123 lines
4.0 KiB
C
123 lines
4.0 KiB
C
#pragma once
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/*
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* Copyright (c) 2016 MariaDB Corporation Ab
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*
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* Use of this software is governed by the Business Source License included
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* in the LICENSE.TXT file and at www.mariadb.com/bsl11.
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*
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* Change Date: 2020-01-01
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*
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* On the date above, in accordance with the Business Source License, use
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* of this software will be governed by version 2 or later of the General
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* Public License.
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*/
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/**
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* @file atomic.h The atomic operations used within the gateway
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*/
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#include <maxscale/cdefs.h>
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MXS_BEGIN_DECLS
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/**
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* Pre 4.7 GCC doesn't support the __atomic builtin functions. The older __sync
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* builtins don't have proper store/load functionality so we use a somewhat ugly
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* hack to emulate the store/load.
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*/
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#if __GNUC__ > 4 || (__GNUC__ == 4 && __GNUC_MINOR__ >= 7)
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#ifndef MXS_USE_ATOMIC_BUILTINS
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#define MXS_USE_ATOMIC_BUILTINS 1
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#endif
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#endif
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/**
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* Implementation of an atomic add operations for the GCC environment.
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*
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* Adds a value to the contents of a location pointed to by the first parameter.
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* The add operation is atomic and the return value is the value stored in the
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* location prior to the operation. The number that is added may be signed,
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* therefore atomic_subtract is merely an atomic add with a negative value.
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*
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* @param variable Pointer the the variable to add to
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* @param value Value to be added
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* @return The value of variable before the add occurred
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*/
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int atomic_add(int *variable, int value);
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uint32_t atomic_add_uint32(uint32_t *variable, int32_t value);
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int64_t atomic_add_int64(int64_t *variable, int64_t value);
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uint64_t atomic_add_uint64(uint64_t *variable, int64_t value);
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/**
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* Implementation of an atomic load operation for the GCC environment.
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*
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* Loads a value from the contents of a location pointed to by the first parameter.
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* The load operation is atomic and it uses the strongest memory ordering.
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*
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* @param variable Pointer the the variable to load from
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* @return The stored value
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*/
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int atomic_load_int(const int *variable);
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int32_t atomic_load_int32(const int32_t *variable);
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int64_t atomic_load_int64(const int64_t *variable);
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uint32_t atomic_load_uint32(const uint32_t *variable);
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uint64_t atomic_load_uint64(const uint64_t *variable);
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void* atomic_load_ptr(void * const *variable);
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/**
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* Implementation of an atomic store operation for the GCC environment.
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*
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* Stores a value to the contents of a location pointed to by the first parameter.
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* The store operation is atomic and it uses the strongest memory ordering.
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*
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* @param variable Pointer the the variable to store to
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* @param value Value to be stored
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*/
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void atomic_store_int32(int *variable, int value);
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void atomic_store_int64(int64_t *variable, int64_t value);
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void atomic_store_uint64(uint64_t *variable, uint64_t value);
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void atomic_store_ptr(void **variable, void *value);
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/**
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* @brief Impose a full memory barrier
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*
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* A full memory barrier guarantees that all store and load operations complete
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* before the function is called.
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*
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* Currently, only the GNUC __sync_synchronize() is used. C11 introduces
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* standard functions for atomic memory operations and should be taken into use.
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*
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* @see https://www.kernel.org/doc/Documentation/memory-barriers.txt
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*/
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static inline void atomic_synchronize()
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{
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#ifdef __GNUC__
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#ifdef MXS_USE_ATOMIC_BUILTINS
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__atomic_thread_fence(__ATOMIC_SEQ_CST);
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#else
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__sync_synchronize(); /* Memory barrier. */
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#endif
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#else
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#error "No GNUC atomics available."
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#endif
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}
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/**
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* @brief Atomic compare-and-swap of pointers
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*
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* @param variable Pointer to the variable
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* @param old_value Pointer to the expected value of @variable
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* @param new_value Stored value if @c variable is equal to @c old_value
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*
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* @return True if @c variable and @c old_value were equal
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*
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* @note If GCC __atomic builtins are available, the contents of @c variable are
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* written to @c old_value if the two are not equal. Do not rely on this behavior
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* and always do a separate read before attempting a compare-and-swap.
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*/
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bool atomic_cas_ptr(void **variable, void** old_value, void *new_value);
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MXS_END_DECLS
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