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/*
* Copyright 2013 John Wittrock.
* Copyright 2013-2015 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_PFLOCK_H
#define CK_PFLOCK_H
/*
* This is an implementation of phase-fair locks derived from the work
* described in:
* Brandenburg, B. and Anderson, J. 2010. Spin-Based
* Reader-Writer Synchronization for Multiprocessor Real-Time Systems
*/
#include <ck_cc.h>
#include <ck_pr.h>
struct ck_pflock {
uint32_t rin;
uint32_t rout;
uint32_t win;
uint32_t wout;
};
typedef struct ck_pflock ck_pflock_t;
#define CK_PFLOCK_LSB 0xFFFFFFF0
#define CK_PFLOCK_RINC 0x100 /* Reader increment value. */
#define CK_PFLOCK_WBITS 0x3 /* Writer bits in reader. */
#define CK_PFLOCK_PRES 0x2 /* Writer present bit. */
#define CK_PFLOCK_PHID 0x1 /* Phase ID bit. */
#define CK_PFLOCK_INITIALIZER {0, 0, 0, 0}
CK_CC_INLINE static void
ck_pflock_init(struct ck_pflock *pf)
{
pf->rin = 0;
pf->rout = 0;
pf->win = 0;
pf->wout = 0;
ck_pr_barrier();
return;
}
CK_CC_INLINE static void
ck_pflock_write_unlock(ck_pflock_t *pf)
{
ck_pr_fence_unlock();
/* Migrate from write phase to read phase. */
ck_pr_and_32(&pf->rin, CK_PFLOCK_LSB);
/* Allow other writers to continue. */
ck_pr_faa_32(&pf->wout, 1);
return;
}
CK_CC_INLINE static void
ck_pflock_write_lock(ck_pflock_t *pf)
{
uint32_t ticket;
/* Acquire ownership of write-phase. */
ticket = ck_pr_faa_32(&pf->win, 1);
while (ck_pr_load_32(&pf->wout) != ticket)
ck_pr_stall();
/*
* Acquire ticket on read-side in order to allow them
* to flush. Indicates to any incoming reader that a
* write-phase is pending.
*/
ticket = ck_pr_faa_32(&pf->rin,
(ticket & CK_PFLOCK_PHID) | CK_PFLOCK_PRES);
/* Wait for any pending readers to flush. */
while (ck_pr_load_32(&pf->rout) != ticket)
ck_pr_stall();
ck_pr_fence_lock();
return;
}
CK_CC_INLINE static void
ck_pflock_read_unlock(ck_pflock_t *pf)
{
ck_pr_fence_unlock();
ck_pr_faa_32(&pf->rout, CK_PFLOCK_RINC);
return;
}
CK_CC_INLINE static void
ck_pflock_read_lock(ck_pflock_t *pf)
{
uint32_t w;
/*
* If no writer is present, then the operation has completed
* successfully.
*/
w = ck_pr_faa_32(&pf->rin, CK_PFLOCK_RINC) & CK_PFLOCK_WBITS;
if (w == 0)
goto leave;
/* Wait for current write phase to complete. */
while ((ck_pr_load_32(&pf->rin) & CK_PFLOCK_WBITS) == w)
ck_pr_stall();
leave:
/* Acquire semantics with respect to readers. */
ck_pr_fence_lock();
return;
}
#endif /* CK_PFLOCK_H */
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