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[urcu.git] / urcu.c
1 #include <stdio.h>
2 #include <pthread.h>
3 #include <signal.h>
4 #include <assert.h>
5 #include <stdlib.h>
6 #include <string.h>
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;
22 int *urcu_active_readers;
23 };
24
25 static struct reader_data *reader_data;
26 static int num_readers, alloc_readers;
27 static int sig_done;
28
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
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 {
62 struct reader_data *index;
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;
69 sig_done = 0;
70 mb(); /* write sig_done before sending the signals */
71 for (index = reader_data; index < reader_data + num_readers; index++)
72 pthread_kill(index->tid, SIGURCU);
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();
79 mb(); /* read sig_done before ending the barrier */
80 }
81
82 void wait_for_quiescent_state(int parity)
83 {
84 struct reader_data *index;
85
86 if (!reader_data)
87 return;
88 /* Wait for each thread urcu_active_readers count to become 0.
89 */
90 for (index = reader_data; index < reader_data + num_readers; index++) {
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.
108 * Called under rcu_write_lock.
109 */
110 void *urcu_publish_content(void **ptr, void *new)
111 {
112 int ret, prev_parity;
113 void *oldptr;
114
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 */
129 force_mb_all_threads();
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
140 return oldptr;
141 }
142
143 void urcu_add_reader(pthread_t id)
144 {
145 struct reader_data *oldarray;
146
147 if (!reader_data) {
148 alloc_readers = INIT_NUM_THREADS;
149 num_readers = 0;
150 reader_data =
151 malloc(sizeof(struct reader_data) * alloc_readers);
152 }
153 if (alloc_readers < num_readers + 1) {
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 {
193 rcu_write_lock();
194 urcu_add_reader(pthread_self());
195 rcu_write_unlock();
196 }
197
198 void urcu_unregister_thread(void)
199 {
200 pthread_t self = pthread_self();
201 rcu_write_lock();
202 urcu_remove_reader(pthread_self());
203 rcu_write_unlock();
204 }
205
206 void sigurcu_handler(int signo, siginfo_t *siginfo, void *context)
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);
219 if (ret) {
220 perror("Error in sigaction");
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);
231 if (ret) {
232 perror("Error in sigaction");
233 exit(-1);
234 }
235 assert(act.sa_sigaction == sigurcu_handler);
236 free(reader_data);
237 }
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