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 void xpthread_key_create(pthread_key_t *, void (*destructor)(void *));
150 void xpthread_key_delete(pthread_key_t);
151 void xpthread_setspecific(pthread_key_t, const void *);
153 void xpthread_create(pthread_t *, pthread_attr_t *, void *(*)(void *), void *);
154 void xpthread_join(pthread_t, void **);
162 * Multiple forms of standard per-thread data exist, each with its own pluses
163 * and minuses. In general, if one of these forms is appropriate, then it's a
164 * good idea to use it:
166 * - POSIX per-thread data via pthread_key_t is portable to any pthreads
167 * implementation, and allows a destructor function to be defined. It
168 * only (directly) supports per-thread pointers, which are always
169 * initialized to NULL. It requires once-only allocation of a
170 * pthread_key_t value. It is relatively slow. Typically few
171 * "pthread_key_t"s are available (POSIX requires only at least 128,
172 * glibc supplies only 1024).
174 * - The thread_local feature newly defined in C11 <threads.h> works with
175 * any data type and initializer, and it is fast. thread_local does not
176 * require once-only initialization like pthread_key_t. C11 does not
177 * define what happens if one attempts to access a thread_local object
178 * from a thread other than the one to which that object belongs. There
179 * is no provision to call a user-specified destructor when a thread
180 * ends. Typical implementations allow for an arbitrary amount of
181 * thread_local storage, but statically allocated only.
183 * - The __thread keyword is a GCC extension similar to thread_local but
184 * with a longer history. __thread is not portable to every GCC version
185 * or environment. __thread does not restrict the use of a thread-local
186 * object outside its own thread.
188 * Here's a handy summary:
190 * pthread_key_t thread_local __thread
191 * ------------- ------------ -------------
192 * portability high low medium
193 * speed low high high
194 * supports destructors? yes no no
195 * needs key allocation? yes no no
196 * arbitrary initializer? no yes yes
197 * cross-thread access? yes no yes
198 * amount available? few arbitrary arbitrary
199 * dynamically allocated? yes no no
205 * OVS provides some extensions and wrappers:
207 * - In a situation where the performance of thread_local or __thread is
208 * desirable, but portability is required, DEFINE_STATIC_PER_THREAD_DATA
209 * and DECLARE_EXTERN_PER_THREAD_DATA/DEFINE_EXTERN_PER_THREAD_DATA may
210 * be appropriate (see below).
212 * - DEFINE_PER_THREAD_MALLOCED_DATA can be convenient for simple
213 * per-thread malloc()'d buffers.
215 * - struct ovs_tsd provides an alternative to pthread_key_t that isn't
216 * limited to a small number of keys.
219 /* For static data, use this macro in a source file:
221 * DEFINE_STATIC_PER_THREAD_DATA(TYPE, NAME, INITIALIZER).
223 * For global data, "declare" the data in the header and "define" it in
224 * the source file, with:
226 * DECLARE_EXTERN_PER_THREAD_DATA(TYPE, NAME).
227 * DEFINE_EXTERN_PER_THREAD_DATA(NAME, INITIALIZER).
229 * One should prefer to use POSIX per-thread data, via pthread_key_t, when its
230 * performance is acceptable, because of its portability (see the table above).
231 * This macro is an alternatives that takes advantage of thread_local (and
232 * __thread), for its performance, when it is available, and falls back to
233 * POSIX per-thread data otherwise.
235 * Defines per-thread variable NAME with the given TYPE, initialized to
236 * INITIALIZER (which must be valid as an initializer for a variable with
239 * The public interface to the variable is:
241 * TYPE *NAME_get(void)
242 * TYPE *NAME_get_unsafe(void)
244 * Returns the address of this thread's instance of NAME.
246 * Use NAME_get() in a context where this might be the first use of the
247 * per-thread variable in the program. Use NAME_get_unsafe(), which
248 * avoids a conditional test and is thus slightly faster, in a context
249 * where one knows that NAME_get() has already been called previously.
251 * There is no "NAME_set()" (or "NAME_set_unsafe()") function. To set the
252 * value of the per-thread variable, dereference the pointer returned by
253 * TYPE_get() or TYPE_get_unsafe(), e.g. *TYPE_get() = 0.
255 #if HAVE_THREAD_LOCAL || HAVE___THREAD
257 #if HAVE_THREAD_LOCAL
260 #define thread_local __thread
265 #define DEFINE_STATIC_PER_THREAD_DATA(TYPE, NAME, ...) \
266 typedef TYPE NAME##_type; \
268 static NAME##_type * \
269 NAME##_get_unsafe(void) \
271 static thread_local NAME##_type var = __VA_ARGS__; \
275 static NAME##_type * \
278 return NAME##_get_unsafe(); \
280 #define DECLARE_EXTERN_PER_THREAD_DATA(TYPE, NAME) \
281 typedef TYPE NAME##_type; \
282 extern thread_local NAME##_type NAME##_var; \
284 static inline NAME##_type * \
285 NAME##_get_unsafe(void) \
287 return &NAME##_var; \
290 static inline NAME##_type * \
293 return NAME##_get_unsafe(); \
295 #define DEFINE_EXTERN_PER_THREAD_DATA(NAME, ...) \
296 thread_local NAME##_type NAME##_var = __VA_ARGS__;
297 #else /* no C implementation support for thread-local storage */
298 #define DEFINE_STATIC_PER_THREAD_DATA(TYPE, NAME, ...) \
299 typedef TYPE NAME##_type; \
300 static pthread_key_t NAME##_key; \
302 static NAME##_type * \
303 NAME##_get_unsafe(void) \
305 return pthread_getspecific(NAME##_key); \
309 NAME##_once_init(void) \
311 if (pthread_key_create(&NAME##_key, free)) { \
316 static NAME##_type * \
319 static pthread_once_t once = PTHREAD_ONCE_INIT; \
320 NAME##_type *value; \
322 pthread_once(&once, NAME##_once_init); \
323 value = NAME##_get_unsafe(); \
325 static const NAME##_type initial_value = __VA_ARGS__; \
327 value = malloc(sizeof *value); \
328 if (value == NULL) { \
331 *value = initial_value; \
332 xpthread_setspecific(NAME##_key, value); \
336 #define DECLARE_EXTERN_PER_THREAD_DATA(TYPE, NAME) \
337 typedef TYPE NAME##_type; \
338 static pthread_key_t NAME##_key; \
340 static inline NAME##_type * \
341 NAME##_get_unsafe(void) \
343 return pthread_getspecific(NAME##_key); \
346 NAME##_type *NAME##_get(void);
347 #define DEFINE_EXTERN_PER_THREAD_DATA(NAME, ...) \
349 NAME##_once_init(void) \
351 if (pthread_key_create(&NAME##_key, free)) { \
359 static pthread_once_t once = PTHREAD_ONCE_INIT; \
360 NAME##_type *value; \
362 pthread_once(&once, NAME##_once_init); \
363 value = NAME##_get_unsafe(); \
365 static const NAME##_type initial_value = __VA_ARGS__; \
367 value = malloc(sizeof *value); \
368 if (value == NULL) { \
371 *value = initial_value; \
372 xpthread_setspecific(NAME##_key, value); \
378 /* DEFINE_PER_THREAD_MALLOCED_DATA(TYPE, NAME).
380 * This is a simple wrapper around POSIX per-thread data primitives. It
381 * defines per-thread variable NAME with the given TYPE, which must be a
382 * pointer type. In each thread, the per-thread variable is initialized to
383 * NULL. When a thread terminates, the variable is freed with free().
385 * The public interface to the variable is:
387 * TYPE NAME_get(void)
388 * TYPE NAME_get_unsafe(void)
390 * Returns the value of per-thread variable NAME in this thread.
392 * Use NAME_get() in a context where this might be the first use of the
393 * per-thread variable in the program. Use NAME_get_unsafe(), which
394 * avoids a conditional test and is thus slightly faster, in a context
395 * where one knows that NAME_get() has already been called previously.
397 * TYPE NAME_set(TYPE new_value)
398 * TYPE NAME_set_unsafe(TYPE new_value)
400 * Sets the value of per-thread variable NAME to 'new_value' in this
401 * thread, and returns its previous value.
403 * Use NAME_set() in a context where this might be the first use of the
404 * per-thread variable in the program. Use NAME_set_unsafe(), which
405 * avoids a conditional test and is thus slightly faster, in a context
406 * where one knows that NAME_set() has already been called previously.
408 #define DEFINE_PER_THREAD_MALLOCED_DATA(TYPE, NAME) \
409 static pthread_key_t NAME##_key; \
412 NAME##_once_init(void) \
414 if (pthread_key_create(&NAME##_key, free)) { \
422 static pthread_once_t once = PTHREAD_ONCE_INIT; \
423 pthread_once(&once, NAME##_once_init); \
427 NAME##_get_unsafe(void) \
429 return pthread_getspecific(NAME##_key); \
432 static OVS_UNUSED TYPE \
436 return NAME##_get_unsafe(); \
440 NAME##_set_unsafe(TYPE value) \
442 TYPE old_value = NAME##_get_unsafe(); \
443 xpthread_setspecific(NAME##_key, value); \
447 static OVS_UNUSED TYPE \
448 NAME##_set(TYPE value) \
451 return NAME##_set_unsafe(value); \
454 /* Dynamically allocated thread-specific data with lots of slots.
456 * pthread_key_t can provide as few as 128 pieces of thread-specific data (even
457 * glibc is limited to 1,024). Thus, one must be careful to allocate only a
458 * few keys globally. One cannot, for example, allocate a key for every
459 * instance of a data structure if there might be an arbitrary number of those
462 * This API is similar to the pthread one (simply search and replace pthread_
463 * by ovsthread_) but it a much larger limit that can be raised if necessary
464 * (by recompiling). Thus, one may more freely use this form of
465 * thread-specific data.
467 * ovsthread_key_t also differs from pthread_key_t in the following ways:
469 * - Destructors must not access thread-specific data (via ovsthread_key).
471 * - The pthread_key_t API allows concurrently exiting threads to start
472 * executing the destructor after pthread_key_delete() returns. The
473 * ovsthread_key_t API guarantees that, when ovsthread_key_delete()
474 * returns, all destructors have returned and no new ones will start
477 typedef struct ovsthread_key *ovsthread_key_t;
479 void ovsthread_key_create(ovsthread_key_t *, void (*destructor)(void *));
480 void ovsthread_key_delete(ovsthread_key_t);
482 void ovsthread_setspecific(ovsthread_key_t, const void *);
483 void *ovsthread_getspecific(ovsthread_key_t);
485 /* Convenient once-only execution.
491 * POSIX provides pthread_once_t and pthread_once() as primitives for running a
492 * set of code only once per process execution. They are used like this:
494 * static void run_once(void) { ...initialization... }
495 * static pthread_once_t once = PTHREAD_ONCE_INIT;
497 * pthread_once(&once, run_once);
499 * pthread_once() does not allow passing any parameters to the initialization
500 * function, which is often inconvenient, because it means that the function
501 * can only access data declared at file scope.
507 * Use ovsthread_once, like this, instead:
509 * static struct ovsthread_once once = OVSTHREAD_ONCE_INITIALIZER;
511 * if (ovsthread_once_start(&once)) {
512 * ...initialization...
513 * ovsthread_once_done(&once);
517 struct ovsthread_once {
519 struct ovs_mutex mutex;
522 #define OVSTHREAD_ONCE_INITIALIZER \
524 ATOMIC_VAR_INIT(false), \
525 OVS_MUTEX_INITIALIZER, \
528 static inline bool ovsthread_once_start(struct ovsthread_once *once)
529 OVS_TRY_LOCK(true, once->mutex);
530 void ovsthread_once_done(struct ovsthread_once *once)
531 OVS_RELEASES(once->mutex);
533 bool ovsthread_once_start__(struct ovsthread_once *once)
534 OVS_TRY_LOCK(false, once->mutex);
537 ovsthread_once_is_done__(struct ovsthread_once *once)
541 atomic_read_explicit(&once->done, &done, memory_order_relaxed);
545 /* Returns true if this is the first call to ovsthread_once_start() for
546 * 'once'. In this case, the caller should perform whatever initialization
547 * actions it needs to do, then call ovsthread_once_done() for 'once'.
549 * Returns false if this is not the first call to ovsthread_once_start() for
550 * 'once'. In this case, the call will not return until after
551 * ovsthread_once_done() has been called. */
553 ovsthread_once_start(struct ovsthread_once *once)
555 return OVS_UNLIKELY(!ovsthread_once_is_done__(once)
556 && !ovsthread_once_start__(once));
561 * pthread_t isn't so nice for some purposes. Its size and representation are
562 * implementation dependent, which means that there is no way to hash it.
563 * This thread ID avoids the problem.
566 DECLARE_EXTERN_PER_THREAD_DATA(unsigned int, ovsthread_id);
568 /* Returns a per-thread identifier unique within the lifetime of the
570 static inline unsigned int
571 ovsthread_id_self(void)
573 return *ovsthread_id_get();
576 /* Simulated global counter.
578 * Incrementing such a counter is meant to be cheaper than incrementing a
579 * global counter protected by a lock. It is probably more expensive than
580 * incrementing a truly thread-local variable, but such a variable has no
581 * straightforward way to get the sum.
587 * Fully thread-safe. */
589 struct ovsthread_counter *ovsthread_counter_create(void);
590 void ovsthread_counter_destroy(struct ovsthread_counter *);
591 void ovsthread_counter_inc(struct ovsthread_counter *, unsigned long long int);
592 unsigned long long int ovsthread_counter_read(
593 const struct ovsthread_counter *);
595 void assert_single_threaded_at(const char *where);
596 #define assert_single_threaded() assert_single_threaded_at(SOURCE_LOCATOR)
598 pid_t xfork_at(const char *where);
599 #define xfork() xfork_at(SOURCE_LOCATOR)
601 void forbid_forking(const char *reason);
604 /* Useful functions related to threading. */
606 int count_cpu_cores(void);
608 #endif /* ovs-thread.h */