X-Git-Url: https://git.lttng.org/?p=urcu.git;a=blobdiff_plain;f=urcu-qsbr.c;h=bb98a199d5138664c4f2e03b14ca7a45cde93c98;hp=a86f6e94d5ae13eb24e5d34610a3d9c5954373b4;hb=efafc824ca148c6b2ca7f95dc86d2aaa38d4a923;hpb=47d2f29ead2c92123069ebf7b84c6e48cf91612a diff --git a/urcu-qsbr.c b/urcu-qsbr.c index a86f6e9..bb98a19 100644 --- a/urcu-qsbr.c +++ b/urcu-qsbr.c @@ -37,7 +37,11 @@ /* Do not #define _LGPL_SOURCE to ensure we can emit the wrapper symbols */ #include "urcu-qsbr.h" -pthread_mutex_t urcu_mutex = PTHREAD_MUTEX_INITIALIZER; +void __attribute__((destructor)) rcu_exit(void); + +static pthread_mutex_t urcu_mutex = PTHREAD_MUTEX_INITIALIZER; + +int gp_futex; /* * Global grace period counter. @@ -48,23 +52,14 @@ unsigned long urcu_gp_ctr = RCU_GP_ONLINE; * Written to only by each individual reader. Read by both the reader and the * writers. */ -unsigned long __thread rcu_reader_qs_gp; - -/* Thread IDs of registered readers */ -#define INIT_NUM_THREADS 4 - -struct reader_registry { - pthread_t tid; - unsigned long *rcu_reader_qs_gp; -}; +struct urcu_reader __thread urcu_reader; #ifdef DEBUG_YIELD unsigned int yield_active; unsigned int __thread rand_yield; #endif -static struct reader_registry *registry; -static int num_readers, alloc_readers; +static LIST_HEAD(registry); static void internal_urcu_lock(void) { @@ -99,24 +94,63 @@ static void internal_urcu_unlock(void) } } +/* + * synchronize_rcu() waiting. Single thread. + */ +static void wait_gp(void) +{ + /* Read reader_gp before read futex */ + smp_rmb(); + if (uatomic_read(&gp_futex) == -1) + futex(&gp_futex, FUTEX_WAIT, -1, + NULL, NULL, 0); +} + static void wait_for_quiescent_state(void) { - struct reader_registry *index; + LIST_HEAD(qsreaders); + int wait_loops = 0; + struct urcu_reader *index, *tmp; - if (!registry) + if (list_empty(®istry)) return; /* * Wait for each thread rcu_reader_qs_gp count to become 0. */ - for (index = registry; index < registry + num_readers; index++) { + for (;;) { + wait_loops++; + if (wait_loops == RCU_QS_ACTIVE_ATTEMPTS) { + uatomic_dec(&gp_futex); + /* Write futex before read reader_gp */ + smp_mb(); + } + + list_for_each_entry_safe(index, tmp, ®istry, head) { + if (!rcu_gp_ongoing(&index->ctr)) + list_move(&index->head, &qsreaders); + } + + if (list_empty(®istry)) { + if (wait_loops == RCU_QS_ACTIVE_ATTEMPTS) { + /* Read reader_gp before write futex */ + smp_mb(); + uatomic_set(&gp_futex, 0); + } + break; + } else { + if (wait_loops == RCU_QS_ACTIVE_ATTEMPTS) { + wait_gp(); + } else { #ifndef HAS_INCOHERENT_CACHES - while (rcu_gp_ongoing(index->rcu_reader_qs_gp)) - cpu_relax(); + cpu_relax(); #else /* #ifndef HAS_INCOHERENT_CACHES */ - while (rcu_gp_ongoing(index->rcu_reader_qs_gp)) - smp_mb(); + smp_mb(); #endif /* #else #ifndef HAS_INCOHERENT_CACHES */ + } + } } + /* put back the reader list in the registry */ + list_splice(&qsreaders, ®istry); } /* @@ -135,12 +169,24 @@ static void switch_next_urcu_qparity(void) void synchronize_rcu(void) { + unsigned long was_online; + + was_online = urcu_reader.ctr; + /* All threads should read qparity before accessing data structure * where new ptr points to. */ /* Write new ptr before changing the qparity */ smp_mb(); + /* + * Mark the writer thread offline to make sure we don't wait for + * our own quiescent state. This allows using synchronize_rcu() in + * threads registered as readers. + */ + if (was_online) + STORE_SHARED(urcu_reader.ctr, 0); + internal_urcu_lock(); switch_next_urcu_qparity(); /* 0 -> 1 */ @@ -183,9 +229,12 @@ void synchronize_rcu(void) internal_urcu_unlock(); - /* Finish waiting for reader threads before letting the old ptr being + /* + * Finish waiting for reader threads before letting the old ptr being * freed. */ + if (was_online) + _STORE_SHARED(urcu_reader.ctr, LOAD_SHARED(urcu_gp_ctr)); smp_mb(); } #else /* !(BITS_PER_LONG < 64) */ @@ -193,7 +242,7 @@ void synchronize_rcu(void) { unsigned long was_online; - was_online = rcu_reader_qs_gp; + was_online = urcu_reader.ctr; /* * Mark the writer thread offline to make sure we don't wait for @@ -202,7 +251,7 @@ void synchronize_rcu(void) */ smp_mb(); if (was_online) - STORE_SHARED(rcu_reader_qs_gp, 0); + STORE_SHARED(urcu_reader.ctr, 0); internal_urcu_lock(); STORE_SHARED(urcu_gp_ctr, urcu_gp_ctr + RCU_GP_CTR); @@ -210,7 +259,7 @@ void synchronize_rcu(void) internal_urcu_unlock(); if (was_online) - _STORE_SHARED(rcu_reader_qs_gp, LOAD_SHARED(urcu_gp_ctr)); + _STORE_SHARED(urcu_reader.ctr, LOAD_SHARED(urcu_gp_ctr)); smp_mb(); } #endif /* !(BITS_PER_LONG < 64) */ @@ -237,13 +286,19 @@ void *rcu_dereference(void *p) void *rcu_assign_pointer_sym(void **p, void *v) { wmb(); - return STORE_SHARED(p, v); + return STORE_SHARED(*p, v); +} + +void *rcu_cmpxchg_pointer_sym(void **p, void *old, void *_new) +{ + wmb(); + return uatomic_cmpxchg(p, old, _new); } void *rcu_xchg_pointer_sym(void **p, void *v) { wmb(); - return xchg(p, v); + return uatomic_xchg(p, v); } void *rcu_publish_content_sym(void **p, void *v) @@ -270,58 +325,13 @@ void rcu_thread_online(void) _rcu_thread_online(); } -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].rcu_reader_qs_gp = &rcu_reader_qs_gp; - num_readers++; -} - -/* - * Never shrink (implementation limitation). - * This is O(nb threads). Eventually use a hash table. - */ -static void rcu_remove_reader(pthread_t id) -{ - 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].rcu_reader_qs_gp = NULL; - num_readers--; - return; - } - } - /* Hrm not found, forgot to register ? */ - assert(0); -} - void rcu_register_thread(void) { + urcu_reader.tid = pthread_self(); + assert(urcu_reader.ctr == 0); + internal_urcu_lock(); - rcu_add_reader(pthread_self()); + list_add(&urcu_reader.head, ®istry); internal_urcu_unlock(); _rcu_thread_online(); } @@ -334,6 +344,11 @@ void rcu_unregister_thread(void) */ _rcu_thread_offline(); internal_urcu_lock(); - rcu_remove_reader(pthread_self()); + list_del(&urcu_reader.head); internal_urcu_unlock(); } + +void rcu_exit(void) +{ + assert(list_empty(®istry)); +}