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 "openvswitch/thread.h"
  25 #include "util.h"
  26
  27 struct seq;
  28
  29 /* Poll-block()-able barrier similar to pthread_barrier_t. */
  30 struct ovs_barrier {
  31     uint32_t size;            /* Number of threads to wait. */
  32     atomic_count count;       /* Number of threads already hit the barrier. */
  33     struct seq *seq;
  34 };
  35
  36 /* Wrappers for pthread_mutexattr_*() that abort the process on any error. */
  37 void xpthread_mutexattr_init(pthread_mutexattr_t *);
  38 void xpthread_mutexattr_destroy(pthread_mutexattr_t *);
  39 void xpthread_mutexattr_settype(pthread_mutexattr_t *, int type);
  40 void xpthread_mutexattr_gettype(pthread_mutexattr_t *, int *typep);
  41
  42 /* Read-write lock.
  43  *
  44  * An ovs_rwlock does not support recursive readers, because POSIX allows
  45  * taking the reader lock recursively to deadlock when a thread is waiting on
  46  * the write-lock.  (NetBSD does deadlock.)  glibc rwlocks in their default
  47  * configuration do not deadlock, but ovs_rwlock_init() initializes rwlocks as
  48  * non-recursive (which will deadlock) for two reasons:
  49  *
  50  *     - glibc only provides fairness to writers in this mode.
  51  *
  52  *     - It's better to find bugs in the primary Open vSwitch target rather
  53  *       than exposing them only to porters. */
  54 struct OVS_LOCKABLE ovs_rwlock {
  55     pthread_rwlock_t lock;
  56     const char *where;          /* NULL if and only if uninitialized. */
  57 };
  58
  59 /* Initializer. */
  60 #ifdef PTHREAD_RWLOCK_WRITER_NONRECURSIVE_INITIALIZER_NP
  61 #define OVS_RWLOCK_INITIALIZER \
  62         { PTHREAD_RWLOCK_WRITER_NONRECURSIVE_INITIALIZER_NP, "<unlocked>" }
  63 #else
  64 #define OVS_RWLOCK_INITIALIZER { PTHREAD_RWLOCK_INITIALIZER, "<unlocked>" }
  65 #endif
  66
  67 /* ovs_rwlock functions analogous to pthread_rwlock_*() functions.
  68  *
  69  * Most of these functions abort the process with an error message on any
  70  * error.  The "trylock" functions are exception: they pass through a 0 or
  71  * EBUSY return value to the caller and abort on any other error. */
  72 void ovs_rwlock_init(const struct ovs_rwlock *);
  73 void ovs_rwlock_destroy(const struct ovs_rwlock *);
  74 void ovs_rwlock_unlock(const struct ovs_rwlock *rwlock) OVS_RELEASES(rwlock);
  75
  76 /* Wrappers for pthread_rwlockattr_*() that abort the process on any error. */
  77 void xpthread_rwlockattr_init(pthread_rwlockattr_t *);
  78 void xpthread_rwlockattr_destroy(pthread_rwlockattr_t *);
  79 #ifdef PTHREAD_RWLOCK_WRITER_NONRECURSIVE_INITIALIZER_NP
  80 void xpthread_rwlockattr_setkind_np(pthread_rwlockattr_t *, int kind);
  81 #endif
  82
  83 void ovs_rwlock_wrlock_at(const struct ovs_rwlock *rwlock, const char *where)
  84     OVS_ACQ_WRLOCK(rwlock);
  85 #define ovs_rwlock_wrlock(rwlock) \
  86         ovs_rwlock_wrlock_at(rwlock, OVS_SOURCE_LOCATOR)
  87
  88 int ovs_rwlock_trywrlock_at(const struct ovs_rwlock *rwlock, const char *where)
  89     OVS_TRY_WRLOCK(0, rwlock);
  90 #define ovs_rwlock_trywrlock(rwlock) \
  91     ovs_rwlock_trywrlock_at(rwlock, OVS_SOURCE_LOCATOR)
  92
  93 void ovs_rwlock_rdlock_at(const struct ovs_rwlock *rwlock, const char *where)
  94     OVS_ACQ_RDLOCK(rwlock);
  95 #define ovs_rwlock_rdlock(rwlock) \
  96         ovs_rwlock_rdlock_at(rwlock, OVS_SOURCE_LOCATOR)
  97
  98 int ovs_rwlock_tryrdlock_at(const struct ovs_rwlock *rwlock, const char *where)
  99     OVS_TRY_RDLOCK(0, rwlock);
 100 #define ovs_rwlock_tryrdlock(rwlock) \
 101         ovs_rwlock_tryrdlock_at(rwlock, OVS_SOURCE_LOCATOR)
 102
 103 /* ovs_barrier functions analogous to pthread_barrier_*() functions. */
 104 void ovs_barrier_init(struct ovs_barrier *, uint32_t count);
 105 void ovs_barrier_destroy(struct ovs_barrier *);
 106 void ovs_barrier_block(struct ovs_barrier *);
 107
 108 /* Wrappers for xpthread_cond_*() that abort the process on any error.
 109  *
 110  * Use ovs_mutex_cond_wait() to wait for a condition. */
 111 void xpthread_cond_init(pthread_cond_t *, pthread_condattr_t *);
 112 void xpthread_cond_destroy(pthread_cond_t *);
 113 void xpthread_cond_signal(pthread_cond_t *);
 114 void xpthread_cond_broadcast(pthread_cond_t *);
 115
 116 void xpthread_key_create(pthread_key_t *, void (*destructor)(void *));
 117 void xpthread_key_delete(pthread_key_t);
 118 void xpthread_setspecific(pthread_key_t, const void *);
 119
 120 #ifndef _WIN32
 121 void xpthread_sigmask(int, const sigset_t *, sigset_t *);
 122 #endif
 123
 124 pthread_t ovs_thread_create(const char *name, void *(*)(void *), void *);
 125 void xpthread_join(pthread_t, void **);
 126 \f
 127 /* Per-thread data.
 128  *
 129  *
 130  * Standard Forms
 131  * ==============
 132  *
 133  * Multiple forms of standard per-thread data exist, each with its own pluses
 134  * and minuses.  In general, if one of these forms is appropriate, then it's a
 135  * good idea to use it:
 136  *
 137  *     - POSIX per-thread data via pthread_key_t is portable to any pthreads
 138  *       implementation, and allows a destructor function to be defined.  It
 139  *       only (directly) supports per-thread pointers, which are always
 140  *       initialized to NULL.  It requires once-only allocation of a
 141  *       pthread_key_t value.  It is relatively slow.  Typically few
 142  *       "pthread_key_t"s are available (POSIX requires only at least 128,
 143  *       glibc supplies only 1024).
 144  *
 145  *     - The thread_local feature newly defined in C11 <threads.h> works with
 146  *       any data type and initializer, and it is fast.  thread_local does not
 147  *       require once-only initialization like pthread_key_t.  C11 does not
 148  *       define what happens if one attempts to access a thread_local object
 149  *       from a thread other than the one to which that object belongs.  There
 150  *       is no provision to call a user-specified destructor when a thread
 151  *       ends.  Typical implementations allow for an arbitrary amount of
 152  *       thread_local storage, but statically allocated only.
 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  * amount available?        few            arbitrary         arbitrary
 170  * dynamically allocated?   yes                no                 no
 171  *
 172  *
 173  * Extensions
 174  * ==========
 175  *
 176  * OVS provides some extensions and wrappers:
 177  *
 178  *     - In a situation where the performance of thread_local or __thread is
 179  *       desirable, but portability is required, DEFINE_STATIC_PER_THREAD_DATA
 180  *       and DECLARE_EXTERN_PER_THREAD_DATA/DEFINE_EXTERN_PER_THREAD_DATA may
 181  *       be appropriate (see below).
 182  *
 183  *     - DEFINE_PER_THREAD_MALLOCED_DATA can be convenient for simple
 184  *       per-thread malloc()'d buffers.
 185  *
 186  *     - struct ovs_tsd provides an alternative to pthread_key_t that isn't
 187  *       limited to a small number of keys.
 188  */
 189
 190 /* For static data, use this macro in a source file:
 191  *
 192  *    DEFINE_STATIC_PER_THREAD_DATA(TYPE, NAME, INITIALIZER).
 193  *
 194  * For global data, "declare" the data in the header and "define" it in
 195  * the source file, with:
 196  *
 197  *    DECLARE_EXTERN_PER_THREAD_DATA(TYPE, NAME).
 198  *    DEFINE_EXTERN_PER_THREAD_DATA(NAME, INITIALIZER).
 199  *
 200  * One should prefer to use POSIX per-thread data, via pthread_key_t, when its
 201  * performance is acceptable, because of its portability (see the table above).
 202  * This macro is an alternatives that takes advantage of thread_local (and
 203  * __thread), for its performance, when it is available, and falls back to
 204  * POSIX per-thread data otherwise.
 205  *
 206  * Defines per-thread variable NAME with the given TYPE, initialized to
 207  * INITIALIZER (which must be valid as an initializer for a variable with
 208  * static lifetime).
 209  *
 210  * The public interface to the variable is:
 211  *
 212  *    TYPE *NAME_get(void)
 213  *    TYPE *NAME_get_unsafe(void)
 214  *
 215  *       Returns the address of this thread's instance of NAME.
 216  *
 217  *       Use NAME_get() in a context where this might be the first use of the
 218  *       per-thread variable in the program.  Use NAME_get_unsafe(), which
 219  *       avoids a conditional test and is thus slightly faster, in a context
 220  *       where one knows that NAME_get() has already been called previously.
 221  *
 222  * There is no "NAME_set()" (or "NAME_set_unsafe()") function.  To set the
 223  * value of the per-thread variable, dereference the pointer returned by
 224  * TYPE_get() or TYPE_get_unsafe(), e.g. *TYPE_get() = 0.
 225  */
 226 #if HAVE_THREAD_LOCAL || HAVE___THREAD
 227
 228 #if HAVE_THREAD_LOCAL
 229 #include <threads.h>
 230 #elif HAVE___THREAD
 231 #define thread_local __thread
 232 #else
 233 #error
 234 #endif
 235
 236 #define DEFINE_STATIC_PER_THREAD_DATA(TYPE, NAME, ...)                  \
 237     typedef TYPE NAME##_type;                                           \
 238                                                                         \
 239     static NAME##_type *                                                \
 240     NAME##_get_unsafe(void)                                             \
 241     {                                                                   \
 242         static thread_local NAME##_type var = __VA_ARGS__;              \
 243         return &var;                                                    \
 244     }                                                                   \
 245                                                                         \
 246     static NAME##_type *                                                \
 247     NAME##_get(void)                                                    \
 248     {                                                                   \
 249         return NAME##_get_unsafe();                                     \
 250     }
 251 #define DECLARE_EXTERN_PER_THREAD_DATA(TYPE, NAME)                      \
 252     typedef TYPE NAME##_type;                                           \
 253     extern thread_local NAME##_type NAME##_var;                         \
 254                                                                         \
 255     static inline NAME##_type *                                         \
 256     NAME##_get_unsafe(void)                                             \
 257     {                                                                   \
 258         return (NAME##_type *)&NAME##_var;                              \
 259     }                                                                   \
 260                                                                         \
 261     static inline NAME##_type *                                         \
 262     NAME##_get(void)                                                    \
 263     {                                                                   \
 264         return NAME##_get_unsafe();                                     \
 265     }
 266 #define DEFINE_EXTERN_PER_THREAD_DATA(NAME, ...)         \
 267     thread_local NAME##_type NAME##_var = __VA_ARGS__;
 268 #else  /* no C implementation support for thread-local storage  */
 269 #define DEFINE_STATIC_PER_THREAD_DATA(TYPE, NAME, ...)                  \
 270     typedef TYPE NAME##_type;                                           \
 271     static pthread_key_t NAME##_key;                                    \
 272                                                                         \
 273     static NAME##_type *                                                \
 274     NAME##_get_unsafe(void)                                             \
 275     {                                                                   \
 276         return pthread_getspecific(NAME##_key);                         \
 277     }                                                                   \
 278                                                                         \
 279     static void                                                         \
 280     NAME##_once_init(void)                                              \
 281     {                                                                   \
 282         if (pthread_key_create(&NAME##_key, free)) {                    \
 283             abort();                                                    \
 284         }                                                               \
 285     }                                                                   \
 286                                                                         \
 287     static NAME##_type *                                                \
 288     NAME##_get(void)                                                    \
 289     {                                                                   \
 290         static pthread_once_t once = PTHREAD_ONCE_INIT;                 \
 291         NAME##_type *value;                                             \
 292                                                                         \
 293         pthread_once(&once, NAME##_once_init);                          \
 294         value = NAME##_get_unsafe();                                    \
 295         if (!value) {                                                   \
 296             static const NAME##_type initial_value = __VA_ARGS__;       \
 297                                                                         \
 298             value = malloc(sizeof *value);                              \
 299             if (value == NULL) {                                        \
 300                 out_of_memory();                                        \
 301             }                                                           \
 302             *value = initial_value;                                     \
 303             xpthread_setspecific(NAME##_key, value);                    \
 304         }                                                               \
 305         return value;                                                   \
 306     }
 307 #define DECLARE_EXTERN_PER_THREAD_DATA(TYPE, NAME)                      \
 308     typedef TYPE NAME##_type;                                           \
 309     static pthread_key_t NAME##_key;                                    \
 310                                                                         \
 311     static inline NAME##_type *                                         \
 312     NAME##_get_unsafe(void)                                             \
 313     {                                                                   \
 314         return (NAME##_type *)pthread_getspecific(NAME##_key);          \
 315     }                                                                   \
 316                                                                         \
 317     NAME##_type *NAME##_get(void);
 318 #define DEFINE_EXTERN_PER_THREAD_DATA(NAME, ...)                        \
 319     static void                                                         \
 320     NAME##_once_init(void)                                              \
 321     {                                                                   \
 322         if (pthread_key_create(&NAME##_key, free)) {                    \
 323             abort();                                                    \
 324         }                                                               \
 325     }                                                                   \
 326                                                                         \
 327     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 #endif
 348
 349 /* DEFINE_PER_THREAD_MALLOCED_DATA(TYPE, NAME).
 350  *
 351  * This is a simple wrapper around POSIX per-thread data primitives.  It
 352  * defines per-thread variable NAME with the given TYPE, which must be a
 353  * pointer type.  In each thread, the per-thread variable is initialized to
 354  * NULL.  When a thread terminates, the variable is freed with free().
 355  *
 356  * The public interface to the variable is:
 357  *
 358  *    TYPE NAME_get(void)
 359  *    TYPE NAME_get_unsafe(void)
 360  *
 361  *       Returns the value of per-thread variable NAME in this thread.
 362  *
 363  *       Use NAME_get() in a context where this might be the first use of the
 364  *       per-thread variable in the program.  Use NAME_get_unsafe(), which
 365  *       avoids a conditional test and is thus slightly faster, in a context
 366  *       where one knows that NAME_get() has already been called previously.
 367  *
 368  *    TYPE NAME_set(TYPE new_value)
 369  *    TYPE NAME_set_unsafe(TYPE new_value)
 370  *
 371  *       Sets the value of per-thread variable NAME to 'new_value' in this
 372  *       thread, and returns its previous value.
 373  *
 374  *       Use NAME_set() in a context where this might be the first use of the
 375  *       per-thread variable in the program.  Use NAME_set_unsafe(), which
 376  *       avoids a conditional test and is thus slightly faster, in a context
 377  *       where one knows that NAME_set() has already been called previously.
 378  */
 379 #define DEFINE_PER_THREAD_MALLOCED_DATA(TYPE, NAME)     \
 380     static pthread_key_t NAME##_key;                    \
 381                                                         \
 382     static void                                         \
 383     NAME##_once_init(void)                              \
 384     {                                                   \
 385         if (pthread_key_create(&NAME##_key, free)) {    \
 386             abort();                                    \
 387         }                                               \
 388     }                                                   \
 389                                                         \
 390     static void                                         \
 391     NAME##_init(void)                                   \
 392     {                                                   \
 393         static pthread_once_t once = PTHREAD_ONCE_INIT; \
 394         pthread_once(&once, NAME##_once_init);          \
 395     }                                                   \
 396                                                         \
 397     static TYPE                                         \
 398     NAME##_get_unsafe(void)                             \
 399     {                                                   \
 400         return pthread_getspecific(NAME##_key);         \
 401     }                                                   \
 402                                                         \
 403     static OVS_UNUSED TYPE                              \
 404     NAME##_get(void)                                    \
 405     {                                                   \
 406         NAME##_init();                                  \
 407         return NAME##_get_unsafe();                     \
 408     }                                                   \
 409                                                         \
 410     static TYPE                                         \
 411     NAME##_set_unsafe(TYPE value)                       \
 412     {                                                   \
 413         TYPE old_value = NAME##_get_unsafe();           \
 414         xpthread_setspecific(NAME##_key, value);        \
 415         return old_value;                               \
 416     }                                                   \
 417                                                         \
 418     static OVS_UNUSED TYPE                              \
 419     NAME##_set(TYPE value)                              \
 420     {                                                   \
 421         NAME##_init();                                  \
 422         return NAME##_set_unsafe(value);                \
 423     }
 424
 425 /* Dynamically allocated thread-specific data with lots of slots.
 426  *
 427  * pthread_key_t can provide as few as 128 pieces of thread-specific data (even
 428  * glibc is limited to 1,024).  Thus, one must be careful to allocate only a
 429  * few keys globally.  One cannot, for example, allocate a key for every
 430  * instance of a data structure if there might be an arbitrary number of those
 431  * data structures.
 432  *
 433  * This API is similar to the pthread one (simply search and replace pthread_
 434  * by ovsthread_) but it a much larger limit that can be raised if necessary
 435  * (by recompiling).  Thus, one may more freely use this form of
 436  * thread-specific data.
 437  *
 438  * ovsthread_key_t also differs from pthread_key_t in the following ways:
 439  *
 440  *    - Destructors must not access thread-specific data (via ovsthread_key).
 441  *
 442  *    - The pthread_key_t API allows concurrently exiting threads to start
 443  *      executing the destructor after pthread_key_delete() returns.  The
 444  *      ovsthread_key_t API guarantees that, when ovsthread_key_delete()
 445  *      returns, all destructors have returned and no new ones will start
 446  *      execution.
 447  */
 448 typedef struct ovsthread_key *ovsthread_key_t;
 449
 450 void ovsthread_key_create(ovsthread_key_t *, void (*destructor)(void *));
 451 void ovsthread_key_delete(ovsthread_key_t);
 452
 453 void ovsthread_setspecific(ovsthread_key_t, const void *);
 454 void *ovsthread_getspecific(ovsthread_key_t);
 455 \f
 456 /* Thread ID.
 457  *
 458  * pthread_t isn't so nice for some purposes.  Its size and representation are
 459  * implementation dependent, which means that there is no way to hash it.
 460  * This thread ID avoids the problem.
 461  */
 462
 463 #define OVSTHREAD_ID_UNSET UINT_MAX
 464 DECLARE_EXTERN_PER_THREAD_DATA(unsigned int, ovsthread_id);
 465
 466 /* Initializes the unique per thread identifier */
 467 unsigned int ovsthread_id_init(void);
 468
 469 /* Returns a per-thread identifier unique within the lifetime of the
 470  * process. */
 471 static inline unsigned int
 472 ovsthread_id_self(void)
 473 {
 474     unsigned int id = *ovsthread_id_get();
 475
 476     if (OVS_UNLIKELY(id == OVSTHREAD_ID_UNSET)) {
 477         id = ovsthread_id_init();
 478     }
 479
 480     return id;
 481 }
 482 \f
 483 /* Simulated global counter.
 484  *
 485  * Incrementing such a counter is meant to be cheaper than incrementing a
 486  * global counter protected by a lock.  It is probably more expensive than
 487  * incrementing a truly thread-local variable, but such a variable has no
 488  * straightforward way to get the sum.
 489  *
 490  *
 491  * Thread-safety
 492  * =============
 493  *
 494  * Fully thread-safe. */
 495
 496 struct ovsthread_stats {
 497     struct ovs_mutex mutex;
 498     void *volatile buckets[16];
 499 };
 500
 501 void ovsthread_stats_init(struct ovsthread_stats *);
 502 void ovsthread_stats_destroy(struct ovsthread_stats *);
 503
 504 void *ovsthread_stats_bucket_get(struct ovsthread_stats *,
 505                                  void *(*new_bucket)(void));
 506
 507 #define OVSTHREAD_STATS_FOR_EACH_BUCKET(BUCKET, IDX, STATS)             \
 508     for ((IDX) = ovs_thread_stats_next_bucket(STATS, 0);                \
 509          ((IDX) < ARRAY_SIZE((STATS)->buckets)                          \
 510           ? ((BUCKET) = (STATS)->buckets[IDX], true)                    \
 511           : false);                                                     \
 512          (IDX) = ovs_thread_stats_next_bucket(STATS, (IDX) + 1))
 513 size_t ovs_thread_stats_next_bucket(const struct ovsthread_stats *, size_t);
 514 \f
 515 bool single_threaded(void);
 516
 517 void assert_single_threaded_at(const char *where);
 518 #define assert_single_threaded() assert_single_threaded_at(OVS_SOURCE_LOCATOR)
 519
 520 #ifndef _WIN32
 521 pid_t xfork_at(const char *where);
 522 #define xfork() xfork_at(OVS_SOURCE_LOCATOR)
 523 #endif
 524
 525 void forbid_forking(const char *reason);
 526 bool may_fork(void);
 527 \f
 528 /* Useful functions related to threading. */
 529
 530 int count_cpu_cores(void);
 531 bool thread_is_pmd(void);
 532
 533 #endif /* ovs-thread.h */