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 <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 /* ovs_mutex functions analogous to pthread_mutex_*() functions.
  41  *
  42  * Most of these functions abort the process with an error message on any
  43  * error.  ovs_mutex_trylock() is an exception: it passes through a 0 or EBUSY
  44  * return value to the caller and aborts on any other error. */
  45 void ovs_mutex_init(const struct ovs_mutex *);
  46 void ovs_mutex_init_recursive(const struct ovs_mutex *);
  47 void ovs_mutex_destroy(const struct ovs_mutex *);
  48 void ovs_mutex_unlock(const struct ovs_mutex *mutex) OVS_RELEASES(mutex);
  49 void ovs_mutex_lock_at(const struct ovs_mutex *mutex, const char *where)
  50     OVS_ACQUIRES(mutex);
  51 #define ovs_mutex_lock(mutex) \
  52         ovs_mutex_lock_at(mutex, SOURCE_LOCATOR)
  53
  54 int ovs_mutex_trylock_at(const struct ovs_mutex *mutex, const char *where)
  55     OVS_TRY_LOCK(0, mutex);
  56 #define ovs_mutex_trylock(mutex) \
  57         ovs_mutex_trylock_at(mutex, SOURCE_LOCATOR)
  58
  59 void ovs_mutex_cond_wait(pthread_cond_t *, const struct ovs_mutex *);
  60
  61 /* Wrappers for pthread_mutex_*() that abort the process on any error.
  62  * This is still needed when ovs-atomic-pthreads.h is used. */
  63 void xpthread_mutex_lock(pthread_mutex_t *mutex);
  64 void xpthread_mutex_unlock(pthread_mutex_t *mutex);
  65
  66 /* Wrappers for pthread_mutexattr_*() that abort the process on any error. */
  67 void xpthread_mutexattr_init(pthread_mutexattr_t *);
  68 void xpthread_mutexattr_destroy(pthread_mutexattr_t *);
  69 void xpthread_mutexattr_settype(pthread_mutexattr_t *, int type);
  70 void xpthread_mutexattr_gettype(pthread_mutexattr_t *, int *typep);
  71
  72 /* Read-write lock. */
  73 struct OVS_LOCKABLE ovs_rwlock {
  74     pthread_rwlock_t lock;
  75     const char *where;
  76 };
  77
  78 /* Initializer. */
  79 #define OVS_RWLOCK_INITIALIZER { PTHREAD_RWLOCK_INITIALIZER, NULL }
  80
  81 /* ovs_rwlock functions analogous to pthread_rwlock_*() functions.
  82  *
  83  * Most of these functions abort the process with an error message on any
  84  * error.  The "trylock" functions are exception: they pass through a 0 or
  85  * EBUSY return value to the caller and abort on any other error. */
  86 void ovs_rwlock_init(const struct ovs_rwlock *);
  87 void ovs_rwlock_destroy(const struct ovs_rwlock *);
  88 void ovs_rwlock_unlock(const struct ovs_rwlock *rwlock) OVS_RELEASES(rwlock);
  89
  90 void ovs_rwlock_wrlock_at(const struct ovs_rwlock *rwlock, const char *where)
  91     OVS_ACQ_WRLOCK(rwlock);
  92 #define ovs_rwlock_wrlock(rwlock) \
  93         ovs_rwlock_wrlock_at(rwlock, SOURCE_LOCATOR)
  94
  95 int ovs_rwlock_trywrlock_at(const struct ovs_rwlock *rwlock, const char *where)
  96     OVS_TRY_WRLOCK(0, rwlock);
  97 #define ovs_rwlock_trywrlock(rwlock) \
  98     ovs_rwlock_trywrlock_at(rwlock, SOURCE_LOCATOR)
  99
 100 void ovs_rwlock_rdlock_at(const struct ovs_rwlock *rwlock, const char *where)
 101     OVS_ACQ_RDLOCK(rwlock);
 102 #define ovs_rwlock_rdlock(rwlock) \
 103         ovs_rwlock_rdlock_at(rwlock, SOURCE_LOCATOR)
 104
 105 int ovs_rwlock_tryrdlock_at(const struct ovs_rwlock *rwlock, const char *where)
 106     OVS_TRY_RDLOCK(0, rwlock);
 107 #define ovs_rwlock_tryrdlock(rwlock) \
 108         ovs_rwlock_tryrdlock_at(rwlock, SOURCE_LOCATOR)
 109
 110 /* Wrappers for xpthread_cond_*() that abort the process on any error.
 111  *
 112  * Use ovs_mutex_cond_wait() to wait for a condition. */
 113 void xpthread_cond_init(pthread_cond_t *, pthread_condattr_t *);
 114 void xpthread_cond_destroy(pthread_cond_t *);
 115 void xpthread_cond_signal(pthread_cond_t *);
 116 void xpthread_cond_broadcast(pthread_cond_t *);
 117
 118 #ifdef __CHECKER__
 119 /* Replace these functions by the macros already defined in the <pthread.h>
 120  * annotations, because the macro definitions have correct semantics for the
 121  * conditional acquisition that can't be captured in a function annotation.
 122  * The difference in semantics from pthread_*() to xpthread_*() does not matter
 123  * because sparse is not a compiler. */
 124 #define xpthread_mutex_trylock pthread_mutex_trylock
 125 #define xpthread_rwlock_tryrdlock pthread_rwlock_tryrdlock
 126 #define xpthread_rwlock_trywrlock pthread_rwlock_trywrlock
 127 #endif
 128
 129 void xpthread_key_create(pthread_key_t *, void (*destructor)(void *));
 130 void xpthread_setspecific(pthread_key_t, const void *);
 131
 132 void xpthread_create(pthread_t *, pthread_attr_t *, void *(*)(void *), void *);
 133 void xpthread_join(pthread_t, void **);
 134 \f
 135 /* Per-thread data.
 136  *
 137  * Multiple forms of per-thread data exist, each with its own pluses and
 138  * minuses:
 139  *
 140  *     - POSIX per-thread data via pthread_key_t is portable to any pthreads
 141  *       implementation, and allows a destructor function to be defined.  It
 142  *       only (directly) supports per-thread pointers, which are always
 143  *       initialized to NULL.  It requires once-only allocation of a
 144  *       pthread_key_t value.  It is relatively slow.
 145  *
 146  *     - The thread_local feature newly defined in C11 <threads.h> works with
 147  *       any data type and initializer, and it is fast.  thread_local does not
 148  *       require once-only initialization like pthread_key_t.  C11 does not
 149  *       define what happens if one attempts to access a thread_local object
 150  *       from a thread other than the one to which that object belongs.  There
 151  *       is no provision to call a user-specified destructor when a thread
 152  *       ends.
 153  *
 154  *     - The __thread keyword is a GCC extension similar to thread_local but
 155  *       with a longer history.  __thread is not portable to every GCC version
 156  *       or environment.  __thread does not restrict the use of a thread-local
 157  *       object outside its own thread.
 158  *
 159  * Here's a handy summary:
 160  *
 161  *                     pthread_key_t     thread_local       __thread
 162  *                     -------------     ------------     -------------
 163  * portability             high               low             medium
 164  * speed                    low              high               high
 165  * supports destructors?    yes                no                 no
 166  * needs key allocation?    yes                no                 no
 167  * arbitrary initializer?    no               yes                yes
 168  * cross-thread access?     yes                no                yes
 169  */
 170
 171 /* For static data, use this macro in a source file:
 172  *
 173  *    DEFINE_STATIC_PER_THREAD_DATA(TYPE, NAME, INITIALIZER).
 174  *
 175  * For global data, "declare" the data in the header and "define" it in
 176  * the source file, with:
 177  *
 178  *    DECLARE_EXTERN_PER_THREAD_DATA(TYPE, NAME).
 179  *    DEFINE_EXTERN_PER_THREAD_DATA(NAME, INITIALIZER).
 180  *
 181  * One should prefer to use POSIX per-thread data, via pthread_key_t, when its
 182  * performance is acceptable, because of its portability (see the table above).
 183  * This macro is an alternatives that takes advantage of thread_local (and
 184  * __thread), for its performance, when it is available, and falls back to
 185  * POSIX per-thread data otherwise.
 186  *
 187  * Defines per-thread variable NAME with the given TYPE, initialized to
 188  * INITIALIZER (which must be valid as an initializer for a variable with
 189  * static lifetime).
 190  *
 191  * The public interface to the variable is:
 192  *
 193  *    TYPE *NAME_get(void)
 194  *    TYPE *NAME_get_unsafe(void)
 195  *
 196  *       Returns the address of this thread's instance of NAME.
 197  *
 198  *       Use NAME_get() in a context where this might be the first use of the
 199  *       per-thread variable in the program.  Use NAME_get_unsafe(), which
 200  *       avoids a conditional test and is thus slightly faster, in a context
 201  *       where one knows that NAME_get() has already been called previously.
 202  *
 203  * There is no "NAME_set()" (or "NAME_set_unsafe()") function.  To set the
 204  * value of the per-thread variable, dereference the pointer returned by
 205  * TYPE_get() or TYPE_get_unsafe(), e.g. *TYPE_get() = 0.
 206  */
 207 #if HAVE_THREAD_LOCAL || HAVE___THREAD
 208
 209 #if HAVE_THREAD_LOCAL
 210 #include <threads.h>
 211 #elif HAVE___THREAD
 212 #define thread_local __thread
 213 #else
 214 #error
 215 #endif
 216
 217 #define DEFINE_STATIC_PER_THREAD_DATA(TYPE, NAME, ...)                  \
 218     typedef TYPE NAME##_type;                                           \
 219                                                                         \
 220     static NAME##_type *                                                \
 221     NAME##_get_unsafe(void)                                             \
 222     {                                                                   \
 223         static thread_local NAME##_type var = __VA_ARGS__;              \
 224         return &var;                                                    \
 225     }                                                                   \
 226                                                                         \
 227     static NAME##_type *                                                \
 228     NAME##_get(void)                                                    \
 229     {                                                                   \
 230         return NAME##_get_unsafe();                                     \
 231     }
 232 #define DECLARE_EXTERN_PER_THREAD_DATA(TYPE, NAME)                      \
 233     typedef TYPE NAME##_type;                                           \
 234     extern thread_local NAME##_type NAME##_var;                         \
 235                                                                         \
 236     static inline NAME##_type *                                         \
 237     NAME##_get_unsafe(void)                                             \
 238     {                                                                   \
 239         return &NAME##_var;                                             \
 240     }                                                                   \
 241                                                                         \
 242     static inline NAME##_type *                                         \
 243     NAME##_get(void)                                                    \
 244     {                                                                   \
 245         return NAME##_get_unsafe();                                     \
 246     }
 247 #define DEFINE_EXTERN_PER_THREAD_DATA(NAME, ...)         \
 248     thread_local NAME##_type NAME##_var = __VA_ARGS__;
 249 #else  /* no C implementation support for thread-local storage  */
 250 #define DEFINE_STATIC_PER_THREAD_DATA(TYPE, NAME, ...)                  \
 251     typedef TYPE NAME##_type;                                           \
 252     static pthread_key_t NAME##_key;                                    \
 253                                                                         \
 254     static NAME##_type *                                                \
 255     NAME##_get_unsafe(void)                                             \
 256     {                                                                   \
 257         return pthread_getspecific(NAME##_key);                         \
 258     }                                                                   \
 259                                                                         \
 260     static void                                                         \
 261     NAME##_once_init(void)                                              \
 262     {                                                                   \
 263         if (pthread_key_create(&NAME##_key, free)) {                    \
 264             abort();                                                    \
 265         }                                                               \
 266     }                                                                   \
 267                                                                         \
 268     static NAME##_type *                                                \
 269     NAME##_get(void)                                                    \
 270     {                                                                   \
 271         static pthread_once_t once = PTHREAD_ONCE_INIT;                 \
 272         NAME##_type *value;                                             \
 273                                                                         \
 274         pthread_once(&once, NAME##_once_init);                          \
 275         value = NAME##_get_unsafe();                                    \
 276         if (!value) {                                                   \
 277             static const NAME##_type initial_value = __VA_ARGS__;       \
 278                                                                         \
 279             value = xmalloc(sizeof *value);                             \
 280             *value = initial_value;                                     \
 281             xpthread_setspecific(NAME##_key, value);                    \
 282         }                                                               \
 283         return value;                                                   \
 284     }
 285 #define DECLARE_EXTERN_PER_THREAD_DATA(TYPE, NAME)                      \
 286     typedef TYPE NAME##_type;                                           \
 287     static pthread_key_t NAME##_key;                                    \
 288                                                                         \
 289     static inline NAME##_type *                                         \
 290     NAME##_get_unsafe(void)                                             \
 291     {                                                                   \
 292         return pthread_getspecific(NAME##_key);                         \
 293     }                                                                   \
 294                                                                         \
 295     NAME##_type *NAME##_get(void);
 296 #define DEFINE_EXTERN_PER_THREAD_DATA(NAME, ...)                        \
 297     static void                                                         \
 298     NAME##_once_init(void)                                              \
 299     {                                                                   \
 300         if (pthread_key_create(&NAME##_key, free)) {                    \
 301             abort();                                                    \
 302         }                                                               \
 303     }                                                                   \
 304                                                                         \
 305     NAME##_type *                                                       \
 306     NAME##_get(void)                                                    \
 307     {                                                                   \
 308         static pthread_once_t once = PTHREAD_ONCE_INIT;                 \
 309         NAME##_type *value;                                             \
 310                                                                         \
 311         pthread_once(&once, NAME##_once_init);                          \
 312         value = NAME##_get_unsafe();                                    \
 313         if (!value) {                                                   \
 314             static const NAME##_type initial_value = __VA_ARGS__;       \
 315                                                                         \
 316             value = xmalloc(sizeof *value);                             \
 317             *value = initial_value;                                     \
 318             xpthread_setspecific(NAME##_key, value);                    \
 319         }                                                               \
 320         return value;                                                   \
 321     }
 322 #endif
 323
 324 /* DEFINE_PER_THREAD_MALLOCED_DATA(TYPE, NAME).
 325  *
 326  * This is a simple wrapper around POSIX per-thread data primitives.  It
 327  * defines per-thread variable NAME with the given TYPE, which must be a
 328  * pointer type.  In each thread, the per-thread variable is initialized to
 329  * NULL.  When a thread terminates, the variable is freed with free().
 330  *
 331  * The public interface to the variable is:
 332  *
 333  *    TYPE NAME_get(void)
 334  *    TYPE NAME_get_unsafe(void)
 335  *
 336  *       Returns the value of per-thread variable NAME in this thread.
 337  *
 338  *       Use NAME_get() in a context where this might be the first use of the
 339  *       per-thread variable in the program.  Use NAME_get_unsafe(), which
 340  *       avoids a conditional test and is thus slightly faster, in a context
 341  *       where one knows that NAME_get() has already been called previously.
 342  *
 343  *    TYPE NAME_set(TYPE new_value)
 344  *    TYPE NAME_set_unsafe(TYPE new_value)
 345  *
 346  *       Sets the value of per-thread variable NAME to 'new_value' in this
 347  *       thread, and returns its previous value.
 348  *
 349  *       Use NAME_set() in a context where this might be the first use of the
 350  *       per-thread variable in the program.  Use NAME_set_unsafe(), which
 351  *       avoids a conditional test and is thus slightly faster, in a context
 352  *       where one knows that NAME_set() has already been called previously.
 353  */
 354 #define DEFINE_PER_THREAD_MALLOCED_DATA(TYPE, NAME)     \
 355     static pthread_key_t NAME##_key;                    \
 356                                                         \
 357     static void                                         \
 358     NAME##_once_init(void)                              \
 359     {                                                   \
 360         if (pthread_key_create(&NAME##_key, free)) {    \
 361             abort();                                    \
 362         }                                               \
 363     }                                                   \
 364                                                         \
 365     static void                                         \
 366     NAME##_init(void)                                   \
 367     {                                                   \
 368         static pthread_once_t once = PTHREAD_ONCE_INIT; \
 369         pthread_once(&once, NAME##_once_init);          \
 370     }                                                   \
 371                                                         \
 372     static TYPE                                         \
 373     NAME##_get_unsafe(void)                             \
 374     {                                                   \
 375         return pthread_getspecific(NAME##_key);         \
 376     }                                                   \
 377                                                         \
 378     static OVS_UNUSED TYPE                              \
 379     NAME##_get(void)                                    \
 380     {                                                   \
 381         NAME##_init();                                  \
 382         return NAME##_get_unsafe();                     \
 383     }                                                   \
 384                                                         \
 385     static TYPE                                         \
 386     NAME##_set_unsafe(TYPE value)                       \
 387     {                                                   \
 388         TYPE old_value = NAME##_get_unsafe();           \
 389         xpthread_setspecific(NAME##_key, value);        \
 390         return old_value;                               \
 391     }                                                   \
 392                                                         \
 393     static OVS_UNUSED TYPE                              \
 394     NAME##_set(TYPE value)                              \
 395     {                                                   \
 396         NAME##_init();                                  \
 397         return NAME##_set_unsafe(value);                \
 398     }
 399 \f
 400 /* Convenient once-only execution.
 401  *
 402  *
 403  * Problem
 404  * =======
 405  *
 406  * POSIX provides pthread_once_t and pthread_once() as primitives for running a
 407  * set of code only once per process execution.  They are used like this:
 408  *
 409  *     static void run_once(void) { ...initialization... }
 410  *     static pthread_once_t once = PTHREAD_ONCE_INIT;
 411  * ...
 412  *     pthread_once(&once, run_once);
 413  *
 414  * pthread_once() does not allow passing any parameters to the initialization
 415  * function, which is often inconvenient, because it means that the function
 416  * can only access data declared at file scope.
 417  *
 418  *
 419  * Solution
 420  * ========
 421  *
 422  * Use ovsthread_once, like this, instead:
 423  *
 424  *     static struct ovsthread_once once = OVSTHREAD_ONCE_INITIALIZER;
 425  *
 426  *     if (ovsthread_once_start(&once)) {
 427  *         ...initialization...
 428  *         ovsthread_once_done(&once);
 429  *     }
 430  */
 431
 432 struct ovsthread_once {
 433     atomic_bool done;
 434     struct ovs_mutex mutex;
 435 };
 436
 437 #define OVSTHREAD_ONCE_INITIALIZER              \
 438     {                                           \
 439         ATOMIC_VAR_INIT(false),                 \
 440         OVS_MUTEX_INITIALIZER,                  \
 441     }
 442
 443 static inline bool ovsthread_once_start(struct ovsthread_once *once)
 444     OVS_TRY_LOCK(true, once->mutex);
 445 void ovsthread_once_done(struct ovsthread_once *once)
 446     OVS_RELEASES(once->mutex);
 447
 448 bool ovsthread_once_start__(struct ovsthread_once *once)
 449     OVS_TRY_LOCK(false, once->mutex);
 450
 451 static inline bool
 452 ovsthread_once_is_done__(struct ovsthread_once *once)
 453 {
 454     bool done;
 455
 456     atomic_read_explicit(&once->done, &done, memory_order_relaxed);
 457     return done;
 458 }
 459
 460 /* Returns true if this is the first call to ovsthread_once_start() for
 461  * 'once'.  In this case, the caller should perform whatever initialization
 462  * actions it needs to do, then call ovsthread_once_done() for 'once'.
 463  *
 464  * Returns false if this is not the first call to ovsthread_once_start() for
 465  * 'once'.  In this case, the call will not return until after
 466  * ovsthread_once_done() has been called. */
 467 static inline bool
 468 ovsthread_once_start(struct ovsthread_once *once)
 469 {
 470     return OVS_UNLIKELY(!ovsthread_once_is_done__(once)
 471                         && !ovsthread_once_start__(once));
 472 }
 473 \f
 474 /* Thread ID.
 475  *
 476  * pthread_t isn't so nice for some purposes.  Its size and representation are
 477  * implementation dependent, which means that there is no way to hash it.
 478  * This thread ID avoids the problem.
 479  */
 480
 481 DECLARE_EXTERN_PER_THREAD_DATA(unsigned int, ovsthread_id);
 482
 483 /* Returns a per-thread identifier unique within the lifetime of the
 484  * process. */
 485 static inline unsigned int
 486 ovsthread_id_self(void)
 487 {
 488     return *ovsthread_id_get();
 489 }
 490 \f
 491 void assert_single_threaded_at(const char *where);
 492 #define assert_single_threaded() assert_single_threaded_at(SOURCE_LOCATOR)
 493
 494 pid_t xfork_at(const char *where);
 495 #define xfork() xfork_at(SOURCE_LOCATOR)
 496
 497 void forbid_forking(const char *reason);
 498 bool may_fork(void);
 499 \f
 500 /* Useful functions related to threading. */
 501
 502 unsigned int count_cpu_cores(void);
 503
 504 #endif /* ovs-thread.h */