From: Mathieu Desnoyers Date: Tue, 9 Jun 2009 21:50:23 +0000 (-0400) Subject: Add missing urcu-qsbr X-Git-Tag: v0.1~182 X-Git-Url: https://git.lttng.org./?a=commitdiff_plain;h=9f1621ca8d6ce9178343ae24aeef406c0ac2564a;p=userspace-rcu.git Add missing urcu-qsbr Signed-off-by: Mathieu Desnoyers --- diff --git a/urcu-qsbr.c b/urcu-qsbr.c new file mode 100644 index 0000000..fd0ebf6 --- /dev/null +++ b/urcu-qsbr.c @@ -0,0 +1,390 @@ +/* + * urcu.c + * + * Userspace RCU library + * + * Copyright (c) 2009 Mathieu Desnoyers + * Copyright (c) 2009 Paul E. McKenney, IBM Corporation. + * + * 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. + */ + +#include +#include +#include +#include +#include +#include +#include +#include + +#include "urcu-static.h" +/* Do not #define _LGPL_SOURCE to ensure we can emit the wrapper symbols */ +#include "urcu.h" + +void __attribute__((constructor)) urcu_init(void); +void __attribute__((destructor)) urcu_exit(void); + +int init_done; + +pthread_mutex_t urcu_mutex = PTHREAD_MUTEX_INITIALIZER; + +/* + * Global grace period counter. + */ +long urcu_gp_ctr = 0; + +/* + * 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; +}; + +#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; + +void internal_urcu_lock(void) +{ + int ret; + +#ifndef DISTRUST_SIGNALS_EXTREME + ret = pthread_mutex_lock(&urcu_mutex); + if (ret) { + perror("Error in pthread mutex lock"); + exit(-1); + } +#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(); + } + poll(NULL,0,10); + } +#endif /* #else #ifndef DISTRUST_SIGNALS_EXTREME */ +} + +void internal_urcu_unlock(void) +{ + int ret; + + ret = pthread_mutex_unlock(&urcu_mutex); + if (ret) { + perror("Error in pthread mutex unlock"); + exit(-1); + } +} + +#ifdef DEBUG_FULL_MB +#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) +{ + smp_mb(); +} +#else /* #ifdef DEBUG_FULL_MB */ +#ifdef HAS_INCOHERENT_CACHES +static void force_mb_single_thread(struct reader_registry *index) +{ + assert(registry); + /* + * 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; + smp_mc(); /* write ->need_mb before sending the signals */ + pthread_kill(index->tid, SIGURCU); + smp_mb(); + /* + * Wait for sighandler (and thus mb()) to execute on every thread. + * BUSY-LOOP. + */ + while (*index->need_mb) { + poll(NULL, 0, 1); + } + smp_mb(); /* read ->need_mb before ending the barrier */ +} +#endif /* #ifdef HAS_INCOHERENT_CACHES */ + +static void force_mb_all_threads(void) +{ + struct reader_registry *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) + return; + /* + * 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. + */ + for (index = registry; index < registry + num_readers; index++) { + *index->need_mb = 1; + smp_mc(); /* write need_mb before sending the signal */ + pthread_kill(index->tid, SIGURCU); + } + /* + * Wait for sighandler (and thus mb()) to execute on every thread. + * + * Note that the pthread_kill() will never be executed on systems + * that correctly deliver signals in a timely manner. However, it + * is not uncommon for kernels to have bugs that can result in + * lost or unduly delayed signals. + * + * If you are seeing the below pthread_kill() executing much at + * all, we suggest testing the underlying kernel and filing the + * 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) { + pthread_kill(index->tid, SIGURCU); + poll(NULL, 0, 1); + } + } + smp_mb(); /* read ->need_mb before ending the barrier */ +} +#endif /* #else #ifdef DEBUG_FULL_MB */ + +void wait_for_quiescent_state(void) +{ + struct reader_registry *index; + + if (!registry) + return; + /* + * Wait for each thread urcu_active_readers count to become 0. + */ + for (index = registry; index < registry + num_readers; index++) { +#ifndef HAS_INCOHERENT_CACHES + while (rcu_old_gp_ongoing(index->urcu_active_readers)) + 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. + */ + while (rcu_old_gp_ongoing(index->urcu_active_readers)) { + if (wait_loops++ == KICK_READER_LOOPS) { + force_mb_single_thread(index); + wait_loops = 0; + } else { + cpu_relax(); + } + } +#endif /* #else #ifndef HAS_INCOHERENT_CACHES */ + } +} + +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(); +} + +/* + * library wrappers to be used by non-LGPL compatible source code. + */ + +void rcu_read_lock(void) +{ + _rcu_read_lock(); +} + +void rcu_read_unlock(void) +{ + _rcu_read_unlock(); +} + +void *rcu_dereference(void *p) +{ + return _rcu_dereference(p); +} + +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 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].urcu_active_readers = &urcu_active_readers; + registry[num_readers].need_mb = &need_mb; + num_readers++; +} + +/* + * Never shrink (implementation limitation). + * This is O(nb threads). Eventually use a hash table. + */ +static void rcu_remove_reader(pthread_t id) +{ + 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); +} + +void rcu_register_thread(void) +{ + internal_urcu_lock(); + urcu_init(); /* In case gcc does not support constructor attribute */ + rcu_add_reader(pthread_self()); + internal_urcu_unlock(); +} + +void rcu_unregister_thread(void) +{ + internal_urcu_lock(); + rcu_remove_reader(pthread_self()); + internal_urcu_unlock(); +} + +#ifndef DEBUG_FULL_MB +static void sigurcu_handler(int signo, siginfo_t *siginfo, void *context) +{ + /* + * Executing this smp_mb() is the only purpose of this signal handler. + * It punctually promotes barrier() into smp_mb() on every thread it is + * executed on. + */ + smp_mb(); + need_mb = 0; + smp_mb(); +} + +/* + * 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; + ret = sigaction(SIGURCU, &act, NULL); + if (ret) { + perror("Error in sigaction"); + exit(-1); + } +} + +void urcu_exit(void) +{ + struct sigaction act; + int ret; + + ret = sigaction(SIGURCU, NULL, &act); + if (ret) { + perror("Error in sigaction"); + exit(-1); + } + assert(act.sa_sigaction == sigurcu_handler); + free(registry); +} +#endif /* #ifndef DEBUG_FULL_MB */