| /* |
| * 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 */ |