Commit | Line | Data |
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b257a10b MD |
1 | /* |
2 | * urcu.c | |
3 | * | |
4 | * Userspace RCU library | |
5 | * | |
6 | * Copyright February 2009 - Mathieu Desnoyers <mathieu.desnoyers@polymtl.ca> | |
7 | * | |
8 | * Distributed under GPLv2 | |
9 | */ | |
10 | ||
27b012e2 MD |
11 | #include <stdio.h> |
12 | #include <pthread.h> | |
13 | #include <signal.h> | |
14 | #include <assert.h> | |
f69f195a MD |
15 | #include <stdlib.h> |
16 | #include <string.h> | |
27b012e2 MD |
17 | |
18 | #include "urcu.h" | |
19 | ||
20 | pthread_mutex_t urcu_mutex = PTHREAD_MUTEX_INITIALIZER; | |
21 | ||
128166c9 MD |
22 | /* |
23 | * Global grace period counter. | |
24 | * Contains the current RCU_GP_CTR_BIT. | |
25 | * Also has a RCU_GP_CTR_BIT of 1, to accelerate the reader fast path. | |
26 | */ | |
27 | long urcu_gp_ctr = RCU_GP_COUNT; | |
27b012e2 | 28 | |
6e8b8429 | 29 | long __thread urcu_active_readers; |
27b012e2 MD |
30 | |
31 | /* Thread IDs of registered readers */ | |
32 | #define INIT_NUM_THREADS 4 | |
33 | ||
34 | struct reader_data { | |
35 | pthread_t tid; | |
128166c9 | 36 | long *urcu_active_readers; |
27b012e2 MD |
37 | }; |
38 | ||
cf380c2f | 39 | #ifdef DEBUG_YIELD |
9d335088 MD |
40 | unsigned int yield_active; |
41 | unsigned int __thread rand_yield; | |
cf380c2f MD |
42 | #endif |
43 | ||
27b012e2 MD |
44 | static struct reader_data *reader_data; |
45 | static int num_readers, alloc_readers; | |
46 | static int sig_done; | |
47 | ||
c265818b | 48 | void internal_urcu_lock(void) |
41718ff9 MD |
49 | { |
50 | int ret; | |
51 | ret = pthread_mutex_lock(&urcu_mutex); | |
52 | if (ret) { | |
53 | perror("Error in pthread mutex lock"); | |
54 | exit(-1); | |
55 | } | |
56 | } | |
57 | ||
c265818b | 58 | void internal_urcu_unlock(void) |
41718ff9 MD |
59 | { |
60 | int ret; | |
61 | ||
62 | ret = pthread_mutex_unlock(&urcu_mutex); | |
63 | if (ret) { | |
64 | perror("Error in pthread mutex unlock"); | |
65 | exit(-1); | |
66 | } | |
67 | } | |
68 | ||
27b012e2 MD |
69 | /* |
70 | * called with urcu_mutex held. | |
71 | */ | |
1430ee0b | 72 | static void switch_next_urcu_qparity(void) |
27b012e2 | 73 | { |
1430ee0b | 74 | urcu_gp_ctr ^= RCU_GP_CTR_BIT; |
27b012e2 MD |
75 | } |
76 | ||
77 | static void force_mb_all_threads(void) | |
78 | { | |
f69f195a | 79 | struct reader_data *index; |
27b012e2 MD |
80 | /* |
81 | * Ask for each threads to execute a mb() so we can consider the | |
82 | * compiler barriers around rcu read lock as real memory barriers. | |
83 | */ | |
84 | if (!reader_data) | |
85 | return; | |
cf380c2f | 86 | debug_yield_write(); |
27b012e2 | 87 | sig_done = 0; |
cf380c2f | 88 | debug_yield_write(); |
f69f195a | 89 | mb(); /* write sig_done before sending the signals */ |
cf380c2f MD |
90 | debug_yield_write(); |
91 | for (index = reader_data; index < reader_data + num_readers; index++) { | |
f69f195a | 92 | pthread_kill(index->tid, SIGURCU); |
cf380c2f MD |
93 | debug_yield_write(); |
94 | } | |
27b012e2 MD |
95 | /* |
96 | * Wait for sighandler (and thus mb()) to execute on every thread. | |
97 | * BUSY-LOOP. | |
98 | */ | |
99 | while (sig_done < num_readers) | |
100 | barrier(); | |
cf380c2f | 101 | debug_yield_write(); |
f69f195a | 102 | mb(); /* read sig_done before ending the barrier */ |
cf380c2f | 103 | debug_yield_write(); |
27b012e2 MD |
104 | } |
105 | ||
1430ee0b | 106 | void wait_for_quiescent_state(void) |
27b012e2 | 107 | { |
f69f195a | 108 | struct reader_data *index; |
27b012e2 MD |
109 | |
110 | if (!reader_data) | |
111 | return; | |
112 | /* Wait for each thread urcu_active_readers count to become 0. | |
113 | */ | |
f69f195a | 114 | for (index = reader_data; index < reader_data + num_readers; index++) { |
27b012e2 MD |
115 | /* |
116 | * BUSY-LOOP. | |
117 | */ | |
1430ee0b | 118 | while (rcu_old_gp_ongoing(index->urcu_active_readers)) |
27b012e2 MD |
119 | barrier(); |
120 | } | |
121 | /* | |
122 | * Locally : read *index->urcu_active_readers before freeing old | |
123 | * pointer. | |
124 | * Remote (reader threads) : Order urcu_qparity update and other | |
125 | * thread's quiescent state counter read. | |
126 | */ | |
127 | force_mb_all_threads(); | |
128 | } | |
129 | ||
2bc59bd7 PM |
130 | static void switch_qparity(void) |
131 | { | |
2bc59bd7 PM |
132 | /* All threads should read qparity before accessing data structure. */ |
133 | /* Write ptr before changing the qparity */ | |
134 | force_mb_all_threads(); | |
cf380c2f | 135 | debug_yield_write(); |
1430ee0b | 136 | switch_next_urcu_qparity(); |
cf380c2f | 137 | debug_yield_write(); |
2bc59bd7 PM |
138 | |
139 | /* | |
140 | * Wait for previous parity to be empty of readers. | |
141 | */ | |
1430ee0b | 142 | wait_for_quiescent_state(); |
2bc59bd7 PM |
143 | } |
144 | ||
145 | void synchronize_rcu(void) | |
146 | { | |
cf380c2f | 147 | debug_yield_write(); |
c265818b | 148 | internal_urcu_lock(); |
cf380c2f | 149 | debug_yield_write(); |
2bc59bd7 | 150 | switch_qparity(); |
cf380c2f | 151 | debug_yield_write(); |
2bc59bd7 | 152 | switch_qparity(); |
cf380c2f | 153 | debug_yield_write(); |
e7b43771 | 154 | internal_urcu_unlock(); |
cf380c2f | 155 | debug_yield_write(); |
2bc59bd7 PM |
156 | } |
157 | ||
27b012e2 MD |
158 | void urcu_add_reader(pthread_t id) |
159 | { | |
f69f195a MD |
160 | struct reader_data *oldarray; |
161 | ||
27b012e2 MD |
162 | if (!reader_data) { |
163 | alloc_readers = INIT_NUM_THREADS; | |
f69f195a | 164 | num_readers = 0; |
27b012e2 MD |
165 | reader_data = |
166 | malloc(sizeof(struct reader_data) * alloc_readers); | |
27b012e2 MD |
167 | } |
168 | if (alloc_readers < num_readers + 1) { | |
27b012e2 MD |
169 | oldarray = reader_data; |
170 | reader_data = malloc(sizeof(struct reader_data) | |
171 | * (alloc_readers << 1)); | |
172 | memcpy(reader_data, oldarray, | |
173 | sizeof(struct reader_data) * alloc_readers); | |
174 | alloc_readers <<= 1; | |
175 | free(oldarray); | |
176 | } | |
177 | reader_data[num_readers].tid = id; | |
178 | /* reference to the TLS of _this_ reader thread. */ | |
1430ee0b | 179 | reader_data[num_readers].urcu_active_readers = &urcu_active_readers; |
27b012e2 MD |
180 | num_readers++; |
181 | } | |
182 | ||
183 | /* | |
184 | * Never shrink (implementation limitation). | |
185 | * This is O(nb threads). Eventually use a hash table. | |
186 | */ | |
187 | void urcu_remove_reader(pthread_t id) | |
188 | { | |
189 | struct reader_data *index; | |
190 | ||
191 | assert(reader_data != NULL); | |
192 | for (index = reader_data; index < reader_data + num_readers; index++) { | |
e6d6e2dc | 193 | if (pthread_equal(index->tid, id)) { |
27b012e2 MD |
194 | memcpy(index, &reader_data[num_readers - 1], |
195 | sizeof(struct reader_data)); | |
196 | reader_data[num_readers - 1].tid = 0; | |
197 | reader_data[num_readers - 1].urcu_active_readers = NULL; | |
198 | num_readers--; | |
199 | return; | |
200 | } | |
201 | } | |
202 | /* Hrm not found, forgot to register ? */ | |
203 | assert(0); | |
204 | } | |
205 | ||
206 | void urcu_register_thread(void) | |
207 | { | |
c265818b | 208 | internal_urcu_lock(); |
41718ff9 | 209 | urcu_add_reader(pthread_self()); |
c265818b | 210 | internal_urcu_unlock(); |
27b012e2 MD |
211 | } |
212 | ||
f69f195a | 213 | void urcu_unregister_thread(void) |
27b012e2 | 214 | { |
c265818b | 215 | internal_urcu_lock(); |
41718ff9 | 216 | urcu_remove_reader(pthread_self()); |
c265818b | 217 | internal_urcu_unlock(); |
27b012e2 MD |
218 | } |
219 | ||
f69f195a | 220 | void sigurcu_handler(int signo, siginfo_t *siginfo, void *context) |
27b012e2 MD |
221 | { |
222 | mb(); | |
223 | atomic_inc(&sig_done); | |
224 | } | |
225 | ||
226 | void __attribute__((constructor)) urcu_init(void) | |
227 | { | |
228 | struct sigaction act; | |
229 | int ret; | |
230 | ||
231 | act.sa_sigaction = sigurcu_handler; | |
232 | ret = sigaction(SIGURCU, &act, NULL); | |
f69f195a MD |
233 | if (ret) { |
234 | perror("Error in sigaction"); | |
27b012e2 MD |
235 | exit(-1); |
236 | } | |
237 | } | |
238 | ||
239 | void __attribute__((destructor)) urcu_exit(void) | |
240 | { | |
241 | struct sigaction act; | |
242 | int ret; | |
243 | ||
244 | ret = sigaction(SIGURCU, NULL, &act); | |
f69f195a MD |
245 | if (ret) { |
246 | perror("Error in sigaction"); | |
27b012e2 MD |
247 | exit(-1); |
248 | } | |
249 | assert(act.sa_sigaction == sigurcu_handler); | |
250 | free(reader_data); | |
251 | } |