2 * Copyright (c) 2013, 2014 Nicira, Inc.
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:
8 * http://www.apache.org/licenses/LICENSE-2.0
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.
27 #include "ovs-thread.h"
28 #include "poll-loop.h"
30 /* A sequence number object. */
32 uint64_t value OVS_GUARDED;
33 struct hmap waiters OVS_GUARDED; /* Contains 'struct seq_waiter's. */
36 /* A thread waiting on a particular seq. */
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. */
42 struct seq_thread *thread OVS_GUARDED; /* Thread preparing to wait. */
43 struct list list_node OVS_GUARDED; /* In 'thread->waiters'. */
45 uint64_t value OVS_GUARDED; /* seq->value we're waiting to change. */
48 /* A thread that might be waiting on one or more seqs. */
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. */
55 static struct ovs_mutex seq_mutex = OVS_MUTEX_INITIALIZER;
57 static uint64_t seq_next OVS_GUARDED_BY(seq_mutex) = 1;
59 static pthread_key_t seq_thread_key;
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);
68 /* Creates and returns a new 'seq' object. */
69 struct seq * OVS_EXCLUDED(seq_mutex)
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);
85 /* Destroys 'seq', waking up threads that were waiting on it, if any. */
87 seq_destroy(struct seq *seq)
88 OVS_EXCLUDED(seq_mutex)
90 ovs_mutex_lock(&seq_mutex);
91 seq_wake_waiters(seq);
92 hmap_destroy(&seq->waiters);
94 ovs_mutex_unlock(&seq_mutex);
97 /* Increments 'seq''s sequence number, waking up any threads that are waiting
100 seq_change(struct seq *seq)
101 OVS_EXCLUDED(seq_mutex)
103 ovs_mutex_lock(&seq_mutex);
104 seq->value = seq_next++;
105 seq_wake_waiters(seq);
106 ovs_mutex_unlock(&seq_mutex);
109 /* Returns 'seq''s current sequence number (which could change immediately).
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. */
115 seq_read(const struct seq *seq)
116 OVS_EXCLUDED(seq_mutex)
120 ovs_mutex_lock(&seq_mutex);
122 ovs_mutex_unlock(&seq_mutex);
128 seq_wait__(struct seq *seq, uint64_t value, const char *where)
129 OVS_REQUIRES(seq_mutex)
131 unsigned int id = ovsthread_id_self();
132 uint32_t hash = hash_int(id, 0);
133 struct seq_waiter *waiter;
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
140 poll_immediate_wake_at(where);
142 /* Already waiting on 'value', nothing more to do. */
148 waiter = xmalloc(sizeof *waiter);
150 hmap_insert(&seq->waiters, &waiter->hmap_node, hash);
151 waiter->ovsthread_id = id;
152 waiter->value = value;
153 waiter->thread = seq_thread_get();
154 list_push_back(&waiter->thread->waiters, &waiter->list_node);
156 if (!waiter->thread->waiting) {
157 latch_wait_at(&waiter->thread->latch, where);
158 waiter->thread->waiting = true;
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
164 * poll_block() won't block at all.)
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.
170 * ('where' is used in debug logging. Commonly one would use seq_wait() to
171 * automatically provide the caller's source file and line number for
174 seq_wait_at(const struct seq *seq_, uint64_t value, const char *where)
175 OVS_EXCLUDED(seq_mutex)
177 struct seq *seq = CONST_CAST(struct seq *, seq_);
179 ovs_mutex_lock(&seq_mutex);
180 if (value == seq->value) {
181 seq_wait__(seq, value, where);
183 poll_immediate_wake_at(where);
185 ovs_mutex_unlock(&seq_mutex);
188 /* Called by poll_block() just before it returns, this function destroys any
189 * seq_waiter objects associated with the current thread. */
192 OVS_EXCLUDED(seq_mutex)
194 struct seq_thread *thread;
198 thread = pthread_getspecific(seq_thread_key);
200 ovs_mutex_lock(&seq_mutex);
201 seq_thread_woke(thread);
202 thread->waiting = false;
203 ovs_mutex_unlock(&seq_mutex);
210 static struct ovsthread_once once = OVSTHREAD_ONCE_INITIALIZER;
212 if (ovsthread_once_start(&once)) {
213 xpthread_key_create(&seq_thread_key, seq_thread_exit);
214 ovsthread_once_done(&once);
218 static struct seq_thread *
220 OVS_REQUIRES(seq_mutex)
222 struct seq_thread *thread = pthread_getspecific(seq_thread_key);
224 thread = xmalloc(sizeof *thread);
225 list_init(&thread->waiters);
226 latch_init(&thread->latch);
227 thread->waiting = false;
229 xpthread_setspecific(seq_thread_key, thread);
235 seq_thread_exit(void *thread_)
236 OVS_EXCLUDED(seq_mutex)
238 struct seq_thread *thread = thread_;
240 ovs_mutex_lock(&seq_mutex);
241 seq_thread_woke(thread);
242 latch_destroy(&thread->latch);
244 ovs_mutex_unlock(&seq_mutex);
248 seq_thread_woke(struct seq_thread *thread)
249 OVS_REQUIRES(seq_mutex)
251 struct seq_waiter *waiter, *next_waiter;
253 LIST_FOR_EACH_SAFE (waiter, next_waiter, list_node, &thread->waiters) {
254 ovs_assert(waiter->thread == thread);
255 seq_waiter_destroy(waiter);
257 latch_poll(&thread->latch);
261 seq_waiter_destroy(struct seq_waiter *waiter)
262 OVS_REQUIRES(seq_mutex)
264 hmap_remove(&waiter->seq->waiters, &waiter->hmap_node);
265 list_remove(&waiter->list_node);
270 seq_wake_waiters(struct seq *seq)
271 OVS_REQUIRES(seq_mutex)
273 struct seq_waiter *waiter, *next_waiter;
275 HMAP_FOR_EACH_SAFE (waiter, next_waiter, hmap_node, &seq->waiters) {
276 latch_set(&waiter->thread->latch);
277 seq_waiter_destroy(waiter);