/* * Copyright (c) 2013 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" /* glibc has some non-portable mutex types and initializers: * * - PTHREAD_MUTEX_ADAPTIVE_NP is a mutex type that works as a spinlock that * falls back to a mutex after spinning for some number of iterations. * * - PTHREAD_ERRORCHECK_MUTEX_INITIALIZER_NP is a non-portable initializer * for an error-checking mutex. * * We use these definitions to fall back to PTHREAD_MUTEX_NORMAL instead in * these cases. * * (glibc has other non-portable initializers, but we can't reasonably * substitute for them here.) */ #ifdef PTHREAD_ADAPTIVE_MUTEX_INITIALIZER_NP #define PTHREAD_MUTEX_ADAPTIVE PTHREAD_MUTEX_ADAPTIVE_NP #define PTHREAD_ADAPTIVE_MUTEX_INITIALIZER \ PTHREAD_ADAPTIVE_MUTEX_INITIALIZER_NP #else #define PTHREAD_MUTEX_ADAPTIVE PTHREAD_MUTEX_NORMAL #define PTHREAD_ADAPTIVE_MUTEX_INITIALIZER PTHREAD_MUTEX_INITIALIZER #endif #ifdef PTHREAD_ERRORCHECK_MUTEX_INITIALIZER_NP #define PTHREAD_ERRORCHECK_MUTEX_INITIALIZER \ PTHREAD_ERRORCHECK_MUTEX_INITIALIZER_NP #else #define PTHREAD_ERRORCHECK_MUTEX_INITIALIZER PTHREAD_MUTEX_INITIALIZER #endif /* Simple wrappers for pthreads functions. Most of these functions abort the * process with an error message on any error. The *_trylock() functions are * exceptions: they pass through a 0 or EBUSY return value to the caller and * abort on any other error. */ void xpthread_mutex_init(pthread_mutex_t *, pthread_mutexattr_t *); void xpthread_mutex_lock(pthread_mutex_t *mutex) OVS_ACQUIRES(mutex); void xpthread_mutex_unlock(pthread_mutex_t *mutex) OVS_RELEASES(mutex); int xpthread_mutex_trylock(pthread_mutex_t *); void xpthread_rwlock_init(pthread_rwlock_t *, pthread_rwlockattr_t *); void xpthread_rwlock_rdlock(pthread_rwlock_t *rwlock) OVS_ACQUIRES(rwlock); void xpthread_rwlock_wrlock(pthread_rwlock_t *rwlock) OVS_ACQUIRES(rwlock); void xpthread_rwlock_unlock(pthread_rwlock_t *rwlock) OVS_RELEASES(rwlock); int xpthread_rwlock_tryrdlock(pthread_rwlock_t *); int xpthread_rwlock_trywrlock(pthread_rwlock_t *); void xpthread_cond_init(pthread_cond_t *, pthread_condattr_t *); void xpthread_cond_signal(pthread_cond_t *); void xpthread_cond_broadcast(pthread_cond_t *); void xpthread_cond_wait(pthread_cond_t *, pthread_mutex_t *mutex) OVS_MUST_HOLD(mutex); #ifdef __CHECKER__ /* Replace these functions by the macros already defined in the * annotations, because the macro definitions have correct semantics for the * conditional acquisition that can't be captured in a function annotation. * The difference in semantics from pthread_*() to xpthread_*() does not matter * because sparse is not a compiler. */ #define xpthread_mutex_trylock pthread_mutex_trylock #define xpthread_rwlock_tryrdlock pthread_rwlock_tryrdlock #define xpthread_rwlock_trywrlock pthread_rwlock_trywrlock #endif void xpthread_key_create(pthread_key_t *, void (*destructor)(void *)); void xpthread_create(pthread_t *, pthread_attr_t *, void *(*)(void *), void *); /* Per-thread data. * * Multiple forms of per-thread data exist, each with its own pluses and * minuses: * * - 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. * * - 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. * * - 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 */ /* DEFINE_PER_THREAD_DATA(TYPE, 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_PER_THREAD_DATA(TYPE, NAME, ...) \ typedef TYPE NAME##_type; \ static thread_local NAME##_type NAME##_var = __VA_ARGS__; \ \ static NAME##_type * \ NAME##_get_unsafe(void) \ { \ return &NAME##_var; \ } \ \ static NAME##_type * \ NAME##_get(void) \ { \ return NAME##_get_unsafe(); \ } #else /* no C implementation support for thread-local storage */ #define DEFINE_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 = xmalloc(sizeof *value); \ *value = initial_value; \ pthread_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(); \ pthread_setspecific(NAME##_key, value); \ return old_value; \ } \ \ static OVS_UNUSED TYPE \ NAME##_set(TYPE value) \ { \ NAME##_init(); \ return NAME##_set_unsafe(value); \ } /* 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; pthread_mutex_t mutex; }; #define OVSTHREAD_ONCE_INITIALIZER \ { \ ATOMIC_VAR_INIT(false), \ PTHREAD_ADAPTIVE_MUTEX_INITIALIZER, \ } static inline bool ovsthread_once_start(struct ovsthread_once *); void ovsthread_once_done(struct ovsthread_once *once) OVS_RELEASES(once); bool ovsthread_once_start__(struct ovsthread_once *); static inline bool ovsthread_once_is_done__(const 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)); } #ifdef __CHECKER__ #define ovsthread_once_start(ONCE) \ ((ONCE)->done ? false : ({ OVS_ACQUIRE(ONCE); true; })) #endif void assert_single_threaded(const char *where); #define assert_single_threaded() assert_single_threaded(SOURCE_LOCATOR) pid_t xfork(const char *where); #define xfork() xfork(SOURCE_LOCATOR) void forbid_forking(const char *reason); bool may_fork(void); #endif /* ovs-thread.h */