1 /* 2 * Copyright 2011-2015 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_EPOCH_H 28 #define CK_EPOCH_H 29 30 /* 31 * The implementation here is inspired from the work described in: 32 * Fraser, K. 2004. Practical Lock-Freedom. PhD Thesis, University 33 * of Cambridge Computing Laboratory. 34 */ 35 36 #include <ck_cc.h> 37 #include <ck_md.h> 38 #include <ck_pr.h> 39 #include <ck_stack.h> 40 #include <ck_stdbool.h> 41 42 #ifndef CK_EPOCH_LENGTH 43 #define CK_EPOCH_LENGTH 4 44 #endif 45 46 /* 47 * This is used for sense detection with-respect to concurrent 48 * epoch sections. 49 */ 50 #define CK_EPOCH_SENSE (2) 51 52 struct ck_epoch_entry; 53 typedef struct ck_epoch_entry ck_epoch_entry_t; 54 typedef void ck_epoch_cb_t(ck_epoch_entry_t *); 55 56 /* 57 * This should be embedded into objects you wish to be the target of 58 * ck_epoch_cb_t functions (with ck_epoch_call). 59 */ 60 struct ck_epoch_entry { 61 ck_epoch_cb_t *function; 62 ck_stack_entry_t stack_entry; 63 }; 64 65 /* 66 * A section object may be passed to every begin-end pair to allow for 67 * forward progress guarantees with-in prolonged active sections. 68 */ 69 struct ck_epoch_section { 70 unsigned int bucket; 71 }; 72 typedef struct ck_epoch_section ck_epoch_section_t; 73 74 /* 75 * Return pointer to ck_epoch_entry container object. 76 */ 77 #define CK_EPOCH_CONTAINER(T, M, N) \ 78 CK_CC_CONTAINER(struct ck_epoch_entry, T, M, N) 79 80 struct ck_epoch_ref { 81 unsigned int epoch; 82 unsigned int count; 83 }; 84 85 struct ck_epoch_record { 86 ck_stack_entry_t record_next; 87 struct ck_epoch *global; 88 unsigned int state; 89 unsigned int epoch; 90 unsigned int active; 91 struct { 92 struct ck_epoch_ref bucket[CK_EPOCH_SENSE]; 93 } local CK_CC_CACHELINE; 94 unsigned int n_pending; 95 unsigned int n_peak; 96 unsigned int n_dispatch; 97 void *ct; 98 ck_stack_t pending[CK_EPOCH_LENGTH]; 99 } CK_CC_CACHELINE; 100 typedef struct ck_epoch_record ck_epoch_record_t; 101 102 struct ck_epoch { 103 unsigned int epoch; 104 unsigned int n_free; 105 ck_stack_t records; 106 }; 107 typedef struct ck_epoch ck_epoch_t; 108 109 /* 110 * Internal functions. 111 */ 112 void _ck_epoch_addref(ck_epoch_record_t *, ck_epoch_section_t *); 113 bool _ck_epoch_delref(ck_epoch_record_t *, ck_epoch_section_t *); 114 115 CK_CC_FORCE_INLINE static void * 116 ck_epoch_record_ct(const ck_epoch_record_t *record) 117 { 118 119 return ck_pr_load_ptr(&record->ct); 120 } 121 122 /* 123 * Marks the beginning of an epoch-protected section. 124 */ 125 CK_CC_FORCE_INLINE static void 126 ck_epoch_begin(ck_epoch_record_t *record, ck_epoch_section_t *section) 127 { 128 struct ck_epoch *epoch = record->global; 129 130 /* 131 * Only observe new epoch if thread is not recursing into a read 132 * section. 133 */ 134 if (record->active == 0) { 135 unsigned int g_epoch; 136 137 /* 138 * It is possible for loads to be re-ordered before the store 139 * is committed into the caller's epoch and active fields. 140 * For this reason, store to load serialization is necessary. 141 */ 142 #if defined(CK_MD_TSO) 143 ck_pr_fas_uint(&record->active, 1); 144 ck_pr_fence_atomic_load(); 145 #else 146 ck_pr_store_uint(&record->active, 1); 147 ck_pr_fence_memory(); 148 #endif 149 150 /* 151 * This load is allowed to be re-ordered prior to setting 152 * active flag due to monotonic nature of the global epoch. 153 * However, stale values lead to measurable performance 154 * degradation in some torture tests so we disallow early load 155 * of global epoch. 156 */ 157 g_epoch = ck_pr_load_uint(&epoch->epoch); 158 ck_pr_store_uint(&record->epoch, g_epoch); 159 } else { 160 ck_pr_store_uint(&record->active, record->active + 1); 161 } 162 163 if (section != NULL) 164 _ck_epoch_addref(record, section); 165 166 return; 167 } 168 169 /* 170 * Marks the end of an epoch-protected section. Returns true if no more 171 * sections exist for the caller. 172 */ 173 CK_CC_FORCE_INLINE static bool 174 ck_epoch_end(ck_epoch_record_t *record, ck_epoch_section_t *section) 175 { 176 177 ck_pr_fence_release(); 178 ck_pr_store_uint(&record->active, record->active - 1); 179 180 if (section != NULL) 181 return _ck_epoch_delref(record, section); 182 183 return record->active == 0; 184 } 185 186 /* 187 * Defers the execution of the function pointed to by the "cb" 188 * argument until an epoch counter loop. This allows for a 189 * non-blocking deferral. 190 * 191 * We can get away without a fence here due to the monotonic nature 192 * of the epoch counter. Worst case, this will result in some delays 193 * before object destruction. 194 */ 195 CK_CC_FORCE_INLINE static void 196 ck_epoch_call(ck_epoch_record_t *record, 197 ck_epoch_entry_t *entry, 198 ck_epoch_cb_t *function) 199 { 200 struct ck_epoch *epoch = record->global; 201 unsigned int e = ck_pr_load_uint(&epoch->epoch); 202 unsigned int offset = e & (CK_EPOCH_LENGTH - 1); 203 204 record->n_pending++; 205 entry->function = function; 206 ck_stack_push_spnc(&record->pending[offset], &entry->stack_entry); 207 return; 208 } 209 210 /* 211 * Same as ck_epoch_call, but allows for records to be shared and is reentrant. 212 */ 213 CK_CC_FORCE_INLINE static void 214 ck_epoch_call_strict(ck_epoch_record_t *record, 215 ck_epoch_entry_t *entry, 216 ck_epoch_cb_t *function) 217 { 218 struct ck_epoch *epoch = record->global; 219 unsigned int e = ck_pr_load_uint(&epoch->epoch); 220 unsigned int offset = e & (CK_EPOCH_LENGTH - 1); 221 222 ck_pr_inc_uint(&record->n_pending); 223 entry->function = function; 224 225 /* Store fence is implied by push operation. */ 226 ck_stack_push_upmc(&record->pending[offset], &entry->stack_entry); 227 return; 228 } 229 230 /* 231 * This callback is used for synchronize_wait to allow for custom blocking 232 * behavior. 233 */ 234 typedef void ck_epoch_wait_cb_t(ck_epoch_t *, ck_epoch_record_t *, 235 void *); 236 237 /* 238 * Return latest epoch value. This operation provides load ordering. 239 */ 240 CK_CC_FORCE_INLINE static unsigned int 241 ck_epoch_value(const ck_epoch_t *ep) 242 { 243 244 ck_pr_fence_load(); 245 return ck_pr_load_uint(&ep->epoch); 246 } 247 248 void ck_epoch_init(ck_epoch_t *); 249 250 /* 251 * Attempts to recycle an unused epoch record. If one is successfully 252 * allocated, the record context pointer is also updated. 253 */ 254 ck_epoch_record_t *ck_epoch_recycle(ck_epoch_t *, void *); 255 256 /* 257 * Registers an epoch record. An optional context pointer may be passed that 258 * is retrievable with ck_epoch_record_ct. 259 */ 260 void ck_epoch_register(ck_epoch_t *, ck_epoch_record_t *, void *); 261 262 /* 263 * Marks a record as available for re-use by a subsequent recycle operation. 264 * Note that the record cannot be physically destroyed. 265 */ 266 void ck_epoch_unregister(ck_epoch_record_t *); 267 268 bool ck_epoch_poll(ck_epoch_record_t *); 269 void ck_epoch_synchronize(ck_epoch_record_t *); 270 void ck_epoch_synchronize_wait(ck_epoch_t *, ck_epoch_wait_cb_t *, void *); 271 void ck_epoch_barrier(ck_epoch_record_t *); 272 void ck_epoch_barrier_wait(ck_epoch_record_t *, ck_epoch_wait_cb_t *, void *); 273 274 /* 275 * Reclaim entries associated with a record. This is safe to call only on 276 * the caller's record or records that are using call_strict. 277 */ 278 void ck_epoch_reclaim(ck_epoch_record_t *); 279 280 #endif /* CK_EPOCH_H */ 281