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/*
* Copyright 2014 Jaidev Sridhar.
* Copyright 2014 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_SWLOCK_H
#define CK_SWLOCK_H
#include <ck_elide.h>
#include <ck_limits.h>
#include <ck_pr.h>
#include <ck_stdbool.h>
#include <ck_stddef.h>
struct ck_swlock {
uint32_t value;
};
typedef struct ck_swlock ck_swlock_t;
#define CK_SWLOCK_INITIALIZER {0}
#define CK_SWLOCK_WRITER_BIT (1UL << 31)
#define CK_SWLOCK_LATCH_BIT (1UL << 30)
#define CK_SWLOCK_WRITER_MASK (CK_SWLOCK_LATCH_BIT | CK_SWLOCK_WRITER_BIT)
#define CK_SWLOCK_READER_MASK (UINT32_MAX ^ CK_SWLOCK_WRITER_MASK)
CK_CC_INLINE static void
ck_swlock_init(struct ck_swlock *rw)
{
rw->value = 0;
ck_pr_barrier();
return;
}
CK_CC_INLINE static void
ck_swlock_write_unlock(ck_swlock_t *rw)
{
ck_pr_fence_unlock();
ck_pr_and_32(&rw->value, CK_SWLOCK_READER_MASK);
return;
}
CK_CC_INLINE static bool
ck_swlock_locked_writer(ck_swlock_t *rw)
{
bool r;
r = ck_pr_load_32(&rw->value) & CK_SWLOCK_WRITER_BIT;
ck_pr_fence_acquire();
return r;
}
CK_CC_INLINE static void
ck_swlock_write_downgrade(ck_swlock_t *rw)
{
ck_pr_inc_32(&rw->value);
ck_swlock_write_unlock(rw);
return;
}
CK_CC_INLINE static bool
ck_swlock_locked(ck_swlock_t *rw)
{
bool r;
r = ck_pr_load_32(&rw->value);
ck_pr_fence_acquire();
return r;
}
CK_CC_INLINE static bool
ck_swlock_write_trylock(ck_swlock_t *rw)
{
bool r;
r = ck_pr_cas_32(&rw->value, 0, CK_SWLOCK_WRITER_BIT);
ck_pr_fence_lock();
return r;
}
CK_ELIDE_TRYLOCK_PROTOTYPE(ck_swlock_write, ck_swlock_t,
ck_swlock_locked, ck_swlock_write_trylock)
CK_CC_INLINE static void
ck_swlock_write_lock(ck_swlock_t *rw)
{
ck_pr_or_32(&rw->value, CK_SWLOCK_WRITER_BIT);
while (ck_pr_load_32(&rw->value) & CK_SWLOCK_READER_MASK)
ck_pr_stall();
ck_pr_fence_lock();
return;
}
CK_CC_INLINE static void
ck_swlock_write_latch(ck_swlock_t *rw)
{
/* Publish intent to acquire lock. */
ck_pr_or_32(&rw->value, CK_SWLOCK_WRITER_BIT);
/* Stall until readers have seen the writer and cleared. */
while (ck_pr_cas_32(&rw->value, CK_SWLOCK_WRITER_BIT,
CK_SWLOCK_WRITER_MASK) == false) {
do {
ck_pr_stall();
} while (ck_pr_load_32(&rw->value) != CK_SWLOCK_WRITER_BIT);
}
ck_pr_fence_lock();
return;
}
CK_CC_INLINE static void
ck_swlock_write_unlatch(ck_swlock_t *rw)
{
ck_pr_fence_unlock();
ck_pr_store_32(&rw->value, 0);
return;
}
CK_ELIDE_PROTOTYPE(ck_swlock_write, ck_swlock_t,
ck_swlock_locked, ck_swlock_write_lock,
ck_swlock_locked_writer, ck_swlock_write_unlock)
CK_ELIDE_TRYLOCK_PROTOTYPE(ck_swlock_read, ck_swlock_t,
ck_swlock_locked_writer, ck_swlock_read_trylock)
CK_CC_INLINE static bool
ck_swlock_read_trylock(ck_swlock_t *rw)
{
uint32_t l = ck_pr_load_32(&rw->value);
if (l & CK_SWLOCK_WRITER_BIT)
return false;
l = ck_pr_faa_32(&rw->value, 1) & CK_SWLOCK_WRITER_MASK;
if (l == CK_SWLOCK_WRITER_BIT)
ck_pr_dec_32(&rw->value);
ck_pr_fence_lock();
return l == 0;
}
CK_CC_INLINE static void
ck_swlock_read_lock(ck_swlock_t *rw)
{
uint32_t l;
for (;;) {
while (ck_pr_load_32(&rw->value) & CK_SWLOCK_WRITER_BIT)
ck_pr_stall();
l = ck_pr_faa_32(&rw->value, 1) & CK_SWLOCK_WRITER_MASK;
if (l == 0)
break;
/*
* If the latch bit has not been set, then the writer would
* have observed the reader and will wait to completion of
* read-side critical section.
*/
if (l == CK_SWLOCK_WRITER_BIT)
ck_pr_dec_32(&rw->value);
}
ck_pr_fence_lock();
return;
}
CK_CC_INLINE static bool
ck_swlock_locked_reader(ck_swlock_t *rw)
{
ck_pr_fence_load();
return ck_pr_load_32(&rw->value) & CK_SWLOCK_READER_MASK;
}
CK_CC_INLINE static void
ck_swlock_read_unlock(ck_swlock_t *rw)
{
ck_pr_fence_unlock();
ck_pr_dec_32(&rw->value);
return;
}
CK_ELIDE_PROTOTYPE(ck_swlock_read, ck_swlock_t,
ck_swlock_locked_writer, ck_swlock_read_lock,
ck_swlock_locked_reader, ck_swlock_read_unlock)
#endif /* CK_SWLOCK_H */
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