284 lines
9.1 KiB
Groff
284 lines
9.1 KiB
Groff
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.\" ========================================================================
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.\"
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.IX Title "CRYPTO_THREAD_RUN_ONCE 3"
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.TH CRYPTO_THREAD_RUN_ONCE 3 "2020-12-08" "1.1.1i" "OpenSSL"
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.\" For nroff, turn off justification. Always turn off hyphenation; it makes
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.\" way too many mistakes in technical documents.
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.if n .ad l
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.nh
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.SH "NAME"
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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
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.SH "SYNOPSIS"
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.IX Header "SYNOPSIS"
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.Vb 1
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\& #include <openssl/crypto.h>
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\&
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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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\&
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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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\&
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\& int CRYPTO_atomic_add(int *val, int amount, int *ret, CRYPTO_RWLOCK *lock);
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.Ve
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.SH "DESCRIPTION"
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.IX Header "DESCRIPTION"
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OpenSSL can be safely used in multi-threaded applications provided that
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support for the underlying \s-1OS\s0 threading \s-1API\s0 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 \s-1API\s0 that is not yet
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supported by OpenSSL.
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.PP
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The following multi-threading function are provided:
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.IP "\(bu" 2
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\&\fBCRYPTO_THREAD_run_once()\fR can be used to perform one-time initialization.
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The \fBonce\fR argument must be a pointer to a static object of type
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\&\fB\s-1CRYPTO_ONCE\s0\fR that was statically initialized to the value
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\&\fB\s-1CRYPTO_ONCE_STATIC_INIT\s0\fR.
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The \fBinit\fR 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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.IP "\(bu" 2
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\&\fBCRYPTO_THREAD_lock_new()\fR allocates, initializes and returns a new read/write
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lock.
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.IP "\(bu" 2
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\&\fBCRYPTO_THREAD_read_lock()\fR locks the provided \fBlock\fR for reading.
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.IP "\(bu" 2
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\&\fBCRYPTO_THREAD_write_lock()\fR locks the provided \fBlock\fR for writing.
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.IP "\(bu" 2
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\&\fBCRYPTO_THREAD_unlock()\fR unlocks the previously locked \fBlock\fR.
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.IP "\(bu" 2
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\&\fBCRYPTO_THREAD_lock_free()\fR frees the provided \fBlock\fR.
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.IP "\(bu" 2
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\&\fBCRYPTO_atomic_add()\fR atomically adds \fBamount\fR to \fBval\fR and returns the
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result of the operation in \fBret\fR. \fBlock\fR 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 \fBCRYPTO_atomic_add()\fR then \fBCRYPTO_atomic_add()\fR must
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be the only way that the variable is modified.
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.SH "RETURN VALUES"
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.IX Header "RETURN VALUES"
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\&\fBCRYPTO_THREAD_run_once()\fR returns 1 on success, or 0 on error.
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.PP
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\&\fBCRYPTO_THREAD_lock_new()\fR returns the allocated lock, or \s-1NULL\s0 on error.
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.PP
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\&\fBCRYPTO_THREAD_lock_free()\fR returns no value.
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.PP
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The other functions return 1 on success, or 0 on error.
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.SH "NOTES"
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.IX Header "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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.SH "EXAMPLES"
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.IX Header "EXAMPLES"
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This example safely initializes and uses a lock.
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.PP
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.Vb 4
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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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\&
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\& static CRYPTO_ONCE once = CRYPTO_ONCE_STATIC_INIT;
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\& static CRYPTO_RWLOCK *lock;
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\&
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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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\&
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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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\&
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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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\&
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\& int serialized(void)
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\& {
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\& int ret = 0;
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\&
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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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.Ve
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.PP
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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 \*(L"leak\*(R" the lock in applications and not
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repeatedly load/unload shared libraries that allocate locks.
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.SH "NOTES"
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.IX Header "NOTES"
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You can find out if OpenSSL was configured with thread support:
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.PP
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.Vb 6
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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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.Ve
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.SH "SEE ALSO"
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.IX Header "SEE ALSO"
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\&\fBcrypto\fR\|(7)
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.SH "COPYRIGHT"
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.IX Header "COPYRIGHT"
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Copyright 2000\-2020 The OpenSSL Project Authors. All Rights Reserved.
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.PP
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Licensed under the OpenSSL license (the \*(L"License\*(R"). 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 \s-1LICENSE\s0 in the source distribution or at
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<https://www.openssl.org/source/license.html>.
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