/*
 * Copyright (c) 2022 UT-Battelle ORNL. All rights reserved
 *
 * This software is available to you under a choice of one of two
 * licenses.  You may choose to be licensed under the terms of the GNU
 * General Public License (GPL) Version 2, available from the file
 * COPYING in the main directory of this source tree, or the
 * BSD license below:
 *
 *     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.
 *
 * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND,
 * EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF
 * MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND
 * NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS
 * BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN
 * ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN
 * CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
 * SOFTWARE.
 */

/* Code derived from Dmitry Vyukov */
/* see:  https://www.1024cores.net/home/lock-free-algorithms/queues/bounded-mpmc-queue */

/*  Multi-producer/multi-consumer bounded queue.
 *  Redistribution and use in source and binary forms, with or without
 *  modification, are permitted provided that the following conditions
 *  are met:
 *     1. Redistributions of source code must retain the above copyright
 *        notice, this list of conditions and the following disclaimer.
 *     2. 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 DMITRY VYUKOV "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 DMITRY VYUKOV 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.  The views and conclusions contained
 *  in the software and documentation are those of the authors and should not be
 *  interpreted as representing official policies, either expressed or implied, of
 *  Dmitry Vyukov.
 */

#ifndef OFI_ATOMIC_QUEUE_H
#define OFI_ATOMIC_QUEUE_H

#include <ofi_atom.h>

/*
 * This is an atomic queue, meaning no need for locking. One example usage
 * for this data structure is to build a command queue shared between
 * different processes. Multiple processes would post commands on a command
 * queue which belongs to another process. The receiving process would
 * read and process commands off the queue.
 *
 * Usage:
 *  . OFI_DECLARE_ATOMIC_Q() to declare the atomic queue
 *  . Allocate shared memory for the queue or call the create method
 *  . call the init() method to ready the queue for usage
 *  . To post on the queue call _next() method
 *     . This will return a buffer of entrytype
 *     . Initialize the entry
 *  . Call _commit() method to post for the reader
 *  . On failure instead of _commit() call _discard()
 *     . This will set the command as a no-op and put it on the queue
 *  . To read off the queue call _head()
 *     . This will return the next available entry on the queue or
 *       -FI_ENOENT if there are no more entries on the queue
 *     . if the entry is a no-op it will be released and another entry
 *       will be fetched off the queue.
 *  . Call _release() after reader is done with the entry
 */

#ifdef __cplusplus
extern "C" {
#endif

#define OFI_CACHE_LINE_SIZE (64)

#define OFI_DECLARE_ATOMIC_Q(entrytype, name)			\
struct name ## _entry {						\
	ofi_atomic64_t	seq;					\
	bool		noop;					\
	entrytype	buf;					\
};								\
struct name {							\
	int		size;					\
	int		size_mask;				\
	ofi_atomic64_t	write_pos;				\
	char		pad0[OFI_CACHE_LINE_SIZE];		\
	ofi_atomic64_t	read_pos;				\
	char		pad1[OFI_CACHE_LINE_SIZE];		\
	struct name ## _entry entry[];				\
} __attribute__((__aligned__(64)));				\
								\
static inline void name ## _init(struct name *aq, size_t size)	\
{								\
	size_t i;						\
	assert(size == roundup_power_of_two(size));		\
	aq->size = size;					\
	aq->size_mask = aq->size - 1;				\
	ofi_atomic_initialize64(&aq->write_pos, 0);		\
	ofi_atomic_initialize64(&aq->read_pos, 0);		\
	for (i = 0; i < size; i++)				\
		ofi_atomic_initialize64(&aq->entry[i].seq, i);	\
}								\
								\
static inline struct name * name ## _create(size_t size)	\
{								\
	struct name *aq;					\
	aq = (struct name*) calloc(1, sizeof(*aq) +		\
		sizeof(struct name ## _entry) *			\
		(roundup_power_of_two(size)));			\
	if (aq)							\
		name ##_init(aq, roundup_power_of_two(size));	\
	return aq;						\
}								\
								\
static inline void name ## _free(struct name *aq)		\
{								\
	free(aq);						\
}								\
static inline int name ## _next(struct name *aq,		\
		entrytype **buf, int64_t *pos)			\
{								\
	struct name ## _entry *ce;				\
	int64_t diff, seq;					\
	*pos = ofi_atomic_load_explicit64(&aq->write_pos,	\
				    memory_order_relaxed);	\
	for (;;) {						\
		ce = &aq->entry[*pos & aq->size_mask];		\
		seq = ofi_atomic_load_explicit64(&(ce->seq),	\
			memory_order_acquire);			\
		diff = seq - *pos;				\
		if (diff == 0) {				\
			if (ofi_atomic_compare_exchange_weak64(	\
				&aq->write_pos, pos,		\
				*pos + 1))			\
				break;				\
		} else if (diff < 0) {				\
			return -FI_ENOENT;			\
		} else {					\
			*pos = ofi_atomic_load_explicit64(	\
				&aq->write_pos,			\
				memory_order_relaxed);		\
		}						\
	}							\
	*buf = &ce->buf;					\
	return FI_SUCCESS;					\
}								\
static inline void name ## _release(struct name *aq,		\
			entrytype *buf,				\
			int64_t pos)				\
{								\
	struct name ## _entry *ce;				\
	ce = container_of(buf, struct name ## _entry, buf);	\
	ofi_atomic_store_explicit64(&ce->seq,			\
			      pos + aq->size,			\
			      memory_order_release);		\
}								\
static inline int name ## _head(struct name *aq,		\
		entrytype **buf, int64_t *pos)			\
{								\
	int64_t diff, seq;					\
	struct name ## _entry *ce;				\
again:								\
	*pos = ofi_atomic_load_explicit64(&aq->read_pos,	\
			memory_order_relaxed);			\
	for (;;) {						\
		ce = &aq->entry[*pos & aq->size_mask];		\
		seq = ofi_atomic_load_explicit64(&(ce->seq),	\
			memory_order_acquire);			\
		diff = seq - (*pos + 1);			\
		if (diff == 0) {				\
			if (ofi_atomic_compare_exchange_weak64(	\
				&aq->read_pos, pos,		\
				*pos + 1))			\
				break;				\
		} else if (diff < 0) {				\
			return -FI_ENOENT;			\
		} else {					\
			*pos = ofi_atomic_load_explicit64(	\
				&aq->read_pos,			\
				memory_order_relaxed);		\
		}						\
	}							\
	*buf = &ce->buf;					\
	if (ce->noop) {						\
		ce->noop = false;				\
		name ##_release(aq, *buf, *pos);		\
		goto again;					\
	}							\
	return FI_SUCCESS;					\
}								\
static inline void name ## _commit(entrytype *buf,		\
				int64_t pos)			\
{								\
	struct name ## _entry *ce;				\
	ce = container_of(buf, struct name ## _entry, buf);	\
	ofi_atomic_store_explicit64(&ce->seq, pos + 1,		\
			      memory_order_release);		\
}								\
static inline void name ## _discard(entrytype *buf,		\
				int64_t pos)			\
{								\
	struct name ## _entry *ce;				\
	ce = container_of(buf, struct name ## _entry, buf);	\
	ce->noop = true;					\
	ofi_atomic_store_explicit64(&ce->seq, pos + 1,		\
			      memory_order_release);		\
}								\
void dummy ## name (void) /* work-around global ; scope */

#ifdef __cplusplus
}
#endif

#endif /* OFI_ATOMIC_QUEUE_H */
