X-Git-Url: http://git.liburcu.org/?p=urcu.git;a=blobdiff_plain;f=urcu-qsbr.c;h=af82fb7e6d3d6bbe3d6ef199c5c9d23ce9253163;hp=3c2c65da4aa14e5b6cbf4a7c8b259ab6d86adf3c;hb=2af1c19e6a553878fcb2a5106f050d5ed7ac0f54;hpb=bf6822a6b57e21a18a01731277355ab2e4eb23f3 diff --git a/urcu-qsbr.c b/urcu-qsbr.c index 3c2c65d..af82fb7 100644 --- a/urcu-qsbr.c +++ b/urcu-qsbr.c @@ -52,14 +52,22 @@ void __attribute__((destructor)) rcu_exit(void); +/* + * rcu_gp_lock ensures mutual exclusion between threads calling + * synchronize_rcu(). + */ static pthread_mutex_t rcu_gp_lock = PTHREAD_MUTEX_INITIALIZER; - -int32_t rcu_gp_futex; - /* - * Global grace period counter. + * rcu_registry_lock ensures mutual exclusion between threads + * registering and unregistering themselves to/from the registry, and + * with threads reading that registry from synchronize_rcu(). However, + * this lock is not held all the way through the completion of awaiting + * for the grace period. It is sporadically released between iterations + * on the registry. + * rcu_registry_lock may nest inside rcu_gp_lock. */ -unsigned long rcu_gp_ctr = RCU_GP_ONLINE; +static pthread_mutex_t rcu_registry_lock = PTHREAD_MUTEX_INITIALIZER; +struct rcu_gp rcu_gp = { .ctr = RCU_GP_ONLINE }; /* * Active attempts to check for reader Q.S. before calling futex(). @@ -72,11 +80,6 @@ unsigned long rcu_gp_ctr = RCU_GP_ONLINE; */ DEFINE_URCU_TLS(struct rcu_reader, rcu_reader); -#ifdef DEBUG_YIELD -unsigned int rcu_yield_active; -DEFINE_URCU_TLS(unsigned int, rcu_rand_yield); -#endif - static CDS_LIST_HEAD(registry); /* @@ -118,27 +121,45 @@ static void wait_gp(void) { /* Read reader_gp before read futex */ cmm_smp_rmb(); - if (uatomic_read(&rcu_gp_futex) == -1) - futex_noasync(&rcu_gp_futex, FUTEX_WAIT, -1, - NULL, NULL, 0); + if (uatomic_read(&rcu_gp.futex) != -1) + return; + while (futex_noasync(&rcu_gp.futex, FUTEX_WAIT, -1, + NULL, NULL, 0)) { + switch (errno) { + case EWOULDBLOCK: + /* Value already changed. */ + return; + case EINTR: + /* Retry if interrupted by signal. */ + break; /* Get out of switch. */ + default: + /* Unexpected error. */ + urcu_die(errno); + } + } } +/* + * Always called with rcu_registry lock held. Releases this lock between + * iterations and grabs it again. Holds the lock when it returns. + */ static void wait_for_readers(struct cds_list_head *input_readers, struct cds_list_head *cur_snap_readers, struct cds_list_head *qsreaders) { - int wait_loops = 0; + unsigned int wait_loops = 0; struct rcu_reader *index, *tmp; /* * Wait for each thread URCU_TLS(rcu_reader).ctr to either * indicate quiescence (offline), or for them to observe the - * current rcu_gp_ctr value. + * current rcu_gp.ctr value. */ for (;;) { - wait_loops++; + if (wait_loops < RCU_QS_ACTIVE_ATTEMPTS) + wait_loops++; if (wait_loops >= RCU_QS_ACTIVE_ATTEMPTS) { - uatomic_set(&rcu_gp_futex, -1); + uatomic_set(&rcu_gp.futex, -1); /* * Write futex before write waiting (the other side * reads them in the opposite order). @@ -177,10 +198,12 @@ static void wait_for_readers(struct cds_list_head *input_readers, if (wait_loops >= RCU_QS_ACTIVE_ATTEMPTS) { /* Read reader_gp before write futex */ cmm_smp_mb(); - uatomic_set(&rcu_gp_futex, 0); + uatomic_set(&rcu_gp.futex, 0); } break; } else { + /* Temporarily unlock the registry lock. */ + mutex_unlock(&rcu_registry_lock); if (wait_loops >= RCU_QS_ACTIVE_ATTEMPTS) { wait_gp(); } else { @@ -190,6 +213,8 @@ static void wait_for_readers(struct cds_list_head *input_readers, cmm_smp_mb(); #endif /* #else #ifndef HAS_INCOHERENT_CACHES */ } + /* Re-lock the registry lock before the next loop. */ + mutex_lock(&rcu_registry_lock); } } } @@ -208,7 +233,7 @@ void synchronize_rcu(void) DEFINE_URCU_WAIT_NODE(wait, URCU_WAIT_WAITING); struct urcu_waiters waiters; - was_online = URCU_TLS(rcu_reader).ctr; + was_online = rcu_read_ongoing(); /* All threads should read qparity before accessing data structure * where new ptr points to. In the "then" case, rcu_thread_offline @@ -243,21 +268,25 @@ void synchronize_rcu(void) */ urcu_move_waiters(&waiters, &gp_waiters); + mutex_lock(&rcu_registry_lock); + if (cds_list_empty(®istry)) goto out; /* * Wait for readers to observe original parity or be quiescent. + * wait_for_readers() can release and grab again rcu_registry_lock + * interally. */ wait_for_readers(®istry, &cur_snap_readers, &qsreaders); /* * Must finish waiting for quiescent state for original parity - * before committing next rcu_gp_ctr update to memory. Failure + * 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 URCU_TLS(rcu_reader).ctr before store - * to rcu_gp_ctr. + * to rcu_gp.ctr. */ cmm_barrier(); @@ -269,13 +298,13 @@ 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); + CMM_STORE_SHARED(rcu_gp.ctr, rcu_gp.ctr ^ RCU_GP_CTR); /* - * Must commit rcu_gp_ctr update to memory before waiting for + * 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 + * (no progress). Enforce compiler-order of store to rcu_gp.ctr * before load URCU_TLS(rcu_reader).ctr. */ cmm_barrier(); @@ -289,6 +318,8 @@ void synchronize_rcu(void) /* * Wait for readers to observe new parity or be quiescent. + * wait_for_readers() can release and grab again rcu_registry_lock + * interally. */ wait_for_readers(&cur_snap_readers, NULL, &qsreaders); @@ -297,6 +328,7 @@ void synchronize_rcu(void) */ cds_list_splice(&qsreaders, ®istry); out: + mutex_unlock(&rcu_registry_lock); mutex_unlock(&rcu_gp_lock); urcu_wake_all_waiters(&waiters); gp_end: @@ -317,7 +349,7 @@ void synchronize_rcu(void) DEFINE_URCU_WAIT_NODE(wait, URCU_WAIT_WAITING); struct urcu_waiters waiters; - was_online = URCU_TLS(rcu_reader).ctr; + was_online = rcu_read_ongoing(); /* * Mark the writer thread offline to make sure we don't wait for @@ -349,17 +381,19 @@ void synchronize_rcu(void) */ urcu_move_waiters(&waiters, &gp_waiters); + mutex_lock(&rcu_registry_lock); + if (cds_list_empty(®istry)) goto out; /* Increment current G.P. */ - CMM_STORE_SHARED(rcu_gp_ctr, rcu_gp_ctr + RCU_GP_CTR); + CMM_STORE_SHARED(rcu_gp.ctr, rcu_gp.ctr + RCU_GP_CTR); /* - * Must commit rcu_gp_ctr update to memory before waiting for + * 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 + * (no progress). Enforce compiler-order of store to rcu_gp.ctr * before load URCU_TLS(rcu_reader).ctr. */ cmm_barrier(); @@ -373,6 +407,8 @@ void synchronize_rcu(void) /* * Wait for readers to observe new count of be quiescent. + * wait_for_readers() can release and grab again rcu_registry_lock + * interally. */ wait_for_readers(®istry, NULL, &qsreaders); @@ -381,6 +417,7 @@ void synchronize_rcu(void) */ cds_list_splice(&qsreaders, ®istry); out: + mutex_unlock(&rcu_registry_lock); mutex_unlock(&rcu_gp_lock); urcu_wake_all_waiters(&waiters); gp_end: @@ -405,6 +442,11 @@ void rcu_read_unlock(void) _rcu_read_unlock(); } +int rcu_read_ongoing(void) +{ + return _rcu_read_ongoing(); +} + void rcu_quiescent_state(void) { _rcu_quiescent_state(); @@ -425,9 +467,11 @@ void rcu_register_thread(void) URCU_TLS(rcu_reader).tid = pthread_self(); assert(URCU_TLS(rcu_reader).ctr == 0); - mutex_lock(&rcu_gp_lock); + mutex_lock(&rcu_registry_lock); + assert(!URCU_TLS(rcu_reader).registered); + URCU_TLS(rcu_reader).registered = 1; cds_list_add(&URCU_TLS(rcu_reader).node, ®istry); - mutex_unlock(&rcu_gp_lock); + mutex_unlock(&rcu_registry_lock); _rcu_thread_online(); } @@ -438,9 +482,11 @@ void rcu_unregister_thread(void) * with a waiting writer. */ _rcu_thread_offline(); - mutex_lock(&rcu_gp_lock); + assert(URCU_TLS(rcu_reader).registered); + URCU_TLS(rcu_reader).registered = 0; + mutex_lock(&rcu_registry_lock); cds_list_del(&URCU_TLS(rcu_reader).node); - mutex_unlock(&rcu_gp_lock); + mutex_unlock(&rcu_registry_lock); } void rcu_exit(void)