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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 | ||
41718ff9 MD |
29 | void rcu_write_lock(void) |
30 | { | |
31 | int ret; | |
32 | ret = pthread_mutex_lock(&urcu_mutex); | |
33 | if (ret) { | |
34 | perror("Error in pthread mutex lock"); | |
35 | exit(-1); | |
36 | } | |
37 | } | |
38 | ||
39 | void rcu_write_unlock(void) | |
40 | { | |
41 | int ret; | |
42 | ||
43 | ret = pthread_mutex_unlock(&urcu_mutex); | |
44 | if (ret) { | |
45 | perror("Error in pthread mutex unlock"); | |
46 | exit(-1); | |
47 | } | |
48 | } | |
49 | ||
27b012e2 MD |
50 | /* |
51 | * called with urcu_mutex held. | |
52 | */ | |
53 | static int switch_next_urcu_qparity(void) | |
54 | { | |
55 | int old_parity = urcu_qparity; | |
56 | urcu_qparity = 1 - old_parity; | |
57 | return old_parity; | |
58 | } | |
59 | ||
60 | static void force_mb_all_threads(void) | |
61 | { | |
f69f195a | 62 | struct reader_data *index; |
27b012e2 MD |
63 | /* |
64 | * Ask for each threads to execute a mb() so we can consider the | |
65 | * compiler barriers around rcu read lock as real memory barriers. | |
66 | */ | |
67 | if (!reader_data) | |
68 | return; | |
27b012e2 | 69 | sig_done = 0; |
f69f195a | 70 | mb(); /* write sig_done before sending the signals */ |
27b012e2 | 71 | for (index = reader_data; index < reader_data + num_readers; index++) |
f69f195a | 72 | pthread_kill(index->tid, SIGURCU); |
27b012e2 MD |
73 | /* |
74 | * Wait for sighandler (and thus mb()) to execute on every thread. | |
75 | * BUSY-LOOP. | |
76 | */ | |
77 | while (sig_done < num_readers) | |
78 | barrier(); | |
f69f195a | 79 | mb(); /* read sig_done before ending the barrier */ |
27b012e2 MD |
80 | } |
81 | ||
82 | void wait_for_quiescent_state(int parity) | |
83 | { | |
f69f195a | 84 | struct reader_data *index; |
27b012e2 MD |
85 | |
86 | if (!reader_data) | |
87 | return; | |
88 | /* Wait for each thread urcu_active_readers count to become 0. | |
89 | */ | |
f69f195a | 90 | for (index = reader_data; index < reader_data + num_readers; index++) { |
27b012e2 MD |
91 | /* |
92 | * BUSY-LOOP. | |
93 | */ | |
94 | while (*index->urcu_active_readers != 0) | |
95 | barrier(); | |
96 | } | |
97 | /* | |
98 | * Locally : read *index->urcu_active_readers before freeing old | |
99 | * pointer. | |
100 | * Remote (reader threads) : Order urcu_qparity update and other | |
101 | * thread's quiescent state counter read. | |
102 | */ | |
103 | force_mb_all_threads(); | |
104 | } | |
105 | ||
106 | /* | |
107 | * Return old pointer, OK to free, no more reference exist. | |
41718ff9 | 108 | * Called under rcu_write_lock. |
27b012e2 MD |
109 | */ |
110 | void *urcu_publish_content(void **ptr, void *new) | |
111 | { | |
112 | int ret, prev_parity; | |
113 | void *oldptr; | |
114 | ||
27b012e2 MD |
115 | /* |
116 | * We can publish the new pointer before we change the current qparity. | |
117 | * Readers seeing the new pointer while being in the previous qparity | |
118 | * window will make us wait until the end of the quiescent state before | |
119 | * we release the unrelated memory area. However, given we hold the | |
120 | * urcu_mutex, we are making sure that no further garbage collection can | |
121 | * occur until we release the mutex, therefore we guarantee that this | |
122 | * given reader will have completed its execution using the new pointer | |
123 | * when the next quiescent state window will be over. | |
124 | */ | |
125 | oldptr = *ptr; | |
126 | *ptr = new; | |
127 | wmb(); /* Write ptr before changing the qparity */ | |
128 | /* All threads should read qparity before ptr */ | |
f69f195a | 129 | force_mb_all_threads(); |
27b012e2 MD |
130 | prev_parity = switch_next_urcu_qparity(); |
131 | ||
132 | /* | |
133 | * Wait for previous parity to be empty of readers. | |
134 | */ | |
135 | wait_for_quiescent_state(prev_parity); | |
136 | /* | |
137 | * Deleting old data is ok ! | |
138 | */ | |
139 | ||
27b012e2 MD |
140 | return oldptr; |
141 | } | |
142 | ||
143 | void urcu_add_reader(pthread_t id) | |
144 | { | |
f69f195a MD |
145 | struct reader_data *oldarray; |
146 | ||
27b012e2 MD |
147 | if (!reader_data) { |
148 | alloc_readers = INIT_NUM_THREADS; | |
f69f195a | 149 | num_readers = 0; |
27b012e2 MD |
150 | reader_data = |
151 | malloc(sizeof(struct reader_data) * alloc_readers); | |
27b012e2 MD |
152 | } |
153 | if (alloc_readers < num_readers + 1) { | |
27b012e2 MD |
154 | oldarray = reader_data; |
155 | reader_data = malloc(sizeof(struct reader_data) | |
156 | * (alloc_readers << 1)); | |
157 | memcpy(reader_data, oldarray, | |
158 | sizeof(struct reader_data) * alloc_readers); | |
159 | alloc_readers <<= 1; | |
160 | free(oldarray); | |
161 | } | |
162 | reader_data[num_readers].tid = id; | |
163 | /* reference to the TLS of _this_ reader thread. */ | |
164 | reader_data[num_readers].urcu_active_readers = urcu_active_readers; | |
165 | num_readers++; | |
166 | } | |
167 | ||
168 | /* | |
169 | * Never shrink (implementation limitation). | |
170 | * This is O(nb threads). Eventually use a hash table. | |
171 | */ | |
172 | void urcu_remove_reader(pthread_t id) | |
173 | { | |
174 | struct reader_data *index; | |
175 | ||
176 | assert(reader_data != NULL); | |
177 | for (index = reader_data; index < reader_data + num_readers; index++) { | |
178 | if (index->tid == id) { | |
179 | memcpy(index, &reader_data[num_readers - 1], | |
180 | sizeof(struct reader_data)); | |
181 | reader_data[num_readers - 1].tid = 0; | |
182 | reader_data[num_readers - 1].urcu_active_readers = NULL; | |
183 | num_readers--; | |
184 | return; | |
185 | } | |
186 | } | |
187 | /* Hrm not found, forgot to register ? */ | |
188 | assert(0); | |
189 | } | |
190 | ||
191 | void urcu_register_thread(void) | |
192 | { | |
41718ff9 MD |
193 | rcu_write_lock(); |
194 | urcu_add_reader(pthread_self()); | |
195 | rcu_write_unlock(); | |
27b012e2 MD |
196 | } |
197 | ||
f69f195a | 198 | void urcu_unregister_thread(void) |
27b012e2 MD |
199 | { |
200 | pthread_t self = pthread_self(); | |
41718ff9 MD |
201 | rcu_write_lock(); |
202 | urcu_remove_reader(pthread_self()); | |
203 | rcu_write_unlock(); | |
27b012e2 MD |
204 | } |
205 | ||
f69f195a | 206 | void sigurcu_handler(int signo, siginfo_t *siginfo, void *context) |
27b012e2 MD |
207 | { |
208 | mb(); | |
209 | atomic_inc(&sig_done); | |
210 | } | |
211 | ||
212 | void __attribute__((constructor)) urcu_init(void) | |
213 | { | |
214 | struct sigaction act; | |
215 | int ret; | |
216 | ||
217 | act.sa_sigaction = sigurcu_handler; | |
218 | ret = sigaction(SIGURCU, &act, NULL); | |
f69f195a MD |
219 | if (ret) { |
220 | perror("Error in sigaction"); | |
27b012e2 MD |
221 | exit(-1); |
222 | } | |
223 | } | |
224 | ||
225 | void __attribute__((destructor)) urcu_exit(void) | |
226 | { | |
227 | struct sigaction act; | |
228 | int ret; | |
229 | ||
230 | ret = sigaction(SIGURCU, NULL, &act); | |
f69f195a MD |
231 | if (ret) { |
232 | perror("Error in sigaction"); | |
27b012e2 MD |
233 | exit(-1); |
234 | } | |
235 | assert(act.sa_sigaction == sigurcu_handler); | |
236 | free(reader_data); | |
237 | } |