/crypto.h header are dependent on some of the types customarily
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made available by including windows.h. The application developer is
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likely to require control over when the latter is included, commonly as
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one of the first included headers. Therefore it is defined as an
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application developer's responsibility to include windows.h prior to
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crypto.h where use of CRYPTO_THREAD_* types and functions is required.
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=head1 EXAMPLES
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This example safely initializes and uses a lock.
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#ifdef _WIN32
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# include <windows.h>
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#endif
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#include <openssl/crypto.h>
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static CRYPTO_ONCE once = CRYPTO_ONCE_STATIC_INIT;
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static CRYPTO_RWLOCK *lock;
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static void myinit(void)
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{
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lock = CRYPTO_THREAD_lock_new();
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}
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static int mylock(void)
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{
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if (!CRYPTO_THREAD_run_once(&once, void init) || lock == NULL)
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return 0;
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return CRYPTO_THREAD_write_lock(lock);
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}
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static int myunlock(void)
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{
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return CRYPTO_THREAD_unlock(lock);
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}
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int serialized(void)
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{
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int ret = 0;
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if (mylock()) {
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/* Your code here, do not return without releasing the lock! */
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ret = ... ;
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}
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myunlock();
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return ret;
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}
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Finalization of locks is an advanced topic, not covered in this example.
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This can only be done at process exit or when a dynamically loaded library is
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no longer in use and is unloaded.
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The simplest solution is to just "leak" the lock in applications and not
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repeatedly load/unload shared libraries that allocate locks.
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=head1 NOTES
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You can find out if OpenSSL was configured with thread support:
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#include <openssl/opensslconf.h>
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#if defined(OPENSSL_THREADS)
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/* thread support enabled */
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#else
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/* no thread support */
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#endif
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=head1 SEE ALSO
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L<crypto(7)>
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=head1 COPYRIGHT
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Copyright 2000-2019 The OpenSSL Project Authors. All Rights Reserved.
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Licensed under the OpenSSL license (the "License"). You may not use
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this file except in compliance with the License. You can obtain a copy
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in the file LICENSE in the source distribution or at
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L<https://www.openssl.org/source/license.html>.
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=cut
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