/* * 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 #include #include #include "ovs-atomic.h" #include "util.h" /* Mutex. */ struct OVS_LOCKABLE ovs_mutex { pthread_mutex_t lock; const char *where; /* NULL if and only if uninitialized. */ }; /* "struct ovs_mutex" initializer. */ #ifdef PTHREAD_ERRORCHECK_MUTEX_INITIALIZER_NP #define OVS_MUTEX_INITIALIZER { PTHREAD_ERRORCHECK_MUTEX_INITIALIZER_NP, \ "" } #else #define OVS_MUTEX_INITIALIZER { PTHREAD_MUTEX_INITIALIZER, "" } #endif #ifdef PTHREAD_ADAPTIVE_MUTEX_INITIALIZER_NP #define OVS_ADAPTIVE_MUTEX_INITIALIZER \ { PTHREAD_ADAPTIVE_MUTEX_INITIALIZER_NP, "" } #else #define OVS_ADAPTIVE_MUTEX_INITIALIZER OVS_MUTEX_INITIALIZER #endif /* ovs_mutex functions analogous to pthread_mutex_*() functions. * * Most of these functions abort the process with an error message on any * error. ovs_mutex_trylock() is an exception: it passes through a 0 or EBUSY * return value to the caller and aborts on any other error. */ void ovs_mutex_init(const struct ovs_mutex *); void ovs_mutex_init_recursive(const struct ovs_mutex *); void ovs_mutex_init_adaptive(const struct ovs_mutex *); void ovs_mutex_destroy(const struct ovs_mutex *); void ovs_mutex_unlock(const struct ovs_mutex *mutex) OVS_RELEASES(mutex); void ovs_mutex_lock_at(const struct ovs_mutex *mutex, const char *where) OVS_ACQUIRES(mutex); #define ovs_mutex_lock(mutex) \ ovs_mutex_lock_at(mutex, SOURCE_LOCATOR) int ovs_mutex_trylock_at(const struct ovs_mutex *mutex, const char *where) OVS_TRY_LOCK(0, mutex); #define ovs_mutex_trylock(mutex) \ ovs_mutex_trylock_at(mutex, SOURCE_LOCATOR) void ovs_mutex_cond_wait(pthread_cond_t *, const struct ovs_mutex *); /* 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, "" } #else #define OVS_RWLOCK_INITIALIZER { PTHREAD_RWLOCK_INITIALIZER, "" } #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, 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, 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, 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, SOURCE_LOCATOR) /* 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 *); /* Wrappers for pthread_barrier_*() that abort the process on any error. */ void xpthread_barrier_init(pthread_barrier_t *, pthread_barrierattr_t *, unsigned int count); int xpthread_barrier_wait(pthread_barrier_t *); void xpthread_barrier_destroy(pthread_barrier_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 *); 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 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 #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); /* 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)); } /* 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(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); /* Useful functions related to threading. */ int count_cpu_cores(void); #endif /* ovs-thread.h */