text: /*
   * Copyright (c) 2013, 2014 Nicira, Inc.
   *
   * Licensed under the Apache License, Version 2.0 (the "License");
   * you may not use this file except in compliance with the License.
   * You may obtain a copy of the License at:
   *
   *     http://www.apache.org/licenses/LICENSE-2.0
   *
   * Unless required by applicable law or agreed to in writing, software
   * distributed under the License is distributed on an "AS IS" BASIS,
   * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
   * See the License for the specific language governing permissions and
   * limitations under the License.
   */
  
  #ifndef OVS_THREAD_H
  #define OVS_THREAD_H 1
  
  #include <pthread.h>
  #include <stddef.h>
  #include <sys/types.h>
  #include "ovs-atomic.h"
  #include "openvswitch/thread.h"
  #include "util.h"
  
  struct seq;
  
  /* Poll-block()-able barrier similar to pthread_barrier_t. */
  struct ovs_barrier {
      uint32_t size;            /* Number of threads to wait. */
      atomic_count count;       /* Number of threads already hit the barrier. */
      struct seq *seq;
  };
  
  /* Wrappers for pthread_mutex_*() that abort the process on any error.
   * This is still needed when ovs-atomic-pthreads.h is used. */
  void xpthread_mutex_lock(pthread_mutex_t *mutex);
  void xpthread_mutex_unlock(pthread_mutex_t *mutex);
  
  /* Wrappers for pthread_mutexattr_*() that abort the process on any error. */
  void xpthread_mutexattr_init(pthread_mutexattr_t *);
  void xpthread_mutexattr_destroy(pthread_mutexattr_t *);
  void xpthread_mutexattr_settype(pthread_mutexattr_t *, int type);
  void xpthread_mutexattr_gettype(pthread_mutexattr_t *, int *typep);
  
  /* Read-write lock.
   *
   * An ovs_rwlock does not support recursive readers, because POSIX allows
   * taking the reader lock recursively to deadlock when a thread is waiting on
   * the write-lock.  (NetBSD does deadlock.)  glibc rwlocks in their default
   * configuration do not deadlock, but ovs_rwlock_init() initializes rwlocks as
   * non-recursive (which will deadlock) for two reasons:
   *
   *     - glibc only provides fairness to writers in this mode.
   *
   *     - It's better to find bugs in the primary Open vSwitch target rather
   *       than exposing them only to porters. */
  struct OVS_LOCKABLE ovs_rwlock {
      pthread_rwlock_t lock;
      const char *where;          /* NULL if and only if uninitialized. */
  };
  
  /* Initializer. */
  #ifdef PTHREAD_RWLOCK_WRITER_NONRECURSIVE_INITIALIZER_NP
  #define OVS_RWLOCK_INITIALIZER \
          { PTHREAD_RWLOCK_WRITER_NONRECURSIVE_INITIALIZER_NP, "<unlocked>" }
  #else
  #define OVS_RWLOCK_INITIALIZER { PTHREAD_RWLOCK_INITIALIZER, "<unlocked>" }
  #endif
  
  /* ovs_rwlock functions analogous to pthread_rwlock_*() functions.
   *
   * Most of these functions abort the process with an error message on any
   * error.  The "trylock" functions are exception: they pass through a 0 or
   * EBUSY return value to the caller and abort on any other error. */
  void ovs_rwlock_init(const struct ovs_rwlock *);
  void ovs_rwlock_destroy(const struct ovs_rwlock *);
  void ovs_rwlock_unlock(const struct ovs_rwlock *rwlock) OVS_RELEASES(rwlock);
  
  /* Wrappers for pthread_rwlockattr_*() that abort the process on any error. */
  void xpthread_rwlockattr_init(pthread_rwlockattr_t *);
  void xpthread_rwlockattr_destroy(pthread_rwlockattr_t *);
  #ifdef PTHREAD_RWLOCK_WRITER_NONRECURSIVE_INITIALIZER_NP
  void xpthread_rwlockattr_setkind_np(pthread_rwlockattr_t *, int kind);
  #endif
  
  void ovs_rwlock_wrlock_at(const struct ovs_rwlock *rwlock, const char *where)
      OVS_ACQ_WRLOCK(rwlock);
  #define ovs_rwlock_wrlock(rwlock) \
          ovs_rwlock_wrlock_at(rwlock, OVS_SOURCE_LOCATOR)
  
  int ovs_rwlock_trywrlock_at(const struct ovs_rwlock *rwlock, const char *where)
      OVS_TRY_WRLOCK(0, rwlock);
  #define ovs_rwlock_trywrlock(rwlock) \
      ovs_rwlock_trywrlock_at(rwlock, OVS_SOURCE_LOCATOR)
  
  void ovs_rwlock_rdlock_at(const struct ovs_rwlock *rwlock, const char *where)
      OVS_ACQ_RDLOCK(rwlock);
  #define ovs_rwlock_rdlock(rwlock) \
          ovs_rwlock_rdlock_at(rwlock, OVS_SOURCE_LOCATOR)
  
  int ovs_rwlock_tryrdlock_at(const struct ovs_rwlock *rwlock, const char *where)
      OVS_TRY_RDLOCK(0, rwlock);
  #define ovs_rwlock_tryrdlock(rwlock) \
          ovs_rwlock_tryrdlock_at(rwlock, OVS_SOURCE_LOCATOR)
  
  /* ovs_barrier functions analogous to pthread_barrier_*() functions. */
  void ovs_barrier_init(struct ovs_barrier *, uint32_t count);
  void ovs_barrier_destroy(struct ovs_barrier *);
  void ovs_barrier_block(struct ovs_barrier *);
  
  /* Wrappers for xpthread_cond_*() that abort the process on any error.
   *
   * Use ovs_mutex_cond_wait() to wait for a condition. */
  void xpthread_cond_init(pthread_cond_t *, pthread_condattr_t *);
  void xpthread_cond_destroy(pthread_cond_t *);
  void xpthread_cond_signal(pthread_cond_t *);
  void xpthread_cond_broadcast(pthread_cond_t *);
  
  void xpthread_key_create(pthread_key_t *, void (*destructor)(void *));
  void xpthread_key_delete(pthread_key_t);
  void xpthread_setspecific(pthread_key_t, const void *);
  
  #ifndef _WIN32
  void xpthread_sigmask(int, const sigset_t *, sigset_t *);
  #endif
  
  pthread_t ovs_thread_create(const char *name, void *(*)(void *), void *);
  void xpthread_join(pthread_t, void **);
  
  /* Per-thread data.
   *
   *
   * Standard Forms
   * ==============
   *
   * Multiple forms of standard per-thread data exist, each with its own pluses
   * and minuses.  In general, if one of these forms is appropriate, then it's a
   * good idea to use it:
   *
   *     - POSIX per-thread data via pthread_key_t is portable to any pthreads
   *       implementation, and allows a destructor function to be defined.  It
   *       only (directly) supports per-thread pointers, which are always
   *       initialized to NULL.  It requires once-only allocation of a
   *       pthread_key_t value.  It is relatively slow.  Typically few
   *       "pthread_key_t"s are available (POSIX requires only at least 128,
   *       glibc supplies only 1024).
   *
   *     - The thread_local feature newly defined in C11 <threads.h> works with
   *       any data type and initializer, and it is fast.  thread_local does not
   *       require once-only initialization like pthread_key_t.  C11 does not
   *       define what happens if one attempts to access a thread_local object
   *       from a thread other than the one to which that object belongs.  There
   *       is no provision to call a user-specified destructor when a thread
   *       ends.  Typical implementations allow for an arbitrary amount of
   *       thread_local storage, but statically allocated only.
   *
   *     - The __thread keyword is a GCC extension similar to thread_local but
   *       with a longer history.  __thread is not portable to every GCC version
   *       or environment.  __thread does not restrict the use of a thread-local
   *       object outside its own thread.
   *
   * Here's a handy summary:
   *
   *                     pthread_key_t     thread_local       __thread
   *                     -------------     ------------     -------------
   * portability             high               low             medium
   * speed                    low              high               high
   * supports destructors?    yes                no                 no
   * needs key allocation?    yes                no                 no
   * arbitrary initializer?    no               yes                yes
   * cross-thread access?     yes                no                yes
   * amount available?        few            arbitrary         arbitrary
   * dynamically allocated?   yes                no                 no
   *
   *
   * Extensions
   * ==========
   *
   * OVS provides some extensions and wrappers:
   *
   *     - In a situation where the performance of thread_local or __thread is
   *       desirable, but portability is required, DEFINE_STATIC_PER_THREAD_DATA
   *       and DECLARE_EXTERN_PER_THREAD_DATA/DEFINE_EXTERN_PER_THREAD_DATA may
   *       be appropriate (see below).
   *
   *     - DEFINE_PER_THREAD_MALLOCED_DATA can be convenient for simple
   *       per-thread malloc()'d buffers.
   *
   *     - struct ovs_tsd provides an alternative to pthread_key_t that isn't
   *       limited to a small number of keys.
   */
  
  /* For static data, use this macro in a source file:
   *
   *    DEFINE_STATIC_PER_THREAD_DATA(TYPE, NAME, INITIALIZER).
   *
   * For global data, "declare" the data in the header and "define" it in
   * the source file, with:
   *
   *    DECLARE_EXTERN_PER_THREAD_DATA(TYPE, NAME).
   *    DEFINE_EXTERN_PER_THREAD_DATA(NAME, INITIALIZER).
   *
   * One should prefer to use POSIX per-thread data, via pthread_key_t, when its
   * performance is acceptable, because of its portability (see the table above).
   * This macro is an alternatives that takes advantage of thread_local (and
   * __thread), for its performance, when it is available, and falls back to
   * POSIX per-thread data otherwise.
   *
   * Defines per-thread variable NAME with the given TYPE, initialized to
   * INITIALIZER (which must be valid as an initializer for a variable with
   * static lifetime).
   *
   * The public interface to the variable is:
   *
   *    TYPE *NAME_get(void)
   *    TYPE *NAME_get_unsafe(void)
   *
   *       Returns the address of this thread's instance of NAME.
   *
   *       Use NAME_get() in a context where this might be the first use of the
   *       per-thread variable in the program.  Use NAME_get_unsafe(), which
   *       avoids a conditional test and is thus slightly faster, in a context
   *       where one knows that NAME_get() has already been called previously.
   *
   * There is no "NAME_set()" (or "NAME_set_unsafe()") function.  To set the
   * value of the per-thread variable, dereference the pointer returned by
   * TYPE_get() or TYPE_get_unsafe(), e.g. *TYPE_get() = 0.
   */
  #if HAVE_THREAD_LOCAL || HAVE___THREAD
  
  #if HAVE_THREAD_LOCAL
  #include <threads.h>
  #elif HAVE___THREAD
  #define thread_local __thread
  #else
  #error
  #endif
  
  #define DEFINE_STATIC_PER_THREAD_DATA(TYPE, NAME, ...)                  \
      typedef TYPE NAME##_type;                                           \
                                                                          \
      static NAME##_type *                                                \
      NAME##_get_unsafe(void)                                             \
      {                                                                   \
          static thread_local NAME##_type var = __VA_ARGS__;              \
          return &var;                                                    \
      }                                                                   \
                                                                          \
      static NAME##_type *                                                \
      NAME##_get(void)                                                    \
      {                                                                   \
          return NAME##_get_unsafe();                                     \
      }
  #define DECLARE_EXTERN_PER_THREAD_DATA(TYPE, NAME)                      \
      typedef TYPE NAME##_type;                                           \
      extern thread_local NAME##_type NAME##_var;                         \
                                                                          \
      static inline NAME##_type *                                         \
      NAME##_get_unsafe(void)                                             \
      {                                                                   \
          return &NAME##_var;                                             \
      }                                                                   \
                                                                          \
      static inline NAME##_type *                                         \
      NAME##_get(void)                                                    \
      {                                                                   \
          return NAME##_get_unsafe();                                     \
      }
  #define DEFINE_EXTERN_PER_THREAD_DATA(NAME, ...)         \
      thread_local NAME##_type NAME##_var = __VA_ARGS__;
  #else  /* no C implementation support for thread-local storage  */
  #define DEFINE_STATIC_PER_THREAD_DATA(TYPE, NAME, ...)                  \
      typedef TYPE NAME##_type;                                           \
      static pthread_key_t NAME##_key;                                    \
                                                                          \
      static NAME##_type *                                                \
      NAME##_get_unsafe(void)                                             \
      {                                                                   \
          return pthread_getspecific(NAME##_key);                         \
      }                                                                   \
                                                                          \
      static void                                                         \
      NAME##_once_init(void)                                              \
      {                                                                   \
          if (pthread_key_create(&NAME##_key, free)) {                    \
              abort();                                                    \
          }                                                               \
      }                                                                   \
                                                                          \
      static NAME##_type *                                                \
      NAME##_get(void)                                                    \
      {                                                                   \
          static pthread_once_t once = PTHREAD_ONCE_INIT;                 \
          NAME##_type *value;                                             \
                                                                          \
          pthread_once(&once, NAME##_once_init);                          \
          value = NAME##_get_unsafe();                                    \
          if (!value) {                                                   \
              static const NAME##_type initial_value = __VA_ARGS__;       \
                                                                          \
              value = malloc(sizeof *value);                              \
              if (value == NULL) {                                        \
                  out_of_memory();                                        \
              }                                                           \
              *value = initial_value;                                     \
              xpthread_setspecific(NAME##_key, value);                    \
          }                                                               \
          return value;                                                   \
      }
  #define DECLARE_EXTERN_PER_THREAD_DATA(TYPE, NAME)                      \
      typedef TYPE NAME##_type;                                           \
      static pthread_key_t NAME##_key;                                    \
                                                                          \
      static inline NAME##_type *                                         \
      NAME##_get_unsafe(void)                                             \
      {                                                                   \
          return pthread_getspecific(NAME##_key);                         \
      }                                                                   \
                                                                          \
      NAME##_type *NAME##_get(void);
  #define DEFINE_EXTERN_PER_THREAD_DATA(NAME, ...)                        \
      static void                                                         \
      NAME##_once_init(void)                                              \
      {                                                                   \
          if (pthread_key_create(&NAME##_key, free)) {                    \
              abort();                                                    \
          }                                                               \
      }                                                                   \
                                                                          \
      NAME##_type *                                                       \
      NAME##_get(void)                                                    \
      {                                                                   \
          static pthread_once_t once = PTHREAD_ONCE_INIT;                 \
          NAME##_type *value;                                             \
                                                                          \
          pthread_once(&once, NAME##_once_init);                          \
          value = NAME##_get_unsafe();                                    \
          if (!value) {                                                   \
              static const NAME##_type initial_value = __VA_ARGS__;       \
                                                                          \
              value = malloc(sizeof *value);                              \
              if (value == NULL) {                                        \
                  out_of_memory();                                        \
              }                                                           \
              *value = initial_value;                                     \
              xpthread_setspecific(NAME##_key, value);                    \
          }                                                               \
          return value;                                                   \
      }
  #endif
  
  /* DEFINE_PER_THREAD_MALLOCED_DATA(TYPE, NAME).
   *
   * This is a simple wrapper around POSIX per-thread data primitives.  It
   * defines per-thread variable NAME with the given TYPE, which must be a
   * pointer type.  In each thread, the per-thread variable is initialized to
   * NULL.  When a thread terminates, the variable is freed with free().
   *
   * The public interface to the variable is:
   *
   *    TYPE NAME_get(void)
   *    TYPE NAME_get_unsafe(void)
   *
   *       Returns the value of per-thread variable NAME in this thread.
   *
   *       Use NAME_get() in a context where this might be the first use of the
   *       per-thread variable in the program.  Use NAME_get_unsafe(), which
   *       avoids a conditional test and is thus slightly faster, in a context
   *       where one knows that NAME_get() has already been called previously.
   *
   *    TYPE NAME_set(TYPE new_value)
   *    TYPE NAME_set_unsafe(TYPE new_value)
   *
   *       Sets the value of per-thread variable NAME to 'new_value' in this
   *       thread, and returns its previous value.
   *
   *       Use NAME_set() in a context where this might be the first use of the
   *       per-thread variable in the program.  Use NAME_set_unsafe(), which
   *       avoids a conditional test and is thus slightly faster, in a context
   *       where one knows that NAME_set() has already been called previously.
   */
  #define DEFINE_PER_THREAD_MALLOCED_DATA(TYPE, NAME)     \
      static pthread_key_t NAME##_key;                    \
                                                          \
      static void                                         \
      NAME##_once_init(void)                              \
      {                                                   \
          if (pthread_key_create(&NAME##_key, free)) {    \
              abort();                                    \
          }                                               \
      }                                                   \
                                                          \
      static void                                         \
      NAME##_init(void)                                   \
      {                                                   \
          static pthread_once_t once = PTHREAD_ONCE_INIT; \
          pthread_once(&once, NAME##_once_init);          \
      }                                                   \
                                                          \
      static TYPE                                         \
      NAME##_get_unsafe(void)                             \
      {                                                   \
          return pthread_getspecific(NAME##_key);         \
      }                                                   \
                                                          \
      static OVS_UNUSED TYPE                              \
      NAME##_get(void)                                    \
      {                                                   \
          NAME##_init();                                  \
          return NAME##_get_unsafe();                     \
      }                                                   \
                                                          \
      static TYPE                                         \
      NAME##_set_unsafe(TYPE value)                       \
      {                                                   \
          TYPE old_value = NAME##_get_unsafe();           \
          xpthread_setspecific(NAME##_key, value);        \
          return old_value;                               \
      }                                                   \
                                                          \
      static OVS_UNUSED TYPE                              \
      NAME##_set(TYPE value)                              \
      {                                                   \
          NAME##_init();                                  \
          return NAME##_set_unsafe(value);                \
      }
  
  /* Dynamically allocated thread-specific data with lots of slots.
   *
   * pthread_key_t can provide as few as 128 pieces of thread-specific data (even
   * glibc is limited to 1,024).  Thus, one must be careful to allocate only a
   * few keys globally.  One cannot, for example, allocate a key for every
   * instance of a data structure if there might be an arbitrary number of those
   * data structures.
   *
   * This API is similar to the pthread one (simply search and replace pthread_
   * by ovsthread_) but it a much larger limit that can be raised if necessary
   * (by recompiling).  Thus, one may more freely use this form of
   * thread-specific data.
   *
   * ovsthread_key_t also differs from pthread_key_t in the following ways:
   *
   *    - Destructors must not access thread-specific data (via ovsthread_key).
   *
   *    - The pthread_key_t API allows concurrently exiting threads to start
   *      executing the destructor after pthread_key_delete() returns.  The
   *      ovsthread_key_t API guarantees that, when ovsthread_key_delete()
   *      returns, all destructors have returned and no new ones will start
   *      execution.
   */
  typedef struct ovsthread_key *ovsthread_key_t;
  
  void ovsthread_key_create(ovsthread_key_t *, void (*destructor)(void *));
  void ovsthread_key_delete(ovsthread_key_t);
  
  void ovsthread_setspecific(ovsthread_key_t, const void *);
  void *ovsthread_getspecific(ovsthread_key_t);
  
  /* Thread ID.
   *
   * pthread_t isn't so nice for some purposes.  Its size and representation are
   * implementation dependent, which means that there is no way to hash it.
   * This thread ID avoids the problem.
   */
  
  #define OVSTHREAD_ID_UNSET UINT_MAX
  DECLARE_EXTERN_PER_THREAD_DATA(unsigned int, ovsthread_id);
  
  /* Initializes the unique per thread identifier */
  unsigned int ovsthread_id_init(void);
  
  /* Returns a per-thread identifier unique within the lifetime of the
   * process. */
  static inline unsigned int
  ovsthread_id_self(void)
  {
      unsigned int id = *ovsthread_id_get();
  
      if (OVS_UNLIKELY(id == OVSTHREAD_ID_UNSET)) {
          id = ovsthread_id_init();
      }
  
      return id;
  }
  
  /* Simulated global counter.
   *
   * Incrementing such a counter is meant to be cheaper than incrementing a
   * global counter protected by a lock.  It is probably more expensive than
   * incrementing a truly thread-local variable, but such a variable has no
   * straightforward way to get the sum.
   *
   *
   * Thread-safety
   * =============
   *
   * Fully thread-safe. */
  
  struct ovsthread_stats {
      struct ovs_mutex mutex;
      void *volatile buckets[16];
  };
  
  void ovsthread_stats_init(struct ovsthread_stats *);
  void ovsthread_stats_destroy(struct ovsthread_stats *);
  
  void *ovsthread_stats_bucket_get(struct ovsthread_stats *,
                                   void *(*new_bucket)(void));
  
  #define OVSTHREAD_STATS_FOR_EACH_BUCKET(BUCKET, IDX, STATS)             \
      for ((IDX) = ovs_thread_stats_next_bucket(STATS, 0);                \
           ((IDX) < ARRAY_SIZE((STATS)->buckets)                          \
            ? ((BUCKET) = (STATS)->buckets[IDX], true)                    \
            : false);                                                     \
           (IDX) = ovs_thread_stats_next_bucket(STATS, (IDX) + 1))
  size_t ovs_thread_stats_next_bucket(const struct ovsthread_stats *, size_t);
  
  bool single_threaded(void);
  
  void assert_single_threaded_at(const char *where);
  #define assert_single_threaded() assert_single_threaded_at(OVS_SOURCE_LOCATOR)
  
  #ifndef _WIN32
  pid_t xfork_at(const char *where);
  #define xfork() xfork_at(OVS_SOURCE_LOCATOR)
  #endif
  
  void forbid_forking(const char *reason);
  bool may_fork(void);
  
  /* Useful functions related to threading. */
  
  int count_cpu_cores(void);
  bool thread_is_pmd(void);
  
  #endif /* ovs-thread.h */
  