X-Git-Url: https://git.lttng.org/?p=urcu.git;a=blobdiff_plain;f=urcu.c;h=c13ad634e7cb7b98f24d8c9a5a756eb26487bf7b;hp=337f7640b44d208855277f6fc53d9322f212d638;hb=efafc824ca148c6b2ca7f95dc86d2aaa38d4a923;hpb=54843abcc17c8e8b7600ed635e966c6970d8d20f diff --git a/urcu.c b/urcu.c index 337f764..c13ad63 100644 --- a/urcu.c +++ b/urcu.c @@ -3,9 +3,22 @@ * * Userspace RCU library * - * Copyright February 2009 - Mathieu Desnoyers + * Copyright (c) 2009 Mathieu Desnoyers + * Copyright (c) 2009 Paul E. McKenney, IBM Corporation. * - * Distributed under GPLv2 + * This library is free software; you can redistribute it and/or + * modify it under the terms of the GNU Lesser General Public + * License as published by the Free Software Foundation; either + * version 2.1 of the License, or (at your option) any later version. + * + * This library is distributed in the hope that it will be useful, + * but WITHOUT ANY WARRANTY; without even the implied warranty of + * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU + * Lesser General Public License for more details. + * + * You should have received a copy of the GNU Lesser General Public + * License along with this library; if not, write to the Free Software + * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA * * IBM's contributions to this file may be relicensed under LGPLv2 or later. */ @@ -19,14 +32,29 @@ #include #include +#include "urcu-static.h" +/* Do not #define _LGPL_SOURCE to ensure we can emit the wrapper symbols */ #include "urcu.h" -pthread_mutex_t urcu_mutex = PTHREAD_MUTEX_INITIALIZER; +#ifndef URCU_MB +static int init_done; + +void __attribute__((constructor)) urcu_init(void); +void __attribute__((destructor)) urcu_exit(void); +#else +void urcu_init(void) +{ +} +#endif + +static pthread_mutex_t urcu_mutex = PTHREAD_MUTEX_INITIALIZER; + +int gp_futex; /* * Global grace period counter. * Contains the current RCU_GP_CTR_BIT. - * Also has a RCU_GP_CTR_BIT of 1, to accelerate the reader fast path. + * Also has a RCU_GP_COUNT of 1, to accelerate the reader fast path. * Written to only by writer with mutex taken. Read by both writer and readers. */ long urcu_gp_ctr = RCU_GP_COUNT; @@ -35,27 +63,16 @@ long urcu_gp_ctr = RCU_GP_COUNT; * Written to only by each individual reader. Read by both the reader and the * writers. */ -long __thread urcu_active_readers; - -/* Thread IDs of registered readers */ -#define INIT_NUM_THREADS 4 - -struct reader_registry { - pthread_t tid; - long *urcu_active_readers; - char *need_mb; -}; +struct urcu_reader __thread urcu_reader; #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; +static LIST_HEAD(registry); -void internal_urcu_lock(void) +static void internal_urcu_lock(void) { int ret; @@ -72,9 +89,9 @@ void internal_urcu_lock(void) perror("Error in pthread mutex lock"); exit(-1); } - if (need_mb) { + if (urcu_reader.need_mb) { smp_mb(); - need_mb = 0; + urcu_reader.need_mb = 0; smp_mb(); } poll(NULL,0,10); @@ -82,7 +99,7 @@ void internal_urcu_lock(void) #endif /* #else #ifndef DISTRUST_SIGNALS_EXTREME */ } -void internal_urcu_unlock(void) +static void internal_urcu_unlock(void) { int ret; @@ -101,30 +118,30 @@ static void switch_next_urcu_qparity(void) STORE_SHARED(urcu_gp_ctr, urcu_gp_ctr ^ RCU_GP_CTR_BIT); } -#ifdef DEBUG_FULL_MB -#ifdef HAS_INCOHERENT_CACHES -static void force_mb_single_thread(struct reader_registry *index) +#ifdef URCU_MB +#if 0 /* unused */ +static void force_mb_single_thread(struct urcu_reader *index) { smp_mb(); } -#endif /* #ifdef HAS_INCOHERENT_CACHES */ +#endif //0 static void force_mb_all_threads(void) { smp_mb(); } -#else /* #ifdef DEBUG_FULL_MB */ -#ifdef HAS_INCOHERENT_CACHES -static void force_mb_single_thread(struct reader_registry *index) +#else /* #ifdef URCU_MB */ +#if 0 /* unused */ +static void force_mb_single_thread(struct urcu_reader *index) { - assert(registry); + assert(!list_empty(®istry)); /* * pthread_kill has a smp_mb(). But beware, we assume it performs * a cache flush on architectures with non-coherent cache. Let's play * safe and don't assume anything : we use smp_mc() to make sure the * cache flush is enforced. */ - *index->need_mb = 1; + index->need_mb = 1; smp_mc(); /* write ->need_mb before sending the signals */ pthread_kill(index->tid, SIGURCU); smp_mb(); @@ -132,21 +149,22 @@ static void force_mb_single_thread(struct reader_registry *index) * Wait for sighandler (and thus mb()) to execute on every thread. * BUSY-LOOP. */ - while (*index->need_mb) { + while (index->need_mb) { poll(NULL, 0, 1); } smp_mb(); /* read ->need_mb before ending the barrier */ } -#endif /* #ifdef HAS_INCOHERENT_CACHES */ +#endif //0 static void force_mb_all_threads(void) { - struct reader_registry *index; + struct urcu_reader *index; + /* * Ask for each threads to execute a smp_mb() so we can consider the * compiler barriers around rcu read lock as real memory barriers. */ - if (!registry) + if (list_empty(®istry)) return; /* * pthread_kill has a smp_mb(). But beware, we assume it performs @@ -154,8 +172,8 @@ static void force_mb_all_threads(void) * safe and don't assume anything : we use smp_mc() to make sure the * cache flush is enforced. */ - for (index = registry; index < registry + num_readers; index++) { - *index->need_mb = 1; + list_for_each_entry(index, ®istry, head) { + index->need_mb = 1; smp_mc(); /* write need_mb before sending the signal */ pthread_kill(index->tid, SIGURCU); } @@ -172,45 +190,95 @@ static void force_mb_all_threads(void) * relevant bug report. For Linux kernels, we recommend getting * the Linux Test Project (LTP). */ - for (index = registry; index < registry + num_readers; index++) { - while (*index->need_mb) { + list_for_each_entry(index, ®istry, head) { + while (index->need_mb) { pthread_kill(index->tid, SIGURCU); poll(NULL, 0, 1); } } smp_mb(); /* read ->need_mb before ending the barrier */ } -#endif /* #else #ifdef DEBUG_FULL_MB */ +#endif /* #else #ifdef URCU_MB */ + +/* + * synchronize_rcu() waiting. Single thread. + */ +static void wait_gp(void) +{ + /* Read reader_gp before read futex */ + force_mb_all_threads(); + if (uatomic_read(&gp_futex) == -1) + futex(&gp_futex, FUTEX_WAIT, -1, + NULL, NULL, 0); +} void wait_for_quiescent_state(void) { - struct reader_registry *index; + LIST_HEAD(qsreaders); + int wait_loops = 0; + struct urcu_reader *index, *tmp; - if (!registry) + if (list_empty(®istry)) return; /* - * Wait for each thread urcu_active_readers count to become 0. + * Wait for each thread urcu_reader.ctr count to become 0. */ - for (index = registry; index < registry + num_readers; index++) { + for (;;) { + wait_loops++; + if (wait_loops == RCU_QS_ACTIVE_ATTEMPTS) { + uatomic_dec(&gp_futex); + /* Write futex before read reader_gp */ + force_mb_all_threads(); + } + + list_for_each_entry_safe(index, tmp, ®istry, head) { + if (!rcu_old_gp_ongoing(&index->ctr)) + list_move(&index->head, &qsreaders); + } + #ifndef HAS_INCOHERENT_CACHES - while (rcu_old_gp_ongoing(index->urcu_active_readers)) - cpu_relax(); + if (list_empty(®istry)) { + if (wait_loops == RCU_QS_ACTIVE_ATTEMPTS) { + /* Read reader_gp before write futex */ + force_mb_all_threads(); + uatomic_set(&gp_futex, 0); + } + break; + } else { + if (wait_loops == RCU_QS_ACTIVE_ATTEMPTS) + wait_gp(); + else + cpu_relax(); + } #else /* #ifndef HAS_INCOHERENT_CACHES */ - int wait_loops = 0; /* * BUSY-LOOP. Force the reader thread to commit its - * urcu_active_readers update to memory if we wait for too long. + * urcu_reader.ctr update to memory if we wait for too long. */ - while (rcu_old_gp_ongoing(index->urcu_active_readers)) { - if (wait_loops++ == KICK_READER_LOOPS) { - force_mb_single_thread(index); + if (list_empty(®istry)) { + if (wait_loops == RCU_QS_ACTIVE_ATTEMPTS) { + /* Read reader_gp before write futex */ + force_mb_all_threads(); + uatomic_set(&gp_futex, 0); + } + break; + } else { + switch (wait_loops) { + case RCU_QS_ACTIVE_ATTEMPTS: + wait_gp(); + break; /* only escape switch */ + case KICK_READER_LOOPS: + force_mb_all_threads(); wait_loops = 0; - } else { + break; /* only escape switch */ + default: cpu_relax(); } } #endif /* #else #ifndef HAS_INCOHERENT_CACHES */ } + /* put back the reader list in the registry */ + list_splice(&qsreaders, ®istry); } void synchronize_rcu(void) @@ -233,6 +301,13 @@ void synchronize_rcu(void) * 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. */ @@ -246,6 +321,13 @@ void synchronize_rcu(void) * 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(); + switch_next_urcu_qparity(); /* 1 -> 0 */ /* @@ -256,6 +338,13 @@ void synchronize_rcu(void) * 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. */ @@ -269,71 +358,73 @@ void synchronize_rcu(void) internal_urcu_unlock(); } -void urcu_add_reader(pthread_t id) +/* + * library wrappers to be used by non-LGPL compatible source code. + */ + +void rcu_read_lock(void) { - struct reader_registry *oldarray; + _rcu_read_lock(); +} - 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].urcu_active_readers = &urcu_active_readers; - registry[num_readers].need_mb = &need_mb; - num_readers++; +void rcu_read_unlock(void) +{ + _rcu_read_unlock(); } -/* - * Never shrink (implementation limitation). - * This is O(nb threads). Eventually use a hash table. - */ -void urcu_remove_reader(pthread_t id) +void *rcu_dereference(void *p) { - 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].urcu_active_readers = NULL; - num_readers--; - return; - } - } - /* Hrm not found, forgot to register ? */ - assert(0); + return _rcu_dereference(p); } -void urcu_register_thread(void) +void *rcu_assign_pointer_sym(void **p, void *v) { + wmb(); + return STORE_SHARED(*p, v); +} + +void *rcu_xchg_pointer_sym(void **p, void *v) +{ + wmb(); + return uatomic_xchg(p, v); +} + +void *rcu_cmpxchg_pointer_sym(void **p, void *old, void *_new) +{ + wmb(); + return uatomic_cmpxchg(p, old, _new); +} + +void *rcu_publish_content_sym(void **p, void *v) +{ + void *oldptr; + + oldptr = _rcu_xchg_pointer(p, v); + synchronize_rcu(); + return oldptr; +} + +void rcu_register_thread(void) +{ + urcu_reader.tid = pthread_self(); + assert(urcu_reader.need_mb == 0); + assert(urcu_reader.ctr == 0); + internal_urcu_lock(); - urcu_add_reader(pthread_self()); + urcu_init(); /* In case gcc does not support constructor attribute */ + list_add(&urcu_reader.head, ®istry); internal_urcu_unlock(); } -void urcu_unregister_thread(void) +void rcu_unregister_thread(void) { internal_urcu_lock(); - urcu_remove_reader(pthread_self()); + list_del(&urcu_reader.head); internal_urcu_unlock(); } -#ifndef DEBUG_FULL_MB -void sigurcu_handler(int signo, siginfo_t *siginfo, void *context) +#ifndef URCU_MB +static void sigurcu_handler(int signo, siginfo_t *siginfo, void *context) { /* * Executing this smp_mb() is the only purpose of this signal handler. @@ -341,16 +432,30 @@ void sigurcu_handler(int signo, siginfo_t *siginfo, void *context) * executed on. */ smp_mb(); - need_mb = 0; + urcu_reader.need_mb = 0; smp_mb(); } -void __attribute__((constructor)) urcu_init(void) +/* + * urcu_init constructor. Called when the library is linked, but also when + * reader threads are calling rcu_register_thread(). + * Should only be called by a single thread at a given time. This is ensured by + * holing the internal_urcu_lock() from rcu_register_thread() or by running at + * library load time, which should not be executed by multiple threads nor + * concurrently with rcu_register_thread() anyway. + */ +void urcu_init(void) { struct sigaction act; int ret; + if (init_done) + return; + init_done = 1; + act.sa_sigaction = sigurcu_handler; + act.sa_flags = SA_SIGINFO | SA_RESTART; + sigemptyset(&act.sa_mask); ret = sigaction(SIGURCU, &act, NULL); if (ret) { perror("Error in sigaction"); @@ -358,7 +463,7 @@ void __attribute__((constructor)) urcu_init(void) } } -void __attribute__((destructor)) urcu_exit(void) +void urcu_exit(void) { struct sigaction act; int ret; @@ -369,6 +474,6 @@ void __attribute__((destructor)) urcu_exit(void) exit(-1); } assert(act.sa_sigaction == sigurcu_handler); - free(registry); + assert(list_empty(®istry)); } -#endif /* #ifndef DEBUG_FULL_MB */ +#endif /* #ifndef URCU_MB */