X-Git-Url: http://git.liburcu.org/?p=urcu.git;a=blobdiff_plain;f=urcu.c;h=140cd19b98add54f276755e08b13bfad9e8c3d0c;hp=8fae8faea8f4bd7b260cdcf6df69777a753a9b58;hb=27d65bc5db18f8563a9120924569acffb845ec4d;hpb=b4ce15269d95cb1fc5542d0e192ec593b2222dd5 diff --git a/urcu.c b/urcu.c index 8fae8fa..140cd19 100644 --- a/urcu.c +++ b/urcu.c @@ -23,6 +23,7 @@ * IBM's contributions to this file may be relicensed under LGPLv2 or later. */ +#define _BSD_SOURCE #include #include #include @@ -36,71 +37,71 @@ /* Do not #define _LGPL_SOURCE to ensure we can emit the wrapper symbols */ #include "urcu.h" -#ifndef CONFIG_URCU_AVOID_SIGNALS -void __attribute__((constructor)) urcu_init(void); -void __attribute__((destructor)) urcu_exit(void); -#else -static inline void urcu_init(void) +#ifdef RCU_MEMBARRIER +static int init_done; +int has_sys_membarrier; + +void __attribute__((constructor)) rcu_init(void); +#endif + +#ifdef RCU_MB +void rcu_init(void) { } #endif -int init_done; +#ifdef RCU_SIGNAL +static int init_done; + +void __attribute__((constructor)) rcu_init(void); +void __attribute__((destructor)) rcu_exit(void); +#endif + +static pthread_mutex_t rcu_gp_lock = PTHREAD_MUTEX_INITIALIZER; -pthread_mutex_t urcu_mutex = PTHREAD_MUTEX_INITIALIZER; +int gp_futex; /* * Global grace period counter. - * Contains the current RCU_GP_CTR_BIT. - * Also has a RCU_GP_CTR_BIT of 1, to accelerate the reader fast path. + * Contains the current RCU_GP_CTR_PHASE. + * Also has a RCU_GP_COUNT of 1, to accelerate the reader fast path. * Written to only by writer with mutex taken. Read by both writer and readers. */ -long urcu_gp_ctr = RCU_GP_COUNT; +unsigned long rcu_gp_ctr = RCU_GP_COUNT; /* * Written to only by each individual reader. Read by both the reader and the * writers. */ -long __thread urcu_active_readers; - -/* Thread IDs of registered readers */ -#define INIT_NUM_THREADS 4 - -struct reader_registry { - pthread_t tid; - long *urcu_active_readers; - char *need_mb; -}; +struct rcu_reader __thread rcu_reader; #ifdef DEBUG_YIELD unsigned int yield_active; unsigned int __thread rand_yield; #endif -static struct reader_registry *registry; -static char __thread need_mb; -static int num_readers, alloc_readers; +static LIST_HEAD(registry); -void internal_urcu_lock(void) +static void mutex_lock(pthread_mutex_t *mutex) { int ret; #ifndef DISTRUST_SIGNALS_EXTREME - ret = pthread_mutex_lock(&urcu_mutex); + ret = pthread_mutex_lock(mutex); if (ret) { perror("Error in pthread mutex lock"); exit(-1); } #else /* #ifndef DISTRUST_SIGNALS_EXTREME */ - while ((ret = pthread_mutex_trylock(&urcu_mutex)) != 0) { + while ((ret = pthread_mutex_trylock(mutex)) != 0) { if (ret != EBUSY && ret != EINTR) { printf("ret = %d, errno = %d\n", ret, errno); perror("Error in pthread mutex lock"); exit(-1); } - if (need_mb) { + if (rcu_reader.need_mb) { smp_mb(); - need_mb = 0; + rcu_reader.need_mb = 0; smp_mb(); } poll(NULL,0,10); @@ -108,71 +109,44 @@ void internal_urcu_lock(void) #endif /* #else #ifndef DISTRUST_SIGNALS_EXTREME */ } -void internal_urcu_unlock(void) +static void mutex_unlock(pthread_mutex_t *mutex) { int ret; - ret = pthread_mutex_unlock(&urcu_mutex); + ret = pthread_mutex_unlock(mutex); if (ret) { perror("Error in pthread mutex unlock"); exit(-1); } } -/* - * called with urcu_mutex held. - */ -static void switch_next_urcu_qparity(void) +#ifdef RCU_MEMBARRIER +static void smp_mb_master(int group) { - STORE_SHARED(urcu_gp_ctr, urcu_gp_ctr ^ RCU_GP_CTR_BIT); + if (likely(has_sys_membarrier)) + membarrier(MEMBARRIER_EXPEDITED); + else + smp_mb(); } +#endif -#ifdef CONFIG_URCU_AVOID_SIGNALS -#ifdef HAS_INCOHERENT_CACHES -static void force_mb_single_thread(struct reader_registry *index) +#ifdef RCU_MB +static void smp_mb_master(int group) { smp_mb(); } -#endif /* #ifdef HAS_INCOHERENT_CACHES */ +#endif -static void force_mb_all_threads(void) -{ - smp_mb(); -} -#else /* #ifdef CONFIG_URCU_AVOID_SIGNALS */ -#ifdef HAS_INCOHERENT_CACHES -static void force_mb_single_thread(struct reader_registry *index) +#ifdef RCU_SIGNAL +static void force_mb_all_readers(void) { - assert(registry); - /* - * pthread_kill has a smp_mb(). But beware, we assume it performs - * a cache flush on architectures with non-coherent cache. Let's play - * safe and don't assume anything : we use smp_mc() to make sure the - * cache flush is enforced. - */ - *index->need_mb = 1; - smp_mc(); /* write ->need_mb before sending the signals */ - pthread_kill(index->tid, SIGURCU); - smp_mb(); - /* - * Wait for sighandler (and thus mb()) to execute on every thread. - * BUSY-LOOP. - */ - while (*index->need_mb) { - poll(NULL, 0, 1); - } - smp_mb(); /* read ->need_mb before ending the barrier */ -} -#endif /* #ifdef HAS_INCOHERENT_CACHES */ + struct rcu_reader *index; -static void force_mb_all_threads(void) -{ - struct reader_registry *index; /* * Ask for each threads to execute a smp_mb() so we can consider the * compiler barriers around rcu read lock as real memory barriers. */ - if (!registry) + if (list_empty(®istry)) return; /* * pthread_kill has a smp_mb(). But beware, we assume it performs @@ -180,10 +154,10 @@ static void force_mb_all_threads(void) * safe and don't assume anything : we use smp_mc() to make sure the * cache flush is enforced. */ - for (index = registry; index < registry + num_readers; index++) { - *index->need_mb = 1; + list_for_each_entry(index, ®istry, head) { + index->need_mb = 1; smp_mc(); /* write need_mb before sending the signal */ - pthread_kill(index->tid, SIGURCU); + pthread_kill(index->tid, SIGRCU); } /* * Wait for sighandler (and thus mb()) to execute on every thread. @@ -198,78 +172,134 @@ static void force_mb_all_threads(void) * relevant bug report. For Linux kernels, we recommend getting * the Linux Test Project (LTP). */ - for (index = registry; index < registry + num_readers; index++) { - while (*index->need_mb) { - pthread_kill(index->tid, SIGURCU); + list_for_each_entry(index, ®istry, head) { + while (index->need_mb) { + pthread_kill(index->tid, SIGRCU); poll(NULL, 0, 1); } } smp_mb(); /* read ->need_mb before ending the barrier */ } -#endif /* #else #ifdef CONFIG_URCU_AVOID_SIGNALS */ -void wait_for_quiescent_state(void) +static void smp_mb_master(int group) { - struct reader_registry *index; + force_mb_all_readers(); +} +#endif /* #ifdef RCU_SIGNAL */ + +/* + * synchronize_rcu() waiting. Single thread. + */ +static void wait_gp(void) +{ + /* Read reader_gp before read futex */ + smp_mb_master(RCU_MB_GROUP); + if (uatomic_read(&gp_futex) == -1) + futex_async(&gp_futex, FUTEX_WAIT, -1, + NULL, NULL, 0); +} + +void update_counter_and_wait(void) +{ + LIST_HEAD(qsreaders); + int wait_loops = 0; + struct rcu_reader *index, *tmp; + + /* Switch parity: 0 -> 1, 1 -> 0 */ + STORE_SHARED(rcu_gp_ctr, rcu_gp_ctr ^ RCU_GP_CTR_PHASE); - if (!registry) - return; /* - * Wait for each thread urcu_active_readers count to become 0. + * Must commit qparity update to memory before waiting for other parity + * quiescent state. Failure to do so could result in the writer waiting + * forever while new readers are always accessing data (no progress). + * Ensured by STORE_SHARED and LOAD_SHARED. */ - for (index = registry; index < registry + num_readers; index++) { + + /* + * Adding a smp_mb() which is _not_ formally required, but makes the + * model easier to understand. It does not have a big performance impact + * anyway, given this is the write-side. + */ + smp_mb(); + + /* + * Wait for each thread rcu_reader.ctr count to become 0. + */ + for (;;) { + wait_loops++; + if (wait_loops == RCU_QS_ACTIVE_ATTEMPTS) { + uatomic_dec(&gp_futex); + /* Write futex before read reader_gp */ + smp_mb_master(RCU_MB_GROUP); + } + + list_for_each_entry_safe(index, tmp, ®istry, head) { + if (!rcu_old_gp_ongoing(&index->ctr)) + list_move(&index->head, &qsreaders); + } + #ifndef HAS_INCOHERENT_CACHES - while (rcu_old_gp_ongoing(index->urcu_active_readers)) - cpu_relax(); + if (list_empty(®istry)) { + if (wait_loops == RCU_QS_ACTIVE_ATTEMPTS) { + /* Read reader_gp before write futex */ + smp_mb_master(RCU_MB_GROUP); + uatomic_set(&gp_futex, 0); + } + break; + } else { + if (wait_loops == RCU_QS_ACTIVE_ATTEMPTS) + wait_gp(); + else + cpu_relax(); + } #else /* #ifndef HAS_INCOHERENT_CACHES */ - int wait_loops = 0; /* * BUSY-LOOP. Force the reader thread to commit its - * urcu_active_readers update to memory if we wait for too long. + * rcu_reader.ctr update to memory if we wait for too long. */ - while (rcu_old_gp_ongoing(index->urcu_active_readers)) { - if (wait_loops++ == KICK_READER_LOOPS) { - force_mb_single_thread(index); + if (list_empty(®istry)) { + if (wait_loops == RCU_QS_ACTIVE_ATTEMPTS) { + /* Read reader_gp before write futex */ + smp_mb_master(RCU_MB_GROUP); + uatomic_set(&gp_futex, 0); + } + break; + } else { + switch (wait_loops) { + case RCU_QS_ACTIVE_ATTEMPTS: + wait_gp(); + break; /* only escape switch */ + case KICK_READER_LOOPS: + smp_mb_master(RCU_MB_GROUP); wait_loops = 0; - } else { + break; /* only escape switch */ + default: cpu_relax(); } } #endif /* #else #ifndef HAS_INCOHERENT_CACHES */ } + /* put back the reader list in the registry */ + list_splice(&qsreaders, ®istry); } void synchronize_rcu(void) { - internal_urcu_lock(); + mutex_lock(&rcu_gp_lock); + + if (list_empty(®istry)) + goto out; /* All threads should read qparity before accessing data structure - * where new ptr points to. Must be done within internal_urcu_lock - * because it iterates on reader threads.*/ + * where new ptr points to. Must be done within rcu_gp_lock because it + * iterates on reader threads.*/ /* Write new ptr before changing the qparity */ - force_mb_all_threads(); - - switch_next_urcu_qparity(); /* 0 -> 1 */ - - /* - * Must commit qparity update to memory before waiting for parity - * 0 quiescent state. Failure to do so could result in the writer - * waiting forever while new readers are always accessing data (no - * progress). - * Ensured by STORE_SHARED and LOAD_SHARED. - */ - - /* - * Adding a smp_mb() which is _not_ formally required, but makes the - * model easier to understand. It does not have a big performance impact - * anyway, given this is the write-side. - */ - smp_mb(); + smp_mb_master(RCU_MB_GROUP); /* * Wait for previous parity to be empty of readers. */ - wait_for_quiescent_state(); /* Wait readers in parity 0 */ + update_counter_and_wait(); /* 0 -> 1, wait readers in parity 0 */ /* * Must finish waiting for quiescent state for parity 0 before @@ -286,34 +316,17 @@ void synchronize_rcu(void) */ smp_mb(); - switch_next_urcu_qparity(); /* 1 -> 0 */ - - /* - * Must commit qparity update to memory before waiting for parity - * 1 quiescent state. Failure to do so could result in the writer - * waiting forever while new readers are always accessing data (no - * progress). - * Ensured by STORE_SHARED and LOAD_SHARED. - */ - - /* - * Adding a smp_mb() which is _not_ formally required, but makes the - * model easier to understand. It does not have a big performance impact - * anyway, given this is the write-side. - */ - smp_mb(); - /* * Wait for previous parity to be empty of readers. */ - wait_for_quiescent_state(); /* Wait readers in parity 1 */ + update_counter_and_wait(); /* 1 -> 0, wait readers in parity 1 */ /* Finish waiting for reader threads before letting the old ptr being - * freed. Must be done within internal_urcu_lock because it iterates on - * reader threads. */ - force_mb_all_threads(); - - internal_urcu_unlock(); + * freed. Must be done within rcu_gp_lock because it iterates on reader + * threads. */ + smp_mb_master(RCU_MB_GROUP); +out: + mutex_unlock(&rcu_gp_lock); } /* @@ -330,98 +343,38 @@ void rcu_read_unlock(void) _rcu_read_unlock(); } -void *rcu_dereference(void *p) -{ - return _rcu_dereference(p); -} - -void *rcu_assign_pointer_sym(void **p, void *v) -{ - wmb(); - return STORE_SHARED(p, v); -} - -void *rcu_xchg_pointer_sym(void **p, void *v) -{ - wmb(); - return xchg(p, v); -} - -void *rcu_publish_content_sym(void **p, void *v) -{ - void *oldptr; - - oldptr = _rcu_xchg_pointer(p, v); - synchronize_rcu(); - return oldptr; -} - -static void rcu_add_reader(pthread_t id) -{ - struct reader_registry *oldarray; - - if (!registry) { - alloc_readers = INIT_NUM_THREADS; - num_readers = 0; - registry = - malloc(sizeof(struct reader_registry) * alloc_readers); - } - if (alloc_readers < num_readers + 1) { - oldarray = registry; - registry = malloc(sizeof(struct reader_registry) - * (alloc_readers << 1)); - memcpy(registry, oldarray, - sizeof(struct reader_registry) * alloc_readers); - alloc_readers <<= 1; - free(oldarray); - } - registry[num_readers].tid = id; - /* reference to the TLS of _this_ reader thread. */ - registry[num_readers].urcu_active_readers = &urcu_active_readers; - registry[num_readers].need_mb = &need_mb; - num_readers++; -} - -/* - * Never shrink (implementation limitation). - * This is O(nb threads). Eventually use a hash table. - */ -static void rcu_remove_reader(pthread_t id) +void rcu_register_thread(void) { - struct reader_registry *index; - - assert(registry != NULL); - for (index = registry; index < registry + num_readers; index++) { - if (pthread_equal(index->tid, id)) { - memcpy(index, ®istry[num_readers - 1], - sizeof(struct reader_registry)); - registry[num_readers - 1].tid = 0; - registry[num_readers - 1].urcu_active_readers = NULL; - num_readers--; - return; - } - } - /* Hrm not found, forgot to register ? */ - assert(0); + rcu_reader.tid = pthread_self(); + assert(rcu_reader.need_mb == 0); + assert(rcu_reader.ctr == 0); + + mutex_lock(&rcu_gp_lock); + rcu_init(); /* In case gcc does not support constructor attribute */ + list_add(&rcu_reader.head, ®istry); + mutex_unlock(&rcu_gp_lock); } -void rcu_register_thread(void) +void rcu_unregister_thread(void) { - internal_urcu_lock(); - urcu_init(); /* In case gcc does not support constructor attribute */ - rcu_add_reader(pthread_self()); - internal_urcu_unlock(); + mutex_lock(&rcu_gp_lock); + list_del(&rcu_reader.head); + mutex_unlock(&rcu_gp_lock); } -void rcu_unregister_thread(void) +#ifdef RCU_MEMBARRIER +void rcu_init(void) { - internal_urcu_lock(); - rcu_remove_reader(pthread_self()); - internal_urcu_unlock(); + if (init_done) + return; + init_done = 1; + if (!membarrier(MEMBARRIER_EXPEDITED | MEMBARRIER_QUERY)) + has_sys_membarrier = 1; } +#endif -#ifndef CONFIG_URCU_AVOID_SIGNALS -static void sigurcu_handler(int signo, siginfo_t *siginfo, void *context) +#ifdef RCU_SIGNAL +static void sigrcu_handler(int signo, siginfo_t *siginfo, void *context) { /* * Executing this smp_mb() is the only purpose of this signal handler. @@ -429,19 +382,19 @@ static void sigurcu_handler(int signo, siginfo_t *siginfo, void *context) * executed on. */ smp_mb(); - need_mb = 0; + rcu_reader.need_mb = 0; smp_mb(); } /* - * urcu_init constructor. Called when the library is linked, but also when + * rcu_init constructor. Called when the library is linked, but also when * reader threads are calling rcu_register_thread(). * Should only be called by a single thread at a given time. This is ensured by - * holing the internal_urcu_lock() from rcu_register_thread() or by running at - * library load time, which should not be executed by multiple threads nor - * concurrently with rcu_register_thread() anyway. + * holing the rcu_gp_lock from rcu_register_thread() or by running at library + * load time, which should not be executed by multiple threads nor concurrently + * with rcu_register_thread() anyway. */ -void urcu_init(void) +void rcu_init(void) { struct sigaction act; int ret; @@ -450,27 +403,27 @@ void urcu_init(void) return; init_done = 1; - act.sa_sigaction = sigurcu_handler; + act.sa_sigaction = sigrcu_handler; act.sa_flags = SA_SIGINFO | SA_RESTART; sigemptyset(&act.sa_mask); - ret = sigaction(SIGURCU, &act, NULL); + ret = sigaction(SIGRCU, &act, NULL); if (ret) { perror("Error in sigaction"); exit(-1); } } -void urcu_exit(void) +void rcu_exit(void) { struct sigaction act; int ret; - ret = sigaction(SIGURCU, NULL, &act); + ret = sigaction(SIGRCU, NULL, &act); if (ret) { perror("Error in sigaction"); exit(-1); } - assert(act.sa_sigaction == sigurcu_handler); - free(registry); + assert(act.sa_sigaction == sigrcu_handler); + assert(list_empty(®istry)); } -#endif /* #ifndef CONFIG_URCU_AVOID_SIGNALS */ +#endif /* #ifdef RCU_SIGNAL */