lib/ovs-thread.h

   1 /*
   2  * Copyright (c) 2013, 2014 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 <stddef.h>
  22 #include <sys/types.h>
  23 #include "ovs-atomic.h"
  24 #include "util.h"
  25
  26
  27 /* Mutex. */
  28 struct OVS_LOCKABLE ovs_mutex {
  29     pthread_mutex_t lock;
  30     const char *where;          /* NULL if and only if uninitialized. */
  31 };
  32
  33 /* "struct ovs_mutex" initializer. */
  34 #ifdef PTHREAD_ERRORCHECK_MUTEX_INITIALIZER_NP
  35 #define OVS_MUTEX_INITIALIZER { PTHREAD_ERRORCHECK_MUTEX_INITIALIZER_NP, \
  36                                 "<unlocked>" }
  37 #else
  38 #define OVS_MUTEX_INITIALIZER { PTHREAD_MUTEX_INITIALIZER, "<unlocked>" }
  39 #endif
  40
  41 #ifdef PTHREAD_ADAPTIVE_MUTEX_INITIALIZER_NP
  42 #define OVS_ADAPTIVE_MUTEX_INITIALIZER                  \
  43     { PTHREAD_ADAPTIVE_MUTEX_INITIALIZER_NP, "<unlocked>" }
  44 #else
  45 #define OVS_ADAPTIVE_MUTEX_INITIALIZER OVS_MUTEX_INITIALIZER
  46 #endif
  47
  48 /* ovs_mutex functions analogous to pthread_mutex_*() functions.
  49  *
  50  * Most of these functions abort the process with an error message on any
  51  * error.  ovs_mutex_trylock() is an exception: it passes through a 0 or EBUSY
  52  * return value to the caller and aborts on any other error. */
  53 void ovs_mutex_init(const struct ovs_mutex *);
  54 void ovs_mutex_init_recursive(const struct ovs_mutex *);
  55 void ovs_mutex_init_adaptive(const struct ovs_mutex *);
  56 void ovs_mutex_destroy(const struct ovs_mutex *);
  57 void ovs_mutex_unlock(const struct ovs_mutex *mutex) OVS_RELEASES(mutex);
  58 void ovs_mutex_lock_at(const struct ovs_mutex *mutex, const char *where)
  59     OVS_ACQUIRES(mutex);
  60 #define ovs_mutex_lock(mutex) \
  61         ovs_mutex_lock_at(mutex, SOURCE_LOCATOR)
  62
  63 int ovs_mutex_trylock_at(const struct ovs_mutex *mutex, const char *where)
  64     OVS_TRY_LOCK(0, mutex);
  65 #define ovs_mutex_trylock(mutex) \
  66         ovs_mutex_trylock_at(mutex, SOURCE_LOCATOR)
  67
  68 void ovs_mutex_cond_wait(pthread_cond_t *, const struct ovs_mutex *);
  69
  70 /* Wrappers for pthread_mutex_*() that abort the process on any error.
  71  * This is still needed when ovs-atomic-pthreads.h is used. */
  72 void xpthread_mutex_lock(pthread_mutex_t *mutex);
  73 void xpthread_mutex_unlock(pthread_mutex_t *mutex);
  74
  75 /* Wrappers for pthread_mutexattr_*() that abort the process on any error. */
  76 void xpthread_mutexattr_init(pthread_mutexattr_t *);
  77 void xpthread_mutexattr_destroy(pthread_mutexattr_t *);
  78 void xpthread_mutexattr_settype(pthread_mutexattr_t *, int type);
  79 void xpthread_mutexattr_gettype(pthread_mutexattr_t *, int *typep);
  80
  81 /* Read-write lock.
  82  *
  83  * An ovs_rwlock does not support recursive readers, because POSIX allows
  84  * taking the reader lock recursively to deadlock when a thread is waiting on
  85  * the write-lock.  (NetBSD does deadlock.)  glibc rwlocks in their default
  86  * configuration do not deadlock, but ovs_rwlock_init() initializes rwlocks as
  87  * non-recursive (which will deadlock) for two reasons:
  88  *
  89  *     - glibc only provides fairness to writers in this mode.
  90  *
  91  *     - It's better to find bugs in the primary Open vSwitch target rather
  92  *       than exposing them only to porters. */
  93 struct OVS_LOCKABLE ovs_rwlock {
  94     pthread_rwlock_t lock;
  95     const char *where;          /* NULL if and only if uninitialized. */
  96 };
  97
  98 /* Initializer. */
  99 #ifdef PTHREAD_RWLOCK_WRITER_NONRECURSIVE_INITIALIZER_NP
 100 #define OVS_RWLOCK_INITIALIZER \
 101         { PTHREAD_RWLOCK_WRITER_NONRECURSIVE_INITIALIZER_NP, "<unlocked>" }
 102 #else
 103 #define OVS_RWLOCK_INITIALIZER { PTHREAD_RWLOCK_INITIALIZER, "<unlocked>" }
 104 #endif
 105
 106 /* ovs_rwlock functions analogous to pthread_rwlock_*() functions.
 107  *
 108  * Most of these functions abort the process with an error message on any
 109  * error.  The "trylock" functions are exception: they pass through a 0 or
 110  * EBUSY return value to the caller and abort on any other error. */
 111 void ovs_rwlock_init(const struct ovs_rwlock *);
 112 void ovs_rwlock_destroy(const struct ovs_rwlock *);
 113 void ovs_rwlock_unlock(const struct ovs_rwlock *rwlock) OVS_RELEASES(rwlock);
 114
 115 /* Wrappers for pthread_rwlockattr_*() that abort the process on any error. */
 116 void xpthread_rwlockattr_init(pthread_rwlockattr_t *);
 117 void xpthread_rwlockattr_destroy(pthread_rwlockattr_t *);
 118 #ifdef PTHREAD_RWLOCK_WRITER_NONRECURSIVE_INITIALIZER_NP
 119 void xpthread_rwlockattr_setkind_np(pthread_rwlockattr_t *, int kind);
 120 #endif
 121
 122 void ovs_rwlock_wrlock_at(const struct ovs_rwlock *rwlock, const char *where)
 123     OVS_ACQ_WRLOCK(rwlock);
 124 #define ovs_rwlock_wrlock(rwlock) \
 125         ovs_rwlock_wrlock_at(rwlock, SOURCE_LOCATOR)
 126
 127 int ovs_rwlock_trywrlock_at(const struct ovs_rwlock *rwlock, const char *where)
 128     OVS_TRY_WRLOCK(0, rwlock);
 129 #define ovs_rwlock_trywrlock(rwlock) \
 130     ovs_rwlock_trywrlock_at(rwlock, SOURCE_LOCATOR)
 131
 132 void ovs_rwlock_rdlock_at(const struct ovs_rwlock *rwlock, const char *where)
 133     OVS_ACQ_RDLOCK(rwlock);
 134 #define ovs_rwlock_rdlock(rwlock) \
 135         ovs_rwlock_rdlock_at(rwlock, SOURCE_LOCATOR)
 136
 137 int ovs_rwlock_tryrdlock_at(const struct ovs_rwlock *rwlock, const char *where)
 138     OVS_TRY_RDLOCK(0, rwlock);
 139 #define ovs_rwlock_tryrdlock(rwlock) \
 140         ovs_rwlock_tryrdlock_at(rwlock, SOURCE_LOCATOR)
 141
 142 /* Wrappers for xpthread_cond_*() that abort the process on any error.
 143  *
 144  * Use ovs_mutex_cond_wait() to wait for a condition. */
 145 void xpthread_cond_init(pthread_cond_t *, pthread_condattr_t *);
 146 void xpthread_cond_destroy(pthread_cond_t *);
 147 void xpthread_cond_signal(pthread_cond_t *);
 148 void xpthread_cond_broadcast(pthread_cond_t *);
 149
 150 /* Wrappers for pthread_barrier_*() that abort the process on any error. */
 151 void xpthread_barrier_init(pthread_barrier_t *, pthread_barrierattr_t *,
 152                            unsigned int count);
 153 int xpthread_barrier_wait(pthread_barrier_t *);
 154 void xpthread_barrier_destroy(pthread_barrier_t *);
 155
 156 void xpthread_key_create(pthread_key_t *, void (*destructor)(void *));
 157 void xpthread_key_delete(pthread_key_t);
 158 void xpthread_setspecific(pthread_key_t, const void *);
 159
 160 #ifndef _WIN32
 161 void xpthread_sigmask(int, const sigset_t *, sigset_t *);
 162 #endif
 163
 164 pthread_t ovs_thread_create(const char *name, void *(*)(void *), void *);
 165 void xpthread_join(pthread_t, void **);
 166 \f
 167 /* Per-thread data.
 168  *
 169  *
 170  * Standard Forms
 171  * ==============
 172  *
 173  * Multiple forms of standard per-thread data exist, each with its own pluses
 174  * and minuses.  In general, if one of these forms is appropriate, then it's a
 175  * good idea to use it:
 176  *
 177  *     - POSIX per-thread data via pthread_key_t is portable to any pthreads
 178  *       implementation, and allows a destructor function to be defined.  It
 179  *       only (directly) supports per-thread pointers, which are always
 180  *       initialized to NULL.  It requires once-only allocation of a
 181  *       pthread_key_t value.  It is relatively slow.  Typically few
 182  *       "pthread_key_t"s are available (POSIX requires only at least 128,
 183  *       glibc supplies only 1024).
 184  *
 185  *     - The thread_local feature newly defined in C11 <threads.h> works with
 186  *       any data type and initializer, and it is fast.  thread_local does not
 187  *       require once-only initialization like pthread_key_t.  C11 does not
 188  *       define what happens if one attempts to access a thread_local object
 189  *       from a thread other than the one to which that object belongs.  There
 190  *       is no provision to call a user-specified destructor when a thread
 191  *       ends.  Typical implementations allow for an arbitrary amount of
 192  *       thread_local storage, but statically allocated only.
 193  *
 194  *     - The __thread keyword is a GCC extension similar to thread_local but
 195  *       with a longer history.  __thread is not portable to every GCC version
 196  *       or environment.  __thread does not restrict the use of a thread-local
 197  *       object outside its own thread.
 198  *
 199  * Here's a handy summary:
 200  *
 201  *                     pthread_key_t     thread_local       __thread
 202  *                     -------------     ------------     -------------
 203  * portability             high               low             medium
 204  * speed                    low              high               high
 205  * supports destructors?    yes                no                 no
 206  * needs key allocation?    yes                no                 no
 207  * arbitrary initializer?    no               yes                yes
 208  * cross-thread access?     yes                no                yes
 209  * amount available?        few            arbitrary         arbitrary
 210  * dynamically allocated?   yes                no                 no
 211  *
 212  *
 213  * Extensions
 214  * ==========
 215  *
 216  * OVS provides some extensions and wrappers:
 217  *
 218  *     - In a situation where the performance of thread_local or __thread is
 219  *       desirable, but portability is required, DEFINE_STATIC_PER_THREAD_DATA
 220  *       and DECLARE_EXTERN_PER_THREAD_DATA/DEFINE_EXTERN_PER_THREAD_DATA may
 221  *       be appropriate (see below).
 222  *
 223  *     - DEFINE_PER_THREAD_MALLOCED_DATA can be convenient for simple
 224  *       per-thread malloc()'d buffers.
 225  *
 226  *     - struct ovs_tsd provides an alternative to pthread_key_t that isn't
 227  *       limited to a small number of keys.
 228  */
 229
 230 /* For static data, use this macro in a source file:
 231  *
 232  *    DEFINE_STATIC_PER_THREAD_DATA(TYPE, NAME, INITIALIZER).
 233  *
 234  * For global data, "declare" the data in the header and "define" it in
 235  * the source file, with:
 236  *
 237  *    DECLARE_EXTERN_PER_THREAD_DATA(TYPE, NAME).
 238  *    DEFINE_EXTERN_PER_THREAD_DATA(NAME, INITIALIZER).
 239  *
 240  * One should prefer to use POSIX per-thread data, via pthread_key_t, when its
 241  * performance is acceptable, because of its portability (see the table above).
 242  * This macro is an alternatives that takes advantage of thread_local (and
 243  * __thread), for its performance, when it is available, and falls back to
 244  * POSIX per-thread data otherwise.
 245  *
 246  * Defines per-thread variable NAME with the given TYPE, initialized to
 247  * INITIALIZER (which must be valid as an initializer for a variable with
 248  * static lifetime).
 249  *
 250  * The public interface to the variable is:
 251  *
 252  *    TYPE *NAME_get(void)
 253  *    TYPE *NAME_get_unsafe(void)
 254  *
 255  *       Returns the address of this thread's instance of NAME.
 256  *
 257  *       Use NAME_get() in a context where this might be the first use of the
 258  *       per-thread variable in the program.  Use NAME_get_unsafe(), which
 259  *       avoids a conditional test and is thus slightly faster, in a context
 260  *       where one knows that NAME_get() has already been called previously.
 261  *
 262  * There is no "NAME_set()" (or "NAME_set_unsafe()") function.  To set the
 263  * value of the per-thread variable, dereference the pointer returned by
 264  * TYPE_get() or TYPE_get_unsafe(), e.g. *TYPE_get() = 0.
 265  */
 266 #if HAVE_THREAD_LOCAL || HAVE___THREAD
 267
 268 #if HAVE_THREAD_LOCAL
 269 #include <threads.h>
 270 #elif HAVE___THREAD
 271 #define thread_local __thread
 272 #else
 273 #error
 274 #endif
 275
 276 #define DEFINE_STATIC_PER_THREAD_DATA(TYPE, NAME, ...)                  \
 277     typedef TYPE NAME##_type;                                           \
 278                                                                         \
 279     static NAME##_type *                                                \
 280     NAME##_get_unsafe(void)                                             \
 281     {                                                                   \
 282         static thread_local NAME##_type var = __VA_ARGS__;              \
 283         return &var;                                                    \
 284     }                                                                   \
 285                                                                         \
 286     static NAME##_type *                                                \
 287     NAME##_get(void)                                                    \
 288     {                                                                   \
 289         return NAME##_get_unsafe();                                     \
 290     }
 291 #define DECLARE_EXTERN_PER_THREAD_DATA(TYPE, NAME)                      \
 292     typedef TYPE NAME##_type;                                           \
 293     extern thread_local NAME##_type NAME##_var;                         \
 294                                                                         \
 295     static inline NAME##_type *                                         \
 296     NAME##_get_unsafe(void)                                             \
 297     {                                                                   \
 298         return &NAME##_var;                                             \
 299     }                                                                   \
 300                                                                         \
 301     static inline NAME##_type *                                         \
 302     NAME##_get(void)                                                    \
 303     {                                                                   \
 304         return NAME##_get_unsafe();                                     \
 305     }
 306 #define DEFINE_EXTERN_PER_THREAD_DATA(NAME, ...)         \
 307     thread_local NAME##_type NAME##_var = __VA_ARGS__;
 308 #else  /* no C implementation support for thread-local storage  */
 309 #define DEFINE_STATIC_PER_THREAD_DATA(TYPE, NAME, ...)                  \
 310     typedef TYPE NAME##_type;                                           \
 311     static pthread_key_t NAME##_key;                                    \
 312                                                                         \
 313     static NAME##_type *                                                \
 314     NAME##_get_unsafe(void)                                             \
 315     {                                                                   \
 316         return pthread_getspecific(NAME##_key);                         \
 317     }                                                                   \
 318                                                                         \
 319     static void                                                         \
 320     NAME##_once_init(void)                                              \
 321     {                                                                   \
 322         if (pthread_key_create(&NAME##_key, free)) {                    \
 323             abort();                                                    \
 324         }                                                               \
 325     }                                                                   \
 326                                                                         \
 327     static NAME##_type *                                                \
 328     NAME##_get(void)                                                    \
 329     {                                                                   \
 330         static pthread_once_t once = PTHREAD_ONCE_INIT;                 \
 331         NAME##_type *value;                                             \
 332                                                                         \
 333         pthread_once(&once, NAME##_once_init);                          \
 334         value = NAME##_get_unsafe();                                    \
 335         if (!value) {                                                   \
 336             static const NAME##_type initial_value = __VA_ARGS__;       \
 337                                                                         \
 338             value = malloc(sizeof *value);                              \
 339             if (value == NULL) {                                        \
 340                 out_of_memory();                                        \
 341             }                                                           \
 342             *value = initial_value;                                     \
 343             xpthread_setspecific(NAME##_key, value);                    \
 344         }                                                               \
 345         return value;                                                   \
 346     }
 347 #define DECLARE_EXTERN_PER_THREAD_DATA(TYPE, NAME)                      \
 348     typedef TYPE NAME##_type;                                           \
 349     static pthread_key_t NAME##_key;                                    \
 350                                                                         \
 351     static inline NAME##_type *                                         \
 352     NAME##_get_unsafe(void)                                             \
 353     {                                                                   \
 354         return pthread_getspecific(NAME##_key);                         \
 355     }                                                                   \
 356                                                                         \
 357     NAME##_type *NAME##_get(void);
 358 #define DEFINE_EXTERN_PER_THREAD_DATA(NAME, ...)                        \
 359     static void                                                         \
 360     NAME##_once_init(void)                                              \
 361     {                                                                   \
 362         if (pthread_key_create(&NAME##_key, free)) {                    \
 363             abort();                                                    \
 364         }                                                               \
 365     }                                                                   \
 366                                                                         \
 367     NAME##_type *                                                       \
 368     NAME##_get(void)                                                    \
 369     {                                                                   \
 370         static pthread_once_t once = PTHREAD_ONCE_INIT;                 \
 371         NAME##_type *value;                                             \
 372                                                                         \
 373         pthread_once(&once, NAME##_once_init);                          \
 374         value = NAME##_get_unsafe();                                    \
 375         if (!value) {                                                   \
 376             static const NAME##_type initial_value = __VA_ARGS__;       \
 377                                                                         \
 378             value = malloc(sizeof *value);                              \
 379             if (value == NULL) {                                        \
 380                 out_of_memory();                                        \
 381             }                                                           \
 382             *value = initial_value;                                     \
 383             xpthread_setspecific(NAME##_key, value);                    \
 384         }                                                               \
 385         return value;                                                   \
 386     }
 387 #endif
 388
 389 /* DEFINE_PER_THREAD_MALLOCED_DATA(TYPE, NAME).
 390  *
 391  * This is a simple wrapper around POSIX per-thread data primitives.  It
 392  * defines per-thread variable NAME with the given TYPE, which must be a
 393  * pointer type.  In each thread, the per-thread variable is initialized to
 394  * NULL.  When a thread terminates, the variable is freed with free().
 395  *
 396  * The public interface to the variable is:
 397  *
 398  *    TYPE NAME_get(void)
 399  *    TYPE NAME_get_unsafe(void)
 400  *
 401  *       Returns the value of per-thread variable NAME in this thread.
 402  *
 403  *       Use NAME_get() in a context where this might be the first use of the
 404  *       per-thread variable in the program.  Use NAME_get_unsafe(), which
 405  *       avoids a conditional test and is thus slightly faster, in a context
 406  *       where one knows that NAME_get() has already been called previously.
 407  *
 408  *    TYPE NAME_set(TYPE new_value)
 409  *    TYPE NAME_set_unsafe(TYPE new_value)
 410  *
 411  *       Sets the value of per-thread variable NAME to 'new_value' in this
 412  *       thread, and returns its previous value.
 413  *
 414  *       Use NAME_set() in a context where this might be the first use of the
 415  *       per-thread variable in the program.  Use NAME_set_unsafe(), which
 416  *       avoids a conditional test and is thus slightly faster, in a context
 417  *       where one knows that NAME_set() has already been called previously.
 418  */
 419 #define DEFINE_PER_THREAD_MALLOCED_DATA(TYPE, NAME)     \
 420     static pthread_key_t NAME##_key;                    \
 421                                                         \
 422     static void                                         \
 423     NAME##_once_init(void)                              \
 424     {                                                   \
 425         if (pthread_key_create(&NAME##_key, free)) {    \
 426             abort();                                    \
 427         }                                               \
 428     }                                                   \
 429                                                         \
 430     static void                                         \
 431     NAME##_init(void)                                   \
 432     {                                                   \
 433         static pthread_once_t once = PTHREAD_ONCE_INIT; \
 434         pthread_once(&once, NAME##_once_init);          \
 435     }                                                   \
 436                                                         \
 437     static TYPE                                         \
 438     NAME##_get_unsafe(void)                             \
 439     {                                                   \
 440         return pthread_getspecific(NAME##_key);         \
 441     }                                                   \
 442                                                         \
 443     static OVS_UNUSED TYPE                              \
 444     NAME##_get(void)                                    \
 445     {                                                   \
 446         NAME##_init();                                  \
 447         return NAME##_get_unsafe();                     \
 448     }                                                   \
 449                                                         \
 450     static TYPE                                         \
 451     NAME##_set_unsafe(TYPE value)                       \
 452     {                                                   \
 453         TYPE old_value = NAME##_get_unsafe();           \
 454         xpthread_setspecific(NAME##_key, value);        \
 455         return old_value;                               \
 456     }                                                   \
 457                                                         \
 458     static OVS_UNUSED TYPE                              \
 459     NAME##_set(TYPE value)                              \
 460     {                                                   \
 461         NAME##_init();                                  \
 462         return NAME##_set_unsafe(value);                \
 463     }
 464
 465 /* Dynamically allocated thread-specific data with lots of slots.
 466  *
 467  * pthread_key_t can provide as few as 128 pieces of thread-specific data (even
 468  * glibc is limited to 1,024).  Thus, one must be careful to allocate only a
 469  * few keys globally.  One cannot, for example, allocate a key for every
 470  * instance of a data structure if there might be an arbitrary number of those
 471  * data structures.
 472  *
 473  * This API is similar to the pthread one (simply search and replace pthread_
 474  * by ovsthread_) but it a much larger limit that can be raised if necessary
 475  * (by recompiling).  Thus, one may more freely use this form of
 476  * thread-specific data.
 477  *
 478  * ovsthread_key_t also differs from pthread_key_t in the following ways:
 479  *
 480  *    - Destructors must not access thread-specific data (via ovsthread_key).
 481  *
 482  *    - The pthread_key_t API allows concurrently exiting threads to start
 483  *      executing the destructor after pthread_key_delete() returns.  The
 484  *      ovsthread_key_t API guarantees that, when ovsthread_key_delete()
 485  *      returns, all destructors have returned and no new ones will start
 486  *      execution.
 487  */
 488 typedef struct ovsthread_key *ovsthread_key_t;
 489
 490 void ovsthread_key_create(ovsthread_key_t *, void (*destructor)(void *));
 491 void ovsthread_key_delete(ovsthread_key_t);
 492
 493 void ovsthread_setspecific(ovsthread_key_t, const void *);
 494 void *ovsthread_getspecific(ovsthread_key_t);
 495 \f
 496 /* Convenient once-only execution.
 497  *
 498  *
 499  * Problem
 500  * =======
 501  *
 502  * POSIX provides pthread_once_t and pthread_once() as primitives for running a
 503  * set of code only once per process execution.  They are used like this:
 504  *
 505  *     static void run_once(void) { ...initialization... }
 506  *     static pthread_once_t once = PTHREAD_ONCE_INIT;
 507  * ...
 508  *     pthread_once(&once, run_once);
 509  *
 510  * pthread_once() does not allow passing any parameters to the initialization
 511  * function, which is often inconvenient, because it means that the function
 512  * can only access data declared at file scope.
 513  *
 514  *
 515  * Solution
 516  * ========
 517  *
 518  * Use ovsthread_once, like this, instead:
 519  *
 520  *     static struct ovsthread_once once = OVSTHREAD_ONCE_INITIALIZER;
 521  *
 522  *     if (ovsthread_once_start(&once)) {
 523  *         ...initialization...
 524  *         ovsthread_once_done(&once);
 525  *     }
 526  */
 527
 528 struct ovsthread_once {
 529     atomic_bool done;
 530     struct ovs_mutex mutex;
 531 };
 532
 533 #define OVSTHREAD_ONCE_INITIALIZER              \
 534     {                                           \
 535         ATOMIC_VAR_INIT(false),                 \
 536         OVS_MUTEX_INITIALIZER,                  \
 537     }
 538
 539 static inline bool ovsthread_once_start(struct ovsthread_once *once)
 540     OVS_TRY_LOCK(true, once->mutex);
 541 void ovsthread_once_done(struct ovsthread_once *once)
 542     OVS_RELEASES(once->mutex);
 543
 544 bool ovsthread_once_start__(struct ovsthread_once *once)
 545     OVS_TRY_LOCK(false, once->mutex);
 546
 547 static inline bool
 548 ovsthread_once_is_done__(struct ovsthread_once *once)
 549 {
 550     bool done;
 551
 552     atomic_read_explicit(&once->done, &done, memory_order_relaxed);
 553     return done;
 554 }
 555
 556 /* Returns true if this is the first call to ovsthread_once_start() for
 557  * 'once'.  In this case, the caller should perform whatever initialization
 558  * actions it needs to do, then call ovsthread_once_done() for 'once'.
 559  *
 560  * Returns false if this is not the first call to ovsthread_once_start() for
 561  * 'once'.  In this case, the call will not return until after
 562  * ovsthread_once_done() has been called. */
 563 static inline bool
 564 ovsthread_once_start(struct ovsthread_once *once)
 565 {
 566     return OVS_UNLIKELY(!ovsthread_once_is_done__(once)
 567                         && !ovsthread_once_start__(once));
 568 }
 569 \f
 570 /* Thread ID.
 571  *
 572  * pthread_t isn't so nice for some purposes.  Its size and representation are
 573  * implementation dependent, which means that there is no way to hash it.
 574  * This thread ID avoids the problem.
 575  */
 576
 577 DECLARE_EXTERN_PER_THREAD_DATA(unsigned int, ovsthread_id);
 578
 579 /* Returns a per-thread identifier unique within the lifetime of the
 580  * process. */
 581 static inline unsigned int
 582 ovsthread_id_self(void)
 583 {
 584     return *ovsthread_id_get();
 585 }
 586 \f
 587 /* Simulated global counter.
 588  *
 589  * Incrementing such a counter is meant to be cheaper than incrementing a
 590  * global counter protected by a lock.  It is probably more expensive than
 591  * incrementing a truly thread-local variable, but such a variable has no
 592  * straightforward way to get the sum.
 593  *
 594  *
 595  * Thread-safety
 596  * =============
 597  *
 598  * Fully thread-safe. */
 599
 600 struct ovsthread_stats {
 601     struct ovs_mutex mutex;
 602     void *volatile buckets[16];
 603 };
 604
 605 void ovsthread_stats_init(struct ovsthread_stats *);
 606 void ovsthread_stats_destroy(struct ovsthread_stats *);
 607
 608 void *ovsthread_stats_bucket_get(struct ovsthread_stats *,
 609                                  void *(*new_bucket)(void));
 610
 611 #define OVSTHREAD_STATS_FOR_EACH_BUCKET(BUCKET, IDX, STATS)             \
 612     for ((IDX) = ovs_thread_stats_next_bucket(STATS, 0);                \
 613          ((IDX) < ARRAY_SIZE((STATS)->buckets)                          \
 614           ? ((BUCKET) = (STATS)->buckets[IDX], true)                    \
 615           : false);                                                     \
 616          (IDX) = ovs_thread_stats_next_bucket(STATS, (IDX) + 1))
 617 size_t ovs_thread_stats_next_bucket(const struct ovsthread_stats *, size_t);
 618 \f
 619 bool single_threaded(void);
 620
 621 void assert_single_threaded_at(const char *where);
 622 #define assert_single_threaded() assert_single_threaded_at(SOURCE_LOCATOR)
 623
 624 #ifndef _WIN32
 625 pid_t xfork_at(const char *where);
 626 #define xfork() xfork_at(SOURCE_LOCATOR)
 627 #endif
 628
 629 void forbid_forking(const char *reason);
 630 bool may_fork(void);
 631 \f
 632 /* Useful functions related to threading. */
 633
 634 int count_cpu_cores(void);
 635
 636 #endif /* ovs-thread.h */