X-Git-Url: http://git.liburcu.org/?p=urcu.git;a=blobdiff_plain;f=urcu.c;h=a78c02bdca6a71f9e7f66c76295fc8f1f33cdd37;hp=10ea7de09efe54ff96800aae4019d7198a9efa24;hb=882f335739b978d1c55be2faeed077f315afe5d7;hpb=d73fb81f74a79aa1e4987d16179f8489b955c812 diff --git a/urcu.c b/urcu.c index 10ea7de..a78c02b 100644 --- a/urcu.c +++ b/urcu.c @@ -43,6 +43,7 @@ #include "urcu/tls-compat.h" #include "urcu-die.h" +#include "urcu-wait.h" /* Do not #define _LGPL_SOURCE to ensure we can emit the wrapper symbols */ #undef _LGPL_SOURCE @@ -63,7 +64,7 @@ #ifdef RCU_MEMBARRIER static int init_done; -int has_sys_membarrier; +int rcu_has_sys_membarrier; void __attribute__((constructor)) rcu_init(void); #endif @@ -83,7 +84,7 @@ void __attribute__((destructor)) rcu_exit(void); static pthread_mutex_t rcu_gp_lock = PTHREAD_MUTEX_INITIALIZER; -int32_t gp_futex; +int32_t rcu_gp_futex; /* * Global grace period counter. @@ -100,12 +101,18 @@ unsigned long rcu_gp_ctr = RCU_GP_COUNT; DEFINE_URCU_TLS(struct rcu_reader, rcu_reader); #ifdef DEBUG_YIELD -unsigned int yield_active; -DEFINE_URCU_TLS(unsigned int, rand_yield); +unsigned int rcu_yield_active; +DEFINE_URCU_TLS(unsigned int, rcu_rand_yield); #endif static CDS_LIST_HEAD(registry); +/* + * Queue keeping threads awaiting to wait for a grace period. Contains + * struct gp_waiters_thread objects. + */ +static DEFINE_URCU_WAIT_QUEUE(gp_waiters); + static void mutex_lock(pthread_mutex_t *mutex) { int ret; @@ -140,7 +147,7 @@ static void mutex_unlock(pthread_mutex_t *mutex) #ifdef RCU_MEMBARRIER static void smp_mb_master(int group) { - if (caa_likely(has_sys_membarrier)) + if (caa_likely(rcu_has_sys_membarrier)) membarrier(MEMBARRIER_EXPEDITED); else cmm_smp_mb(); @@ -210,58 +217,60 @@ 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, + if (uatomic_read(&rcu_gp_futex) == -1) + futex_async(&rcu_gp_futex, FUTEX_WAIT, -1, NULL, NULL, 0); } -void update_counter_and_wait(void) +static void wait_for_readers(struct cds_list_head *input_readers, + struct cds_list_head *cur_snap_readers, + struct cds_list_head *qsreaders) { - CDS_LIST_HEAD(qsreaders); int wait_loops = 0; struct rcu_reader *index, *tmp; - /* Switch parity: 0 -> 1, 1 -> 0 */ - CMM_STORE_SHARED(rcu_gp_ctr, rcu_gp_ctr ^ RCU_GP_CTR_PHASE); - /* - * 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. - */ - cmm_barrier(); - - /* - * - * Adding a cmm_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. - */ - cmm_smp_mb(); - - /* - * Wait for each thread URCU_TLS(rcu_reader).ctr count to become 0. + * Wait for each thread URCU_TLS(rcu_reader).ctr to either + * indicate quiescence (not nested), or observe the current + * rcu_gp_ctr value. */ for (;;) { wait_loops++; if (wait_loops == RCU_QS_ACTIVE_ATTEMPTS) { - uatomic_dec(&gp_futex); + uatomic_dec(&rcu_gp_futex); /* Write futex before read reader_gp */ smp_mb_master(RCU_MB_GROUP); } - cds_list_for_each_entry_safe(index, tmp, ®istry, node) { - if (!rcu_gp_ongoing(&index->ctr)) - cds_list_move(&index->node, &qsreaders); + cds_list_for_each_entry_safe(index, tmp, input_readers, node) { + switch (rcu_reader_state(&index->ctr)) { + case RCU_READER_ACTIVE_CURRENT: + if (cur_snap_readers) { + cds_list_move(&index->node, + cur_snap_readers); + break; + } + /* Fall-through */ + case RCU_READER_INACTIVE: + cds_list_move(&index->node, qsreaders); + break; + case RCU_READER_ACTIVE_OLD: + /* + * Old snapshot. Leaving node in + * input_readers will make us busy-loop + * until the snapshot becomes current or + * the reader becomes inactive. + */ + break; + } } #ifndef HAS_INCOHERENT_CACHES - if (cds_list_empty(®istry)) { + if (cds_list_empty(input_readers)) { if (wait_loops == RCU_QS_ACTIVE_ATTEMPTS) { /* Read reader_gp before write futex */ smp_mb_master(RCU_MB_GROUP); - uatomic_set(&gp_futex, 0); + uatomic_set(&rcu_gp_futex, 0); } break; } else { @@ -276,11 +285,11 @@ void update_counter_and_wait(void) * URCU_TLS(rcu_reader).ctr update to memory if we wait * for too long. */ - if (cds_list_empty(®istry)) { + if (cds_list_empty(input_readers)) { if (wait_loops == RCU_QS_ACTIVE_ATTEMPTS) { /* Read reader_gp before write futex */ smp_mb_master(RCU_MB_GROUP); - uatomic_set(&gp_futex, 0); + uatomic_set(&rcu_gp_futex, 0); } break; } else { @@ -298,14 +307,40 @@ void update_counter_and_wait(void) } #endif /* #else #ifndef HAS_INCOHERENT_CACHES */ } - /* put back the reader list in the registry */ - cds_list_splice(&qsreaders, ®istry); } void synchronize_rcu(void) { + CDS_LIST_HEAD(cur_snap_readers); + CDS_LIST_HEAD(qsreaders); + DEFINE_URCU_WAIT_NODE(wait, URCU_WAIT_WAITING); + struct urcu_waiters waiters; + + /* + * Add ourself to gp_waiters queue of threads awaiting to wait + * for a grace period. Proceed to perform the grace period only + * if we are the first thread added into the queue. + * The implicit memory barrier before urcu_wait_add() + * orders prior memory accesses of threads put into the wait + * queue before their insertion into the wait queue. + */ + if (urcu_wait_add(&gp_waiters, &wait) != 0) { + /* Not first in queue: will be awakened by another thread. */ + urcu_adaptative_busy_wait(&wait); + /* Order following memory accesses after grace period. */ + cmm_smp_mb(); + return; + } + /* We won't need to wake ourself up */ + urcu_wait_set_state(&wait, URCU_WAIT_RUNNING); + mutex_lock(&rcu_gp_lock); + /* + * Move all waiters into our local queue. + */ + urcu_move_waiters(&waiters, &gp_waiters); + if (cds_list_empty(®istry)) goto out; @@ -316,12 +351,12 @@ void synchronize_rcu(void) smp_mb_master(RCU_MB_GROUP); /* - * Wait for previous parity to be empty of readers. + * Wait for readers to observe original parity or be quiescent. */ - update_counter_and_wait(); /* 0 -> 1, wait readers in parity 0 */ + wait_for_readers(®istry, &cur_snap_readers, &qsreaders); /* - * Must finish waiting for quiescent state for parity 0 before + * Must finish waiting for quiescent state for original parity before * 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 @@ -336,10 +371,34 @@ void synchronize_rcu(void) */ cmm_smp_mb(); + /* Switch parity: 0 -> 1, 1 -> 0 */ + CMM_STORE_SHARED(rcu_gp_ctr, rcu_gp_ctr ^ RCU_GP_CTR_PHASE); + + /* + * 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. + */ + cmm_barrier(); + + /* + * + * Adding a cmm_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. + */ + cmm_smp_mb(); + + /* + * Wait for readers to observe new parity or be quiescent. + */ + wait_for_readers(&cur_snap_readers, NULL, &qsreaders); + /* - * Wait for previous parity to be empty of readers. + * Put quiescent reader list back into registry. */ - update_counter_and_wait(); /* 1 -> 0, wait readers in parity 1 */ + cds_list_splice(&qsreaders, ®istry); /* Finish waiting for reader threads before letting the old ptr being * freed. Must be done within rcu_gp_lock because it iterates on reader @@ -347,6 +406,13 @@ void synchronize_rcu(void) smp_mb_master(RCU_MB_GROUP); out: mutex_unlock(&rcu_gp_lock); + + /* + * Wakeup waiters only after we have completed the grace period + * and have ensured the memory barriers at the end of the grace + * period have been issued. + */ + urcu_wake_all_waiters(&waiters); } /* @@ -363,6 +429,11 @@ void rcu_read_unlock(void) _rcu_read_unlock(); } +int rcu_read_ongoing(void) +{ + return _rcu_read_ongoing(); +} + void rcu_register_thread(void) { URCU_TLS(rcu_reader).tid = pthread_self(); @@ -389,7 +460,7 @@ void rcu_init(void) return; init_done = 1; if (!membarrier(MEMBARRIER_EXPEDITED | MEMBARRIER_QUERY)) - has_sys_membarrier = 1; + rcu_has_sys_membarrier = 1; } #endif