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