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