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/*
* Copyright 2010-2015 Samy Al Bahra.
* All rights reserved.
*
* 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 THE AUTHOR 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 AUTHOR 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 CK_SEQUENCE_H
#define CK_SEQUENCE_H
#include <ck_cc.h>
#include <ck_pr.h>
#include <ck_stdbool.h>
struct ck_sequence {
unsigned int sequence;
};
typedef struct ck_sequence ck_sequence_t;
#define CK_SEQUENCE_INITIALIZER { .sequence = 0 }
CK_CC_INLINE static void
ck_sequence_init(struct ck_sequence *sq)
{
ck_pr_store_uint(&sq->sequence, 0);
return;
}
CK_CC_INLINE static unsigned int
ck_sequence_read_begin(const struct ck_sequence *sq)
{
unsigned int version;
for (;;) {
version = ck_pr_load_uint(&sq->sequence);
/*
* If a sequence is even then associated data may be in a
* consistent state.
*/
if (CK_CC_LIKELY((version & 1) == 0))
break;
/*
* If a sequence is odd then a thread is in the middle of an
* update. Retry the read to avoid operating on inconsistent
* data.
*/
ck_pr_stall();
}
ck_pr_fence_load();
return version;
}
CK_CC_INLINE static bool
ck_sequence_read_retry(const struct ck_sequence *sq, unsigned int version)
{
/*
* If the sequence number was updated then a read should be
* re-attempted.
*/
ck_pr_fence_load();
return ck_pr_load_uint(&sq->sequence) != version;
}
#define CK_SEQUENCE_READ(seqlock, version) \
for (*(version) = 1; \
(*(version) != 0) && (*(version) = ck_sequence_read_begin(seqlock), 1); \
*(version) = ck_sequence_read_retry(seqlock, *(version)))
/*
* This must be called after a successful mutex acquisition.
*/
CK_CC_INLINE static void
ck_sequence_write_begin(struct ck_sequence *sq)
{
/*
* Increment the sequence to an odd number to indicate
* the beginning of a write update.
*/
ck_pr_store_uint(&sq->sequence, sq->sequence + 1);
ck_pr_fence_store();
return;
}
/*
* This must be called before mutex ownership is relinquished.
*/
CK_CC_INLINE static void
ck_sequence_write_end(struct ck_sequence *sq)
{
/*
* Increment the sequence to an even number to indicate
* completion of a write update.
*/
ck_pr_fence_store();
ck_pr_store_uint(&sq->sequence, sq->sequence + 1);
return;
}
#endif /* CK_SEQUENCE_H */