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27b012e2 MD |
1 | #include <stdio.h> |
2 | #include <pthread.h> | |
3 | #include <signal.h> | |
4 | #include <assert.h> | |
f69f195a MD |
5 | #include <stdlib.h> |
6 | #include <string.h> | |
27b012e2 MD |
7 | |
8 | #include "urcu.h" | |
9 | ||
10 | pthread_mutex_t urcu_mutex = PTHREAD_MUTEX_INITIALIZER; | |
11 | ||
12 | /* Global quiescent period parity */ | |
13 | int urcu_qparity; | |
14 | ||
15 | int __thread urcu_active_readers[2]; | |
16 | ||
17 | /* Thread IDs of registered readers */ | |
18 | #define INIT_NUM_THREADS 4 | |
19 | ||
20 | struct reader_data { | |
21 | pthread_t tid; | |
f69f195a | 22 | int *urcu_active_readers; |
27b012e2 MD |
23 | }; |
24 | ||
25 | static struct reader_data *reader_data; | |
26 | static int num_readers, alloc_readers; | |
27 | static int sig_done; | |
28 | ||
29 | /* | |
30 | * called with urcu_mutex held. | |
31 | */ | |
32 | static int switch_next_urcu_qparity(void) | |
33 | { | |
34 | int old_parity = urcu_qparity; | |
35 | urcu_qparity = 1 - old_parity; | |
36 | return old_parity; | |
37 | } | |
38 | ||
39 | static void force_mb_all_threads(void) | |
40 | { | |
f69f195a | 41 | struct reader_data *index; |
27b012e2 MD |
42 | /* |
43 | * Ask for each threads to execute a mb() so we can consider the | |
44 | * compiler barriers around rcu read lock as real memory barriers. | |
45 | */ | |
46 | if (!reader_data) | |
47 | return; | |
27b012e2 | 48 | sig_done = 0; |
f69f195a | 49 | mb(); /* write sig_done before sending the signals */ |
27b012e2 | 50 | for (index = reader_data; index < reader_data + num_readers; index++) |
f69f195a | 51 | pthread_kill(index->tid, SIGURCU); |
27b012e2 MD |
52 | /* |
53 | * Wait for sighandler (and thus mb()) to execute on every thread. | |
54 | * BUSY-LOOP. | |
55 | */ | |
56 | while (sig_done < num_readers) | |
57 | barrier(); | |
f69f195a | 58 | mb(); /* read sig_done before ending the barrier */ |
27b012e2 MD |
59 | } |
60 | ||
61 | void wait_for_quiescent_state(int parity) | |
62 | { | |
f69f195a | 63 | struct reader_data *index; |
27b012e2 MD |
64 | |
65 | if (!reader_data) | |
66 | return; | |
67 | /* Wait for each thread urcu_active_readers count to become 0. | |
68 | */ | |
f69f195a | 69 | for (index = reader_data; index < reader_data + num_readers; index++) { |
27b012e2 MD |
70 | /* |
71 | * BUSY-LOOP. | |
72 | */ | |
73 | while (*index->urcu_active_readers != 0) | |
74 | barrier(); | |
75 | } | |
76 | /* | |
77 | * Locally : read *index->urcu_active_readers before freeing old | |
78 | * pointer. | |
79 | * Remote (reader threads) : Order urcu_qparity update and other | |
80 | * thread's quiescent state counter read. | |
81 | */ | |
82 | force_mb_all_threads(); | |
83 | } | |
84 | ||
85 | /* | |
86 | * Return old pointer, OK to free, no more reference exist. | |
87 | */ | |
88 | void *urcu_publish_content(void **ptr, void *new) | |
89 | { | |
90 | int ret, prev_parity; | |
91 | void *oldptr; | |
92 | ||
93 | ret = pthread_mutex_lock(&urcu_mutex); | |
94 | if (ret) { | |
f69f195a | 95 | perror("Error in pthread mutex lock"); |
27b012e2 MD |
96 | exit(-1); |
97 | } | |
98 | ||
99 | /* | |
100 | * We can publish the new pointer before we change the current qparity. | |
101 | * Readers seeing the new pointer while being in the previous qparity | |
102 | * window will make us wait until the end of the quiescent state before | |
103 | * we release the unrelated memory area. However, given we hold the | |
104 | * urcu_mutex, we are making sure that no further garbage collection can | |
105 | * occur until we release the mutex, therefore we guarantee that this | |
106 | * given reader will have completed its execution using the new pointer | |
107 | * when the next quiescent state window will be over. | |
108 | */ | |
109 | oldptr = *ptr; | |
110 | *ptr = new; | |
111 | wmb(); /* Write ptr before changing the qparity */ | |
112 | /* All threads should read qparity before ptr */ | |
f69f195a | 113 | force_mb_all_threads(); |
27b012e2 MD |
114 | prev_parity = switch_next_urcu_qparity(); |
115 | ||
116 | /* | |
117 | * Wait for previous parity to be empty of readers. | |
118 | */ | |
119 | wait_for_quiescent_state(prev_parity); | |
120 | /* | |
121 | * Deleting old data is ok ! | |
122 | */ | |
123 | ||
124 | ret = pthread_mutex_unlock(&urcu_mutex); | |
125 | if (ret) { | |
f69f195a | 126 | perror("Error in pthread mutex lock"); |
27b012e2 MD |
127 | exit(-1); |
128 | } | |
129 | return oldptr; | |
130 | } | |
131 | ||
132 | void urcu_add_reader(pthread_t id) | |
133 | { | |
f69f195a MD |
134 | struct reader_data *oldarray; |
135 | ||
27b012e2 MD |
136 | if (!reader_data) { |
137 | alloc_readers = INIT_NUM_THREADS; | |
f69f195a | 138 | num_readers = 0; |
27b012e2 MD |
139 | reader_data = |
140 | malloc(sizeof(struct reader_data) * alloc_readers); | |
27b012e2 MD |
141 | } |
142 | if (alloc_readers < num_readers + 1) { | |
27b012e2 MD |
143 | oldarray = reader_data; |
144 | reader_data = malloc(sizeof(struct reader_data) | |
145 | * (alloc_readers << 1)); | |
146 | memcpy(reader_data, oldarray, | |
147 | sizeof(struct reader_data) * alloc_readers); | |
148 | alloc_readers <<= 1; | |
149 | free(oldarray); | |
150 | } | |
151 | reader_data[num_readers].tid = id; | |
152 | /* reference to the TLS of _this_ reader thread. */ | |
153 | reader_data[num_readers].urcu_active_readers = urcu_active_readers; | |
154 | num_readers++; | |
155 | } | |
156 | ||
157 | /* | |
158 | * Never shrink (implementation limitation). | |
159 | * This is O(nb threads). Eventually use a hash table. | |
160 | */ | |
161 | void urcu_remove_reader(pthread_t id) | |
162 | { | |
163 | struct reader_data *index; | |
164 | ||
165 | assert(reader_data != NULL); | |
166 | for (index = reader_data; index < reader_data + num_readers; index++) { | |
167 | if (index->tid == id) { | |
168 | memcpy(index, &reader_data[num_readers - 1], | |
169 | sizeof(struct reader_data)); | |
170 | reader_data[num_readers - 1].tid = 0; | |
171 | reader_data[num_readers - 1].urcu_active_readers = NULL; | |
172 | num_readers--; | |
173 | return; | |
174 | } | |
175 | } | |
176 | /* Hrm not found, forgot to register ? */ | |
177 | assert(0); | |
178 | } | |
179 | ||
180 | void urcu_register_thread(void) | |
181 | { | |
182 | pthread_t self = pthread_self(); | |
f69f195a | 183 | int ret; |
27b012e2 MD |
184 | |
185 | ret = pthread_mutex_lock(&urcu_mutex); | |
186 | if (ret) { | |
f69f195a | 187 | perror("Error in pthread mutex lock"); |
27b012e2 MD |
188 | exit(-1); |
189 | } | |
190 | ||
191 | urcu_add_reader(self); | |
192 | ||
193 | ||
194 | ret = pthread_mutex_unlock(&urcu_mutex); | |
195 | if (ret) { | |
f69f195a | 196 | perror("Error in pthread mutex unlock"); |
27b012e2 MD |
197 | exit(-1); |
198 | } | |
199 | } | |
200 | ||
f69f195a | 201 | void urcu_unregister_thread(void) |
27b012e2 MD |
202 | { |
203 | pthread_t self = pthread_self(); | |
f69f195a | 204 | int ret; |
27b012e2 MD |
205 | |
206 | ret = pthread_mutex_lock(&urcu_mutex); | |
207 | if (ret) { | |
f69f195a | 208 | perror("Error in pthread mutex lock"); |
27b012e2 MD |
209 | exit(-1); |
210 | } | |
211 | ||
212 | urcu_remove_reader(self); | |
213 | ||
214 | ret = pthread_mutex_unlock(&urcu_mutex); | |
215 | if (ret) { | |
f69f195a | 216 | perror("Error in pthread mutex unlock"); |
27b012e2 MD |
217 | exit(-1); |
218 | } | |
219 | ||
220 | } | |
221 | ||
f69f195a | 222 | void sigurcu_handler(int signo, siginfo_t *siginfo, void *context) |
27b012e2 MD |
223 | { |
224 | mb(); | |
225 | atomic_inc(&sig_done); | |
226 | } | |
227 | ||
228 | void __attribute__((constructor)) urcu_init(void) | |
229 | { | |
230 | struct sigaction act; | |
231 | int ret; | |
232 | ||
233 | act.sa_sigaction = sigurcu_handler; | |
234 | ret = sigaction(SIGURCU, &act, NULL); | |
f69f195a MD |
235 | if (ret) { |
236 | perror("Error in sigaction"); | |
27b012e2 MD |
237 | exit(-1); |
238 | } | |
239 | } | |
240 | ||
241 | void __attribute__((destructor)) urcu_exit(void) | |
242 | { | |
243 | struct sigaction act; | |
244 | int ret; | |
245 | ||
246 | ret = sigaction(SIGURCU, NULL, &act); | |
f69f195a MD |
247 | if (ret) { |
248 | perror("Error in sigaction"); | |
27b012e2 MD |
249 | exit(-1); |
250 | } | |
251 | assert(act.sa_sigaction == sigurcu_handler); | |
252 | free(reader_data); | |
253 | } |