2 * Copyright (c) 2013 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"
26 /* glibc has some non-portable mutex types and initializers:
28 * - PTHREAD_MUTEX_ADAPTIVE_NP is a mutex type that works as a spinlock that
29 * falls back to a mutex after spinning for some number of iterations.
31 * - PTHREAD_ERRORCHECK_MUTEX_INITIALIZER_NP is a non-portable initializer
32 * for an error-checking mutex.
34 * We use these definitions to fall back to PTHREAD_MUTEX_NORMAL instead in
37 * (glibc has other non-portable initializers, but we can't reasonably
38 * substitute for them here.) */
39 #ifdef PTHREAD_ADAPTIVE_MUTEX_INITIALIZER_NP
40 #define PTHREAD_MUTEX_ADAPTIVE PTHREAD_MUTEX_ADAPTIVE_NP
41 #define PTHREAD_ADAPTIVE_MUTEX_INITIALIZER \
42 PTHREAD_ADAPTIVE_MUTEX_INITIALIZER_NP
44 #define PTHREAD_MUTEX_ADAPTIVE PTHREAD_MUTEX_NORMAL
45 #define PTHREAD_ADAPTIVE_MUTEX_INITIALIZER PTHREAD_MUTEX_INITIALIZER
48 #ifdef PTHREAD_ERRORCHECK_MUTEX_INITIALIZER_NP
49 #define PTHREAD_ERRORCHECK_MUTEX_INITIALIZER \
50 PTHREAD_ERRORCHECK_MUTEX_INITIALIZER_NP
52 #define PTHREAD_ERRORCHECK_MUTEX_INITIALIZER PTHREAD_MUTEX_INITIALIZER
55 /* Simple wrappers for pthreads functions. Most of these functions abort the
56 * process with an error message on any error. The *_trylock() functions are
57 * exceptions: they pass through a 0 or EBUSY return value to the caller and
58 * abort on any other error. */
60 void xpthread_mutex_init(pthread_mutex_t *, pthread_mutexattr_t *);
61 void xpthread_mutex_destroy(pthread_mutex_t *);
62 void xpthread_mutex_lock(pthread_mutex_t *mutex) OVS_ACQUIRES(mutex);
63 void xpthread_mutex_unlock(pthread_mutex_t *mutex) OVS_RELEASES(mutex);
64 int xpthread_mutex_trylock(pthread_mutex_t *);
66 void xpthread_mutexattr_init(pthread_mutexattr_t *);
67 void xpthread_mutexattr_destroy(pthread_mutexattr_t *);
68 void xpthread_mutexattr_settype(pthread_mutexattr_t *, int type);
69 void xpthread_mutexattr_gettype(pthread_mutexattr_t *, int *typep);
71 void xpthread_rwlock_init(pthread_rwlock_t *, pthread_rwlockattr_t *);
72 void xpthread_rwlock_destroy(pthread_rwlock_t *);
73 void xpthread_rwlock_rdlock(pthread_rwlock_t *rwlock) OVS_ACQUIRES(rwlock);
74 void xpthread_rwlock_wrlock(pthread_rwlock_t *rwlock) OVS_ACQUIRES(rwlock);
75 void xpthread_rwlock_unlock(pthread_rwlock_t *rwlock) OVS_RELEASES(rwlock);
76 int xpthread_rwlock_tryrdlock(pthread_rwlock_t *);
77 int xpthread_rwlock_trywrlock(pthread_rwlock_t *);
79 void xpthread_cond_init(pthread_cond_t *, pthread_condattr_t *);
80 void xpthread_cond_destroy(pthread_cond_t *);
81 void xpthread_cond_signal(pthread_cond_t *);
82 void xpthread_cond_broadcast(pthread_cond_t *);
83 void xpthread_cond_wait(pthread_cond_t *, pthread_mutex_t *mutex)
87 /* Replace these functions by the macros already defined in the <pthread.h>
88 * annotations, because the macro definitions have correct semantics for the
89 * conditional acquisition that can't be captured in a function annotation.
90 * The difference in semantics from pthread_*() to xpthread_*() does not matter
91 * because sparse is not a compiler. */
92 #define xpthread_mutex_trylock pthread_mutex_trylock
93 #define xpthread_rwlock_tryrdlock pthread_rwlock_tryrdlock
94 #define xpthread_rwlock_trywrlock pthread_rwlock_trywrlock
97 void xpthread_key_create(pthread_key_t *, void (*destructor)(void *));
99 void xpthread_create(pthread_t *, pthread_attr_t *, void *(*)(void *), void *);
103 * Multiple forms of per-thread data exist, each with its own pluses and
106 * - POSIX per-thread data via pthread_key_t is portable to any pthreads
107 * implementation, and allows a destructor function to be defined. It
108 * only (directly) supports per-thread pointers, which are always
109 * initialized to NULL. It requires once-only allocation of a
110 * pthread_key_t value. It is relatively slow.
112 * - The thread_local feature newly defined in C11 <threads.h> works with
113 * any data type and initializer, and it is fast. thread_local does not
114 * require once-only initialization like pthread_key_t. C11 does not
115 * define what happens if one attempts to access a thread_local object
116 * from a thread other than the one to which that object belongs. There
117 * is no provision to call a user-specified destructor when a thread
120 * - The __thread keyword is a GCC extension similar to thread_local but
121 * with a longer history. __thread is not portable to every GCC version
122 * or environment. __thread does not restrict the use of a thread-local
123 * object outside its own thread.
125 * Here's a handy summary:
127 * pthread_key_t thread_local __thread
128 * ------------- ------------ -------------
129 * portability high low medium
130 * speed low high high
131 * supports destructors? yes no no
132 * needs key allocation? yes no no
133 * arbitrary initializer? no yes yes
134 * cross-thread access? yes no yes
137 /* DEFINE_PER_THREAD_DATA(TYPE, NAME, INITIALIZER).
139 * One should prefer to use POSIX per-thread data, via pthread_key_t, when its
140 * performance is acceptable, because of its portability (see the table above).
141 * This macro is an alternatives that takes advantage of thread_local (and
142 * __thread), for its performance, when it is available, and falls back to
143 * POSIX per-thread data otherwise.
145 * Defines per-thread variable NAME with the given TYPE, initialized to
146 * INITIALIZER (which must be valid as an initializer for a variable with
149 * The public interface to the variable is:
151 * TYPE *NAME_get(void)
152 * TYPE *NAME_get_unsafe(void)
154 * Returns the address of this thread's instance of NAME.
156 * Use NAME_get() in a context where this might be the first use of the
157 * per-thread variable in the program. Use NAME_get_unsafe(), which
158 * avoids a conditional test and is thus slightly faster, in a context
159 * where one knows that NAME_get() has already been called previously.
161 * There is no "NAME_set()" (or "NAME_set_unsafe()") function. To set the
162 * value of the per-thread variable, dereference the pointer returned by
163 * TYPE_get() or TYPE_get_unsafe(), e.g. *TYPE_get() = 0.
165 #if HAVE_THREAD_LOCAL || HAVE___THREAD
167 #if HAVE_THREAD_LOCAL
170 #define thread_local __thread
175 #define DEFINE_PER_THREAD_DATA(TYPE, NAME, ...) \
176 typedef TYPE NAME##_type; \
177 static thread_local NAME##_type NAME##_var = __VA_ARGS__; \
179 static NAME##_type * \
180 NAME##_get_unsafe(void) \
182 return &NAME##_var; \
185 static NAME##_type * \
188 return NAME##_get_unsafe(); \
190 #else /* no C implementation support for thread-local storage */
191 #define DEFINE_PER_THREAD_DATA(TYPE, NAME, ...) \
192 typedef TYPE NAME##_type; \
193 static pthread_key_t NAME##_key; \
195 static NAME##_type * \
196 NAME##_get_unsafe(void) \
198 return pthread_getspecific(NAME##_key); \
202 NAME##_once_init(void) \
204 if (pthread_key_create(&NAME##_key, free)) { \
209 static NAME##_type * \
212 static pthread_once_t once = PTHREAD_ONCE_INIT; \
213 NAME##_type *value; \
215 pthread_once(&once, NAME##_once_init); \
216 value = NAME##_get_unsafe(); \
218 static const NAME##_type initial_value = __VA_ARGS__; \
220 value = xmalloc(sizeof *value); \
221 *value = initial_value; \
222 pthread_setspecific(NAME##_key, value); \
228 /* DEFINE_PER_THREAD_MALLOCED_DATA(TYPE, NAME).
230 * This is a simple wrapper around POSIX per-thread data primitives. It
231 * defines per-thread variable NAME with the given TYPE, which must be a
232 * pointer type. In each thread, the per-thread variable is initialized to
233 * NULL. When a thread terminates, the variable is freed with free().
235 * The public interface to the variable is:
237 * TYPE NAME_get(void)
238 * TYPE NAME_get_unsafe(void)
240 * Returns the value of per-thread variable NAME in this thread.
242 * Use NAME_get() in a context where this might be the first use of the
243 * per-thread variable in the program. Use NAME_get_unsafe(), which
244 * avoids a conditional test and is thus slightly faster, in a context
245 * where one knows that NAME_get() has already been called previously.
247 * TYPE NAME_set(TYPE new_value)
248 * TYPE NAME_set_unsafe(TYPE new_value)
250 * Sets the value of per-thread variable NAME to 'new_value' in this
251 * thread, and returns its previous value.
253 * Use NAME_set() in a context where this might be the first use of the
254 * per-thread variable in the program. Use NAME_set_unsafe(), which
255 * avoids a conditional test and is thus slightly faster, in a context
256 * where one knows that NAME_set() has already been called previously.
258 #define DEFINE_PER_THREAD_MALLOCED_DATA(TYPE, NAME) \
259 static pthread_key_t NAME##_key; \
262 NAME##_once_init(void) \
264 if (pthread_key_create(&NAME##_key, free)) { \
272 static pthread_once_t once = PTHREAD_ONCE_INIT; \
273 pthread_once(&once, NAME##_once_init); \
277 NAME##_get_unsafe(void) \
279 return pthread_getspecific(NAME##_key); \
282 static OVS_UNUSED TYPE \
286 return NAME##_get_unsafe(); \
290 NAME##_set_unsafe(TYPE value) \
292 TYPE old_value = NAME##_get_unsafe(); \
293 pthread_setspecific(NAME##_key, value); \
297 static OVS_UNUSED TYPE \
298 NAME##_set(TYPE value) \
301 return NAME##_set_unsafe(value); \
304 /* Convenient once-only execution.
310 * POSIX provides pthread_once_t and pthread_once() as primitives for running a
311 * set of code only once per process execution. They are used like this:
313 * static void run_once(void) { ...initialization... }
314 * static pthread_once_t once = PTHREAD_ONCE_INIT;
316 * pthread_once(&once, run_once);
318 * pthread_once() does not allow passing any parameters to the initialization
319 * function, which is often inconvenient, because it means that the function
320 * can only access data declared at file scope.
326 * Use ovsthread_once, like this, instead:
328 * static struct ovsthread_once once = OVSTHREAD_ONCE_INITIALIZER;
330 * if (ovsthread_once_start(&once)) {
331 * ...initialization...
332 * ovsthread_once_done(&once);
336 struct ovsthread_once {
338 pthread_mutex_t mutex;
341 #define OVSTHREAD_ONCE_INITIALIZER \
343 ATOMIC_VAR_INIT(false), \
344 PTHREAD_ADAPTIVE_MUTEX_INITIALIZER, \
347 static inline bool ovsthread_once_start(struct ovsthread_once *);
348 void ovsthread_once_done(struct ovsthread_once *once) OVS_RELEASES(once);
350 bool ovsthread_once_start__(struct ovsthread_once *);
353 ovsthread_once_is_done__(const struct ovsthread_once *once)
357 atomic_read_explicit(&once->done, &done, memory_order_relaxed);
361 /* Returns true if this is the first call to ovsthread_once_start() for
362 * 'once'. In this case, the caller should perform whatever initialization
363 * actions it needs to do, then call ovsthread_once_done() for 'once'.
365 * Returns false if this is not the first call to ovsthread_once_start() for
366 * 'once'. In this case, the call will not return until after
367 * ovsthread_once_done() has been called. */
369 ovsthread_once_start(struct ovsthread_once *once)
371 return OVS_UNLIKELY(!ovsthread_once_is_done__(once)
372 && !ovsthread_once_start__(once));
376 #define ovsthread_once_start(ONCE) \
377 ((ONCE)->done ? false : ({ OVS_ACQUIRE(ONCE); true; }))
380 void assert_single_threaded_at(const char *where);
381 #define assert_single_threaded() assert_single_threaded_at(SOURCE_LOCATOR)
383 pid_t xfork_at(const char *where);
384 #define xfork() xfork_at(SOURCE_LOCATOR)
386 void forbid_forking(const char *reason);
389 #endif /* ovs-thread.h */