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1 | /* |
2 | * Copyright (c) 2013 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 "hash.h" | |
24 | #include "hmap.h" | |
25 | #include "latch.h" | |
26 | #include "list.h" | |
27 | #include "ovs-thread.h" | |
28 | #include "poll-loop.h" | |
29 | ||
30 | /* A sequence number object. */ | |
31 | struct seq { | |
32 | uint64_t value OVS_GUARDED; | |
33 | struct hmap waiters OVS_GUARDED; /* Contains 'struct seq_waiter's. */ | |
34 | }; | |
35 | ||
36 | /* A thread waiting on a particular seq. */ | |
37 | struct seq_waiter { | |
38 | struct seq *seq OVS_GUARDED; /* Seq being waited for. */ | |
39 | struct hmap_node hmap_node OVS_GUARDED; /* In 'seq->waiters'. */ | |
40 | unsigned int ovsthread_id OVS_GUARDED; /* Key in 'waiters' hmap. */ | |
41 | ||
42 | struct seq_thread *thread OVS_GUARDED; /* Thread preparing to wait. */ | |
43 | struct list list_node OVS_GUARDED; /* In 'thread->waiters'. */ | |
44 | ||
45 | uint64_t value OVS_GUARDED; /* seq->value we're waiting to change. */ | |
46 | }; | |
47 | ||
48 | /* A thread that might be waiting on one or more seqs. */ | |
49 | struct seq_thread { | |
50 | struct list waiters OVS_GUARDED; /* Contains 'struct seq_waiter's. */ | |
51 | struct latch latch OVS_GUARDED; /* Wakeup latch for this thread. */ | |
52 | bool waiting OVS_GUARDED; /* True if latch_wait() already called. */ | |
53 | }; | |
54 | ||
55 | static struct ovs_mutex seq_mutex = OVS_ADAPTIVE_MUTEX_INITIALIZER; | |
56 | ||
57 | static uint64_t seq_next OVS_GUARDED_BY(seq_mutex) = 1; | |
58 | ||
59 | static pthread_key_t seq_thread_key; | |
60 | ||
61 | static void seq_init(void); | |
62 | static struct seq_thread *seq_thread_get(void) OVS_REQUIRES(seq_mutex); | |
63 | static void seq_thread_exit(void *thread_) OVS_EXCLUDED(seq_mutex); | |
64 | static void seq_thread_woke(struct seq_thread *) OVS_REQUIRES(seq_mutex); | |
65 | static void seq_waiter_destroy(struct seq_waiter *) OVS_REQUIRES(seq_mutex); | |
66 | static void seq_wake_waiters(struct seq *) OVS_REQUIRES(seq_mutex); | |
67 | ||
68 | /* Creates and returns a new 'seq' object. */ | |
69 | struct seq * OVS_EXCLUDED(seq_mutex) | |
70 | seq_create(void) | |
71 | { | |
72 | struct seq *seq; | |
73 | ||
74 | seq_init(); | |
75 | ||
76 | seq = xmalloc(sizeof *seq); | |
77 | ovs_mutex_lock(&seq_mutex); | |
78 | seq->value = seq_next++; | |
79 | hmap_init(&seq->waiters); | |
80 | ovs_mutex_unlock(&seq_mutex); | |
81 | ||
82 | return seq; | |
83 | } | |
84 | ||
85 | /* Destroys 'seq', waking up threads that were waiting on it, if any. */ | |
86 | void | |
87 | seq_destroy(struct seq *seq) | |
88 | OVS_EXCLUDED(seq_mutex) | |
89 | { | |
90 | ovs_mutex_lock(&seq_mutex); | |
91 | seq_wake_waiters(seq); | |
92 | hmap_destroy(&seq->waiters); | |
93 | free(seq); | |
94 | ovs_mutex_unlock(&seq_mutex); | |
95 | } | |
96 | ||
97 | /* Increments 'seq''s sequence number, waking up any threads that are waiting | |
98 | * on 'seq'. */ | |
99 | void | |
100 | seq_change(struct seq *seq) | |
101 | OVS_EXCLUDED(seq_mutex) | |
102 | { | |
103 | ovs_mutex_lock(&seq_mutex); | |
104 | seq->value = seq_next++; | |
105 | seq_wake_waiters(seq); | |
106 | ovs_mutex_unlock(&seq_mutex); | |
107 | } | |
108 | ||
5d389d55 BP |
109 | /* Returns 'seq''s current sequence number (which could change immediately). |
110 | * | |
111 | * seq_read() and seq_wait() can be used together to yield a race-free wakeup | |
112 | * when an object changes, even without an ability to lock the object. See | |
113 | * Usage in seq.h for details. */ | |
55b40355 BP |
114 | uint64_t |
115 | seq_read(const struct seq *seq) | |
116 | OVS_EXCLUDED(seq_mutex) | |
117 | { | |
118 | uint64_t value; | |
119 | ||
120 | ovs_mutex_lock(&seq_mutex); | |
121 | value = seq->value; | |
122 | ovs_mutex_unlock(&seq_mutex); | |
123 | ||
124 | return value; | |
125 | } | |
126 | ||
127 | static void | |
128 | seq_wait__(struct seq *seq, uint64_t value) | |
129 | OVS_REQUIRES(seq_mutex) | |
130 | { | |
131 | unsigned int id = ovsthread_id_self(); | |
132 | uint32_t hash = hash_int(id, 0); | |
133 | struct seq_waiter *waiter; | |
134 | ||
135 | HMAP_FOR_EACH_IN_BUCKET (waiter, hmap_node, hash, &seq->waiters) { | |
136 | if (waiter->ovsthread_id == id) { | |
137 | if (waiter->value != value) { | |
138 | /* The current value is different from the value we've already | |
139 | * waited for, */ | |
140 | poll_immediate_wake(); | |
141 | } else { | |
142 | /* Already waiting on 'value', nothing more to do. */ | |
143 | } | |
144 | return; | |
145 | } | |
146 | } | |
147 | ||
148 | waiter = xmalloc(sizeof *waiter); | |
149 | waiter->seq = seq; | |
150 | hmap_insert(&seq->waiters, &waiter->hmap_node, hash); | |
f4aa1da8 | 151 | waiter->ovsthread_id = id; |
55b40355 BP |
152 | waiter->value = value; |
153 | waiter->thread = seq_thread_get(); | |
154 | list_push_back(&waiter->thread->waiters, &waiter->list_node); | |
155 | ||
156 | if (!waiter->thread->waiting) { | |
157 | latch_wait(&waiter->thread->latch); | |
158 | waiter->thread->waiting = true; | |
159 | } | |
160 | } | |
161 | ||
162 | /* Causes the following poll_block() to wake up when 'seq''s sequence number | |
163 | * changes from 'value'. (If 'seq''s sequence number isn't 'value', then | |
5d389d55 BP |
164 | * poll_block() won't block at all.) |
165 | * | |
166 | * seq_read() and seq_wait() can be used together to yield a race-free wakeup | |
167 | * when an object changes, even without an ability to lock the object. See | |
168 | * Usage in seq.h for details. */ | |
55b40355 BP |
169 | void |
170 | seq_wait(const struct seq *seq_, uint64_t value) | |
171 | OVS_EXCLUDED(seq_mutex) | |
172 | { | |
173 | struct seq *seq = CONST_CAST(struct seq *, seq_); | |
174 | ||
175 | ovs_mutex_lock(&seq_mutex); | |
176 | if (value == seq->value) { | |
177 | seq_wait__(seq, value); | |
178 | } else { | |
179 | poll_immediate_wake(); | |
180 | } | |
181 | ovs_mutex_unlock(&seq_mutex); | |
182 | } | |
183 | ||
184 | /* Called by poll_block() just before it returns, this function destroys any | |
185 | * seq_waiter objects associated with the current thread. */ | |
186 | void | |
187 | seq_woke(void) | |
188 | OVS_EXCLUDED(seq_mutex) | |
189 | { | |
190 | struct seq_thread *thread; | |
191 | ||
192 | seq_init(); | |
193 | ||
194 | thread = pthread_getspecific(seq_thread_key); | |
195 | if (thread) { | |
196 | ovs_mutex_lock(&seq_mutex); | |
197 | seq_thread_woke(thread); | |
198 | thread->waiting = false; | |
199 | ovs_mutex_unlock(&seq_mutex); | |
200 | } | |
201 | } | |
202 | \f | |
203 | static void | |
204 | seq_init(void) | |
205 | { | |
206 | static struct ovsthread_once once = OVSTHREAD_ONCE_INITIALIZER; | |
207 | ||
208 | if (ovsthread_once_start(&once)) { | |
209 | xpthread_key_create(&seq_thread_key, seq_thread_exit); | |
210 | ovsthread_once_done(&once); | |
211 | } | |
212 | } | |
213 | ||
214 | static struct seq_thread * | |
215 | seq_thread_get(void) | |
216 | OVS_REQUIRES(seq_mutex) | |
217 | { | |
218 | struct seq_thread *thread = pthread_getspecific(seq_thread_key); | |
219 | if (!thread) { | |
220 | thread = xmalloc(sizeof *thread); | |
221 | list_init(&thread->waiters); | |
222 | latch_init(&thread->latch); | |
223 | thread->waiting = false; | |
224 | ||
225 | xpthread_setspecific(seq_thread_key, thread); | |
226 | } | |
227 | return thread; | |
228 | } | |
229 | ||
230 | static void | |
231 | seq_thread_exit(void *thread_) | |
232 | OVS_EXCLUDED(seq_mutex) | |
233 | { | |
234 | struct seq_thread *thread = thread_; | |
235 | ||
236 | ovs_mutex_lock(&seq_mutex); | |
237 | seq_thread_woke(thread); | |
238 | latch_destroy(&thread->latch); | |
239 | free(thread); | |
240 | ovs_mutex_unlock(&seq_mutex); | |
241 | } | |
242 | ||
243 | static void | |
244 | seq_thread_woke(struct seq_thread *thread) | |
245 | OVS_REQUIRES(seq_mutex) | |
246 | { | |
247 | struct seq_waiter *waiter, *next_waiter; | |
248 | ||
249 | LIST_FOR_EACH_SAFE (waiter, next_waiter, list_node, &thread->waiters) { | |
250 | ovs_assert(waiter->thread == thread); | |
251 | seq_waiter_destroy(waiter); | |
252 | } | |
253 | latch_poll(&thread->latch); | |
254 | } | |
255 | ||
256 | static void | |
257 | seq_waiter_destroy(struct seq_waiter *waiter) | |
258 | OVS_REQUIRES(seq_mutex) | |
259 | { | |
260 | hmap_remove(&waiter->seq->waiters, &waiter->hmap_node); | |
261 | list_remove(&waiter->list_node); | |
262 | free(waiter); | |
263 | } | |
264 | ||
265 | static void | |
266 | seq_wake_waiters(struct seq *seq) | |
267 | OVS_REQUIRES(seq_mutex) | |
268 | { | |
269 | struct seq_waiter *waiter, *next_waiter; | |
270 | ||
271 | HMAP_FOR_EACH_SAFE (waiter, next_waiter, hmap_node, &seq->waiters) { | |
272 | latch_set(&waiter->thread->latch); | |
273 | seq_waiter_destroy(waiter); | |
274 | } | |
275 | } |