ck/include/ck_swlock.h

/*
 * 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 <stdbool.h>
#include <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_release();
	ck_pr_and_32(&rw->value, CK_SWLOCK_READER_MASK);
	return;
}

CK_CC_INLINE static bool
ck_swlock_locked_writer(ck_swlock_t *rw)
{

	ck_pr_fence_load();
	return ck_pr_load_32(&rw->value) & CK_SWLOCK_WRITER_BIT;
}

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)
{

	ck_pr_fence_load();
	return ck_pr_load_32(&rw->value);
}

CK_CC_INLINE static bool
ck_swlock_write_trylock(ck_swlock_t *rw)
{

	ck_pr_fence_acquire();
	return ck_pr_cas_32(&rw->value, 0, CK_SWLOCK_WRITER_BIT);
}

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_acquire();
	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 seen 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_acquire();
	return;
}

CK_CC_INLINE static void
ck_swlock_write_unlatch(ck_swlock_t *rw)
{

	ck_pr_fence_release();
	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 == 0) {
		ck_pr_fence_acquire();
		return true;
	}

	if (l == CK_SWLOCK_WRITER_BIT)
		ck_pr_dec_32(&rw->value);

	return false;
}

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_acquire();
	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_release();
	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 */