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