+void xpthread_key_delete(pthread_key_t);
+void xpthread_setspecific(pthread_key_t, const void *);
+
+pthread_t ovs_thread_create(const char *name, void *(*)(void *), void *);
+void xpthread_join(pthread_t, void **);
+\f
+/* 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);
+\f
+/* Convenient once-only execution.
+ *
+ *
+ * Problem
+ * =======
+ *
+ * POSIX provides pthread_once_t and pthread_once() as primitives for running a
+ * set of code only once per process execution. They are used like this:
+ *
+ * static void run_once(void) { ...initialization... }
+ * static pthread_once_t once = PTHREAD_ONCE_INIT;
+ * ...
+ * pthread_once(&once, run_once);
+ *
+ * pthread_once() does not allow passing any parameters to the initialization
+ * function, which is often inconvenient, because it means that the function
+ * can only access data declared at file scope.
+ *
+ *
+ * Solution
+ * ========
+ *
+ * Use ovsthread_once, like this, instead:
+ *
+ * static struct ovsthread_once once = OVSTHREAD_ONCE_INITIALIZER;
+ *
+ * if (ovsthread_once_start(&once)) {
+ * ...initialization...
+ * ovsthread_once_done(&once);
+ * }
+ */
+
+struct ovsthread_once {
+ atomic_bool done;
+ struct ovs_mutex mutex;
+};
+
+#define OVSTHREAD_ONCE_INITIALIZER \
+ { \
+ ATOMIC_VAR_INIT(false), \
+ OVS_MUTEX_INITIALIZER, \
+ }
+
+static inline bool ovsthread_once_start(struct ovsthread_once *once)
+ OVS_TRY_LOCK(true, once->mutex);
+void ovsthread_once_done(struct ovsthread_once *once)
+ OVS_RELEASES(once->mutex);
+
+bool ovsthread_once_start__(struct ovsthread_once *once)
+ OVS_TRY_LOCK(false, once->mutex);
+
+static inline bool
+ovsthread_once_is_done__(struct ovsthread_once *once)
+{
+ bool done;
+
+ atomic_read_explicit(&once->done, &done, memory_order_relaxed);
+ return done;
+}
+
+/* Returns true if this is the first call to ovsthread_once_start() for
+ * 'once'. In this case, the caller should perform whatever initialization
+ * actions it needs to do, then call ovsthread_once_done() for 'once'.
+ *
+ * Returns false if this is not the first call to ovsthread_once_start() for
+ * 'once'. In this case, the call will not return until after
+ * ovsthread_once_done() has been called. */
+static inline bool
+ovsthread_once_start(struct ovsthread_once *once)
+{
+ return OVS_UNLIKELY(!ovsthread_once_is_done__(once)
+ && !ovsthread_once_start__(once));
+}
+\f
+/* 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.
+ */
+
+DECLARE_EXTERN_PER_THREAD_DATA(unsigned int, ovsthread_id);
+
+/* Returns a per-thread identifier unique within the lifetime of the
+ * process. */
+static inline unsigned int
+ovsthread_id_self(void)
+{
+ return *ovsthread_id_get();
+}
+\f
+/* 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);
+\f
+bool single_threaded(void);
+
+void assert_single_threaded_at(const char *where);
+#define assert_single_threaded() assert_single_threaded_at(SOURCE_LOCATOR)
+
+#ifndef _WIN32
+pid_t xfork_at(const char *where);
+#define xfork() xfork_at(SOURCE_LOCATOR)
+#endif
+
+void forbid_forking(const char *reason);
+bool may_fork(void);
+\f
+/* Useful functions related to threading. */