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 /* glibc has some non-portable mutex types and initializers:
  27  *
  28  *    - PTHREAD_MUTEX_ADAPTIVE_NP is a mutex type that works as a spinlock that
  29  *      falls back to a mutex after spinning for some number of iterations.
  30  *
  31  *    - PTHREAD_ERRORCHECK_MUTEX_INITIALIZER_NP is a non-portable initializer
  32  *      for an error-checking mutex.
  33  *
  34  * We use these definitions to fall back to PTHREAD_MUTEX_NORMAL instead in
  35  * these cases.
  36  *
  37  * (glibc has other non-portable initializers, but we can't reasonably
  38  * substitute for them here.) */
  39 #ifdef PTHREAD_ADAPTIVE_MUTEX_INITIALIZER_NP
  40 #define PTHREAD_MUTEX_ADAPTIVE PTHREAD_MUTEX_ADAPTIVE_NP
  41 #define PTHREAD_ADAPTIVE_MUTEX_INITIALIZER \
  42     PTHREAD_ADAPTIVE_MUTEX_INITIALIZER_NP
  43 #else
  44 #define PTHREAD_MUTEX_ADAPTIVE PTHREAD_MUTEX_NORMAL
  45 #define PTHREAD_ADAPTIVE_MUTEX_INITIALIZER PTHREAD_MUTEX_INITIALIZER
  46 #endif
  47
  48 #ifdef PTHREAD_ERRORCHECK_MUTEX_INITIALIZER_NP
  49 #define PTHREAD_ERRORCHECK_MUTEX_INITIALIZER \
  50     PTHREAD_ERRORCHECK_MUTEX_INITIALIZER_NP
  51 #else
  52 #define PTHREAD_ERRORCHECK_MUTEX_INITIALIZER PTHREAD_MUTEX_INITIALIZER
  53 #endif
  54 \f
  55 /* Simple wrappers for pthreads functions.  Most of these functions abort the
  56  * process with an error message on any error.  The *_trylock() functions are
  57  * exceptions: they pass through a 0 or EBUSY return value to the caller and
  58  * abort on any other error. */
  59 void xpthread_mutex_init(pthread_mutex_t *, pthread_mutexattr_t *);
  60 void xpthread_mutex_lock(pthread_mutex_t *mutex) OVS_ACQUIRES(mutex);
  61 void xpthread_mutex_unlock(pthread_mutex_t *mutex) OVS_RELEASES(mutex);
  62 int xpthread_mutex_trylock(pthread_mutex_t *);
  63
  64 void xpthread_rwlock_init(pthread_rwlock_t *, pthread_rwlockattr_t *);
  65 void xpthread_rwlock_rdlock(pthread_rwlock_t *rwlock) OVS_ACQUIRES(rwlock);
  66 void xpthread_rwlock_wrlock(pthread_rwlock_t *rwlock) OVS_ACQUIRES(rwlock);
  67 void xpthread_rwlock_unlock(pthread_rwlock_t *rwlock) OVS_RELEASES(rwlock);
  68 int xpthread_rwlock_tryrdlock(pthread_rwlock_t *);
  69 int xpthread_rwlock_trywrlock(pthread_rwlock_t *);
  70
  71 void xpthread_cond_init(pthread_cond_t *, pthread_condattr_t *);
  72 void xpthread_cond_signal(pthread_cond_t *);
  73 void xpthread_cond_broadcast(pthread_cond_t *);
  74 void xpthread_cond_wait(pthread_cond_t *, pthread_mutex_t *mutex)
  75     OVS_MUST_HOLD(mutex);
  76
  77 #ifdef __CHECKER__
  78 /* Replace these functions by the macros already defined in the <pthread.h>
  79  * annotations, because the macro definitions have correct semantics for the
  80  * conditional acquisition that can't be captured in a function annotation.
  81  * The difference in semantics from pthread_*() to xpthread_*() does not matter
  82  * because sparse is not a compiler. */
  83 #define xpthread_mutex_trylock pthread_mutex_trylock
  84 #define xpthread_rwlock_tryrdlock pthread_rwlock_tryrdlock
  85 #define xpthread_rwlock_trywrlock pthread_rwlock_trywrlock
  86 #endif
  87
  88 void xpthread_key_create(pthread_key_t *, void (*destructor)(void *));
  89
  90 void xpthread_create(pthread_t *, pthread_attr_t *, void *(*)(void *), void *);
  91 \f
  92 /* Per-thread data.
  93  *
  94  * Multiple forms of per-thread data exist, each with its own pluses and
  95  * minuses:
  96  *
  97  *     - POSIX per-thread data via pthread_key_t is portable to any pthreads
  98  *       implementation, and allows a destructor function to be defined.  It
  99  *       only (directly) supports per-thread pointers, which are always
 100  *       initialized to NULL.  It requires once-only allocation of a
 101  *       pthread_key_t value.  It is relatively slow.
 102  *
 103  *     - The thread_local feature newly defined in C11 <threads.h> works with
 104  *       any data type and initializer, and it is fast.  thread_local does not
 105  *       require once-only initialization like pthread_key_t.  C11 does not
 106  *       define what happens if one attempts to access a thread_local object
 107  *       from a thread other than the one to which that object belongs.  There
 108  *       is no provision to call a user-specified destructor when a thread
 109  *       ends.
 110  *
 111  *     - The __thread keyword is a GCC extension similar to thread_local but
 112  *       with a longer history.  __thread is not portable to every GCC version
 113  *       or environment.  __thread does not restrict the use of a thread-local
 114  *       object outside its own thread.
 115  *
 116  * Here's a handy summary:
 117  *
 118  *                     pthread_key_t     thread_local       __thread
 119  *                     -------------     ------------     -------------
 120  * portability             high               low             medium
 121  * speed                    low              high               high
 122  * supports destructors?    yes                no                 no
 123  * needs key allocation?    yes                no                 no
 124  * arbitrary initializer?    no               yes                yes
 125  * cross-thread access?     yes                no                yes
 126  */
 127
 128 /* DEFINE_PER_THREAD_DATA(TYPE, NAME, INITIALIZER).
 129  *
 130  * One should prefer to use POSIX per-thread data, via pthread_key_t, when its
 131  * performance is acceptable, because of its portability (see the table above).
 132  * This macro is an alternatives that takes advantage of thread_local (and
 133  * __thread), for its performance, when it is available, and falls back to
 134  * POSIX per-thread data otherwise.
 135  *
 136  * Defines per-thread variable NAME with the given TYPE, initialized to
 137  * INITIALIZER (which must be valid as an initializer for a variable with
 138  * static lifetime).
 139  *
 140  * The public interface to the variable is:
 141  *
 142  *    TYPE *NAME_get(void)
 143  *    TYPE *NAME_get_unsafe(void)
 144  *
 145  *       Returns the address of this thread's instance of NAME.
 146  *
 147  *       Use NAME_get() in a context where this might be the first use of the
 148  *       per-thread variable in the program.  Use NAME_get_unsafe(), which
 149  *       avoids a conditional test and is thus slightly faster, in a context
 150  *       where one knows that NAME_get() has already been called previously.
 151  *
 152  * There is no "NAME_set()" (or "NAME_set_unsafe()") function.  To set the
 153  * value of the per-thread variable, dereference the pointer returned by
 154  * TYPE_get() or TYPE_get_unsafe(), e.g. *TYPE_get() = 0.
 155  */
 156 #if HAVE_THREAD_LOCAL || HAVE___THREAD
 157
 158 #if HAVE_THREAD_LOCAL
 159 #include <threads.h>
 160 #elif HAVE___THREAD
 161 #define thread_local __thread
 162 #else
 163 #error
 164 #endif
 165
 166 #define DEFINE_PER_THREAD_DATA(TYPE, NAME, ...)                 \
 167     typedef TYPE NAME##_type;                                   \
 168     static thread_local NAME##_type NAME##_var = __VA_ARGS__;   \
 169                                                                 \
 170     static NAME##_type *                                        \
 171     NAME##_get_unsafe(void)                                     \
 172     {                                                           \
 173         return &NAME##_var;                                     \
 174     }                                                           \
 175                                                                 \
 176     static NAME##_type *                                        \
 177     NAME##_get(void)                                            \
 178     {                                                           \
 179         return NAME##_get_unsafe();                             \
 180     }
 181 #else  /* no C implementation support for thread-local storage  */
 182 #define DEFINE_PER_THREAD_DATA(TYPE, NAME, ...)                         \
 183     typedef TYPE NAME##_type;                                           \
 184     static pthread_key_t NAME##_key;                                    \
 185                                                                         \
 186     static NAME##_type *                                                \
 187     NAME##_get_unsafe(void)                                             \
 188     {                                                                   \
 189         return pthread_getspecific(NAME##_key);                         \
 190     }                                                                   \
 191                                                                         \
 192     static void                                                         \
 193     NAME##_once_init(void)                                              \
 194     {                                                                   \
 195         if (pthread_key_create(&NAME##_key, free)) {                    \
 196             abort();                                                    \
 197         }                                                               \
 198     }                                                                   \
 199                                                                         \
 200     static NAME##_type *                                                \
 201     NAME##_get(void)                                                    \
 202     {                                                                   \
 203         static pthread_once_t once = PTHREAD_ONCE_INIT;                 \
 204         NAME##_type *value;                                             \
 205                                                                         \
 206         pthread_once(&once, NAME##_once_init);                          \
 207         value = NAME##_get_unsafe();                                    \
 208         if (!value) {                                                   \
 209             static const NAME##_type initial_value = __VA_ARGS__;       \
 210                                                                         \
 211             value = xmalloc(sizeof *value);                             \
 212             *value = initial_value;                                     \
 213             pthread_setspecific(NAME##_key, value);                     \
 214         }                                                               \
 215         return value;                                                   \
 216     }
 217 #endif
 218
 219 /* DEFINE_PER_THREAD_MALLOCED_DATA(TYPE, NAME).
 220  *
 221  * This is a simple wrapper around POSIX per-thread data primitives.  It
 222  * defines per-thread variable NAME with the given TYPE, which must be a
 223  * pointer type.  In each thread, the per-thread variable is initialized to
 224  * NULL.  When a thread terminates, the variable is freed with free().
 225  *
 226  * The public interface to the variable is:
 227  *
 228  *    TYPE NAME_get(void)
 229  *    TYPE NAME_get_unsafe(void)
 230  *
 231  *       Returns the value of per-thread variable NAME in this thread.
 232  *
 233  *       Use NAME_get() in a context where this might be the first use of the
 234  *       per-thread variable in the program.  Use NAME_get_unsafe(), which
 235  *       avoids a conditional test and is thus slightly faster, in a context
 236  *       where one knows that NAME_get() has already been called previously.
 237  *
 238  *    TYPE NAME_set(TYPE new_value)
 239  *    TYPE NAME_set_unsafe(TYPE new_value)
 240  *
 241  *       Sets the value of per-thread variable NAME to 'new_value' in this
 242  *       thread, and returns its previous value.
 243  *
 244  *       Use NAME_set() in a context where this might be the first use of the
 245  *       per-thread variable in the program.  Use NAME_set_unsafe(), which
 246  *       avoids a conditional test and is thus slightly faster, in a context
 247  *       where one knows that NAME_set() has already been called previously.
 248  */
 249 #define DEFINE_PER_THREAD_MALLOCED_DATA(TYPE, NAME)     \
 250     static pthread_key_t NAME##_key;                    \
 251                                                         \
 252     static void                                         \
 253     NAME##_once_init(void)                              \
 254     {                                                   \
 255         if (pthread_key_create(&NAME##_key, free)) {    \
 256             abort();                                    \
 257         }                                               \
 258     }                                                   \
 259                                                         \
 260     static void                                         \
 261     NAME##_init(void)                                   \
 262     {                                                   \
 263         static pthread_once_t once = PTHREAD_ONCE_INIT; \
 264         pthread_once(&once, NAME##_once_init);          \
 265     }                                                   \
 266                                                         \
 267     static TYPE                                         \
 268     NAME##_get_unsafe(void)                             \
 269     {                                                   \
 270         return pthread_getspecific(NAME##_key);         \
 271     }                                                   \
 272                                                         \
 273     static OVS_UNUSED TYPE                              \
 274     NAME##_get(void)                                    \
 275     {                                                   \
 276         NAME##_init();                                  \
 277         return NAME##_get_unsafe();                     \
 278     }                                                   \
 279                                                         \
 280     static TYPE                                         \
 281     NAME##_set_unsafe(TYPE value)                       \
 282     {                                                   \
 283         TYPE old_value = NAME##_get_unsafe();           \
 284         pthread_setspecific(NAME##_key, value);         \
 285         return old_value;                               \
 286     }                                                   \
 287                                                         \
 288     static OVS_UNUSED TYPE                              \
 289     NAME##_set(TYPE value)                              \
 290     {                                                   \
 291         NAME##_init();                                  \
 292         return NAME##_set_unsafe(value);                \
 293     }
 294 \f
 295 /* Convenient once-only execution.
 296  *
 297  *
 298  * Problem
 299  * =======
 300  *
 301  * POSIX provides pthread_once_t and pthread_once() as primitives for running a
 302  * set of code only once per process execution.  They are used like this:
 303  *
 304  *     static void run_once(void) { ...initialization... }
 305  *     static pthread_once_t once = PTHREAD_ONCE_INIT;
 306  * ...
 307  *     pthread_once(&once, run_once);
 308  *
 309  * pthread_once() does not allow passing any parameters to the initialization
 310  * function, which is often inconvenient, because it means that the function
 311  * can only access data declared at file scope.
 312  *
 313  *
 314  * Solution
 315  * ========
 316  *
 317  * Use ovsthread_once, like this, instead:
 318  *
 319  *     static struct ovsthread_once once = OVSTHREAD_ONCE_INITIALIZER;
 320  *
 321  *     if (ovsthread_once_start(&once)) {
 322  *         ...initialization...
 323  *         ovsthread_once_done(&once);
 324  *     }
 325  */
 326
 327 struct ovsthread_once {
 328     atomic_bool done;
 329     pthread_mutex_t mutex;
 330 };
 331
 332 #define OVSTHREAD_ONCE_INITIALIZER              \
 333     {                                           \
 334         ATOMIC_VAR_INIT(false),                 \
 335         PTHREAD_ADAPTIVE_MUTEX_INITIALIZER,     \
 336     }
 337
 338 static inline bool ovsthread_once_start(struct ovsthread_once *);
 339 void ovsthread_once_done(struct ovsthread_once *once) OVS_RELEASES(once);
 340
 341 bool ovsthread_once_start__(struct ovsthread_once *);
 342
 343 static inline bool
 344 ovsthread_once_is_done__(const struct ovsthread_once *once)
 345 {
 346     bool done;
 347
 348     atomic_read_explicit(&once->done, &done, memory_order_relaxed);
 349     return done;
 350 }
 351
 352 /* Returns true if this is the first call to ovsthread_once_start() for
 353  * 'once'.  In this case, the caller should perform whatever initialization
 354  * actions it needs to do, then call ovsthread_once_done() for 'once'.
 355  *
 356  * Returns false if this is not the first call to ovsthread_once_start() for
 357  * 'once'.  In this case, the call will not return until after
 358  * ovsthread_once_done() has been called. */
 359 static inline bool
 360 ovsthread_once_start(struct ovsthread_once *once)
 361 {
 362     return OVS_UNLIKELY(!ovsthread_once_is_done__(once)
 363                         && !ovsthread_once_start__(once));
 364 }
 365
 366 #ifdef __CHECKER__
 367 #define ovsthread_once_start(ONCE) \
 368     ((ONCE)->done ? false : ({ OVS_ACQUIRE(ONCE); true; }))
 369 #endif
 370 \f
 371 void assert_single_threaded(const char *where);
 372 #define assert_single_threaded() assert_single_threaded(SOURCE_LOCATOR)
 373
 374 pid_t xfork(const char *where);
 375 #define xfork() xfork(SOURCE_LOCATOR)
 376
 377 void forbid_forking(const char *reason);
 378 bool may_fork(void);
 379
 380 #endif /* ovs-thread.h */