lib/ovs-thread.h

   1 /*
   2  * Copyright (c) 2013 Nicira, Inc.
   3  *
   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:
   7  *
   8  *     http://www.apache.org/licenses/LICENSE-2.0
   9  *
  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.
  15  */
  16
  17 #ifndef OVS_THREAD_H
  18 #define OVS_THREAD_H 1
  19
  20 #include <pthread.h>
  21 #include "ovs-atomic.h"
  22 #include "util.h"
  23
  24 /* glibc has some non-portable mutex types and initializers:
  25  *
  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.
  28  *
  29  *    - PTHREAD_ERRORCHECK_MUTEX_INITIALIZER_NP is a non-portable initializer
  30  *      for an error-checking mutex.
  31  *
  32  * We use these definitions to fall back to PTHREAD_MUTEX_NORMAL instead in
  33  * these cases.
  34  *
  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
  41 #else
  42 #define PTHREAD_MUTEX_ADAPTIVE PTHREAD_MUTEX_NORMAL
  43 #define PTHREAD_ADAPTIVE_MUTEX_INITIALIZER PTHREAD_MUTEX_INITIALIZER
  44 #endif
  45
  46 #ifdef PTHREAD_ERRORCHECK_MUTEX_INITIALIZER_NP
  47 #define PTHREAD_ERRORCHECK_MUTEX_INITIALIZER \
  48     PTHREAD_ERRORCHECK_MUTEX_INITIALIZER_NP
  49 #else
  50 #define PTHREAD_ERRORCHECK_MUTEX_INITIALIZER PTHREAD_MUTEX_INITIALIZER
  51 #endif
  52 \f
  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 *);
  61
  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 *);
  68
  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)
  73     OVS_MUST_HOLD(mutex);
  74
  75 #ifdef __CHECKER__
  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
  84 #endif
  85
  86 void xpthread_key_create(pthread_key_t *, void (*destructor)(void *));
  87
  88 void xpthread_create(pthread_t *, pthread_attr_t *, void *(*)(void *), void *);
  89 \f
  90 /* Per-thread data.
  91  *
  92  * Multiple forms of per-thread data exist, each with its own pluses and
  93  * minuses:
  94  *
  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.
 100  *
 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
 107  *       ends.
 108  *
 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.
 113  *
 114  * Here's a handy summary:
 115  *
 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
 124  */
 125
 126 /* DEFINE_PER_THREAD_DATA(TYPE, NAME, INITIALIZER).
 127  *
 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.
 133  *
 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
 136  * static lifetime).
 137  *
 138  * The public interface to the variable is:
 139  *
 140  *    TYPE *NAME_get(void)
 141  *    TYPE *NAME_get_unsafe(void)
 142  *
 143  *       Returns the address of this thread's instance of NAME.
 144  *
 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.
 149  *
 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.
 153  */
 154 #if HAVE_THREAD_LOCAL || HAVE___THREAD
 155
 156 #if HAVE_THREAD_LOCAL
 157 #include <threads.h>
 158 #elif HAVE___THREAD
 159 #define thread_local __thread
 160 #else
 161 #error
 162 #endif
 163
 164 #define DEFINE_PER_THREAD_DATA(TYPE, NAME, ...)                 \
 165     typedef TYPE NAME##_type;                                   \
 166     static thread_local NAME##_type NAME##_var = __VA_ARGS__;   \
 167                                                                 \
 168     static NAME##_type *                                        \
 169     NAME##_get_unsafe(void)                                     \
 170     {                                                           \
 171         return &NAME##_var;                                     \
 172     }                                                           \
 173                                                                 \
 174     static NAME##_type *                                        \
 175     NAME##_get(void)                                            \
 176     {                                                           \
 177         return NAME##_get_unsafe();                             \
 178     }
 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;                                    \
 183                                                                         \
 184     static NAME##_type *                                                \
 185     NAME##_get_unsafe(void)                                             \
 186     {                                                                   \
 187         return pthread_getspecific(NAME##_key);                         \
 188     }                                                                   \
 189                                                                         \
 190     static void                                                         \
 191     NAME##_once_init(void)                                              \
 192     {                                                                   \
 193         if (pthread_key_create(&NAME##_key, free)) {                    \
 194             abort();                                                    \
 195         }                                                               \
 196     }                                                                   \
 197                                                                         \
 198     static NAME##_type *                                                \
 199     NAME##_get(void)                                                    \
 200     {                                                                   \
 201         static pthread_once_t once = PTHREAD_ONCE_INIT;                 \
 202         NAME##_type *value;                                             \
 203                                                                         \
 204         pthread_once(&once, NAME##_once_init);                          \
 205         value = NAME##_get_unsafe();                                    \
 206         if (!value) {                                                   \
 207             static const NAME##_type initial_value = __VA_ARGS__;       \
 208                                                                         \
 209             value = xmalloc(sizeof *value);                             \
 210             *value = initial_value;                                     \
 211             pthread_setspecific(NAME##_key, value);                     \
 212         }                                                               \
 213         return value;                                                   \
 214     }
 215 #endif
 216
 217 /* DEFINE_PER_THREAD_MALLOCED_DATA(TYPE, NAME).
 218  *
 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().
 223  *
 224  * The public interface to the variable is:
 225  *
 226  *    TYPE NAME_get(void)
 227  *    TYPE NAME_get_unsafe(void)
 228  *
 229  *       Returns the value of per-thread variable NAME in this thread.
 230  *
 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.
 235  *
 236  *    TYPE NAME_set(TYPE new_value)
 237  *    TYPE NAME_set_unsafe(TYPE new_value)
 238  *
 239  *       Sets the value of per-thread variable NAME to 'new_value' in this
 240  *       thread, and returns its previous value.
 241  *
 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.
 246  */
 247 #define DEFINE_PER_THREAD_MALLOCED_DATA(TYPE, NAME)     \
 248     static pthread_key_t NAME##_key;                    \
 249                                                         \
 250     static void                                         \
 251     NAME##_once_init(void)                              \
 252     {                                                   \
 253         if (pthread_key_create(&NAME##_key, free)) {    \
 254             abort();                                    \
 255         }                                               \
 256     }                                                   \
 257                                                         \
 258     static void                                         \
 259     NAME##_init(void)                                   \
 260     {                                                   \
 261         static pthread_once_t once = PTHREAD_ONCE_INIT; \
 262         pthread_once(&once, NAME##_once_init);          \
 263     }                                                   \
 264                                                         \
 265     static TYPE                                         \
 266     NAME##_get_unsafe(void)                             \
 267     {                                                   \
 268         return pthread_getspecific(NAME##_key);         \
 269     }                                                   \
 270                                                         \
 271     static OVS_UNUSED TYPE                              \
 272     NAME##_get(void)                                    \
 273     {                                                   \
 274         NAME##_init();                                  \
 275         return NAME##_get_unsafe();                     \
 276     }                                                   \
 277                                                         \
 278     static TYPE                                         \
 279     NAME##_set_unsafe(TYPE value)                       \
 280     {                                                   \
 281         TYPE old_value = NAME##_get_unsafe();           \
 282         pthread_setspecific(NAME##_key, value);         \
 283         return old_value;                               \
 284     }                                                   \
 285                                                         \
 286     static OVS_UNUSED TYPE                              \
 287     NAME##_set(TYPE value)                              \
 288     {                                                   \
 289         NAME##_init();                                  \
 290         return NAME##_set_unsafe(value);                \
 291     }
 292 \f
 293 /* Convenient once-only execution.
 294  *
 295  *
 296  * Problem
 297  * =======
 298  *
 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:
 301  *
 302  *     static void run_once(void) { ...initialization... }
 303  *     static pthread_once_t once = PTHREAD_ONCE_INIT;
 304  * ...
 305  *     pthread_once(&once, run_once);
 306  *
 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.
 310  *
 311  *
 312  * Solution
 313  * ========
 314  *
 315  * Use ovsthread_once, like this, instead:
 316  *
 317  *     static struct ovsthread_once once = OVSTHREAD_ONCE_INITIALIZER;
 318  *
 319  *     if (ovsthread_once_start(&once)) {
 320  *         ...initialization...
 321  *         ovsthread_once_done(&once);
 322  *     }
 323  */
 324
 325 struct ovsthread_once {
 326     atomic_bool done;
 327     pthread_mutex_t mutex;
 328 };
 329
 330 #define OVSTHREAD_ONCE_INITIALIZER              \
 331     {                                           \
 332         ATOMIC_VAR_INIT(false),                 \
 333         PTHREAD_ADAPTIVE_MUTEX_INITIALIZER,     \
 334     }
 335
 336 static inline bool ovsthread_once_start(struct ovsthread_once *);
 337 void ovsthread_once_done(struct ovsthread_once *once) OVS_RELEASES(once);
 338
 339 bool ovsthread_once_start__(struct ovsthread_once *);
 340
 341 static inline bool
 342 ovsthread_once_is_done__(const struct ovsthread_once *once)
 343 {
 344     bool done;
 345
 346     atomic_read_explicit(&once->done, &done, memory_order_relaxed);
 347     return done;
 348 }
 349
 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'.
 353  *
 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. */
 357 static inline bool
 358 ovsthread_once_start(struct ovsthread_once *once)
 359 {
 360     return OVS_UNLIKELY(!ovsthread_once_is_done__(once)
 361                         && !ovsthread_once_start__(once));
 362 }
 363
 364 #ifdef __CHECKER__
 365 #define ovsthread_once_start(ONCE) \
 366     ((ONCE)->done ? false : ({ OVS_ACQUIRE(ONCE); true; }))
 367 #endif
 368
 369 #endif /* ovs-thread.h */