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.
18 #define OVS_THREAD_H 1
22 #include <sys/types.h>
23 #include "ovs-atomic.h"
28 struct OVS_LOCKABLE ovs_mutex {
33 /* "struct ovs_mutex" initializer. */
34 #ifdef PTHREAD_ERRORCHECK_MUTEX_INITIALIZER_NP
35 #define OVS_MUTEX_INITIALIZER { PTHREAD_ERRORCHECK_MUTEX_INITIALIZER_NP, NULL }
37 #define OVS_MUTEX_INITIALIZER { PTHREAD_MUTEX_INITIALIZER, NULL }
40 #ifdef PTHREAD_ADAPTIVE_MUTEX_INITIALIZER_NP
41 #define OVS_ADAPTIVE_MUTEX_INITIALIZER \
42 { PTHREAD_ADAPTIVE_MUTEX_INITIALIZER_NP, NULL }
44 #define OVS_ADAPTIVE_MUTEX_INITIALIZER OVS_MUTEX_INITIALIZER
47 /* ovs_mutex functions analogous to pthread_mutex_*() functions.
49 * Most of these functions abort the process with an error message on any
50 * error. ovs_mutex_trylock() is an exception: it passes through a 0 or EBUSY
51 * return value to the caller and aborts on any other error. */
52 void ovs_mutex_init(const struct ovs_mutex *);
53 void ovs_mutex_init_recursive(const struct ovs_mutex *);
54 void ovs_mutex_init_adaptive(const struct ovs_mutex *);
55 void ovs_mutex_destroy(const struct ovs_mutex *);
56 void ovs_mutex_unlock(const struct ovs_mutex *mutex) OVS_RELEASES(mutex);
57 void ovs_mutex_lock_at(const struct ovs_mutex *mutex, const char *where)
59 #define ovs_mutex_lock(mutex) \
60 ovs_mutex_lock_at(mutex, SOURCE_LOCATOR)
62 int ovs_mutex_trylock_at(const struct ovs_mutex *mutex, const char *where)
63 OVS_TRY_LOCK(0, mutex);
64 #define ovs_mutex_trylock(mutex) \
65 ovs_mutex_trylock_at(mutex, SOURCE_LOCATOR)
67 void ovs_mutex_cond_wait(pthread_cond_t *, const struct ovs_mutex *);
69 /* Wrappers for pthread_mutex_*() that abort the process on any error.
70 * This is still needed when ovs-atomic-pthreads.h is used. */
71 void xpthread_mutex_lock(pthread_mutex_t *mutex);
72 void xpthread_mutex_unlock(pthread_mutex_t *mutex);
74 /* Wrappers for pthread_mutexattr_*() that abort the process on any error. */
75 void xpthread_mutexattr_init(pthread_mutexattr_t *);
76 void xpthread_mutexattr_destroy(pthread_mutexattr_t *);
77 void xpthread_mutexattr_settype(pthread_mutexattr_t *, int type);
78 void xpthread_mutexattr_gettype(pthread_mutexattr_t *, int *typep);
82 * An ovs_rwlock does not support recursive readers, because POSIX allows
83 * taking the reader lock recursively to deadlock when a thread is waiting on
84 * the write-lock. (NetBSD does deadlock.) glibc rwlocks in their default
85 * configuration do not deadlock, but ovs_rwlock_init() initializes rwlocks as
86 * non-recursive (which will deadlock) for two reasons:
88 * - glibc only provides fairness to writers in this mode.
90 * - It's better to find bugs in the primary Open vSwitch target rather
91 * than exposing them only to porters. */
92 struct OVS_LOCKABLE ovs_rwlock {
93 pthread_rwlock_t lock;
98 #ifdef PTHREAD_RWLOCK_WRITER_NONRECURSIVE_INITIALIZER_NP
99 #define OVS_RWLOCK_INITIALIZER \
100 { PTHREAD_RWLOCK_WRITER_NONRECURSIVE_INITIALIZER_NP, NULL }
102 #define OVS_RWLOCK_INITIALIZER { PTHREAD_RWLOCK_INITIALIZER, NULL }
105 /* ovs_rwlock functions analogous to pthread_rwlock_*() functions.
107 * Most of these functions abort the process with an error message on any
108 * error. The "trylock" functions are exception: they pass through a 0 or
109 * EBUSY return value to the caller and abort on any other error. */
110 void ovs_rwlock_init(const struct ovs_rwlock *);
111 void ovs_rwlock_destroy(const struct ovs_rwlock *);
112 void ovs_rwlock_unlock(const struct ovs_rwlock *rwlock) OVS_RELEASES(rwlock);
114 /* Wrappers for pthread_rwlockattr_*() that abort the process on any error. */
115 void xpthread_rwlockattr_init(pthread_rwlockattr_t *);
116 void xpthread_rwlockattr_destroy(pthread_rwlockattr_t *);
117 #ifdef PTHREAD_RWLOCK_WRITER_NONRECURSIVE_INITIALIZER_NP
118 void xpthread_rwlockattr_setkind_np(pthread_rwlockattr_t *, int kind);
121 void ovs_rwlock_wrlock_at(const struct ovs_rwlock *rwlock, const char *where)
122 OVS_ACQ_WRLOCK(rwlock);
123 #define ovs_rwlock_wrlock(rwlock) \
124 ovs_rwlock_wrlock_at(rwlock, SOURCE_LOCATOR)
126 int ovs_rwlock_trywrlock_at(const struct ovs_rwlock *rwlock, const char *where)
127 OVS_TRY_WRLOCK(0, rwlock);
128 #define ovs_rwlock_trywrlock(rwlock) \
129 ovs_rwlock_trywrlock_at(rwlock, SOURCE_LOCATOR)
131 void ovs_rwlock_rdlock_at(const struct ovs_rwlock *rwlock, const char *where)
132 OVS_ACQ_RDLOCK(rwlock);
133 #define ovs_rwlock_rdlock(rwlock) \
134 ovs_rwlock_rdlock_at(rwlock, SOURCE_LOCATOR)
136 int ovs_rwlock_tryrdlock_at(const struct ovs_rwlock *rwlock, const char *where)
137 OVS_TRY_RDLOCK(0, rwlock);
138 #define ovs_rwlock_tryrdlock(rwlock) \
139 ovs_rwlock_tryrdlock_at(rwlock, SOURCE_LOCATOR)
141 /* Wrappers for xpthread_cond_*() that abort the process on any error.
143 * Use ovs_mutex_cond_wait() to wait for a condition. */
144 void xpthread_cond_init(pthread_cond_t *, pthread_condattr_t *);
145 void xpthread_cond_destroy(pthread_cond_t *);
146 void xpthread_cond_signal(pthread_cond_t *);
147 void xpthread_cond_broadcast(pthread_cond_t *);
149 /* Wrappers for pthread_barrier_*() that abort the process on any error. */
150 void xpthread_barrier_init(pthread_barrier_t *, pthread_barrierattr_t *,
152 int xpthread_barrier_wait(pthread_barrier_t *);
153 void xpthread_barrier_destroy(pthread_barrier_t *);
155 void xpthread_key_create(pthread_key_t *, void (*destructor)(void *));
156 void xpthread_key_delete(pthread_key_t);
157 void xpthread_setspecific(pthread_key_t, const void *);
159 void xpthread_create(pthread_t *, pthread_attr_t *, void *(*)(void *), void *);
160 void xpthread_join(pthread_t, void **);
168 * Multiple forms of standard per-thread data exist, each with its own pluses
169 * and minuses. In general, if one of these forms is appropriate, then it's a
170 * good idea to use it:
172 * - POSIX per-thread data via pthread_key_t is portable to any pthreads
173 * implementation, and allows a destructor function to be defined. It
174 * only (directly) supports per-thread pointers, which are always
175 * initialized to NULL. It requires once-only allocation of a
176 * pthread_key_t value. It is relatively slow. Typically few
177 * "pthread_key_t"s are available (POSIX requires only at least 128,
178 * glibc supplies only 1024).
180 * - The thread_local feature newly defined in C11 <threads.h> works with
181 * any data type and initializer, and it is fast. thread_local does not
182 * require once-only initialization like pthread_key_t. C11 does not
183 * define what happens if one attempts to access a thread_local object
184 * from a thread other than the one to which that object belongs. There
185 * is no provision to call a user-specified destructor when a thread
186 * ends. Typical implementations allow for an arbitrary amount of
187 * thread_local storage, but statically allocated only.
189 * - The __thread keyword is a GCC extension similar to thread_local but
190 * with a longer history. __thread is not portable to every GCC version
191 * or environment. __thread does not restrict the use of a thread-local
192 * object outside its own thread.
194 * Here's a handy summary:
196 * pthread_key_t thread_local __thread
197 * ------------- ------------ -------------
198 * portability high low medium
199 * speed low high high
200 * supports destructors? yes no no
201 * needs key allocation? yes no no
202 * arbitrary initializer? no yes yes
203 * cross-thread access? yes no yes
204 * amount available? few arbitrary arbitrary
205 * dynamically allocated? yes no no
211 * OVS provides some extensions and wrappers:
213 * - In a situation where the performance of thread_local or __thread is
214 * desirable, but portability is required, DEFINE_STATIC_PER_THREAD_DATA
215 * and DECLARE_EXTERN_PER_THREAD_DATA/DEFINE_EXTERN_PER_THREAD_DATA may
216 * be appropriate (see below).
218 * - DEFINE_PER_THREAD_MALLOCED_DATA can be convenient for simple
219 * per-thread malloc()'d buffers.
221 * - struct ovs_tsd provides an alternative to pthread_key_t that isn't
222 * limited to a small number of keys.
225 /* For static data, use this macro in a source file:
227 * DEFINE_STATIC_PER_THREAD_DATA(TYPE, NAME, INITIALIZER).
229 * For global data, "declare" the data in the header and "define" it in
230 * the source file, with:
232 * DECLARE_EXTERN_PER_THREAD_DATA(TYPE, NAME).
233 * DEFINE_EXTERN_PER_THREAD_DATA(NAME, INITIALIZER).
235 * One should prefer to use POSIX per-thread data, via pthread_key_t, when its
236 * performance is acceptable, because of its portability (see the table above).
237 * This macro is an alternatives that takes advantage of thread_local (and
238 * __thread), for its performance, when it is available, and falls back to
239 * POSIX per-thread data otherwise.
241 * Defines per-thread variable NAME with the given TYPE, initialized to
242 * INITIALIZER (which must be valid as an initializer for a variable with
245 * The public interface to the variable is:
247 * TYPE *NAME_get(void)
248 * TYPE *NAME_get_unsafe(void)
250 * Returns the address of this thread's instance of NAME.
252 * Use NAME_get() in a context where this might be the first use of the
253 * per-thread variable in the program. Use NAME_get_unsafe(), which
254 * avoids a conditional test and is thus slightly faster, in a context
255 * where one knows that NAME_get() has already been called previously.
257 * There is no "NAME_set()" (or "NAME_set_unsafe()") function. To set the
258 * value of the per-thread variable, dereference the pointer returned by
259 * TYPE_get() or TYPE_get_unsafe(), e.g. *TYPE_get() = 0.
261 #if HAVE_THREAD_LOCAL || HAVE___THREAD
263 #if HAVE_THREAD_LOCAL
266 #define thread_local __thread
271 #define DEFINE_STATIC_PER_THREAD_DATA(TYPE, NAME, ...) \
272 typedef TYPE NAME##_type; \
274 static NAME##_type * \
275 NAME##_get_unsafe(void) \
277 static thread_local NAME##_type var = __VA_ARGS__; \
281 static NAME##_type * \
284 return NAME##_get_unsafe(); \
286 #define DECLARE_EXTERN_PER_THREAD_DATA(TYPE, NAME) \
287 typedef TYPE NAME##_type; \
288 extern thread_local NAME##_type NAME##_var; \
290 static inline NAME##_type * \
291 NAME##_get_unsafe(void) \
293 return &NAME##_var; \
296 static inline NAME##_type * \
299 return NAME##_get_unsafe(); \
301 #define DEFINE_EXTERN_PER_THREAD_DATA(NAME, ...) \
302 thread_local NAME##_type NAME##_var = __VA_ARGS__;
303 #else /* no C implementation support for thread-local storage */
304 #define DEFINE_STATIC_PER_THREAD_DATA(TYPE, NAME, ...) \
305 typedef TYPE NAME##_type; \
306 static pthread_key_t NAME##_key; \
308 static NAME##_type * \
309 NAME##_get_unsafe(void) \
311 return pthread_getspecific(NAME##_key); \
315 NAME##_once_init(void) \
317 if (pthread_key_create(&NAME##_key, free)) { \
322 static NAME##_type * \
325 static pthread_once_t once = PTHREAD_ONCE_INIT; \
326 NAME##_type *value; \
328 pthread_once(&once, NAME##_once_init); \
329 value = NAME##_get_unsafe(); \
331 static const NAME##_type initial_value = __VA_ARGS__; \
333 value = malloc(sizeof *value); \
334 if (value == NULL) { \
337 *value = initial_value; \
338 xpthread_setspecific(NAME##_key, value); \
342 #define DECLARE_EXTERN_PER_THREAD_DATA(TYPE, NAME) \
343 typedef TYPE NAME##_type; \
344 static pthread_key_t NAME##_key; \
346 static inline NAME##_type * \
347 NAME##_get_unsafe(void) \
349 return pthread_getspecific(NAME##_key); \
352 NAME##_type *NAME##_get(void);
353 #define DEFINE_EXTERN_PER_THREAD_DATA(NAME, ...) \
355 NAME##_once_init(void) \
357 if (pthread_key_create(&NAME##_key, free)) { \
365 static pthread_once_t once = PTHREAD_ONCE_INIT; \
366 NAME##_type *value; \
368 pthread_once(&once, NAME##_once_init); \
369 value = NAME##_get_unsafe(); \
371 static const NAME##_type initial_value = __VA_ARGS__; \
373 value = malloc(sizeof *value); \
374 if (value == NULL) { \
377 *value = initial_value; \
378 xpthread_setspecific(NAME##_key, value); \
384 /* DEFINE_PER_THREAD_MALLOCED_DATA(TYPE, NAME).
386 * This is a simple wrapper around POSIX per-thread data primitives. It
387 * defines per-thread variable NAME with the given TYPE, which must be a
388 * pointer type. In each thread, the per-thread variable is initialized to
389 * NULL. When a thread terminates, the variable is freed with free().
391 * The public interface to the variable is:
393 * TYPE NAME_get(void)
394 * TYPE NAME_get_unsafe(void)
396 * Returns the value of per-thread variable NAME in this thread.
398 * Use NAME_get() in a context where this might be the first use of the
399 * per-thread variable in the program. Use NAME_get_unsafe(), which
400 * avoids a conditional test and is thus slightly faster, in a context
401 * where one knows that NAME_get() has already been called previously.
403 * TYPE NAME_set(TYPE new_value)
404 * TYPE NAME_set_unsafe(TYPE new_value)
406 * Sets the value of per-thread variable NAME to 'new_value' in this
407 * thread, and returns its previous value.
409 * Use NAME_set() in a context where this might be the first use of the
410 * per-thread variable in the program. Use NAME_set_unsafe(), which
411 * avoids a conditional test and is thus slightly faster, in a context
412 * where one knows that NAME_set() has already been called previously.
414 #define DEFINE_PER_THREAD_MALLOCED_DATA(TYPE, NAME) \
415 static pthread_key_t NAME##_key; \
418 NAME##_once_init(void) \
420 if (pthread_key_create(&NAME##_key, free)) { \
428 static pthread_once_t once = PTHREAD_ONCE_INIT; \
429 pthread_once(&once, NAME##_once_init); \
433 NAME##_get_unsafe(void) \
435 return pthread_getspecific(NAME##_key); \
438 static OVS_UNUSED TYPE \
442 return NAME##_get_unsafe(); \
446 NAME##_set_unsafe(TYPE value) \
448 TYPE old_value = NAME##_get_unsafe(); \
449 xpthread_setspecific(NAME##_key, value); \
453 static OVS_UNUSED TYPE \
454 NAME##_set(TYPE value) \
457 return NAME##_set_unsafe(value); \
460 /* Dynamically allocated thread-specific data with lots of slots.
462 * pthread_key_t can provide as few as 128 pieces of thread-specific data (even
463 * glibc is limited to 1,024). Thus, one must be careful to allocate only a
464 * few keys globally. One cannot, for example, allocate a key for every
465 * instance of a data structure if there might be an arbitrary number of those
468 * This API is similar to the pthread one (simply search and replace pthread_
469 * by ovsthread_) but it a much larger limit that can be raised if necessary
470 * (by recompiling). Thus, one may more freely use this form of
471 * thread-specific data.
473 * ovsthread_key_t also differs from pthread_key_t in the following ways:
475 * - Destructors must not access thread-specific data (via ovsthread_key).
477 * - The pthread_key_t API allows concurrently exiting threads to start
478 * executing the destructor after pthread_key_delete() returns. The
479 * ovsthread_key_t API guarantees that, when ovsthread_key_delete()
480 * returns, all destructors have returned and no new ones will start
483 typedef struct ovsthread_key *ovsthread_key_t;
485 void ovsthread_key_create(ovsthread_key_t *, void (*destructor)(void *));
486 void ovsthread_key_delete(ovsthread_key_t);
488 void ovsthread_setspecific(ovsthread_key_t, const void *);
489 void *ovsthread_getspecific(ovsthread_key_t);
491 /* Convenient once-only execution.
497 * POSIX provides pthread_once_t and pthread_once() as primitives for running a
498 * set of code only once per process execution. They are used like this:
500 * static void run_once(void) { ...initialization... }
501 * static pthread_once_t once = PTHREAD_ONCE_INIT;
503 * pthread_once(&once, run_once);
505 * pthread_once() does not allow passing any parameters to the initialization
506 * function, which is often inconvenient, because it means that the function
507 * can only access data declared at file scope.
513 * Use ovsthread_once, like this, instead:
515 * static struct ovsthread_once once = OVSTHREAD_ONCE_INITIALIZER;
517 * if (ovsthread_once_start(&once)) {
518 * ...initialization...
519 * ovsthread_once_done(&once);
523 struct ovsthread_once {
525 struct ovs_mutex mutex;
528 #define OVSTHREAD_ONCE_INITIALIZER \
530 ATOMIC_VAR_INIT(false), \
531 OVS_MUTEX_INITIALIZER, \
534 static inline bool ovsthread_once_start(struct ovsthread_once *once)
535 OVS_TRY_LOCK(true, once->mutex);
536 void ovsthread_once_done(struct ovsthread_once *once)
537 OVS_RELEASES(once->mutex);
539 bool ovsthread_once_start__(struct ovsthread_once *once)
540 OVS_TRY_LOCK(false, once->mutex);
543 ovsthread_once_is_done__(struct ovsthread_once *once)
547 atomic_read_explicit(&once->done, &done, memory_order_relaxed);
551 /* Returns true if this is the first call to ovsthread_once_start() for
552 * 'once'. In this case, the caller should perform whatever initialization
553 * actions it needs to do, then call ovsthread_once_done() for 'once'.
555 * Returns false if this is not the first call to ovsthread_once_start() for
556 * 'once'. In this case, the call will not return until after
557 * ovsthread_once_done() has been called. */
559 ovsthread_once_start(struct ovsthread_once *once)
561 return OVS_UNLIKELY(!ovsthread_once_is_done__(once)
562 && !ovsthread_once_start__(once));
567 * pthread_t isn't so nice for some purposes. Its size and representation are
568 * implementation dependent, which means that there is no way to hash it.
569 * This thread ID avoids the problem.
572 DECLARE_EXTERN_PER_THREAD_DATA(unsigned int, ovsthread_id);
574 /* Returns a per-thread identifier unique within the lifetime of the
576 static inline unsigned int
577 ovsthread_id_self(void)
579 return *ovsthread_id_get();
582 /* Simulated global counter.
584 * Incrementing such a counter is meant to be cheaper than incrementing a
585 * global counter protected by a lock. It is probably more expensive than
586 * incrementing a truly thread-local variable, but such a variable has no
587 * straightforward way to get the sum.
593 * Fully thread-safe. */
595 struct ovsthread_stats {
596 struct ovs_mutex mutex;
597 void *volatile buckets[16];
600 void ovsthread_stats_init(struct ovsthread_stats *);
601 void ovsthread_stats_destroy(struct ovsthread_stats *);
603 void *ovsthread_stats_bucket_get(struct ovsthread_stats *,
604 void *(*new_bucket)(void));
606 #define OVSTHREAD_STATS_FOR_EACH_BUCKET(BUCKET, IDX, STATS) \
607 for ((IDX) = ovs_thread_stats_next_bucket(STATS, 0); \
608 ((IDX) < ARRAY_SIZE((STATS)->buckets) \
609 ? ((BUCKET) = (STATS)->buckets[IDX], true) \
611 (IDX) = ovs_thread_stats_next_bucket(STATS, (IDX) + 1))
612 size_t ovs_thread_stats_next_bucket(const struct ovsthread_stats *, size_t);
614 bool single_threaded(void);
616 void assert_single_threaded_at(const char *where);
617 #define assert_single_threaded() assert_single_threaded_at(SOURCE_LOCATOR)
620 pid_t xfork_at(const char *where);
621 #define xfork() xfork_at(SOURCE_LOCATOR)
624 void forbid_forking(const char *reason);
627 /* Useful functions related to threading. */
629 int count_cpu_cores(void);
631 #endif /* ovs-thread.h */