X-Git-Url: https://git.liburcu.org/?p=urcu.git;a=blobdiff_plain;f=urcu-qsbr.c;h=619df60511b67ce9f5408d13e5ef33f7326ee7f5;hp=0576f4142754e14840b839be35c71e72b200938a;hb=b0a841b4ff807dd29fe0cdbfe24900312f0e627b;hpb=5f373c844a426494807d41d6fd3482649f3dc400 diff --git a/urcu-qsbr.c b/urcu-qsbr.c index 0576f41..619df60 100644 --- a/urcu-qsbr.c +++ b/urcu-qsbr.c @@ -1,9 +1,9 @@ /* - * urcu.c + * urcu-qsbr.c * - * Userspace RCU library + * Userspace RCU QSBR library * - * Copyright (c) 2009 Mathieu Desnoyers + * Copyright (c) 2009 Mathieu Desnoyers * Copyright (c) 2009 Paul E. McKenney, IBM Corporation. * * This library is free software; you can redistribute it and/or @@ -23,142 +23,410 @@ * IBM's contributions to this file may be relicensed under LGPLv2 or later. */ +#define _GNU_SOURCE +#define _LGPL_SOURCE #include #include #include #include #include +#include #include #include #include -#include "urcu-qsbr.h" +#include "urcu/wfcqueue.h" +#include "urcu/map/urcu-qsbr.h" +#define BUILD_QSBR_LIB +#include "urcu/static/urcu-qsbr.h" +#include "urcu-pointer.h" +#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 */ -//#include "urcu.h" +#undef _LGPL_SOURCE +#include "urcu-qsbr.h" +#define _LGPL_SOURCE + +void __attribute__((destructor)) rcu_exit(void); -pthread_mutex_t urcu_mutex = PTHREAD_MUTEX_INITIALIZER; +/* + * rcu_gp_lock ensures mutual exclusion between threads calling + * synchronize_rcu(). + */ +static pthread_mutex_t rcu_gp_lock = PTHREAD_MUTEX_INITIALIZER; +/* + * 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. + */ +static pthread_mutex_t rcu_registry_lock = PTHREAD_MUTEX_INITIALIZER; +struct rcu_gp rcu_gp = { .ctr = RCU_GP_ONLINE }; /* - * Global grace period counter. + * Active attempts to check for reader Q.S. before calling futex(). */ -long urcu_gp_ctr = 0; +#define RCU_QS_ACTIVE_ATTEMPTS 100 /* * Written to only by each individual reader. Read by both the reader and the * writers. */ -long __thread rcu_reader_qs_gp; +DEFINE_URCU_TLS(struct rcu_reader, rcu_reader); -/* Thread IDs of registered readers */ -#define INIT_NUM_THREADS 4 +static CDS_LIST_HEAD(registry); -struct reader_registry { - pthread_t tid; - long *rcu_reader_qs_gp; - char *need_mb; -}; - -#ifdef DEBUG_YIELD -unsigned int yield_active; -unsigned int __thread rand_yield; -#endif - -static struct reader_registry *registry; -static char __thread need_mb; -static int num_readers, alloc_readers; +/* + * Queue keeping threads awaiting to wait for a grace period. Contains + * struct gp_waiters_thread objects. + */ +static DEFINE_URCU_WAIT_QUEUE(gp_waiters); -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); - if (ret) { - perror("Error in pthread mutex lock"); - exit(-1); - } + ret = pthread_mutex_lock(mutex); + if (ret) + urcu_die(ret); #else /* #ifndef DISTRUST_SIGNALS_EXTREME */ - while ((ret = pthread_mutex_trylock(&urcu_mutex)) != 0) { - if (ret != EBUSY && ret != EINTR) { - printf("ret = %d, errno = %d\n", ret, errno); - perror("Error in pthread mutex lock"); - exit(-1); - } - if (need_mb) { - smp_mb(); - need_mb = 0; - smp_mb(); - } + while ((ret = pthread_mutex_trylock(mutex)) != 0) { + if (ret != EBUSY && ret != EINTR) + urcu_die(ret); poll(NULL,0,10); } #endif /* #else #ifndef DISTRUST_SIGNALS_EXTREME */ } -void internal_urcu_unlock(void) +static void mutex_unlock(pthread_mutex_t *mutex) { int ret; - ret = pthread_mutex_unlock(&urcu_mutex); - if (ret) { - perror("Error in pthread mutex unlock"); - exit(-1); - } + ret = pthread_mutex_unlock(mutex); + if (ret) + urcu_die(ret); } -#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(void) { - smp_mb(); + /* Read reader_gp before read futex */ + cmm_smp_rmb(); + 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); + } + } } -void wait_for_quiescent_state(void) +/* + * 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) { - struct reader_registry *index; + unsigned int wait_loops = 0; + struct rcu_reader *index, *tmp; - if (!registry) - return; /* - * Wait for each thread rcu_reader_qs_gp count to become 0. + * 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. */ - for (index = registry; index < registry + num_readers; index++) { + for (;;) { + if (wait_loops < RCU_QS_ACTIVE_ATTEMPTS) + wait_loops++; + if (wait_loops >= RCU_QS_ACTIVE_ATTEMPTS) { + uatomic_set(&rcu_gp.futex, -1); + /* + * Write futex before write waiting (the other side + * reads them in the opposite order). + */ + cmm_smp_wmb(); + cds_list_for_each_entry(index, input_readers, node) { + _CMM_STORE_SHARED(index->waiting, 1); + } + /* Write futex before read reader_gp */ + cmm_smp_mb(); + } + 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; + } + } + + if (cds_list_empty(input_readers)) { + if (wait_loops >= RCU_QS_ACTIVE_ATTEMPTS) { + /* Read reader_gp before write futex */ + cmm_smp_mb(); + 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 { #ifndef HAS_INCOHERENT_CACHES - while (rcu_gp_ongoing(index->rcu_reader_qs_gp) && - (*index->rcu_reader_qs_gp - urcu_gp_ctr < 0)) - cpu_relax(); + caa_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; - } else { - cpu_relax(); + cmm_smp_mb(); +#endif /* #else #ifndef HAS_INCOHERENT_CACHES */ } + /* Re-lock the registry lock before the next loop. */ + mutex_lock(&rcu_registry_lock); } -#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 (CAA_BITS_PER_LONG < 64) +void synchronize_rcu(void) +{ + CDS_LIST_HEAD(cur_snap_readers); + CDS_LIST_HEAD(qsreaders); + unsigned long was_online; + DEFINE_URCU_WAIT_NODE(wait, URCU_WAIT_WAITING); + struct urcu_waiters waiters; + + 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 + * includes a memory barrier. + * + * 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) + rcu_thread_offline(); + else + cmm_smp_mb(); + + /* + * 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. + */ + if (urcu_wait_add(&gp_waiters, &wait) != 0) { + /* Not first in queue: will be awakened by another thread. */ + urcu_adaptative_busy_wait(&wait); + goto gp_end; + } + /* 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); + + 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 + * 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. + */ + 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(); + + /* Switch parity: 0 -> 1, 1 -> 0 */ + CMM_STORE_SHARED(rcu_gp.ctr, rcu_gp.ctr ^ RCU_GP_CTR); + + /* + * 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 URCU_TLS(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() can release and grab again rcu_registry_lock + * interally. + */ + wait_for_readers(&cur_snap_readers, NULL, &qsreaders); + + /* + * Put quiescent reader list back into registry. + */ + cds_list_splice(&qsreaders, ®istry); +out: + mutex_unlock(&rcu_registry_lock); + mutex_unlock(&rcu_gp_lock); + urcu_wake_all_waiters(&waiters); +gp_end: + /* + * Finish waiting for reader threads before letting the old ptr being + * freed. + */ + if (was_online) + rcu_thread_online(); + else + cmm_smp_mb(); +} +#else /* !(CAA_BITS_PER_LONG < 64) */ void synchronize_rcu(void) { - internal_urcu_lock(); - force_mb_all_threads(); - urcu_gp_ctr += 2; - wait_for_quiescent_state(); - force_mb_all_threads(); - internal_urcu_unlock(); + CDS_LIST_HEAD(qsreaders); + unsigned long was_online; + DEFINE_URCU_WAIT_NODE(wait, URCU_WAIT_WAITING); + struct urcu_waiters waiters; + + was_online = rcu_read_ongoing(); + + /* + * 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) + rcu_thread_offline(); + else + cmm_smp_mb(); + + /* + * 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. + */ + if (urcu_wait_add(&gp_waiters, &wait) != 0) { + /* Not first in queue: will be awakened by another thread. */ + urcu_adaptative_busy_wait(&wait); + goto gp_end; + } + /* 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); + + 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); + + /* + * 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 URCU_TLS(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 count of be quiescent. + * wait_for_readers() can release and grab again rcu_registry_lock + * interally. + */ + wait_for_readers(®istry, NULL, &qsreaders); + + /* + * Put quiescent reader list back into registry. + */ + cds_list_splice(&qsreaders, ®istry); +out: + mutex_unlock(&rcu_registry_lock); + mutex_unlock(&rcu_gp_lock); + urcu_wake_all_waiters(&waiters); +gp_end: + if (was_online) + rcu_thread_online(); + else + cmm_smp_mb(); } +#endif /* !(CAA_BITS_PER_LONG < 64) */ /* * library wrappers to be used by non-LGPL compatible source code. @@ -174,86 +442,34 @@ void rcu_read_unlock(void) _rcu_read_unlock(); } -void *rcu_dereference(void *p) +int rcu_read_ongoing(void) { - return _rcu_dereference(p); + return _rcu_read_ongoing(); } -void *rcu_assign_pointer_sym(void **p, void *v) +void rcu_quiescent_state(void) { - wmb(); - return STORE_SHARED(p, v); + _rcu_quiescent_state(); } -void *rcu_xchg_pointer_sym(void **p, void *v) +void rcu_thread_offline(void) { - 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; -} - -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; - registry[num_readers].need_mb = &need_mb; - num_readers++; + _rcu_thread_offline(); } -/* - * Never shrink (implementation limitation). - * This is O(nb threads). Eventually use a hash table. - */ -static void rcu_remove_reader(pthread_t id) +void rcu_thread_online(void) { - 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); + _rcu_thread_online(); } void rcu_register_thread(void) { - internal_urcu_lock(); - rcu_add_reader(pthread_self()); - internal_urcu_unlock(); + URCU_TLS(rcu_reader).tid = pthread_self(); + assert(URCU_TLS(rcu_reader).ctr == 0); + + mutex_lock(&rcu_registry_lock); + cds_list_add(&URCU_TLS(rcu_reader).node, ®istry); + mutex_unlock(&rcu_registry_lock); _rcu_thread_online(); } @@ -264,7 +480,21 @@ 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_registry_lock); + cds_list_del(&URCU_TLS(rcu_reader).node); + mutex_unlock(&rcu_registry_lock); +} + +void rcu_exit(void) +{ + /* + * Assertion disabled because call_rcu threads are now rcu + * readers, and left running at exit. + * assert(cds_list_empty(®istry)); + */ } + +DEFINE_RCU_FLAVOR(rcu_flavor); + +#include "urcu-call-rcu-impl.h" +#include "urcu-defer-impl.h"