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 = malloc(sizeof *value);                              \
 280             if (value == NULL) {                                        \
 281                 out_of_memory();                                        \
 282             }                                                           \
 283             *value = initial_value;                                     \
 284             xpthread_setspecific(NAME##_key, value);                    \
 285         }                                                               \
 286         return value;                                                   \
 287     }
 288 #define DECLARE_EXTERN_PER_THREAD_DATA(TYPE, NAME)                      \
 289     typedef TYPE NAME##_type;                                           \
 290     static pthread_key_t NAME##_key;                                    \
 291                                                                         \
 292     static inline NAME##_type *                                         \
 293     NAME##_get_unsafe(void)                                             \
 294     {                                                                   \
 295         return pthread_getspecific(NAME##_key);                         \
 296     }                                                                   \
 297                                                                         \
 298     NAME##_type *NAME##_get(void);
 299 #define DEFINE_EXTERN_PER_THREAD_DATA(NAME, ...)                        \
 300     static void                                                         \
 301     NAME##_once_init(void)                                              \
 302     {                                                                   \
 303         if (pthread_key_create(&NAME##_key, free)) {                    \
 304             abort();                                                    \
 305         }                                                               \
 306     }                                                                   \
 307                                                                         \
 308     NAME##_type *                                                       \
 309     NAME##_get(void)                                                    \
 310     {                                                                   \
 311         static pthread_once_t once = PTHREAD_ONCE_INIT;                 \
 312         NAME##_type *value;                                             \
 313                                                                         \
 314         pthread_once(&once, NAME##_once_init);                          \
 315         value = NAME##_get_unsafe();                                    \
 316         if (!value) {                                                   \
 317             static const NAME##_type initial_value = __VA_ARGS__;       \
 318                                                                         \
 319             value = malloc(sizeof *value);                              \
 320             if (value == NULL) {                                        \
 321                 out_of_memory();                                        \
 322             }                                                           \
 323             *value = initial_value;                                     \
 324             xpthread_setspecific(NAME##_key, value);                    \
 325         }                                                               \
 326         return value;                                                   \
 327     }
 328 #endif
 329
 330 /* DEFINE_PER_THREAD_MALLOCED_DATA(TYPE, NAME).
 331  *
 332  * This is a simple wrapper around POSIX per-thread data primitives.  It
 333  * defines per-thread variable NAME with the given TYPE, which must be a
 334  * pointer type.  In each thread, the per-thread variable is initialized to
 335  * NULL.  When a thread terminates, the variable is freed with free().
 336  *
 337  * The public interface to the variable is:
 338  *
 339  *    TYPE NAME_get(void)
 340  *    TYPE NAME_get_unsafe(void)
 341  *
 342  *       Returns the value of per-thread variable NAME in this thread.
 343  *
 344  *       Use NAME_get() in a context where this might be the first use of the
 345  *       per-thread variable in the program.  Use NAME_get_unsafe(), which
 346  *       avoids a conditional test and is thus slightly faster, in a context
 347  *       where one knows that NAME_get() has already been called previously.
 348  *
 349  *    TYPE NAME_set(TYPE new_value)
 350  *    TYPE NAME_set_unsafe(TYPE new_value)
 351  *
 352  *       Sets the value of per-thread variable NAME to 'new_value' in this
 353  *       thread, and returns its previous value.
 354  *
 355  *       Use NAME_set() in a context where this might be the first use of the
 356  *       per-thread variable in the program.  Use NAME_set_unsafe(), which
 357  *       avoids a conditional test and is thus slightly faster, in a context
 358  *       where one knows that NAME_set() has already been called previously.
 359  */
 360 #define DEFINE_PER_THREAD_MALLOCED_DATA(TYPE, NAME)     \
 361     static pthread_key_t NAME##_key;                    \
 362                                                         \
 363     static void                                         \
 364     NAME##_once_init(void)                              \
 365     {                                                   \
 366         if (pthread_key_create(&NAME##_key, free)) {    \
 367             abort();                                    \
 368         }                                               \
 369     }                                                   \
 370                                                         \
 371     static void                                         \
 372     NAME##_init(void)                                   \
 373     {                                                   \
 374         static pthread_once_t once = PTHREAD_ONCE_INIT; \
 375         pthread_once(&once, NAME##_once_init);          \
 376     }                                                   \
 377                                                         \
 378     static TYPE                                         \
 379     NAME##_get_unsafe(void)                             \
 380     {                                                   \
 381         return pthread_getspecific(NAME##_key);         \
 382     }                                                   \
 383                                                         \
 384     static OVS_UNUSED TYPE                              \
 385     NAME##_get(void)                                    \
 386     {                                                   \
 387         NAME##_init();                                  \
 388         return NAME##_get_unsafe();                     \
 389     }                                                   \
 390                                                         \
 391     static TYPE                                         \
 392     NAME##_set_unsafe(TYPE value)                       \
 393     {                                                   \
 394         TYPE old_value = NAME##_get_unsafe();           \
 395         xpthread_setspecific(NAME##_key, value);        \
 396         return old_value;                               \
 397     }                                                   \
 398                                                         \
 399     static OVS_UNUSED TYPE                              \
 400     NAME##_set(TYPE value)                              \
 401     {                                                   \
 402         NAME##_init();                                  \
 403         return NAME##_set_unsafe(value);                \
 404     }
 405 \f
 406 /* Convenient once-only execution.
 407  *
 408  *
 409  * Problem
 410  * =======
 411  *
 412  * POSIX provides pthread_once_t and pthread_once() as primitives for running a
 413  * set of code only once per process execution.  They are used like this:
 414  *
 415  *     static void run_once(void) { ...initialization... }
 416  *     static pthread_once_t once = PTHREAD_ONCE_INIT;
 417  * ...
 418  *     pthread_once(&once, run_once);
 419  *
 420  * pthread_once() does not allow passing any parameters to the initialization
 421  * function, which is often inconvenient, because it means that the function
 422  * can only access data declared at file scope.
 423  *
 424  *
 425  * Solution
 426  * ========
 427  *
 428  * Use ovsthread_once, like this, instead:
 429  *
 430  *     static struct ovsthread_once once = OVSTHREAD_ONCE_INITIALIZER;
 431  *
 432  *     if (ovsthread_once_start(&once)) {
 433  *         ...initialization...
 434  *         ovsthread_once_done(&once);
 435  *     }
 436  */
 437
 438 struct ovsthread_once {
 439     atomic_bool done;
 440     struct ovs_mutex mutex;
 441 };
 442
 443 #define OVSTHREAD_ONCE_INITIALIZER              \
 444     {                                           \
 445         ATOMIC_VAR_INIT(false),                 \
 446         OVS_MUTEX_INITIALIZER,                  \
 447     }
 448
 449 static inline bool ovsthread_once_start(struct ovsthread_once *once)
 450     OVS_TRY_LOCK(true, once->mutex);
 451 void ovsthread_once_done(struct ovsthread_once *once)
 452     OVS_RELEASES(once->mutex);
 453
 454 bool ovsthread_once_start__(struct ovsthread_once *once)
 455     OVS_TRY_LOCK(false, once->mutex);
 456
 457 static inline bool
 458 ovsthread_once_is_done__(struct ovsthread_once *once)
 459 {
 460     bool done;
 461
 462     atomic_read_explicit(&once->done, &done, memory_order_relaxed);
 463     return done;
 464 }
 465
 466 /* Returns true if this is the first call to ovsthread_once_start() for
 467  * 'once'.  In this case, the caller should perform whatever initialization
 468  * actions it needs to do, then call ovsthread_once_done() for 'once'.
 469  *
 470  * Returns false if this is not the first call to ovsthread_once_start() for
 471  * 'once'.  In this case, the call will not return until after
 472  * ovsthread_once_done() has been called. */
 473 static inline bool
 474 ovsthread_once_start(struct ovsthread_once *once)
 475 {
 476     return OVS_UNLIKELY(!ovsthread_once_is_done__(once)
 477                         && !ovsthread_once_start__(once));
 478 }
 479 \f
 480 /* Thread ID.
 481  *
 482  * pthread_t isn't so nice for some purposes.  Its size and representation are
 483  * implementation dependent, which means that there is no way to hash it.
 484  * This thread ID avoids the problem.
 485  */
 486
 487 DECLARE_EXTERN_PER_THREAD_DATA(unsigned int, ovsthread_id);
 488
 489 /* Returns a per-thread identifier unique within the lifetime of the
 490  * process. */
 491 static inline unsigned int
 492 ovsthread_id_self(void)
 493 {
 494     return *ovsthread_id_get();
 495 }
 496 \f
 497 void assert_single_threaded_at(const char *where);
 498 #define assert_single_threaded() assert_single_threaded_at(SOURCE_LOCATOR)
 499
 500 pid_t xfork_at(const char *where);
 501 #define xfork() xfork_at(SOURCE_LOCATOR)
 502
 503 void forbid_forking(const char *reason);
 504 bool may_fork(void);
 505 \f
 506 /* Useful functions related to threading. */
 507
 508 int count_cpu_cores(void);
 509
 510 #endif /* ovs-thread.h */