X-Git-Url: https://git.liburcu.org/?p=urcu.git;a=blobdiff_plain;f=urcu-qsbr.c;h=0e1252fdbba707e4515cbbabe8c8a837a6408c79;hp=dac664935d7b898bd3dcce494845c7471c09749d;hb=0ecb3fde04135d76545ce55d80abea9aef465b54;hpb=bc6c15bba37d0e6192c006c4d9815201b36d1988 diff --git a/urcu-qsbr.c b/urcu-qsbr.c index dac6649..0e1252f 100644 --- a/urcu-qsbr.c +++ b/urcu-qsbr.c @@ -37,49 +37,42 @@ /* Do not #define _LGPL_SOURCE to ensure we can emit the wrapper symbols */ #include "urcu-qsbr.h" -static pthread_mutex_t urcu_mutex = PTHREAD_MUTEX_INITIALIZER; +void __attribute__((destructor)) rcu_exit(void); + +static pthread_mutex_t rcu_gp_lock = PTHREAD_MUTEX_INITIALIZER; int gp_futex; /* * Global grace period counter. */ -unsigned long urcu_gp_ctr = RCU_GP_ONLINE; +unsigned long rcu_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 rcu_reader __thread rcu_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) +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"); @@ -90,11 +83,11 @@ static void internal_urcu_lock(void) #endif /* #else #ifndef DISTRUST_SIGNALS_EXTREME */ } -static 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); @@ -104,39 +97,70 @@ static void internal_urcu_unlock(void) /* * synchronize_rcu() waiting. Single thread. */ -static void wait_gp(struct reader_registry *index) +static void wait_gp(void) { - atomic_dec(&gp_futex); - smp_mb(); /* Write futex before read reader_gp */ - if (!rcu_gp_ongoing(index->rcu_reader_qs_gp)) { - /* Read reader_gp before write futex */ - smp_mb(); - /* Callbacks are queued, don't wait. */ - atomic_set(&gp_futex, 0); - } else { - /* Read reader_gp before read futex */ - smp_rmb(); - if (atomic_read(&gp_futex) == -1) - futex(&gp_futex, FUTEX_WAIT, -1, - NULL, NULL, 0); - } + /* Read reader_gp before read futex */ + smp_rmb(); + if (uatomic_read(&gp_futex) == -1) + futex_noasync(&gp_futex, FUTEX_WAIT, -1, + NULL, NULL, 0); } -static void wait_for_quiescent_state(void) +static void update_counter_and_wait(void) { - struct reader_registry *index; + LIST_HEAD(qsreaders); + int wait_loops = 0; + struct rcu_reader *index, *tmp; + +#if (BITS_PER_LONG < 64) + /* Switch parity: 0 -> 1, 1 -> 0 */ + STORE_SHARED(rcu_gp_ctr, rcu_gp_ctr ^ RCU_GP_CTR); +#else /* !(BITS_PER_LONG < 64) */ + /* Increment current G.P. */ + STORE_SHARED(rcu_gp_ctr, rcu_gp_ctr + RCU_GP_CTR); +#endif /* !(BITS_PER_LONG < 64) */ + + /* + * Must commit rcu_gp_ctr update to memory before waiting for quiescent + * state. Failure to do so could result in the writer waiting forever + * while new readers are always accessing data (no progress). Enforce + * compiler-order of store to rcu_gp_ctr before load rcu_reader ctr. + */ + barrier(); + + /* + * 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(); - if (!registry) - return; /* * Wait for each thread rcu_reader_qs_gp count to become 0. */ - for (index = registry; index < registry + num_readers; index++) { - int wait_loops = 0; + 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, node) { + if (!rcu_gp_ongoing(&index->ctr)) + list_move(&index->node, &qsreaders); + } - while (rcu_gp_ongoing(index->rcu_reader_qs_gp)) { - if (wait_loops++ == RCU_QS_ACTIVE_ATTEMPTS) { - wait_gp(index); + 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 cpu_relax(); @@ -146,6 +170,8 @@ static void wait_for_quiescent_state(void) } } } + /* put back the reader list in the registry */ + list_splice(&qsreaders, ®istry); } /* @@ -154,19 +180,11 @@ static void wait_for_quiescent_state(void) */ #if (BITS_PER_LONG < 64) -/* - * called with urcu_mutex held. - */ -static void switch_next_urcu_qparity(void) -{ - STORE_SHARED(urcu_gp_ctr, urcu_gp_ctr ^ RCU_GP_CTR); -} - void synchronize_rcu(void) { unsigned long was_online; - was_online = rcu_reader_qs_gp; + was_online = rcu_reader.ctr; /* All threads should read qparity before accessing data structure * where new ptr points to. @@ -180,56 +198,47 @@ void synchronize_rcu(void) * threads registered as readers. */ if (was_online) - STORE_SHARED(rcu_reader_qs_gp, 0); + STORE_SHARED(rcu_reader.ctr, 0); - internal_urcu_lock(); + mutex_lock(&rcu_gp_lock); - 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. - */ + if (list_empty(®istry)) + goto out; /* * 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 - * committing qparity update to memory. 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. + * committing next rcu_gp_ctr update to memory. Failure to do so could + * result in the writer waiting forever while new readers are always + * accessing data (no progress). Enforce compiler-order of load + * rcu_reader ctr before store to rcu_gp_ctr. */ - - switch_next_urcu_qparity(); /* 1 -> 0 */ + barrier(); /* - * 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 */ - - internal_urcu_unlock(); + update_counter_and_wait(); /* 1 -> 0, wait readers in parity 1 */ +out: + mutex_unlock(&rcu_gp_lock); /* * Finish waiting for reader threads before letting the old ptr being * freed. */ if (was_online) - _STORE_SHARED(rcu_reader_qs_gp, LOAD_SHARED(urcu_gp_ctr)); + _STORE_SHARED(rcu_reader.ctr, LOAD_SHARED(rcu_gp_ctr)); smp_mb(); } #else /* !(BITS_PER_LONG < 64) */ @@ -237,7 +246,7 @@ void synchronize_rcu(void) { unsigned long was_online; - was_online = rcu_reader_qs_gp; + was_online = rcu_reader.ctr; /* * Mark the writer thread offline to make sure we don't wait for @@ -246,15 +255,17 @@ void synchronize_rcu(void) */ smp_mb(); if (was_online) - STORE_SHARED(rcu_reader_qs_gp, 0); + STORE_SHARED(rcu_reader.ctr, 0); - internal_urcu_lock(); - STORE_SHARED(urcu_gp_ctr, urcu_gp_ctr + RCU_GP_CTR); - wait_for_quiescent_state(); - internal_urcu_unlock(); + mutex_lock(&rcu_gp_lock); + if (list_empty(®istry)) + goto out; + update_counter_and_wait(); +out: + mutex_unlock(&rcu_gp_lock); if (was_online) - _STORE_SHARED(rcu_reader_qs_gp, LOAD_SHARED(urcu_gp_ctr)); + _STORE_SHARED(rcu_reader.ctr, LOAD_SHARED(rcu_gp_ctr)); smp_mb(); } #endif /* !(BITS_PER_LONG < 64) */ @@ -273,38 +284,6 @@ 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_cmpxchg_pointer_sym(void **p, void *old, void *_new) -{ - wmb(); - return cmpxchg(p, old, _new); -} - -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; -} - void rcu_quiescent_state(void) { _rcu_quiescent_state(); @@ -320,59 +299,14 @@ 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) { - internal_urcu_lock(); - rcu_add_reader(pthread_self()); - internal_urcu_unlock(); + rcu_reader.tid = pthread_self(); + assert(rcu_reader.ctr == 0); + + mutex_lock(&rcu_gp_lock); + list_add(&rcu_reader.node, ®istry); + mutex_unlock(&rcu_gp_lock); _rcu_thread_online(); } @@ -383,7 +317,12 @@ void rcu_unregister_thread(void) * with a waiting writer. */ _rcu_thread_offline(); - internal_urcu_lock(); - rcu_remove_reader(pthread_self()); - internal_urcu_unlock(); + mutex_lock(&rcu_gp_lock); + list_del(&rcu_reader.node); + mutex_unlock(&rcu_gp_lock); +} + +void rcu_exit(void) +{ + assert(list_empty(®istry)); }