1 /* 2 * Copyright 2014 Samy Al Bahra. 3 * All rights reserved. 4 * 5 * Redistribution and use in source and binary forms, with or without 6 * modification, are permitted provided that the following conditions 7 * are met: 8 * 1. Redistributions of source code must retain the above copyright 9 * notice, this list of conditions and the following disclaimer. 10 * 2. Redistributions in binary form must reproduce the above copyright 11 * notice, this list of conditions and the following disclaimer in the 12 * documentation and/or other materials provided with the distribution. 13 * 14 * THIS SOFTWARE IS PROVIDED BY THE AUTHOR AND CONTRIBUTORS ``AS IS'' AND 15 * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE 16 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE 17 * ARE DISCLAIMED. IN NO EVENT SHALL THE AUTHOR OR CONTRIBUTORS BE LIABLE 18 * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL 19 * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS 20 * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) 21 * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT 22 * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY 23 * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF 24 * SUCH DAMAGE. 25 */ 26 27 #ifndef CK_TFLOCK_TICKET_H 28 #define CK_TFLOCK_TICKET_H 29 30 /* 31 * This is an implementation of task-fair locks derived from the work 32 * described in: 33 * John M. Mellor-Crummey and Michael L. Scott. 1991. 34 * Scalable reader-writer synchronization for shared-memory 35 * multiprocessors. SIGPLAN Not. 26, 7 (April 1991), 106-113. 36 */ 37 38 #include <ck_cc.h> 39 #include <ck_pr.h> 40 41 struct ck_tflock_ticket { 42 uint32_t request; 43 uint32_t completion; 44 }; 45 typedef struct ck_tflock_ticket ck_tflock_ticket_t; 46 47 #define CK_TFLOCK_TICKET_INITIALIZER { 0, 0 } 48 49 #define CK_TFLOCK_TICKET_RC_INCR 0x10000U /* Read-side increment. */ 50 #define CK_TFLOCK_TICKET_WC_INCR 0x1U /* Write-side increment. */ 51 #define CK_TFLOCK_TICKET_W_MASK 0xffffU /* Write-side mask. */ 52 #define CK_TFLOCK_TICKET_WC_TOPMSK 0x8000U /* Write clear mask for overflow. */ 53 #define CK_TFLOCK_TICKET_RC_TOPMSK 0x80000000U /* Read clear mask for overflow. */ 54 55 CK_CC_INLINE static uint32_t 56 ck_tflock_ticket_fca_32(uint32_t *target, uint32_t mask, uint32_t delta) 57 { 58 uint32_t snapshot = ck_pr_load_32(target); 59 uint32_t goal; 60 61 for (;;) { 62 goal = (snapshot & ~mask) + delta; 63 if (ck_pr_cas_32_value(target, snapshot, goal, &snapshot) == true) 64 break; 65 66 ck_pr_stall(); 67 } 68 69 return snapshot; 70 } 71 72 CK_CC_INLINE static void 73 ck_tflock_ticket_init(struct ck_tflock_ticket *pf) 74 { 75 76 pf->request = pf->completion = 0; 77 ck_pr_barrier(); 78 return; 79 } 80 81 CK_CC_INLINE static void 82 ck_tflock_ticket_write_lock(struct ck_tflock_ticket *lock) 83 { 84 uint32_t previous; 85 86 previous = ck_tflock_ticket_fca_32(&lock->request, CK_TFLOCK_TICKET_WC_TOPMSK, 87 CK_TFLOCK_TICKET_WC_INCR); 88 ck_pr_fence_atomic_load(); 89 while (ck_pr_load_32(&lock->completion) != previous) 90 ck_pr_stall(); 91 92 ck_pr_fence_lock(); 93 return; 94 } 95 96 CK_CC_INLINE static void 97 ck_tflock_ticket_write_unlock(struct ck_tflock_ticket *lock) 98 { 99 100 ck_pr_fence_unlock(); 101 ck_tflock_ticket_fca_32(&lock->completion, CK_TFLOCK_TICKET_WC_TOPMSK, 102 CK_TFLOCK_TICKET_WC_INCR); 103 return; 104 } 105 106 CK_CC_INLINE static void 107 ck_tflock_ticket_read_lock(struct ck_tflock_ticket *lock) 108 { 109 uint32_t previous; 110 111 previous = ck_tflock_ticket_fca_32(&lock->request, 112 CK_TFLOCK_TICKET_RC_TOPMSK, CK_TFLOCK_TICKET_RC_INCR) & 113 CK_TFLOCK_TICKET_W_MASK; 114 115 ck_pr_fence_atomic_load(); 116 117 while ((ck_pr_load_32(&lock->completion) & 118 CK_TFLOCK_TICKET_W_MASK) != previous) { 119 ck_pr_stall(); 120 } 121 122 ck_pr_fence_lock(); 123 return; 124 } 125 126 CK_CC_INLINE static void 127 ck_tflock_ticket_read_unlock(struct ck_tflock_ticket *lock) 128 { 129 130 ck_pr_fence_unlock(); 131 ck_tflock_ticket_fca_32(&lock->completion, CK_TFLOCK_TICKET_RC_TOPMSK, 132 CK_TFLOCK_TICKET_RC_INCR); 133 return; 134 } 135 136 #endif /* CK_TFLOCK_TICKET_H */ 137