1 /* 2 * Copyright 2013 John Wittrock. 3 * Copyright 2013-2015 Samy Al Bahra. 4 * All rights reserved. 5 * 6 * Redistribution and use in source and binary forms, with or without 7 * modification, are permitted provided that the following conditions 8 * are met: 9 * 1. Redistributions of source code must retain the above copyright 10 * notice, this list of conditions and the following disclaimer. 11 * 2. Redistributions in binary form must reproduce the above copyright 12 * notice, this list of conditions and the following disclaimer in the 13 * documentation and/or other materials provided with the distribution. 14 * 15 * THIS SOFTWARE IS PROVIDED BY THE AUTHOR AND CONTRIBUTORS ``AS IS'' AND 16 * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE 17 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE 18 * ARE DISCLAIMED. IN NO EVENT SHALL THE AUTHOR OR CONTRIBUTORS BE LIABLE 19 * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL 20 * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS 21 * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) 22 * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT 23 * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY 24 * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF 25 * SUCH DAMAGE. 26 */ 27 28 #ifndef CK_PFLOCK_H 29 #define CK_PFLOCK_H 30 31 /* 32 * This is an implementation of phase-fair locks derived from the work 33 * described in: 34 * Brandenburg, B. and Anderson, J. 2010. Spin-Based 35 * Reader-Writer Synchronization for Multiprocessor Real-Time Systems 36 */ 37 38 #include <ck_cc.h> 39 #include <ck_pr.h> 40 41 struct ck_pflock { 42 uint32_t rin; 43 uint32_t rout; 44 uint32_t win; 45 uint32_t wout; 46 }; 47 typedef struct ck_pflock ck_pflock_t; 48 49 #define CK_PFLOCK_LSB 0xFFFFFFF0 50 #define CK_PFLOCK_RINC 0x100 /* Reader increment value. */ 51 #define CK_PFLOCK_WBITS 0x3 /* Writer bits in reader. */ 52 #define CK_PFLOCK_PRES 0x2 /* Writer present bit. */ 53 #define CK_PFLOCK_PHID 0x1 /* Phase ID bit. */ 54 55 #define CK_PFLOCK_INITIALIZER {0, 0, 0, 0} 56 57 CK_CC_INLINE static void 58 ck_pflock_init(struct ck_pflock *pf) 59 { 60 61 pf->rin = 0; 62 pf->rout = 0; 63 pf->win = 0; 64 pf->wout = 0; 65 ck_pr_barrier(); 66 67 return; 68 } 69 70 CK_CC_INLINE static void 71 ck_pflock_write_unlock(ck_pflock_t *pf) 72 { 73 74 ck_pr_fence_unlock(); 75 76 /* Migrate from write phase to read phase. */ 77 ck_pr_and_32(&pf->rin, CK_PFLOCK_LSB); 78 79 /* Allow other writers to continue. */ 80 ck_pr_faa_32(&pf->wout, 1); 81 return; 82 } 83 84 CK_CC_INLINE static void 85 ck_pflock_write_lock(ck_pflock_t *pf) 86 { 87 uint32_t ticket; 88 89 /* Acquire ownership of write-phase. */ 90 ticket = ck_pr_faa_32(&pf->win, 1); 91 while (ck_pr_load_32(&pf->wout) != ticket) 92 ck_pr_stall(); 93 94 /* 95 * Acquire ticket on read-side in order to allow them 96 * to flush. Indicates to any incoming reader that a 97 * write-phase is pending. 98 */ 99 ticket = ck_pr_faa_32(&pf->rin, 100 (ticket & CK_PFLOCK_PHID) | CK_PFLOCK_PRES); 101 102 /* Wait for any pending readers to flush. */ 103 while (ck_pr_load_32(&pf->rout) != ticket) 104 ck_pr_stall(); 105 106 ck_pr_fence_lock(); 107 return; 108 } 109 110 CK_CC_INLINE static void 111 ck_pflock_read_unlock(ck_pflock_t *pf) 112 { 113 114 ck_pr_fence_unlock(); 115 ck_pr_faa_32(&pf->rout, CK_PFLOCK_RINC); 116 return; 117 } 118 119 CK_CC_INLINE static void 120 ck_pflock_read_lock(ck_pflock_t *pf) 121 { 122 uint32_t w; 123 124 /* 125 * If no writer is present, then the operation has completed 126 * successfully. 127 */ 128 w = ck_pr_faa_32(&pf->rin, CK_PFLOCK_RINC) & CK_PFLOCK_WBITS; 129 if (w == 0) 130 goto leave; 131 132 /* Wait for current write phase to complete. */ 133 while ((ck_pr_load_32(&pf->rin) & CK_PFLOCK_WBITS) == w) 134 ck_pr_stall(); 135 136 leave: 137 /* Acquire semantics with respect to readers. */ 138 ck_pr_fence_lock(); 139 return; 140 } 141 142 #endif /* CK_PFLOCK_H */ 143