ded551e199
This allows safer lock-free reads to be done on lists that never shrink in size. The main use-case for this is to allow servers to be added to a service without locking the service each time a new session is created. Synchronizing the memory before adding new components into a list guarantees that if a session reads from the list and sees the new list item, the memory pointed by the item is valid.
71 lines
2.1 KiB
C
71 lines
2.1 KiB
C
#pragma once
|
|
/*
|
|
* Copyright (c) 2016 MariaDB Corporation Ab
|
|
*
|
|
* Use of this software is governed by the Business Source License included
|
|
* in the LICENSE.TXT file and at www.mariadb.com/bsl.
|
|
*
|
|
* Change Date: 2019-07-01
|
|
*
|
|
* On the date above, in accordance with the Business Source License, use
|
|
* of this software will be governed by version 2 or later of the General
|
|
* Public License.
|
|
*/
|
|
|
|
/**
|
|
* @file atomic.h The atomic operations used within the gateway
|
|
*
|
|
* @verbatim
|
|
* Revision History
|
|
*
|
|
* Date Who Description
|
|
* 10/06/13 Mark Riddoch Initial implementation
|
|
* 23/06/15 Martin Brampton Alternative for C++
|
|
*
|
|
* @endverbatim
|
|
*/
|
|
|
|
#include <maxscale/cdefs.h>
|
|
|
|
MXS_BEGIN_DECLS
|
|
|
|
/**
|
|
* Implementation of an atomic add operation for the GCC environment, or the
|
|
* X86 processor. If we are working within GNU C then we can use the GCC
|
|
* atomic add built in function, which is portable across platforms that
|
|
* implement GCC. Otherwise, this function currently supports only X86
|
|
* architecture (without further development).
|
|
*
|
|
* Adds a value to the contents of a location pointed to by the first parameter.
|
|
* The add operation is atomic and the return value is the value stored in the
|
|
* location prior to the operation. The number that is added may be signed,
|
|
* therefore atomic_subtract is merely an atomic add with a negative value.
|
|
*
|
|
* @param variable Pointer the the variable to add to
|
|
* @param value Value to be added
|
|
* @return The value of variable before the add occurred
|
|
*/
|
|
int atomic_add(int *variable, int value);
|
|
|
|
/**
|
|
* @brief Impose a full memory barrier
|
|
*
|
|
* A full memory barrier guarantees that all store and load operations complete
|
|
* before the function is called.
|
|
*
|
|
* Currently, only the GNUC __sync_synchronize() is used. C11 introduces
|
|
* standard functions for atomic memory operations and should be taken into use.
|
|
*
|
|
* @see https://www.kernel.org/doc/Documentation/memory-barriers.txt
|
|
*/
|
|
static inline void atomic_synchronize()
|
|
{
|
|
#ifdef __GNUC__
|
|
__sync_synchronize(); /* Memory barrier. */
|
|
#else
|
|
#error "No GNUC atomics available."
|
|
#endif
|
|
}
|
|
|
|
MXS_END_DECLS
|