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_destroy(pthread_mutex_t *);
  62 void xpthread_mutex_lock(pthread_mutex_t *mutex) OVS_ACQUIRES(mutex);
  63 void xpthread_mutex_unlock(pthread_mutex_t *mutex) OVS_RELEASES(mutex);
  64 int xpthread_mutex_trylock(pthread_mutex_t *);
  65
  66 void xpthread_mutexattr_init(pthread_mutexattr_t *);
  67 void xpthread_mutexattr_destroy(pthread_mutexattr_t *);
  68 void xpthread_mutexattr_settype(pthread_mutexattr_t *, int type);
  69 void xpthread_mutexattr_gettype(pthread_mutexattr_t *, int *typep);
  70
  71 void xpthread_rwlock_init(pthread_rwlock_t *, pthread_rwlockattr_t *);
  72 void xpthread_rwlock_destroy(pthread_rwlock_t *);
  73 void xpthread_rwlock_rdlock(pthread_rwlock_t *rwlock) OVS_ACQUIRES(rwlock);
  74 void xpthread_rwlock_wrlock(pthread_rwlock_t *rwlock) OVS_ACQUIRES(rwlock);
  75 void xpthread_rwlock_unlock(pthread_rwlock_t *rwlock) OVS_RELEASES(rwlock);
  76 int xpthread_rwlock_tryrdlock(pthread_rwlock_t *);
  77 int xpthread_rwlock_trywrlock(pthread_rwlock_t *);
  78
  79 void xpthread_cond_init(pthread_cond_t *, pthread_condattr_t *);
  80 void xpthread_cond_destroy(pthread_cond_t *);
  81 void xpthread_cond_signal(pthread_cond_t *);
  82 void xpthread_cond_broadcast(pthread_cond_t *);
  83 void xpthread_cond_wait(pthread_cond_t *, pthread_mutex_t *mutex)
  84     OVS_MUST_HOLD(mutex);
  85
  86 #ifdef __CHECKER__
  87 /* Replace these functions by the macros already defined in the <pthread.h>
  88  * annotations, because the macro definitions have correct semantics for the
  89  * conditional acquisition that can't be captured in a function annotation.
  90  * The difference in semantics from pthread_*() to xpthread_*() does not matter
  91  * because sparse is not a compiler. */
  92 #define xpthread_mutex_trylock pthread_mutex_trylock
  93 #define xpthread_rwlock_tryrdlock pthread_rwlock_tryrdlock
  94 #define xpthread_rwlock_trywrlock pthread_rwlock_trywrlock
  95 #endif
  96
  97 void xpthread_key_create(pthread_key_t *, void (*destructor)(void *));
  98
  99 void xpthread_create(pthread_t *, pthread_attr_t *, void *(*)(void *), void *);
 100 \f
 101 /* Per-thread data.
 102  *
 103  * Multiple forms of per-thread data exist, each with its own pluses and
 104  * minuses:
 105  *
 106  *     - POSIX per-thread data via pthread_key_t is portable to any pthreads
 107  *       implementation, and allows a destructor function to be defined.  It
 108  *       only (directly) supports per-thread pointers, which are always
 109  *       initialized to NULL.  It requires once-only allocation of a
 110  *       pthread_key_t value.  It is relatively slow.
 111  *
 112  *     - The thread_local feature newly defined in C11 <threads.h> works with
 113  *       any data type and initializer, and it is fast.  thread_local does not
 114  *       require once-only initialization like pthread_key_t.  C11 does not
 115  *       define what happens if one attempts to access a thread_local object
 116  *       from a thread other than the one to which that object belongs.  There
 117  *       is no provision to call a user-specified destructor when a thread
 118  *       ends.
 119  *
 120  *     - The __thread keyword is a GCC extension similar to thread_local but
 121  *       with a longer history.  __thread is not portable to every GCC version
 122  *       or environment.  __thread does not restrict the use of a thread-local
 123  *       object outside its own thread.
 124  *
 125  * Here's a handy summary:
 126  *
 127  *                     pthread_key_t     thread_local       __thread
 128  *                     -------------     ------------     -------------
 129  * portability             high               low             medium
 130  * speed                    low              high               high
 131  * supports destructors?    yes                no                 no
 132  * needs key allocation?    yes                no                 no
 133  * arbitrary initializer?    no               yes                yes
 134  * cross-thread access?     yes                no                yes
 135  */
 136
 137 /* DEFINE_PER_THREAD_DATA(TYPE, NAME, INITIALIZER).
 138  *
 139  * One should prefer to use POSIX per-thread data, via pthread_key_t, when its
 140  * performance is acceptable, because of its portability (see the table above).
 141  * This macro is an alternatives that takes advantage of thread_local (and
 142  * __thread), for its performance, when it is available, and falls back to
 143  * POSIX per-thread data otherwise.
 144  *
 145  * Defines per-thread variable NAME with the given TYPE, initialized to
 146  * INITIALIZER (which must be valid as an initializer for a variable with
 147  * static lifetime).
 148  *
 149  * The public interface to the variable is:
 150  *
 151  *    TYPE *NAME_get(void)
 152  *    TYPE *NAME_get_unsafe(void)
 153  *
 154  *       Returns the address of this thread's instance of NAME.
 155  *
 156  *       Use NAME_get() in a context where this might be the first use of the
 157  *       per-thread variable in the program.  Use NAME_get_unsafe(), which
 158  *       avoids a conditional test and is thus slightly faster, in a context
 159  *       where one knows that NAME_get() has already been called previously.
 160  *
 161  * There is no "NAME_set()" (or "NAME_set_unsafe()") function.  To set the
 162  * value of the per-thread variable, dereference the pointer returned by
 163  * TYPE_get() or TYPE_get_unsafe(), e.g. *TYPE_get() = 0.
 164  */
 165 #if HAVE_THREAD_LOCAL || HAVE___THREAD
 166
 167 #if HAVE_THREAD_LOCAL
 168 #include <threads.h>
 169 #elif HAVE___THREAD
 170 #define thread_local __thread
 171 #else
 172 #error
 173 #endif
 174
 175 #define DEFINE_PER_THREAD_DATA(TYPE, NAME, ...)                 \
 176     typedef TYPE NAME##_type;                                   \
 177     static thread_local NAME##_type NAME##_var = __VA_ARGS__;   \
 178                                                                 \
 179     static NAME##_type *                                        \
 180     NAME##_get_unsafe(void)                                     \
 181     {                                                           \
 182         return &NAME##_var;                                     \
 183     }                                                           \
 184                                                                 \
 185     static NAME##_type *                                        \
 186     NAME##_get(void)                                            \
 187     {                                                           \
 188         return NAME##_get_unsafe();                             \
 189     }
 190 #else  /* no C implementation support for thread-local storage  */
 191 #define DEFINE_PER_THREAD_DATA(TYPE, NAME, ...)                         \
 192     typedef TYPE NAME##_type;                                           \
 193     static pthread_key_t NAME##_key;                                    \
 194                                                                         \
 195     static NAME##_type *                                                \
 196     NAME##_get_unsafe(void)                                             \
 197     {                                                                   \
 198         return pthread_getspecific(NAME##_key);                         \
 199     }                                                                   \
 200                                                                         \
 201     static void                                                         \
 202     NAME##_once_init(void)                                              \
 203     {                                                                   \
 204         if (pthread_key_create(&NAME##_key, free)) {                    \
 205             abort();                                                    \
 206         }                                                               \
 207     }                                                                   \
 208                                                                         \
 209     static NAME##_type *                                                \
 210     NAME##_get(void)                                                    \
 211     {                                                                   \
 212         static pthread_once_t once = PTHREAD_ONCE_INIT;                 \
 213         NAME##_type *value;                                             \
 214                                                                         \
 215         pthread_once(&once, NAME##_once_init);                          \
 216         value = NAME##_get_unsafe();                                    \
 217         if (!value) {                                                   \
 218             static const NAME##_type initial_value = __VA_ARGS__;       \
 219                                                                         \
 220             value = xmalloc(sizeof *value);                             \
 221             *value = initial_value;                                     \
 222             pthread_setspecific(NAME##_key, value);                     \
 223         }                                                               \
 224         return value;                                                   \
 225     }
 226 #endif
 227
 228 /* DEFINE_PER_THREAD_MALLOCED_DATA(TYPE, NAME).
 229  *
 230  * This is a simple wrapper around POSIX per-thread data primitives.  It
 231  * defines per-thread variable NAME with the given TYPE, which must be a
 232  * pointer type.  In each thread, the per-thread variable is initialized to
 233  * NULL.  When a thread terminates, the variable is freed with free().
 234  *
 235  * The public interface to the variable is:
 236  *
 237  *    TYPE NAME_get(void)
 238  *    TYPE NAME_get_unsafe(void)
 239  *
 240  *       Returns the value of per-thread variable NAME in this thread.
 241  *
 242  *       Use NAME_get() in a context where this might be the first use of the
 243  *       per-thread variable in the program.  Use NAME_get_unsafe(), which
 244  *       avoids a conditional test and is thus slightly faster, in a context
 245  *       where one knows that NAME_get() has already been called previously.
 246  *
 247  *    TYPE NAME_set(TYPE new_value)
 248  *    TYPE NAME_set_unsafe(TYPE new_value)
 249  *
 250  *       Sets the value of per-thread variable NAME to 'new_value' in this
 251  *       thread, and returns its previous value.
 252  *
 253  *       Use NAME_set() in a context where this might be the first use of the
 254  *       per-thread variable in the program.  Use NAME_set_unsafe(), which
 255  *       avoids a conditional test and is thus slightly faster, in a context
 256  *       where one knows that NAME_set() has already been called previously.
 257  */
 258 #define DEFINE_PER_THREAD_MALLOCED_DATA(TYPE, NAME)     \
 259     static pthread_key_t NAME##_key;                    \
 260                                                         \
 261     static void                                         \
 262     NAME##_once_init(void)                              \
 263     {                                                   \
 264         if (pthread_key_create(&NAME##_key, free)) {    \
 265             abort();                                    \
 266         }                                               \
 267     }                                                   \
 268                                                         \
 269     static void                                         \
 270     NAME##_init(void)                                   \
 271     {                                                   \
 272         static pthread_once_t once = PTHREAD_ONCE_INIT; \
 273         pthread_once(&once, NAME##_once_init);          \
 274     }                                                   \
 275                                                         \
 276     static TYPE                                         \
 277     NAME##_get_unsafe(void)                             \
 278     {                                                   \
 279         return pthread_getspecific(NAME##_key);         \
 280     }                                                   \
 281                                                         \
 282     static OVS_UNUSED TYPE                              \
 283     NAME##_get(void)                                    \
 284     {                                                   \
 285         NAME##_init();                                  \
 286         return NAME##_get_unsafe();                     \
 287     }                                                   \
 288                                                         \
 289     static TYPE                                         \
 290     NAME##_set_unsafe(TYPE value)                       \
 291     {                                                   \
 292         TYPE old_value = NAME##_get_unsafe();           \
 293         pthread_setspecific(NAME##_key, value);         \
 294         return old_value;                               \
 295     }                                                   \
 296                                                         \
 297     static OVS_UNUSED TYPE                              \
 298     NAME##_set(TYPE value)                              \
 299     {                                                   \
 300         NAME##_init();                                  \
 301         return NAME##_set_unsafe(value);                \
 302     }
 303 \f
 304 /* Convenient once-only execution.
 305  *
 306  *
 307  * Problem
 308  * =======
 309  *
 310  * POSIX provides pthread_once_t and pthread_once() as primitives for running a
 311  * set of code only once per process execution.  They are used like this:
 312  *
 313  *     static void run_once(void) { ...initialization... }
 314  *     static pthread_once_t once = PTHREAD_ONCE_INIT;
 315  * ...
 316  *     pthread_once(&once, run_once);
 317  *
 318  * pthread_once() does not allow passing any parameters to the initialization
 319  * function, which is often inconvenient, because it means that the function
 320  * can only access data declared at file scope.
 321  *
 322  *
 323  * Solution
 324  * ========
 325  *
 326  * Use ovsthread_once, like this, instead:
 327  *
 328  *     static struct ovsthread_once once = OVSTHREAD_ONCE_INITIALIZER;
 329  *
 330  *     if (ovsthread_once_start(&once)) {
 331  *         ...initialization...
 332  *         ovsthread_once_done(&once);
 333  *     }
 334  */
 335
 336 struct ovsthread_once {
 337     atomic_bool done;
 338     pthread_mutex_t mutex;
 339 };
 340
 341 #define OVSTHREAD_ONCE_INITIALIZER              \
 342     {                                           \
 343         ATOMIC_VAR_INIT(false),                 \
 344         PTHREAD_ADAPTIVE_MUTEX_INITIALIZER,     \
 345     }
 346
 347 static inline bool ovsthread_once_start(struct ovsthread_once *);
 348 void ovsthread_once_done(struct ovsthread_once *once) OVS_RELEASES(once);
 349
 350 bool ovsthread_once_start__(struct ovsthread_once *);
 351
 352 static inline bool
 353 ovsthread_once_is_done__(const struct ovsthread_once *once)
 354 {
 355     bool done;
 356
 357     atomic_read_explicit(&once->done, &done, memory_order_relaxed);
 358     return done;
 359 }
 360
 361 /* Returns true if this is the first call to ovsthread_once_start() for
 362  * 'once'.  In this case, the caller should perform whatever initialization
 363  * actions it needs to do, then call ovsthread_once_done() for 'once'.
 364  *
 365  * Returns false if this is not the first call to ovsthread_once_start() for
 366  * 'once'.  In this case, the call will not return until after
 367  * ovsthread_once_done() has been called. */
 368 static inline bool
 369 ovsthread_once_start(struct ovsthread_once *once)
 370 {
 371     return OVS_UNLIKELY(!ovsthread_once_is_done__(once)
 372                         && !ovsthread_once_start__(once));
 373 }
 374
 375 #ifdef __CHECKER__
 376 #define ovsthread_once_start(ONCE) \
 377     ((ONCE)->done ? false : ({ OVS_ACQUIRE(ONCE); true; }))
 378 #endif
 379 \f
 380 void assert_single_threaded(const char *where);
 381 #define assert_single_threaded() assert_single_threaded(SOURCE_LOCATOR)
 382
 383 pid_t xfork(const char *where);
 384 #define xfork() xfork(SOURCE_LOCATOR)
 385
 386 void forbid_forking(const char *reason);
 387 bool may_fork(void);
 388
 389 #endif /* ovs-thread.h */