ovs-thread.h

/*
 * 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.
 */

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();
}

/* 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);

#endif /* ovs-thread.h */