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
  60 void xpthread_mutex_init(pthread_mutex_t *, pthread_mutexattr_t *);
  61 void xpthread_mutex_lock(pthread_mutex_t *mutex) OVS_ACQUIRES(mutex);
  62 void xpthread_mutex_unlock(pthread_mutex_t *mutex) OVS_RELEASES(mutex);
  63 int xpthread_mutex_trylock(pthread_mutex_t *);
  64
  65 void xpthread_mutexattr_init(pthread_mutexattr_t *);
  66 void xpthread_mutexattr_destroy(pthread_mutexattr_t *);
  67 void xpthread_mutexattr_settype(pthread_mutexattr_t *, int type);
  68 void xpthread_mutexattr_gettype(pthread_mutexattr_t *, int *typep);
  69
  70 void xpthread_rwlock_init(pthread_rwlock_t *, pthread_rwlockattr_t *);
  71 void xpthread_rwlock_rdlock(pthread_rwlock_t *rwlock) OVS_ACQUIRES(rwlock);
  72 void xpthread_rwlock_wrlock(pthread_rwlock_t *rwlock) OVS_ACQUIRES(rwlock);
  73 void xpthread_rwlock_unlock(pthread_rwlock_t *rwlock) OVS_RELEASES(rwlock);
  74 int xpthread_rwlock_tryrdlock(pthread_rwlock_t *);
  75 int xpthread_rwlock_trywrlock(pthread_rwlock_t *);
  76
  77 void xpthread_cond_init(pthread_cond_t *, pthread_condattr_t *);
  78 void xpthread_cond_signal(pthread_cond_t *);
  79 void xpthread_cond_broadcast(pthread_cond_t *);
  80 void xpthread_cond_wait(pthread_cond_t *, pthread_mutex_t *mutex)
  81     OVS_MUST_HOLD(mutex);
  82
  83 #ifdef __CHECKER__
  84 /* Replace these functions by the macros already defined in the <pthread.h>
  85  * annotations, because the macro definitions have correct semantics for the
  86  * conditional acquisition that can't be captured in a function annotation.
  87  * The difference in semantics from pthread_*() to xpthread_*() does not matter
  88  * because sparse is not a compiler. */
  89 #define xpthread_mutex_trylock pthread_mutex_trylock
  90 #define xpthread_rwlock_tryrdlock pthread_rwlock_tryrdlock
  91 #define xpthread_rwlock_trywrlock pthread_rwlock_trywrlock
  92 #endif
  93
  94 void xpthread_key_create(pthread_key_t *, void (*destructor)(void *));
  95
  96 void xpthread_create(pthread_t *, pthread_attr_t *, void *(*)(void *), void *);
  97 \f
  98 /* Per-thread data.
  99  *
 100  * Multiple forms of per-thread data exist, each with its own pluses and
 101  * minuses:
 102  *
 103  *     - POSIX per-thread data via pthread_key_t is portable to any pthreads
 104  *       implementation, and allows a destructor function to be defined.  It
 105  *       only (directly) supports per-thread pointers, which are always
 106  *       initialized to NULL.  It requires once-only allocation of a
 107  *       pthread_key_t value.  It is relatively slow.
 108  *
 109  *     - The thread_local feature newly defined in C11 <threads.h> works with
 110  *       any data type and initializer, and it is fast.  thread_local does not
 111  *       require once-only initialization like pthread_key_t.  C11 does not
 112  *       define what happens if one attempts to access a thread_local object
 113  *       from a thread other than the one to which that object belongs.  There
 114  *       is no provision to call a user-specified destructor when a thread
 115  *       ends.
 116  *
 117  *     - The __thread keyword is a GCC extension similar to thread_local but
 118  *       with a longer history.  __thread is not portable to every GCC version
 119  *       or environment.  __thread does not restrict the use of a thread-local
 120  *       object outside its own thread.
 121  *
 122  * Here's a handy summary:
 123  *
 124  *                     pthread_key_t     thread_local       __thread
 125  *                     -------------     ------------     -------------
 126  * portability             high               low             medium
 127  * speed                    low              high               high
 128  * supports destructors?    yes                no                 no
 129  * needs key allocation?    yes                no                 no
 130  * arbitrary initializer?    no               yes                yes
 131  * cross-thread access?     yes                no                yes
 132  */
 133
 134 /* DEFINE_PER_THREAD_DATA(TYPE, NAME, INITIALIZER).
 135  *
 136  * One should prefer to use POSIX per-thread data, via pthread_key_t, when its
 137  * performance is acceptable, because of its portability (see the table above).
 138  * This macro is an alternatives that takes advantage of thread_local (and
 139  * __thread), for its performance, when it is available, and falls back to
 140  * POSIX per-thread data otherwise.
 141  *
 142  * Defines per-thread variable NAME with the given TYPE, initialized to
 143  * INITIALIZER (which must be valid as an initializer for a variable with
 144  * static lifetime).
 145  *
 146  * The public interface to the variable is:
 147  *
 148  *    TYPE *NAME_get(void)
 149  *    TYPE *NAME_get_unsafe(void)
 150  *
 151  *       Returns the address of this thread's instance of NAME.
 152  *
 153  *       Use NAME_get() in a context where this might be the first use of the
 154  *       per-thread variable in the program.  Use NAME_get_unsafe(), which
 155  *       avoids a conditional test and is thus slightly faster, in a context
 156  *       where one knows that NAME_get() has already been called previously.
 157  *
 158  * There is no "NAME_set()" (or "NAME_set_unsafe()") function.  To set the
 159  * value of the per-thread variable, dereference the pointer returned by
 160  * TYPE_get() or TYPE_get_unsafe(), e.g. *TYPE_get() = 0.
 161  */
 162 #if HAVE_THREAD_LOCAL || HAVE___THREAD
 163
 164 #if HAVE_THREAD_LOCAL
 165 #include <threads.h>
 166 #elif HAVE___THREAD
 167 #define thread_local __thread
 168 #else
 169 #error
 170 #endif
 171
 172 #define DEFINE_PER_THREAD_DATA(TYPE, NAME, ...)                 \
 173     typedef TYPE NAME##_type;                                   \
 174     static thread_local NAME##_type NAME##_var = __VA_ARGS__;   \
 175                                                                 \
 176     static NAME##_type *                                        \
 177     NAME##_get_unsafe(void)                                     \
 178     {                                                           \
 179         return &NAME##_var;                                     \
 180     }                                                           \
 181                                                                 \
 182     static NAME##_type *                                        \
 183     NAME##_get(void)                                            \
 184     {                                                           \
 185         return NAME##_get_unsafe();                             \
 186     }
 187 #else  /* no C implementation support for thread-local storage  */
 188 #define DEFINE_PER_THREAD_DATA(TYPE, NAME, ...)                         \
 189     typedef TYPE NAME##_type;                                           \
 190     static pthread_key_t NAME##_key;                                    \
 191                                                                         \
 192     static NAME##_type *                                                \
 193     NAME##_get_unsafe(void)                                             \
 194     {                                                                   \
 195         return pthread_getspecific(NAME##_key);                         \
 196     }                                                                   \
 197                                                                         \
 198     static void                                                         \
 199     NAME##_once_init(void)                                              \
 200     {                                                                   \
 201         if (pthread_key_create(&NAME##_key, free)) {                    \
 202             abort();                                                    \
 203         }                                                               \
 204     }                                                                   \
 205                                                                         \
 206     static NAME##_type *                                                \
 207     NAME##_get(void)                                                    \
 208     {                                                                   \
 209         static pthread_once_t once = PTHREAD_ONCE_INIT;                 \
 210         NAME##_type *value;                                             \
 211                                                                         \
 212         pthread_once(&once, NAME##_once_init);                          \
 213         value = NAME##_get_unsafe();                                    \
 214         if (!value) {                                                   \
 215             static const NAME##_type initial_value = __VA_ARGS__;       \
 216                                                                         \
 217             value = xmalloc(sizeof *value);                             \
 218             *value = initial_value;                                     \
 219             pthread_setspecific(NAME##_key, value);                     \
 220         }                                                               \
 221         return value;                                                   \
 222     }
 223 #endif
 224
 225 /* DEFINE_PER_THREAD_MALLOCED_DATA(TYPE, NAME).
 226  *
 227  * This is a simple wrapper around POSIX per-thread data primitives.  It
 228  * defines per-thread variable NAME with the given TYPE, which must be a
 229  * pointer type.  In each thread, the per-thread variable is initialized to
 230  * NULL.  When a thread terminates, the variable is freed with free().
 231  *
 232  * The public interface to the variable is:
 233  *
 234  *    TYPE NAME_get(void)
 235  *    TYPE NAME_get_unsafe(void)
 236  *
 237  *       Returns the value of per-thread variable NAME in this thread.
 238  *
 239  *       Use NAME_get() in a context where this might be the first use of the
 240  *       per-thread variable in the program.  Use NAME_get_unsafe(), which
 241  *       avoids a conditional test and is thus slightly faster, in a context
 242  *       where one knows that NAME_get() has already been called previously.
 243  *
 244  *    TYPE NAME_set(TYPE new_value)
 245  *    TYPE NAME_set_unsafe(TYPE new_value)
 246  *
 247  *       Sets the value of per-thread variable NAME to 'new_value' in this
 248  *       thread, and returns its previous value.
 249  *
 250  *       Use NAME_set() in a context where this might be the first use of the
 251  *       per-thread variable in the program.  Use NAME_set_unsafe(), which
 252  *       avoids a conditional test and is thus slightly faster, in a context
 253  *       where one knows that NAME_set() has already been called previously.
 254  */
 255 #define DEFINE_PER_THREAD_MALLOCED_DATA(TYPE, NAME)     \
 256     static pthread_key_t NAME##_key;                    \
 257                                                         \
 258     static void                                         \
 259     NAME##_once_init(void)                              \
 260     {                                                   \
 261         if (pthread_key_create(&NAME##_key, free)) {    \
 262             abort();                                    \
 263         }                                               \
 264     }                                                   \
 265                                                         \
 266     static void                                         \
 267     NAME##_init(void)                                   \
 268     {                                                   \
 269         static pthread_once_t once = PTHREAD_ONCE_INIT; \
 270         pthread_once(&once, NAME##_once_init);          \
 271     }                                                   \
 272                                                         \
 273     static TYPE                                         \
 274     NAME##_get_unsafe(void)                             \
 275     {                                                   \
 276         return pthread_getspecific(NAME##_key);         \
 277     }                                                   \
 278                                                         \
 279     static OVS_UNUSED TYPE                              \
 280     NAME##_get(void)                                    \
 281     {                                                   \
 282         NAME##_init();                                  \
 283         return NAME##_get_unsafe();                     \
 284     }                                                   \
 285                                                         \
 286     static TYPE                                         \
 287     NAME##_set_unsafe(TYPE value)                       \
 288     {                                                   \
 289         TYPE old_value = NAME##_get_unsafe();           \
 290         pthread_setspecific(NAME##_key, value);         \
 291         return old_value;                               \
 292     }                                                   \
 293                                                         \
 294     static OVS_UNUSED TYPE                              \
 295     NAME##_set(TYPE value)                              \
 296     {                                                   \
 297         NAME##_init();                                  \
 298         return NAME##_set_unsafe(value);                \
 299     }
 300 \f
 301 /* Convenient once-only execution.
 302  *
 303  *
 304  * Problem
 305  * =======
 306  *
 307  * POSIX provides pthread_once_t and pthread_once() as primitives for running a
 308  * set of code only once per process execution.  They are used like this:
 309  *
 310  *     static void run_once(void) { ...initialization... }
 311  *     static pthread_once_t once = PTHREAD_ONCE_INIT;
 312  * ...
 313  *     pthread_once(&once, run_once);
 314  *
 315  * pthread_once() does not allow passing any parameters to the initialization
 316  * function, which is often inconvenient, because it means that the function
 317  * can only access data declared at file scope.
 318  *
 319  *
 320  * Solution
 321  * ========
 322  *
 323  * Use ovsthread_once, like this, instead:
 324  *
 325  *     static struct ovsthread_once once = OVSTHREAD_ONCE_INITIALIZER;
 326  *
 327  *     if (ovsthread_once_start(&once)) {
 328  *         ...initialization...
 329  *         ovsthread_once_done(&once);
 330  *     }
 331  */
 332
 333 struct ovsthread_once {
 334     atomic_bool done;
 335     pthread_mutex_t mutex;
 336 };
 337
 338 #define OVSTHREAD_ONCE_INITIALIZER              \
 339     {                                           \
 340         ATOMIC_VAR_INIT(false),                 \
 341         PTHREAD_ADAPTIVE_MUTEX_INITIALIZER,     \
 342     }
 343
 344 static inline bool ovsthread_once_start(struct ovsthread_once *);
 345 void ovsthread_once_done(struct ovsthread_once *once) OVS_RELEASES(once);
 346
 347 bool ovsthread_once_start__(struct ovsthread_once *);
 348
 349 static inline bool
 350 ovsthread_once_is_done__(const struct ovsthread_once *once)
 351 {
 352     bool done;
 353
 354     atomic_read_explicit(&once->done, &done, memory_order_relaxed);
 355     return done;
 356 }
 357
 358 /* Returns true if this is the first call to ovsthread_once_start() for
 359  * 'once'.  In this case, the caller should perform whatever initialization
 360  * actions it needs to do, then call ovsthread_once_done() for 'once'.
 361  *
 362  * Returns false if this is not the first call to ovsthread_once_start() for
 363  * 'once'.  In this case, the call will not return until after
 364  * ovsthread_once_done() has been called. */
 365 static inline bool
 366 ovsthread_once_start(struct ovsthread_once *once)
 367 {
 368     return OVS_UNLIKELY(!ovsthread_once_is_done__(once)
 369                         && !ovsthread_once_start__(once));
 370 }
 371
 372 #ifdef __CHECKER__
 373 #define ovsthread_once_start(ONCE) \
 374     ((ONCE)->done ? false : ({ OVS_ACQUIRE(ONCE); true; }))
 375 #endif
 376 \f
 377 void assert_single_threaded(const char *where);
 378 #define assert_single_threaded() assert_single_threaded(SOURCE_LOCATOR)
 379
 380 pid_t xfork(const char *where);
 381 #define xfork() xfork(SOURCE_LOCATOR)
 382
 383 void forbid_forking(const char *reason);
 384 bool may_fork(void);
 385
 386 #endif /* ovs-thread.h */