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 ovs_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 ovs_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
);