/* * 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 */