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 /* DEFINE_PER_THREAD_DATA(TYPE, NAME, INITIALIZER).
 197  *
 198  * One should prefer to use POSIX per-thread data, via pthread_key_t, when its
 199  * performance is acceptable, because of its portability (see the table above).
 200  * This macro is an alternatives that takes advantage of thread_local (and
 201  * __thread), for its performance, when it is available, and falls back to
 202  * POSIX per-thread data otherwise.
 203  *
 204  * Defines per-thread variable NAME with the given TYPE, initialized to
 205  * INITIALIZER (which must be valid as an initializer for a variable with
 206  * static lifetime).
 207  *
 208  * The public interface to the variable is:
 209  *
 210  *    TYPE *NAME_get(void)
 211  *    TYPE *NAME_get_unsafe(void)
 212  *
 213  *       Returns the address of this thread's instance of NAME.
 214  *
 215  *       Use NAME_get() in a context where this might be the first use of the
 216  *       per-thread variable in the program.  Use NAME_get_unsafe(), which
 217  *       avoids a conditional test and is thus slightly faster, in a context
 218  *       where one knows that NAME_get() has already been called previously.
 219  *
 220  * There is no "NAME_set()" (or "NAME_set_unsafe()") function.  To set the
 221  * value of the per-thread variable, dereference the pointer returned by
 222  * TYPE_get() or TYPE_get_unsafe(), e.g. *TYPE_get() = 0.
 223  */
 224 #if HAVE_THREAD_LOCAL || HAVE___THREAD
 225
 226 #if HAVE_THREAD_LOCAL
 227 #include <threads.h>
 228 #elif HAVE___THREAD
 229 #define thread_local __thread
 230 #else
 231 #error
 232 #endif
 233
 234 #define DEFINE_PER_THREAD_DATA(TYPE, NAME, ...)                 \
 235     typedef TYPE NAME##_type;                                   \
 236     static thread_local NAME##_type NAME##_var = __VA_ARGS__;   \
 237                                                                 \
 238     static NAME##_type *                                        \
 239     NAME##_get_unsafe(void)                                     \
 240     {                                                           \
 241         return &NAME##_var;                                     \
 242     }                                                           \
 243                                                                 \
 244     static NAME##_type *                                        \
 245     NAME##_get(void)                                            \
 246     {                                                           \
 247         return NAME##_get_unsafe();                             \
 248     }
 249 #else  /* no C implementation support for thread-local storage  */
 250 #define DEFINE_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 #endif
 286
 287 /* DEFINE_PER_THREAD_MALLOCED_DATA(TYPE, NAME).
 288  *
 289  * This is a simple wrapper around POSIX per-thread data primitives.  It
 290  * defines per-thread variable NAME with the given TYPE, which must be a
 291  * pointer type.  In each thread, the per-thread variable is initialized to
 292  * NULL.  When a thread terminates, the variable is freed with free().
 293  *
 294  * The public interface to the variable is:
 295  *
 296  *    TYPE NAME_get(void)
 297  *    TYPE NAME_get_unsafe(void)
 298  *
 299  *       Returns the value of per-thread variable NAME in this thread.
 300  *
 301  *       Use NAME_get() in a context where this might be the first use of the
 302  *       per-thread variable in the program.  Use NAME_get_unsafe(), which
 303  *       avoids a conditional test and is thus slightly faster, in a context
 304  *       where one knows that NAME_get() has already been called previously.
 305  *
 306  *    TYPE NAME_set(TYPE new_value)
 307  *    TYPE NAME_set_unsafe(TYPE new_value)
 308  *
 309  *       Sets the value of per-thread variable NAME to 'new_value' in this
 310  *       thread, and returns its previous value.
 311  *
 312  *       Use NAME_set() in a context where this might be the first use of the
 313  *       per-thread variable in the program.  Use NAME_set_unsafe(), which
 314  *       avoids a conditional test and is thus slightly faster, in a context
 315  *       where one knows that NAME_set() has already been called previously.
 316  */
 317 #define DEFINE_PER_THREAD_MALLOCED_DATA(TYPE, NAME)     \
 318     static pthread_key_t NAME##_key;                    \
 319                                                         \
 320     static void                                         \
 321     NAME##_once_init(void)                              \
 322     {                                                   \
 323         if (pthread_key_create(&NAME##_key, free)) {    \
 324             abort();                                    \
 325         }                                               \
 326     }                                                   \
 327                                                         \
 328     static void                                         \
 329     NAME##_init(void)                                   \
 330     {                                                   \
 331         static pthread_once_t once = PTHREAD_ONCE_INIT; \
 332         pthread_once(&once, NAME##_once_init);          \
 333     }                                                   \
 334                                                         \
 335     static TYPE                                         \
 336     NAME##_get_unsafe(void)                             \
 337     {                                                   \
 338         return pthread_getspecific(NAME##_key);         \
 339     }                                                   \
 340                                                         \
 341     static OVS_UNUSED TYPE                              \
 342     NAME##_get(void)                                    \
 343     {                                                   \
 344         NAME##_init();                                  \
 345         return NAME##_get_unsafe();                     \
 346     }                                                   \
 347                                                         \
 348     static TYPE                                         \
 349     NAME##_set_unsafe(TYPE value)                       \
 350     {                                                   \
 351         TYPE old_value = NAME##_get_unsafe();           \
 352         xpthread_setspecific(NAME##_key, value);        \
 353         return old_value;                               \
 354     }                                                   \
 355                                                         \
 356     static OVS_UNUSED TYPE                              \
 357     NAME##_set(TYPE value)                              \
 358     {                                                   \
 359         NAME##_init();                                  \
 360         return NAME##_set_unsafe(value);                \
 361     }
 362 \f
 363 /* Convenient once-only execution.
 364  *
 365  *
 366  * Problem
 367  * =======
 368  *
 369  * POSIX provides pthread_once_t and pthread_once() as primitives for running a
 370  * set of code only once per process execution.  They are used like this:
 371  *
 372  *     static void run_once(void) { ...initialization... }
 373  *     static pthread_once_t once = PTHREAD_ONCE_INIT;
 374  * ...
 375  *     pthread_once(&once, run_once);
 376  *
 377  * pthread_once() does not allow passing any parameters to the initialization
 378  * function, which is often inconvenient, because it means that the function
 379  * can only access data declared at file scope.
 380  *
 381  *
 382  * Solution
 383  * ========
 384  *
 385  * Use ovsthread_once, like this, instead:
 386  *
 387  *     static struct ovsthread_once once = OVSTHREAD_ONCE_INITIALIZER;
 388  *
 389  *     if (ovsthread_once_start(&once)) {
 390  *         ...initialization...
 391  *         ovsthread_once_done(&once);
 392  *     }
 393  */
 394
 395 struct ovsthread_once {
 396     atomic_bool done;
 397     struct ovs_mutex mutex;
 398 };
 399
 400 #define OVSTHREAD_ONCE_INITIALIZER              \
 401     {                                           \
 402         ATOMIC_VAR_INIT(false),                 \
 403         OVS_ADAPTIVE_MUTEX_INITIALIZER,         \
 404     }
 405
 406 static inline bool ovsthread_once_start(struct ovsthread_once *once)
 407     OVS_TRY_LOCK(true, &once->mutex);
 408 void ovsthread_once_done(struct ovsthread_once *once)
 409     OVS_RELEASES(&once->mutex);
 410
 411 bool ovsthread_once_start__(struct ovsthread_once *once)
 412     OVS_TRY_LOCK(false, &once->mutex);
 413
 414 static inline bool
 415 ovsthread_once_is_done__(const struct ovsthread_once *once)
 416 {
 417     bool done;
 418
 419     atomic_read_explicit(&once->done, &done, memory_order_relaxed);
 420     return done;
 421 }
 422
 423 /* Returns true if this is the first call to ovsthread_once_start() for
 424  * 'once'.  In this case, the caller should perform whatever initialization
 425  * actions it needs to do, then call ovsthread_once_done() for 'once'.
 426  *
 427  * Returns false if this is not the first call to ovsthread_once_start() for
 428  * 'once'.  In this case, the call will not return until after
 429  * ovsthread_once_done() has been called. */
 430 static inline bool
 431 ovsthread_once_start(struct ovsthread_once *once)
 432 {
 433     return OVS_UNLIKELY(!ovsthread_once_is_done__(once)
 434                         && !ovsthread_once_start__(once));
 435 }
 436
 437 #ifdef __CHECKER__
 438 #define ovsthread_once_start(ONCE) \
 439     ((ONCE)->done ? false : ({ OVS_MACRO_LOCK((&ONCE->mutex)); true; }))
 440 #endif
 441 \f
 442 void assert_single_threaded_at(const char *where);
 443 #define assert_single_threaded() assert_single_threaded_at(SOURCE_LOCATOR)
 444
 445 pid_t xfork_at(const char *where);
 446 #define xfork() xfork_at(SOURCE_LOCATOR)
 447
 448 void forbid_forking(const char *reason);
 449 bool may_fork(void);
 450
 451 #endif /* ovs-thread.h */