atomic.h

00001 // ----------------------------------------------------------------------------
00002 // Copyright 2015-2017 ARM Ltd.
00003 //
00004 // SPDX-License-Identifier: Apache-2.0
00005 //
00006 // Licensed under the Apache License, Version 2.0 (the "License");
00007 // you may not use this file except in compliance with the License.
00008 // You may obtain a copy of the License at
00009 //
00010 //     http://www.apache.org/licenses/LICENSE-2.0
00011 //
00012 // Unless required by applicable law or agreed to in writing, software
00013 // distributed under the License is distributed on an "AS IS" BASIS,
00014 // WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
00015 // See the License for the specific language governing permissions and
00016 // limitations under the License.
00017 // ----------------------------------------------------------------------------
00018 
00019 #ifndef ATOMIC_QUEUE_ATOMIC_H
00020 #define ATOMIC_QUEUE_ATOMIC_H
00021 #include <stdint.h>
00022 
00023 
00024 
00025 #ifdef __cplusplus
00026 extern "C" {
00027 #endif
00028 
00029 enum {
00030     AQ_ATOMIC_CAS_DEREF_SUCCESS = 0,
00031     AQ_ATOMIC_CAS_DEREF_NULLPTR,
00032     AQ_ATOMIC_CAS_DEREF_VALUE,
00033     AQ_ATOMIC_CAS_DEREF_INTERUPTED,
00034 };
00035 
00036 /**
00037  * @brief Atomically compares the value of a dereferenced pointer, replacing the pointer on success.
00038  * @detail aq_atomic_cas_deref_uintptr provides a mechanism to atomically change a pointer based on a value contained
00039  *     in the structure referenced by the pointer. This is done in the following sequence of operations:
00040  *
00041  *     1. Load the value of `*ptrAddr`
00042  *     2. Optionally store the current value of `*ptrAddr`
00043  *     3. Check that the pointer is valid: `*ptrAddr != NULL`
00044  *     4. Check the value of the referenced location: `*(*ptrAddr + valueOffset) == expectedDerefValue` (casts omitted)
00045  *     5. If 3 and 4 succeeded, store newPtrValue: `*ptrAddr = newPtrValue` (NOTE: in non-blocking implementations, this step can fail)
00046  *     6. Return a status code based on the results of 3, 4, 5.
00047  *
00048  * @param[in,out] ptrAddr            The address of the pointer to manipulate
00049  * @param[out]    currentPtrValue    A pointer to a container for the current value of *ptrAddr
00050  * @param[in]     expectedDerefValue This is the value that is expected at *(uintptr_t *)((uintptr_t)*ptrAddr + valueOffset)
00051  * @param[in]     newPtrValue        The value to store to *ptrAddr if the comparison is successful
00052  * @param[in]     valueOffset        The offset of the target value from *ptrAddr
00053  *
00054  * @retval AQ_ATOMIC_CAS_DEREF_SUCCESS    The compare and set has succeeded
00055  * @retval AQ_ATOMIC_CAS_DEREF_NULLPTR    `*ptrAddr` was `NULL`
00056  * @retval AQ_ATOMIC_CAS_DEREF_VALUE      The value test failed (*(*ptrAddr + valueOffset) != expectedDerefValue`)
00057  * @retval AQ_ATOMIC_CAS_DEREF_INTERUPTED Another context modified `*ptrAddr`
00058  */
00059 int aq_atomic_cas_deref_uintptr(uintptr_t *volatile *ptrAddr,
00060                                 uintptr_t **currentPtrValue,
00061                                 uintptr_t expectedDerefValue,
00062                                 uintptr_t *newPtrValue,
00063                                 uintptr_t valueOffset);
00064 
00065 #ifdef __cplusplus
00066 } // extern "C"
00067 #endif
00068 #endif // ATOMIC_QUEUE_ATOMIC_H