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
21 #include "ovs-atomic.h"
24 /* glibc has some non-portable mutex types and initializers:
26 * - PTHREAD_MUTEX_ADAPTIVE_NP is a mutex type that works as a spinlock that
27 * falls back to a mutex after spinning for some number of iterations.
29 * - PTHREAD_ERRORCHECK_MUTEX_INITIALIZER_NP is a non-portable initializer
30 * for an error-checking mutex.
32 * We use these definitions to fall back to PTHREAD_MUTEX_NORMAL instead in
35 * (glibc has other non-portable initializers, but we can't reasonably
36 * substitute for them here.) */
37 #ifdef PTHREAD_ADAPTIVE_MUTEX_INITIALIZER_NP
38 #define PTHREAD_MUTEX_ADAPTIVE PTHREAD_MUTEX_ADAPTIVE_NP
39 #define PTHREAD_ADAPTIVE_MUTEX_INITIALIZER \
40 PTHREAD_ADAPTIVE_MUTEX_INITIALIZER_NP
42 #define PTHREAD_MUTEX_ADAPTIVE PTHREAD_MUTEX_NORMAL
43 #define PTHREAD_ADAPTIVE_MUTEX_INITIALIZER PTHREAD_MUTEX_INITIALIZER
46 #ifdef PTHREAD_ERRORCHECK_MUTEX_INITIALIZER_NP
47 #define PTHREAD_ERRORCHECK_MUTEX_INITIALIZER \
48 PTHREAD_ERRORCHECK_MUTEX_INITIALIZER_NP
50 #define PTHREAD_ERRORCHECK_MUTEX_INITIALIZER PTHREAD_MUTEX_INITIALIZER
53 /* Simple wrappers for pthreads functions. Most of these functions abort the
54 * process with an error message on any error. The *_trylock() functions are
55 * exceptions: they pass through a 0 or EBUSY return value to the caller and
56 * abort on any other error. */
57 void xpthread_mutex_init(pthread_mutex_t *, pthread_mutexattr_t *);
58 void xpthread_mutex_lock(pthread_mutex_t *mutex) OVS_ACQUIRES(mutex);
59 void xpthread_mutex_unlock(pthread_mutex_t *mutex) OVS_RELEASES(mutex);
60 int xpthread_mutex_trylock(pthread_mutex_t *);
62 void xpthread_rwlock_init(pthread_rwlock_t *, pthread_rwlockattr_t *);
63 void xpthread_rwlock_rdlock(pthread_rwlock_t *rwlock) OVS_ACQUIRES(rwlock);
64 void xpthread_rwlock_wrlock(pthread_rwlock_t *rwlock) OVS_ACQUIRES(rwlock);
65 void xpthread_rwlock_unlock(pthread_rwlock_t *rwlock) OVS_RELEASES(rwlock);
66 int xpthread_rwlock_tryrdlock(pthread_rwlock_t *);
67 int xpthread_rwlock_trywrlock(pthread_rwlock_t *);
69 void xpthread_cond_init(pthread_cond_t *, pthread_condattr_t *);
70 void xpthread_cond_signal(pthread_cond_t *);
71 void xpthread_cond_broadcast(pthread_cond_t *);
72 void xpthread_cond_wait(pthread_cond_t *, pthread_mutex_t *mutex)
76 /* Replace these functions by the macros already defined in the <pthread.h>
77 * annotations, because the macro definitions have correct semantics for the
78 * conditional acquisition that can't be captured in a function annotation.
79 * The difference in semantics from pthread_*() to xpthread_*() does not matter
80 * because sparse is not a compiler. */
81 #define xpthread_mutex_trylock pthread_mutex_trylock
82 #define xpthread_rwlock_tryrdlock pthread_rwlock_tryrdlock
83 #define xpthread_rwlock_trywrlock pthread_rwlock_trywrlock
86 void xpthread_key_create(pthread_key_t *, void (*destructor)(void *));
88 void xpthread_create(pthread_t *, pthread_attr_t *, void *(*)(void *), void *);
92 * Multiple forms of per-thread data exist, each with its own pluses and
95 * - POSIX per-thread data via pthread_key_t is portable to any pthreads
96 * implementation, and allows a destructor function to be defined. It
97 * only (directly) supports per-thread pointers, which are always
98 * initialized to NULL. It requires once-only allocation of a
99 * pthread_key_t value. It is relatively slow.
101 * - The thread_local feature newly defined in C11 <threads.h> works with
102 * any data type and initializer, and it is fast. thread_local does not
103 * require once-only initialization like pthread_key_t. C11 does not
104 * define what happens if one attempts to access a thread_local object
105 * from a thread other than the one to which that object belongs. There
106 * is no provision to call a user-specified destructor when a thread
109 * - The __thread keyword is a GCC extension similar to thread_local but
110 * with a longer history. __thread is not portable to every GCC version
111 * or environment. __thread does not restrict the use of a thread-local
112 * object outside its own thread.
114 * Here's a handy summary:
116 * pthread_key_t thread_local __thread
117 * ------------- ------------ -------------
118 * portability high low medium
119 * speed low high high
120 * supports destructors? yes no no
121 * needs key allocation? yes no no
122 * arbitrary initializer? no yes yes
123 * cross-thread access? yes no yes
126 /* DEFINE_PER_THREAD_DATA(TYPE, NAME, INITIALIZER).
128 * One should prefer to use POSIX per-thread data, via pthread_key_t, when its
129 * performance is acceptable, because of its portability (see the table above).
130 * This macro is an alternatives that takes advantage of thread_local (and
131 * __thread), for its performance, when it is available, and falls back to
132 * POSIX per-thread data otherwise.
134 * Defines per-thread variable NAME with the given TYPE, initialized to
135 * INITIALIZER (which must be valid as an initializer for a variable with
138 * The public interface to the variable is:
140 * TYPE *NAME_get(void)
141 * TYPE *NAME_get_unsafe(void)
143 * Returns the address of this thread's instance of NAME.
145 * Use NAME_get() in a context where this might be the first use of the
146 * per-thread variable in the program. Use NAME_get_unsafe(), which
147 * avoids a conditional test and is thus slightly faster, in a context
148 * where one knows that NAME_get() has already been called previously.
150 * There is no "NAME_set()" (or "NAME_set_unsafe()") function. To set the
151 * value of the per-thread variable, dereference the pointer returned by
152 * TYPE_get() or TYPE_get_unsafe(), e.g. *TYPE_get() = 0.
154 #if HAVE_THREAD_LOCAL || HAVE___THREAD
156 #if HAVE_THREAD_LOCAL
159 #define thread_local __thread
164 #define DEFINE_PER_THREAD_DATA(TYPE, NAME, ...) \
165 typedef TYPE NAME##_type; \
166 static thread_local NAME##_type NAME##_var = __VA_ARGS__; \
168 static NAME##_type * \
169 NAME##_get_unsafe(void) \
171 return &NAME##_var; \
174 static NAME##_type * \
177 return NAME##_get_unsafe(); \
179 #else /* no C implementation support for thread-local storage */
180 #define DEFINE_PER_THREAD_DATA(TYPE, NAME, ...) \
181 typedef TYPE NAME##_type; \
182 static pthread_key_t NAME##_key; \
184 static NAME##_type * \
185 NAME##_get_unsafe(void) \
187 return pthread_getspecific(NAME##_key); \
191 NAME##_once_init(void) \
193 if (pthread_key_create(&NAME##_key, free)) { \
198 static NAME##_type * \
201 static pthread_once_t once = PTHREAD_ONCE_INIT; \
202 NAME##_type *value; \
204 pthread_once(&once, NAME##_once_init); \
205 value = NAME##_get_unsafe(); \
207 static const NAME##_type initial_value = __VA_ARGS__; \
209 value = xmalloc(sizeof *value); \
210 *value = initial_value; \
211 pthread_setspecific(NAME##_key, value); \
217 /* DEFINE_PER_THREAD_MALLOCED_DATA(TYPE, NAME).
219 * This is a simple wrapper around POSIX per-thread data primitives. It
220 * defines per-thread variable NAME with the given TYPE, which must be a
221 * pointer type. In each thread, the per-thread variable is initialized to
222 * NULL. When a thread terminates, the variable is freed with free().
224 * The public interface to the variable is:
226 * TYPE NAME_get(void)
227 * TYPE NAME_get_unsafe(void)
229 * Returns the value of per-thread variable NAME in this thread.
231 * Use NAME_get() in a context where this might be the first use of the
232 * per-thread variable in the program. Use NAME_get_unsafe(), which
233 * avoids a conditional test and is thus slightly faster, in a context
234 * where one knows that NAME_get() has already been called previously.
236 * TYPE NAME_set(TYPE new_value)
237 * TYPE NAME_set_unsafe(TYPE new_value)
239 * Sets the value of per-thread variable NAME to 'new_value' in this
240 * thread, and returns its previous value.
242 * Use NAME_set() in a context where this might be the first use of the
243 * per-thread variable in the program. Use NAME_set_unsafe(), which
244 * avoids a conditional test and is thus slightly faster, in a context
245 * where one knows that NAME_set() has already been called previously.
247 #define DEFINE_PER_THREAD_MALLOCED_DATA(TYPE, NAME) \
248 static pthread_key_t NAME##_key; \
251 NAME##_once_init(void) \
253 if (pthread_key_create(&NAME##_key, free)) { \
261 static pthread_once_t once = PTHREAD_ONCE_INIT; \
262 pthread_once(&once, NAME##_once_init); \
266 NAME##_get_unsafe(void) \
268 return pthread_getspecific(NAME##_key); \
271 static OVS_UNUSED TYPE \
275 return NAME##_get_unsafe(); \
279 NAME##_set_unsafe(TYPE value) \
281 TYPE old_value = NAME##_get_unsafe(); \
282 pthread_setspecific(NAME##_key, value); \
286 static OVS_UNUSED TYPE \
287 NAME##_set(TYPE value) \
290 return NAME##_set_unsafe(value); \
293 /* Convenient once-only execution.
299 * POSIX provides pthread_once_t and pthread_once() as primitives for running a
300 * set of code only once per process execution. They are used like this:
302 * static void run_once(void) { ...initialization... }
303 * static pthread_once_t once = PTHREAD_ONCE_INIT;
305 * pthread_once(&once, run_once);
307 * pthread_once() does not allow passing any parameters to the initialization
308 * function, which is often inconvenient, because it means that the function
309 * can only access data declared at file scope.
315 * Use ovsthread_once, like this, instead:
317 * static struct ovsthread_once once = OVSTHREAD_ONCE_INITIALIZER;
319 * if (ovsthread_once_start(&once)) {
320 * ...initialization...
321 * ovsthread_once_done(&once);
325 struct ovsthread_once {
327 pthread_mutex_t mutex;
330 #define OVSTHREAD_ONCE_INITIALIZER \
332 ATOMIC_VAR_INIT(false), \
333 PTHREAD_ADAPTIVE_MUTEX_INITIALIZER, \
336 static inline bool ovsthread_once_start(struct ovsthread_once *);
337 void ovsthread_once_done(struct ovsthread_once *once) OVS_RELEASES(once);
339 bool ovsthread_once_start__(struct ovsthread_once *);
342 ovsthread_once_is_done__(const struct ovsthread_once *once)
346 atomic_read_explicit(&once->done, &done, memory_order_relaxed);
350 /* Returns true if this is the first call to ovsthread_once_start() for
351 * 'once'. In this case, the caller should perform whatever initialization
352 * actions it needs to do, then call ovsthread_once_done() for 'once'.
354 * Returns false if this is not the first call to ovsthread_once_start() for
355 * 'once'. In this case, the call will not return until after
356 * ovsthread_once_done() has been called. */
358 ovsthread_once_start(struct ovsthread_once *once)
360 return OVS_UNLIKELY(!ovsthread_once_is_done__(once)
361 && !ovsthread_once_start__(once));
365 #define ovsthread_once_start(ONCE) \
366 ((ONCE)->done ? false : ({ OVS_ACQUIRE(ONCE); true; }))
369 #endif /* ovs-thread.h */