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 | ||
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; | |
f69f195a | 32 | int *urcu_active_readers; |
27b012e2 MD |
33 | }; |
34 | ||
35 | static struct reader_data *reader_data; | |
36 | static int num_readers, alloc_readers; | |
37 | static int sig_done; | |
38 | ||
41718ff9 MD |
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 | ||
27b012e2 MD |
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 | { | |
f69f195a | 72 | struct reader_data *index; |
27b012e2 MD |
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; | |
27b012e2 | 79 | sig_done = 0; |
f69f195a | 80 | mb(); /* write sig_done before sending the signals */ |
27b012e2 | 81 | for (index = reader_data; index < reader_data + num_readers; index++) |
f69f195a | 82 | pthread_kill(index->tid, SIGURCU); |
27b012e2 MD |
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(); | |
f69f195a | 89 | mb(); /* read sig_done before ending the barrier */ |
27b012e2 MD |
90 | } |
91 | ||
92 | void wait_for_quiescent_state(int parity) | |
93 | { | |
f69f195a | 94 | struct reader_data *index; |
27b012e2 MD |
95 | |
96 | if (!reader_data) | |
97 | return; | |
98 | /* Wait for each thread urcu_active_readers count to become 0. | |
99 | */ | |
f69f195a | 100 | for (index = reader_data; index < reader_data + num_readers; index++) { |
27b012e2 MD |
101 | /* |
102 | * BUSY-LOOP. | |
103 | */ | |
f858d07a | 104 | while (index->urcu_active_readers[parity] != 0) |
27b012e2 MD |
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. | |
41718ff9 | 118 | * Called under rcu_write_lock. |
27b012e2 | 119 | */ |
cdcb92bb | 120 | void *urcu_publish_content(void **ptr, void *new) |
27b012e2 | 121 | { |
5e7e64b9 | 122 | int prev_parity; |
27b012e2 MD |
123 | void *oldptr; |
124 | ||
27b012e2 MD |
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; | |
27b012e2 | 137 | /* All threads should read qparity before ptr */ |
f858d07a | 138 | /* Write ptr before changing the qparity */ |
f69f195a | 139 | force_mb_all_threads(); |
27b012e2 MD |
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 | ||
27b012e2 MD |
150 | return oldptr; |
151 | } | |
152 | ||
153 | void urcu_add_reader(pthread_t id) | |
154 | { | |
f69f195a MD |
155 | struct reader_data *oldarray; |
156 | ||
27b012e2 MD |
157 | if (!reader_data) { |
158 | alloc_readers = INIT_NUM_THREADS; | |
f69f195a | 159 | num_readers = 0; |
27b012e2 MD |
160 | reader_data = |
161 | malloc(sizeof(struct reader_data) * alloc_readers); | |
27b012e2 MD |
162 | } |
163 | if (alloc_readers < num_readers + 1) { | |
27b012e2 MD |
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++) { | |
e6d6e2dc | 188 | if (pthread_equal(index->tid, id)) { |
27b012e2 MD |
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 | { | |
41718ff9 MD |
203 | rcu_write_lock(); |
204 | urcu_add_reader(pthread_self()); | |
205 | rcu_write_unlock(); | |
27b012e2 MD |
206 | } |
207 | ||
f69f195a | 208 | void urcu_unregister_thread(void) |
27b012e2 | 209 | { |
41718ff9 MD |
210 | rcu_write_lock(); |
211 | urcu_remove_reader(pthread_self()); | |
212 | rcu_write_unlock(); | |
27b012e2 MD |
213 | } |
214 | ||
f69f195a | 215 | void sigurcu_handler(int signo, siginfo_t *siginfo, void *context) |
27b012e2 MD |
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); | |
f69f195a MD |
228 | if (ret) { |
229 | perror("Error in sigaction"); | |
27b012e2 MD |
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); | |
f69f195a MD |
240 | if (ret) { |
241 | perror("Error in sigaction"); | |
27b012e2 MD |
242 | exit(-1); |
243 | } | |
244 | assert(act.sa_sigaction == sigurcu_handler); | |
245 | free(reader_data); | |
246 | } |