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" initializers:
  34  *
  35  *    - OVS_MUTEX_INITIALIZER: common case.
  36  *
  37  *    - OVS_ADAPTIVE_MUTEX_INITIALIZER for a mutex that spins briefly then goes
  38  *      to sleeps after some number of iterations.
  39  *
  40  *    - OVS_ERRORCHECK_MUTEX_INITIALIZER for a mutex that is used for
  41  *      error-checking. */
  42 #define OVS_MUTEX_INITIALIZER { PTHREAD_MUTEX_INITIALIZER, NULL }
  43 #ifdef PTHREAD_ADAPTIVE_MUTEX_INITIALIZER_NP
  44 #define OVS_ADAPTIVE_MUTEX_INITIALIZER \
  45     { PTHREAD_ADAPTIVE_MUTEX_INITIALIZER_NP, NULL }
  46 #else
  47 #define OVS_ADAPTIVE_MUTEX_INITIALIZER OVS_MUTEX_INITIALIZER
  48 #endif
  49 #ifdef PTHREAD_ERRORCHECK_MUTEX_INITIALIZER_NP
  50 #define OVS_ERRORCHECK_MUTEX_INITIALIZER \
  51     { PTHREAD_ERRORCHECK_MUTEX_INITIALIZER_NP, NULL }
  52 #else
  53 #define OVS_ERRORCHECK_MUTEX_INITIALIZER OVS_MUTEX_INITIALIZER
  54 #endif
  55 \f
  56 /* Mutex types, suitable for use with pthread_mutexattr_settype().
  57  * There is only one nonstandard type:
  58  *
  59  *    - PTHREAD_MUTEX_ADAPTIVE_NP, the type used for
  60  *      OVS_ADAPTIVE_MUTEX_INITIALIZER. */
  61 #ifdef PTHREAD_ADAPTIVE_MUTEX_INITIALIZER_NP
  62 #define OVS_MUTEX_ADAPTIVE PTHREAD_MUTEX_ADAPTIVE_NP
  63 #else
  64 #define OVS_MUTEX_ADAPTIVE PTHREAD_MUTEX_NORMAL
  65 #endif
  66
  67 /* ovs_mutex functions analogous to pthread_mutex_*() functions.
  68  *
  69  * Most of these functions abort the process with an error message on any
  70  * error.  ovs_mutex_trylock() is an exception: it passes through a 0 or EBUSY
  71  * return value to the caller and aborts on any other error. */
  72 void ovs_mutex_init(const struct ovs_mutex *, int type);
  73 void ovs_mutex_destroy(const struct ovs_mutex *);
  74 void ovs_mutex_unlock(const struct ovs_mutex *mutex) OVS_RELEASES(mutex);
  75 void ovs_mutex_lock_at(const struct ovs_mutex *mutex, const char *where)
  76     OVS_ACQUIRES(mutex);
  77 #define ovs_mutex_lock(mutex) \
  78         ovs_mutex_lock_at(mutex, SOURCE_LOCATOR)
  79
  80 int ovs_mutex_trylock_at(const struct ovs_mutex *mutex, const char *where)
  81     OVS_TRY_LOCK(0, mutex);
  82 #define ovs_mutex_trylock(mutex) \
  83         ovs_mutex_trylock_at(mutex, SOURCE_LOCATOR)
  84
  85 void ovs_mutex_cond_wait(pthread_cond_t *, const struct ovs_mutex *);
  86
  87 /* Wrappers for pthread_mutex_*() that abort the process on any error.
  88  * This is still needed when ovs-atomic-pthreads.h is used. */
  89 void xpthread_mutex_lock(pthread_mutex_t *mutex);
  90 void xpthread_mutex_unlock(pthread_mutex_t *mutex);
  91
  92 /* Wrappers for pthread_mutexattr_*() that abort the process on any error. */
  93 void xpthread_mutexattr_init(pthread_mutexattr_t *);
  94 void xpthread_mutexattr_destroy(pthread_mutexattr_t *);
  95 void xpthread_mutexattr_settype(pthread_mutexattr_t *, int type);
  96 void xpthread_mutexattr_gettype(pthread_mutexattr_t *, int *typep);
  97
  98 /* Read-write lock. */
  99 struct OVS_LOCKABLE ovs_rwlock {
 100     pthread_rwlock_t lock;
 101     const char *where;
 102 };
 103
 104 /* Initializer. */
 105 #define OVS_RWLOCK_INITIALIZER { PTHREAD_RWLOCK_INITIALIZER, NULL }
 106
 107 /* ovs_rwlock functions analogous to pthread_rwlock_*() functions.
 108  *
 109  * Most of these functions abort the process with an error message on any
 110  * error.  The "trylock" functions are exception: they pass through a 0 or
 111  * EBUSY return value to the caller and abort on any other error. */
 112 void ovs_rwlock_init(const struct ovs_rwlock *);
 113 void ovs_rwlock_destroy(const struct ovs_rwlock *);
 114 void ovs_rwlock_unlock(const struct ovs_rwlock *rwlock) OVS_RELEASES(rwlock);
 115
 116 void ovs_rwlock_wrlock_at(const struct ovs_rwlock *rwlock, const char *where)
 117     OVS_ACQ_WRLOCK(rwlock);
 118 #define ovs_rwlock_wrlock(rwlock) \
 119         ovs_rwlock_wrlock_at(rwlock, SOURCE_LOCATOR);
 120
 121 int ovs_rwlock_trywrlock_at(const struct ovs_rwlock *rwlock, const char *where)
 122     OVS_TRY_WRLOCK(0, rwlock);
 123 #define ovs_rwlock_trywrlock(rwlock) \
 124     ovs_rwlock_trywrlock_at(rwlock, SOURCE_LOCATOR)
 125
 126 void ovs_rwlock_rdlock_at(const struct ovs_rwlock *rwlock, const char *where)
 127     OVS_ACQ_RDLOCK(rwlock);
 128 #define ovs_rwlock_rdlock(rwlock) \
 129         ovs_rwlock_rdlock_at(rwlock, SOURCE_LOCATOR);
 130
 131 int ovs_rwlock_tryrdlock_at(const struct ovs_rwlock *rwlock, const char *where)
 132     OVS_TRY_RDLOCK(0, rwlock);
 133 #define ovs_rwlock_tryrdlock(rwlock) \
 134         ovs_rwlock_tryrdlock_at(rwlock, SOURCE_LOCATOR)
 135
 136 /* Wrappers for xpthread_cond_*() that abort the process on any error.
 137  *
 138  * Use ovs_mutex_cond_wait() to wait for a condition. */
 139 void xpthread_cond_init(pthread_cond_t *, pthread_condattr_t *);
 140 void xpthread_cond_destroy(pthread_cond_t *);
 141 void xpthread_cond_signal(pthread_cond_t *);
 142 void xpthread_cond_broadcast(pthread_cond_t *);
 143
 144 #ifdef __CHECKER__
 145 /* Replace these functions by the macros already defined in the <pthread.h>
 146  * annotations, because the macro definitions have correct semantics for the
 147  * conditional acquisition that can't be captured in a function annotation.
 148  * The difference in semantics from pthread_*() to xpthread_*() does not matter
 149  * because sparse is not a compiler. */
 150 #define xpthread_mutex_trylock pthread_mutex_trylock
 151 #define xpthread_rwlock_tryrdlock pthread_rwlock_tryrdlock
 152 #define xpthread_rwlock_trywrlock pthread_rwlock_trywrlock
 153 #endif
 154
 155 void xpthread_key_create(pthread_key_t *, void (*destructor)(void *));
 156 void xpthread_setspecific(pthread_key_t, const void *);
 157
 158 void xpthread_create(pthread_t *, pthread_attr_t *, void *(*)(void *), void *);
 159 \f
 160 /* Per-thread data.
 161  *
 162  * Multiple forms of per-thread data exist, each with its own pluses and
 163  * minuses:
 164  *
 165  *     - POSIX per-thread data via pthread_key_t is portable to any pthreads
 166  *       implementation, and allows a destructor function to be defined.  It
 167  *       only (directly) supports per-thread pointers, which are always
 168  *       initialized to NULL.  It requires once-only allocation of a
 169  *       pthread_key_t value.  It is relatively slow.
 170  *
 171  *     - The thread_local feature newly defined in C11 <threads.h> works with
 172  *       any data type and initializer, and it is fast.  thread_local does not
 173  *       require once-only initialization like pthread_key_t.  C11 does not
 174  *       define what happens if one attempts to access a thread_local object
 175  *       from a thread other than the one to which that object belongs.  There
 176  *       is no provision to call a user-specified destructor when a thread
 177  *       ends.
 178  *
 179  *     - The __thread keyword is a GCC extension similar to thread_local but
 180  *       with a longer history.  __thread is not portable to every GCC version
 181  *       or environment.  __thread does not restrict the use of a thread-local
 182  *       object outside its own thread.
 183  *
 184  * Here's a handy summary:
 185  *
 186  *                     pthread_key_t     thread_local       __thread
 187  *                     -------------     ------------     -------------
 188  * portability             high               low             medium
 189  * speed                    low              high               high
 190  * supports destructors?    yes                no                 no
 191  * needs key allocation?    yes                no                 no
 192  * arbitrary initializer?    no               yes                yes
 193  * cross-thread access?     yes                no                yes
 194  */
 195
 196 /* For static data, use this macro in a source file:
 197  *
 198  *    DEFINE_STATIC_PER_THREAD_DATA(TYPE, NAME, INITIALIZER).
 199  *
 200  * For global data, "declare" the data in the header and "define" it in
 201  * the source file, with:
 202  *
 203  *    DECLARE_EXTERN_PER_THREAD_DATA(TYPE, NAME).
 204  *    DEFINE_EXTERN_PER_THREAD_DATA(NAME, INITIALIZER).
 205  *
 206  * One should prefer to use POSIX per-thread data, via pthread_key_t, when its
 207  * performance is acceptable, because of its portability (see the table above).
 208  * This macro is an alternatives that takes advantage of thread_local (and
 209  * __thread), for its performance, when it is available, and falls back to
 210  * POSIX per-thread data otherwise.
 211  *
 212  * Defines per-thread variable NAME with the given TYPE, initialized to
 213  * INITIALIZER (which must be valid as an initializer for a variable with
 214  * static lifetime).
 215  *
 216  * The public interface to the variable is:
 217  *
 218  *    TYPE *NAME_get(void)
 219  *    TYPE *NAME_get_unsafe(void)
 220  *
 221  *       Returns the address of this thread's instance of NAME.
 222  *
 223  *       Use NAME_get() in a context where this might be the first use of the
 224  *       per-thread variable in the program.  Use NAME_get_unsafe(), which
 225  *       avoids a conditional test and is thus slightly faster, in a context
 226  *       where one knows that NAME_get() has already been called previously.
 227  *
 228  * There is no "NAME_set()" (or "NAME_set_unsafe()") function.  To set the
 229  * value of the per-thread variable, dereference the pointer returned by
 230  * TYPE_get() or TYPE_get_unsafe(), e.g. *TYPE_get() = 0.
 231  */
 232 #if HAVE_THREAD_LOCAL || HAVE___THREAD
 233
 234 #if HAVE_THREAD_LOCAL
 235 #include <threads.h>
 236 #elif HAVE___THREAD
 237 #define thread_local __thread
 238 #else
 239 #error
 240 #endif
 241
 242 #define DEFINE_STATIC_PER_THREAD_DATA(TYPE, NAME, ...)                  \
 243     typedef TYPE NAME##_type;                                           \
 244                                                                         \
 245     static NAME##_type *                                                \
 246     NAME##_get_unsafe(void)                                             \
 247     {                                                                   \
 248         static thread_local NAME##_type var = __VA_ARGS__;              \
 249         return &var;                                                    \
 250     }                                                                   \
 251                                                                         \
 252     static NAME##_type *                                                \
 253     NAME##_get(void)                                                    \
 254     {                                                                   \
 255         return NAME##_get_unsafe();                                     \
 256     }
 257 #define DECLARE_EXTERN_PER_THREAD_DATA(TYPE, NAME)                      \
 258     typedef TYPE NAME##_type;                                           \
 259     extern thread_local NAME##_type NAME##_var;                         \
 260                                                                         \
 261     static inline NAME##_type *                                         \
 262     NAME##_get_unsafe(void)                                             \
 263     {                                                                   \
 264         return &NAME##_var;                                             \
 265     }                                                                   \
 266                                                                         \
 267     static inline NAME##_type *                                         \
 268     NAME##_get(void)                                                    \
 269     {                                                                   \
 270         return NAME##_get_unsafe();                                     \
 271     }
 272 #define DEFINE_EXTERN_PER_THREAD_DATA(NAME, ...)         \
 273     thread_local NAME##_type NAME##_var = __VA_ARGS__;
 274 #else  /* no C implementation support for thread-local storage  */
 275 #define DEFINE_STATIC_PER_THREAD_DATA(TYPE, NAME, ...)                  \
 276     typedef TYPE NAME##_type;                                           \
 277     static pthread_key_t NAME##_key;                                    \
 278                                                                         \
 279     static NAME##_type *                                                \
 280     NAME##_get_unsafe(void)                                             \
 281     {                                                                   \
 282         return pthread_getspecific(NAME##_key);                         \
 283     }                                                                   \
 284                                                                         \
 285     static void                                                         \
 286     NAME##_once_init(void)                                              \
 287     {                                                                   \
 288         if (pthread_key_create(&NAME##_key, free)) {                    \
 289             abort();                                                    \
 290         }                                                               \
 291     }                                                                   \
 292                                                                         \
 293     static NAME##_type *                                                \
 294     NAME##_get(void)                                                    \
 295     {                                                                   \
 296         static pthread_once_t once = PTHREAD_ONCE_INIT;                 \
 297         NAME##_type *value;                                             \
 298                                                                         \
 299         pthread_once(&once, NAME##_once_init);                          \
 300         value = NAME##_get_unsafe();                                    \
 301         if (!value) {                                                   \
 302             static const NAME##_type initial_value = __VA_ARGS__;       \
 303                                                                         \
 304             value = xmalloc(sizeof *value);                             \
 305             *value = initial_value;                                     \
 306             xpthread_setspecific(NAME##_key, value);                    \
 307         }                                                               \
 308         return value;                                                   \
 309     }
 310 #define DECLARE_EXTERN_PER_THREAD_DATA(TYPE, NAME)                      \
 311     typedef TYPE NAME##_type;                                           \
 312     static pthread_key_t NAME##_key;                                    \
 313                                                                         \
 314     static inline NAME##_type *                                         \
 315     NAME##_get_unsafe(void)                                             \
 316     {                                                                   \
 317         return pthread_getspecific(NAME##_key);                         \
 318     }                                                                   \
 319                                                                         \
 320     NAME##_type *NAME##_get(void);
 321 #define DEFINE_EXTERN_PER_THREAD_DATA(NAME, ...)                        \
 322     static void                                                         \
 323     NAME##_once_init(void)                                              \
 324     {                                                                   \
 325         if (pthread_key_create(&NAME##_key, free)) {                    \
 326             abort();                                                    \
 327         }                                                               \
 328     }                                                                   \
 329                                                                         \
 330     NAME##_type *                                                       \
 331     NAME##_get(void)                                                    \
 332     {                                                                   \
 333         static pthread_once_t once = PTHREAD_ONCE_INIT;                 \
 334         NAME##_type *value;                                             \
 335                                                                         \
 336         pthread_once(&once, NAME##_once_init);                          \
 337         value = NAME##_get_unsafe();                                    \
 338         if (!value) {                                                   \
 339             static const NAME##_type initial_value = __VA_ARGS__;       \
 340                                                                         \
 341             value = xmalloc(sizeof *value);                             \
 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 \f
 425 /* Convenient once-only execution.
 426  *
 427  *
 428  * Problem
 429  * =======
 430  *
 431  * POSIX provides pthread_once_t and pthread_once() as primitives for running a
 432  * set of code only once per process execution.  They are used like this:
 433  *
 434  *     static void run_once(void) { ...initialization... }
 435  *     static pthread_once_t once = PTHREAD_ONCE_INIT;
 436  * ...
 437  *     pthread_once(&once, run_once);
 438  *
 439  * pthread_once() does not allow passing any parameters to the initialization
 440  * function, which is often inconvenient, because it means that the function
 441  * can only access data declared at file scope.
 442  *
 443  *
 444  * Solution
 445  * ========
 446  *
 447  * Use ovsthread_once, like this, instead:
 448  *
 449  *     static struct ovsthread_once once = OVSTHREAD_ONCE_INITIALIZER;
 450  *
 451  *     if (ovsthread_once_start(&once)) {
 452  *         ...initialization...
 453  *         ovsthread_once_done(&once);
 454  *     }
 455  */
 456
 457 struct ovsthread_once {
 458     atomic_bool done;
 459     struct ovs_mutex mutex;
 460 };
 461
 462 #define OVSTHREAD_ONCE_INITIALIZER              \
 463     {                                           \
 464         ATOMIC_VAR_INIT(false),                 \
 465         OVS_ADAPTIVE_MUTEX_INITIALIZER,         \
 466     }
 467
 468 static inline bool ovsthread_once_start(struct ovsthread_once *once)
 469     OVS_TRY_LOCK(true, &once->mutex);
 470 void ovsthread_once_done(struct ovsthread_once *once)
 471     OVS_RELEASES(&once->mutex);
 472
 473 bool ovsthread_once_start__(struct ovsthread_once *once)
 474     OVS_TRY_LOCK(false, &once->mutex);
 475
 476 static inline bool
 477 ovsthread_once_is_done__(const struct ovsthread_once *once)
 478 {
 479     bool done;
 480
 481     atomic_read_explicit(&once->done, &done, memory_order_relaxed);
 482     return done;
 483 }
 484
 485 /* Returns true if this is the first call to ovsthread_once_start() for
 486  * 'once'.  In this case, the caller should perform whatever initialization
 487  * actions it needs to do, then call ovsthread_once_done() for 'once'.
 488  *
 489  * Returns false if this is not the first call to ovsthread_once_start() for
 490  * 'once'.  In this case, the call will not return until after
 491  * ovsthread_once_done() has been called. */
 492 static inline bool
 493 ovsthread_once_start(struct ovsthread_once *once)
 494 {
 495     return OVS_UNLIKELY(!ovsthread_once_is_done__(once)
 496                         && !ovsthread_once_start__(once));
 497 }
 498
 499 #ifdef __CHECKER__
 500 #define ovsthread_once_start(ONCE) \
 501     ((ONCE)->done ? false : ({ OVS_MACRO_LOCK((&ONCE->mutex)); true; }))
 502 #endif
 503 \f
 504 void assert_single_threaded_at(const char *where);
 505 #define assert_single_threaded() assert_single_threaded_at(SOURCE_LOCATOR)
 506
 507 pid_t xfork_at(const char *where);
 508 #define xfork() xfork_at(SOURCE_LOCATOR)
 509
 510 void forbid_forking(const char *reason);
 511 bool may_fork(void);
 512
 513 #endif /* ovs-thread.h */