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1 | /* | |
2 | * Copyright (c) 2013, 2014 Nicira, Inc. | |
3 | * | |
4 | * Licensed under the Apache License, Version 2.0 (the "License"); | |
5 | * you may not use this file except in compliance with the License. | |
6 | * You may obtain a copy of the License at: | |
7 | * | |
8 | * http://www.apache.org/licenses/LICENSE-2.0 | |
9 | * | |
10 | * Unless required by applicable law or agreed to in writing, software | |
11 | * distributed under the License is distributed on an "AS IS" BASIS, | |
12 | * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. | |
13 | * See the License for the specific language governing permissions and | |
14 | * limitations under the License. | |
15 | */ | |
16 | ||
17 | #include <config.h> | |
18 | ||
19 | #include "seq.h" | |
20 | ||
21 | #include <stdbool.h> | |
22 | ||
23 | #include "coverage.h" | |
24 | #include "hash.h" | |
25 | #include "hmap.h" | |
26 | #include "latch.h" | |
27 | #include "openvswitch/list.h" | |
28 | #include "ovs-thread.h" | |
29 | #include "poll-loop.h" | |
30 | ||
31 | COVERAGE_DEFINE(seq_change); | |
32 | ||
33 | /* A sequence number object. */ | |
34 | struct seq { | |
35 | uint64_t value OVS_GUARDED; | |
36 | struct hmap waiters OVS_GUARDED; /* Contains 'struct seq_waiter's. */ | |
37 | }; | |
38 | ||
39 | /* A thread waiting on a particular seq. */ | |
40 | struct seq_waiter { | |
41 | struct seq *seq OVS_GUARDED; /* Seq being waited for. */ | |
42 | struct hmap_node hmap_node OVS_GUARDED; /* In 'seq->waiters'. */ | |
43 | unsigned int ovsthread_id OVS_GUARDED; /* Key in 'waiters' hmap. */ | |
44 | ||
45 | struct seq_thread *thread OVS_GUARDED; /* Thread preparing to wait. */ | |
46 | struct ovs_list list_node OVS_GUARDED; /* In 'thread->waiters'. */ | |
47 | ||
48 | uint64_t value OVS_GUARDED; /* seq->value we're waiting to change. */ | |
49 | }; | |
50 | ||
51 | /* A thread that might be waiting on one or more seqs. */ | |
52 | struct seq_thread { | |
53 | struct ovs_list waiters OVS_GUARDED; /* Contains 'struct seq_waiter's. */ | |
54 | struct latch latch OVS_GUARDED; /* Wakeup latch for this thread. */ | |
55 | bool waiting OVS_GUARDED; /* True if latch_wait() already called. */ | |
56 | }; | |
57 | ||
58 | static struct ovs_mutex seq_mutex = OVS_MUTEX_INITIALIZER; | |
59 | ||
60 | static uint64_t seq_next OVS_GUARDED_BY(seq_mutex) = 1; | |
61 | ||
62 | static pthread_key_t seq_thread_key; | |
63 | ||
64 | static void seq_init(void); | |
65 | static struct seq_thread *seq_thread_get(void) OVS_REQUIRES(seq_mutex); | |
66 | static void seq_thread_exit(void *thread_) OVS_EXCLUDED(seq_mutex); | |
67 | static void seq_thread_woke(struct seq_thread *) OVS_REQUIRES(seq_mutex); | |
68 | static void seq_waiter_destroy(struct seq_waiter *) OVS_REQUIRES(seq_mutex); | |
69 | static void seq_wake_waiters(struct seq *) OVS_REQUIRES(seq_mutex); | |
70 | ||
71 | /* Creates and returns a new 'seq' object. */ | |
72 | struct seq * OVS_EXCLUDED(seq_mutex) | |
73 | seq_create(void) | |
74 | { | |
75 | struct seq *seq; | |
76 | ||
77 | seq_init(); | |
78 | ||
79 | seq = xmalloc(sizeof *seq); | |
80 | ||
81 | COVERAGE_INC(seq_change); | |
82 | ||
83 | ovs_mutex_lock(&seq_mutex); | |
84 | seq->value = seq_next++; | |
85 | hmap_init(&seq->waiters); | |
86 | ovs_mutex_unlock(&seq_mutex); | |
87 | ||
88 | return seq; | |
89 | } | |
90 | ||
91 | /* Destroys 'seq', waking up threads that were waiting on it, if any. */ | |
92 | void | |
93 | seq_destroy(struct seq *seq) | |
94 | OVS_EXCLUDED(seq_mutex) | |
95 | { | |
96 | ovs_mutex_lock(&seq_mutex); | |
97 | seq_wake_waiters(seq); | |
98 | hmap_destroy(&seq->waiters); | |
99 | free(seq); | |
100 | ovs_mutex_unlock(&seq_mutex); | |
101 | } | |
102 | ||
103 | /* Increments 'seq''s sequence number, waking up any threads that are waiting | |
104 | * on 'seq'. */ | |
105 | void | |
106 | seq_change(struct seq *seq) | |
107 | OVS_EXCLUDED(seq_mutex) | |
108 | { | |
109 | COVERAGE_INC(seq_change); | |
110 | ||
111 | ovs_mutex_lock(&seq_mutex); | |
112 | seq->value = seq_next++; | |
113 | seq_wake_waiters(seq); | |
114 | ovs_mutex_unlock(&seq_mutex); | |
115 | } | |
116 | ||
117 | /* Returns 'seq''s current sequence number (which could change immediately). | |
118 | * | |
119 | * seq_read() and seq_wait() can be used together to yield a race-free wakeup | |
120 | * when an object changes, even without an ability to lock the object. See | |
121 | * Usage in seq.h for details. */ | |
122 | uint64_t | |
123 | seq_read(const struct seq *seq) | |
124 | OVS_EXCLUDED(seq_mutex) | |
125 | { | |
126 | uint64_t value; | |
127 | ||
128 | ovs_mutex_lock(&seq_mutex); | |
129 | value = seq->value; | |
130 | ovs_mutex_unlock(&seq_mutex); | |
131 | ||
132 | return value; | |
133 | } | |
134 | ||
135 | static void | |
136 | seq_wait__(struct seq *seq, uint64_t value, const char *where) | |
137 | OVS_REQUIRES(seq_mutex) | |
138 | { | |
139 | unsigned int id = ovsthread_id_self(); | |
140 | uint32_t hash = hash_int(id, 0); | |
141 | struct seq_waiter *waiter; | |
142 | ||
143 | HMAP_FOR_EACH_IN_BUCKET (waiter, hmap_node, hash, &seq->waiters) { | |
144 | if (waiter->ovsthread_id == id) { | |
145 | if (waiter->value != value) { | |
146 | /* The current value is different from the value we've already | |
147 | * waited for, */ | |
148 | poll_immediate_wake_at(where); | |
149 | } else { | |
150 | /* Already waiting on 'value', nothing more to do. */ | |
151 | } | |
152 | return; | |
153 | } | |
154 | } | |
155 | ||
156 | waiter = xmalloc(sizeof *waiter); | |
157 | waiter->seq = seq; | |
158 | hmap_insert(&seq->waiters, &waiter->hmap_node, hash); | |
159 | waiter->ovsthread_id = id; | |
160 | waiter->value = value; | |
161 | waiter->thread = seq_thread_get(); | |
162 | ovs_list_push_back(&waiter->thread->waiters, &waiter->list_node); | |
163 | ||
164 | if (!waiter->thread->waiting) { | |
165 | latch_wait_at(&waiter->thread->latch, where); | |
166 | waiter->thread->waiting = true; | |
167 | } | |
168 | } | |
169 | ||
170 | /* Causes the following poll_block() to wake up when 'seq''s sequence number | |
171 | * changes from 'value'. (If 'seq''s sequence number isn't 'value', then | |
172 | * poll_block() won't block at all.) | |
173 | * | |
174 | * seq_read() and seq_wait() can be used together to yield a race-free wakeup | |
175 | * when an object changes, even without an ability to lock the object. See | |
176 | * Usage in seq.h for details. | |
177 | * | |
178 | * ('where' is used in debug logging. Commonly one would use seq_wait() to | |
179 | * automatically provide the caller's source file and line number for | |
180 | * 'where'.) */ | |
181 | void | |
182 | seq_wait_at(const struct seq *seq_, uint64_t value, const char *where) | |
183 | OVS_EXCLUDED(seq_mutex) | |
184 | { | |
185 | struct seq *seq = CONST_CAST(struct seq *, seq_); | |
186 | ||
187 | ovs_mutex_lock(&seq_mutex); | |
188 | if (value == seq->value) { | |
189 | seq_wait__(seq, value, where); | |
190 | } else { | |
191 | poll_immediate_wake_at(where); | |
192 | } | |
193 | ovs_mutex_unlock(&seq_mutex); | |
194 | } | |
195 | ||
196 | /* Called by poll_block() just before it returns, this function destroys any | |
197 | * seq_waiter objects associated with the current thread. */ | |
198 | void | |
199 | seq_woke(void) | |
200 | OVS_EXCLUDED(seq_mutex) | |
201 | { | |
202 | struct seq_thread *thread; | |
203 | ||
204 | seq_init(); | |
205 | ||
206 | thread = pthread_getspecific(seq_thread_key); | |
207 | if (thread) { | |
208 | ovs_mutex_lock(&seq_mutex); | |
209 | seq_thread_woke(thread); | |
210 | thread->waiting = false; | |
211 | ovs_mutex_unlock(&seq_mutex); | |
212 | } | |
213 | } | |
214 | \f | |
215 | static void | |
216 | seq_init(void) | |
217 | { | |
218 | static struct ovsthread_once once = OVSTHREAD_ONCE_INITIALIZER; | |
219 | ||
220 | if (ovsthread_once_start(&once)) { | |
221 | xpthread_key_create(&seq_thread_key, seq_thread_exit); | |
222 | ovsthread_once_done(&once); | |
223 | } | |
224 | } | |
225 | ||
226 | static struct seq_thread * | |
227 | seq_thread_get(void) | |
228 | OVS_REQUIRES(seq_mutex) | |
229 | { | |
230 | struct seq_thread *thread = pthread_getspecific(seq_thread_key); | |
231 | if (!thread) { | |
232 | thread = xmalloc(sizeof *thread); | |
233 | ovs_list_init(&thread->waiters); | |
234 | latch_init(&thread->latch); | |
235 | thread->waiting = false; | |
236 | ||
237 | xpthread_setspecific(seq_thread_key, thread); | |
238 | } | |
239 | return thread; | |
240 | } | |
241 | ||
242 | static void | |
243 | seq_thread_exit(void *thread_) | |
244 | OVS_EXCLUDED(seq_mutex) | |
245 | { | |
246 | struct seq_thread *thread = thread_; | |
247 | ||
248 | ovs_mutex_lock(&seq_mutex); | |
249 | seq_thread_woke(thread); | |
250 | latch_destroy(&thread->latch); | |
251 | free(thread); | |
252 | ovs_mutex_unlock(&seq_mutex); | |
253 | } | |
254 | ||
255 | static void | |
256 | seq_thread_woke(struct seq_thread *thread) | |
257 | OVS_REQUIRES(seq_mutex) | |
258 | { | |
259 | struct seq_waiter *waiter, *next_waiter; | |
260 | ||
261 | LIST_FOR_EACH_SAFE (waiter, next_waiter, list_node, &thread->waiters) { | |
262 | ovs_assert(waiter->thread == thread); | |
263 | seq_waiter_destroy(waiter); | |
264 | } | |
265 | latch_poll(&thread->latch); | |
266 | } | |
267 | ||
268 | static void | |
269 | seq_waiter_destroy(struct seq_waiter *waiter) | |
270 | OVS_REQUIRES(seq_mutex) | |
271 | { | |
272 | hmap_remove(&waiter->seq->waiters, &waiter->hmap_node); | |
273 | ovs_list_remove(&waiter->list_node); | |
274 | free(waiter); | |
275 | } | |
276 | ||
277 | static void | |
278 | seq_wake_waiters(struct seq *seq) | |
279 | OVS_REQUIRES(seq_mutex) | |
280 | { | |
281 | struct seq_waiter *waiter, *next_waiter; | |
282 | ||
283 | HMAP_FOR_EACH_SAFE (waiter, next_waiter, hmap_node, &seq->waiters) { | |
284 | latch_set(&waiter->thread->latch); | |
285 | seq_waiter_destroy(waiter); | |
286 | } | |
287 | } |