X-Git-Url: http://git.liburcu.org/?p=urcu.git;a=blobdiff_plain;f=urcu-qsbr.c;h=dac664935d7b898bd3dcce494845c7471c09749d;hp=c0f055441930ab8718cd4d4347325bd6671dc2fc;hb=ba59a0c7b244a0939a2298fc76a9002436ef9674;hpb=d1238495fdaf1c85447690231bf5d1838b83bf88 diff --git a/urcu-qsbr.c b/urcu-qsbr.c index c0f0554..dac6649 100644 --- a/urcu-qsbr.c +++ b/urcu-qsbr.c @@ -32,29 +32,32 @@ #include #include +#define BUILD_QSBR_LIB #include "urcu-qsbr-static.h" /* 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; +static pthread_mutex_t urcu_mutex = PTHREAD_MUTEX_INITIALIZER; + +int gp_futex; /* * Global grace period counter. */ -long urcu_gp_ctr = 0; +unsigned long urcu_gp_ctr = RCU_GP_ONLINE; /* * Written to only by each individual reader. Read by both the reader and the * writers. */ -long __thread rcu_reader_qs_gp; +unsigned long __thread rcu_reader_qs_gp; /* Thread IDs of registered readers */ #define INIT_NUM_THREADS 4 struct reader_registry { pthread_t tid; - long *rcu_reader_qs_gp; + unsigned long *rcu_reader_qs_gp; }; #ifdef DEBUG_YIELD @@ -98,63 +101,163 @@ static void internal_urcu_unlock(void) } } -#ifdef HAS_INCOHERENT_CACHES -static void force_mb_single_thread(struct reader_registry *index) -{ - smp_mb(); -} -#endif /* #ifdef HAS_INCOHERENT_CACHES */ - -static void force_mb_all_threads(void) +/* + * synchronize_rcu() waiting. Single thread. + */ +static void wait_gp(struct reader_registry *index) { - smp_mb(); + 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); + } } static void wait_for_quiescent_state(void) { struct reader_registry *index; - if (rcu_reader_qs_gp & 1) - rcu_reader_qs_gp = urcu_gp_ctr + 1; - if (!registry) return; /* * Wait for each thread rcu_reader_qs_gp count to become 0. */ for (index = registry; index < registry + num_readers; index++) { -#ifndef HAS_INCOHERENT_CACHES - while (rcu_gp_ongoing(index->rcu_reader_qs_gp) && - (*index->rcu_reader_qs_gp - urcu_gp_ctr < 0)) - cpu_relax(); -#else /* #ifndef HAS_INCOHERENT_CACHES */ int wait_loops = 0; - /* - * BUSY-LOOP. Force the reader thread to commit its - * rcu_reader_qs_gp update to memory if we wait for too long. - */ - while (rcu_gp_ongoing(index->rcu_reader_qs_gp) && - (*index->rcu_reader_qs_gp - urcu_gp_ctr < 0)) { - if (wait_loops++ == KICK_READER_LOOPS) { - force_mb_single_thread(index); - wait_loops = 0; + + while (rcu_gp_ongoing(index->rcu_reader_qs_gp)) { + if (wait_loops++ == RCU_QS_ACTIVE_ATTEMPTS) { + wait_gp(index); } else { +#ifndef HAS_INCOHERENT_CACHES cpu_relax(); +#else /* #ifndef HAS_INCOHERENT_CACHES */ + smp_mb(); +#endif /* #else #ifndef HAS_INCOHERENT_CACHES */ } } -#endif /* #else #ifndef HAS_INCOHERENT_CACHES */ } } +/* + * Using a two-subphases algorithm for architectures with smaller than 64-bit + * long-size to ensure we do not encounter an overflow bug. + */ + +#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; + + /* 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(rcu_reader_qs_gp, 0); + + internal_urcu_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. + */ + + /* + * Wait for previous parity to be empty of readers. + */ + wait_for_quiescent_state(); /* 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. + */ + + 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. + */ + + /* + * Wait for previous parity to be empty of readers. + */ + wait_for_quiescent_state(); /* Wait readers in parity 1 */ + + internal_urcu_unlock(); + + /* + * 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)); + smp_mb(); +} +#else /* !(BITS_PER_LONG < 64) */ void synchronize_rcu(void) { + unsigned long was_online; + + was_online = rcu_reader_qs_gp; + + /* + * 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. + */ + smp_mb(); + if (was_online) + STORE_SHARED(rcu_reader_qs_gp, 0); + internal_urcu_lock(); - force_mb_all_threads(); - urcu_gp_ctr += 2; + STORE_SHARED(urcu_gp_ctr, urcu_gp_ctr + RCU_GP_CTR); wait_for_quiescent_state(); - force_mb_all_threads(); internal_urcu_unlock(); + + if (was_online) + _STORE_SHARED(rcu_reader_qs_gp, LOAD_SHARED(urcu_gp_ctr)); + smp_mb(); } +#endif /* !(BITS_PER_LONG < 64) */ /* * library wrappers to be used by non-LGPL compatible source code. @@ -181,6 +284,12 @@ void *rcu_assign_pointer_sym(void **p, void *v) 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();