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Steffen Vogel 2016-08-14 16:54:15 -04:00
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# Lock-free Single-Producer Single-consumer (SPSC) queue
## Design decissions
- Static indexed ring buffer or dynamically linked-lists?
## Some reading material
- http://moodycamel.com/blog/2013/a-fast-lock-free-queue-for-c++
- https://github.com/cameron314/readerwriterqueue
- http://www.1024cores.net/home/lock-free-algorithms/queues/unbounded-spsc-queue
## Credits
- Umar Farooq
- Steffen Vogel <post@steffenvogel.de>
## License
#### BSD 2-Clause License
All rights reserved.
- Redistribution and use in source and binary forms, with or without modification, are permitted provided that the following conditions are met:
- Redistributions of source code must retain the above copyright notice, this list of conditions and the following disclaimer.
- Redistributions in binary form must reproduce the above copyright notice, this list of conditions and the following disclaimer in the documentation and/or other materials provided with the distribution.
```
THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"
AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE
DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT HOLDER OR CONTRIBUTORS BE LIABLE
FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR
SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER
CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY,
OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
```

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/** Lock-free Single-Producer Single-consumer (SPSC) queue.
*
* @author Steffen Vogel <post@steffenvogel.de>
* @copyright 2016 Steffen Vogel
* @license BSD 2-Clause License
*
* All rights reserved.
*
* Redistribution and use in source and binary forms, with or without
* modification, are permitted provided that the following conditions are met:
*
* * Redistributions of source code must retain the above copyright notice, this
* list of conditions and the following disclaimer.
*
* * Redistributions in binary form must reproduce the above copyright notice,
* this list of conditions and the following disclaimer in the documentation
* and/or other materials provided with the distribution.
*
* THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"
* AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
* IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE
* DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT HOLDER OR CONTRIBUTORS BE LIABLE
* FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
* DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR
* SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER
* CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY,
* OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
* OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
*/
#include "queue.h"
int queue_init(struct queue *q, size_t size)
{
q->size = size;
q->pointers = malloc(size * sizeof(void *));
if (q->pointers == NULL)
return -1;
q->tail = atomic_init(0);
q->head = atomic_init(0);
return 0;
}
void queue_destroy(struct queue *q)
{
free(q->pointers);
}
int queue_get(struct queue *q, void **ptr)
{
}
int queue_push(struct queue *q, void *ptr)
{
}
int queue_pull(struct queue *q, void **ptr, qptr_t *head)
{
}
int queue_get_many(struct queue *q, void *ptrs[], size_t cnt, qptr_t head)
{
}
int queue_push_many(struct queue *q, void **ptrs, size_t cnt)
{
}
int queue_pull_many(struct queue *q, void **ptrs, size_t cnt, qptr_t *head)
{
}

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/** Lock-free Single-Producer Single-consumer (SPSC) queue.
*
* @author Steffen Vogel <post@steffenvogel.de>
* @copyright 2016 Steffen Vogel
* @license BSD 2-Clause License
*
* All rights reserved.
*
* Redistribution and use in source and binary forms, with or without
* modification, are permitted provided that the following conditions are met:
*
* * Redistributions of source code must retain the above copyright notice, this
* list of conditions and the following disclaimer.
*
* * Redistributions in binary form must reproduce the above copyright notice,
* this list of conditions and the following disclaimer in the documentation
* and/or other materials provided with the distribution.
*
* THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"
* AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
* IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE
* DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT HOLDER OR CONTRIBUTORS BE LIABLE
* FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
* DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR
* SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER
* CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY,
* OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
* OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
*/
#ifndef _QUEUE_H_
#define _QUEUE_H_
#include <stddef.h>
#include <stdint.h>
#include <stdatomic.h>
struct queue {
size_t size; /**< Number of pointers in queue::array */
void **pointers; /**< Circular buffer. */
_Atomic int head; /**< */
_Atomic int tail; /**< Tail pointer of queue*/
};
/** Initiliaze a new queue and allocate memory. */
int queue_init(struct queue *q, size_t size);
/** Release memory of queue. */
void queue_destroy(struct queue *q);
/** Enqueue up to \p cnt elements from \p ptrs[] at the queue tail pointed by \p tail.
*
* It may happen that the queue is (nearly) full and there is no more
* space to enqueue more elments.
* In this case a call to this function will return a value which is smaller than \p cnt
* or even zero if the queue was already full.
*
* @param q A pointer to the queue datastructure.
* @param[in] ptrs An array of void-pointers which should be enqueued.
* @param cnt The length of the pointer array \p ptrs.
* @return The function returns the number of successfully enqueued elements from \p ptrs.
*/
int queue_push_many(struct queue *q, void *ptrs[], size_t cnt);
/** Dequeue up to \p cnt elements from the queue and place them into the array \p ptrs[].
*
* @param q A pointer to the queue datastructure.
* @param[out] ptrs An array with space at least \cnt elements which will receive pointers to the released elements.
* @param cnt The maximum number of elements which should be dequeued. It defines the size of \p ptrs.
* @param[in,out] head A pointer to a queue head. The value will be updated to reflect the new head.
* @return The number of elements which have been dequeued <b>and whose reference counts have reached zero</b>.
*/
int queue_pull_many(struct queue *q, void *ptrs[], size_t cnt);
/** Fill \p ptrs with \p cnt elements of the queue starting at entry \p pos. */
int queue_get_many(struct queue *q, void *ptrs[], size_t cnt);
/** Get the first element in the queue */
int queue_get(struct queue *q, void **ptr);
/** Enqueue a new block at the tail of the queue. */
int queue_push(struct queue *q, void *ptr);
/** Dequeue the first block at the head of the queue. */
int queue_pull(struct queue *q, void **ptr);
#endif /* _QUEUE_H_ */