X-Git-Url: http://git.liburcu.org/?p=urcu.git;a=blobdiff_plain;f=urcu.c;h=b4346551b2403127da9822f08223f875c991e4ca;hp=232a57bb718fbf12be651cebd6a808b01976c924;hb=541d828d3101283ccdb1e25fa5a885e1d1743c1a;hpb=f858d07ab45c9a50e458cdcc9d5b26cbaa765de3 diff --git a/urcu.c b/urcu.c index 232a57b..b434655 100644 --- a/urcu.c +++ b/urcu.c @@ -3,245 +3,456 @@ * * 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. */ +#define _BSD_SOURCE +#define _GNU_SOURCE +#define _LGPL_SOURCE #include #include #include #include #include +#include #include +#include +#include +#include "urcu/wfqueue.h" +#include "urcu/map/urcu.h" +#include "urcu/static/urcu.h" +#include "urcu-pointer.h" + +/* Do not #define _LGPL_SOURCE to ensure we can emit the wrapper symbols */ +#undef _LGPL_SOURCE #include "urcu.h" +#define _LGPL_SOURCE + +/* + * If a reader is really non-cooperative and refuses to commit its + * rcu_active_readers count to memory (there is no barrier in the reader + * per-se), kick it after a few loops waiting for it. + */ +#define KICK_READER_LOOPS 10000 + +/* + * Active attempts to check for reader Q.S. before calling futex(). + */ +#define RCU_QS_ACTIVE_ATTEMPTS 100 + +#ifdef RCU_MEMBARRIER +static int init_done; +int has_sys_membarrier; + +void __attribute__((constructor)) rcu_init(void); +#endif -pthread_mutex_t urcu_mutex = PTHREAD_MUTEX_INITIALIZER; +#ifdef RCU_MB +void rcu_init(void) +{ +} +#endif + +#ifdef RCU_SIGNAL +static int init_done; -/* Global quiescent period parity */ -int urcu_qparity; +void __attribute__((constructor)) rcu_init(void); +void __attribute__((destructor)) rcu_exit(void); +#endif -int __thread urcu_active_readers[2]; +static pthread_mutex_t rcu_gp_lock = PTHREAD_MUTEX_INITIALIZER; + +int32_t gp_futex; + +/* + * Global grace period counter. + * Contains the current RCU_GP_CTR_PHASE. + * 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. + */ +unsigned long rcu_gp_ctr = RCU_GP_COUNT; -/* Thread IDs of registered readers */ -#define INIT_NUM_THREADS 4 +/* + * Written to only by each individual reader. Read by both the reader and the + * writers. + */ +struct rcu_reader __thread rcu_reader; -struct reader_data { - pthread_t tid; - int *urcu_active_readers; -}; +#ifdef DEBUG_YIELD +unsigned int yield_active; +unsigned int __thread rand_yield; +#endif -static struct reader_data *reader_data; -static int num_readers, alloc_readers; -static int sig_done; +static CDS_LIST_HEAD(registry); -void rcu_write_lock(void) +static void mutex_lock(pthread_mutex_t *mutex) { int ret; - ret = pthread_mutex_lock(&urcu_mutex); + +#ifndef DISTRUST_SIGNALS_EXTREME + ret = pthread_mutex_lock(mutex); if (ret) { perror("Error in pthread mutex lock"); exit(-1); } +#else /* #ifndef DISTRUST_SIGNALS_EXTREME */ + while ((ret = pthread_mutex_trylock(mutex)) != 0) { + if (ret != EBUSY && ret != EINTR) { + printf("ret = %d, errno = %d\n", ret, errno); + perror("Error in pthread mutex lock"); + exit(-1); + } + if (CMM_LOAD_SHARED(rcu_reader.need_mb)) { + cmm_smp_mb(); + _CMM_STORE_SHARED(rcu_reader.need_mb, 0); + cmm_smp_mb(); + } + poll(NULL,0,10); + } +#endif /* #else #ifndef DISTRUST_SIGNALS_EXTREME */ } -void rcu_write_unlock(void) +static void mutex_unlock(pthread_mutex_t *mutex) { int ret; - ret = pthread_mutex_unlock(&urcu_mutex); + ret = pthread_mutex_unlock(mutex); if (ret) { perror("Error in pthread mutex unlock"); exit(-1); } } -/* - * called with urcu_mutex held. - */ -static int switch_next_urcu_qparity(void) +#ifdef RCU_MEMBARRIER +static void smp_mb_master(int group) +{ + if (caa_likely(has_sys_membarrier)) + membarrier(MEMBARRIER_EXPEDITED); + else + cmm_smp_mb(); +} +#endif + +#ifdef RCU_MB +static void smp_mb_master(int group) { - int old_parity = urcu_qparity; - urcu_qparity = 1 - old_parity; - return old_parity; + cmm_smp_mb(); } +#endif -static void force_mb_all_threads(void) +#ifdef RCU_SIGNAL +static void force_mb_all_readers(void) { - struct reader_data *index; + struct rcu_reader *index; + /* - * Ask for each threads to execute a mb() so we can consider the + * Ask for each threads to execute a cmm_smp_mb() so we can consider the * compiler barriers around rcu read lock as real memory barriers. */ - if (!reader_data) + if (cds_list_empty(®istry)) return; - sig_done = 0; - mb(); /* write sig_done before sending the signals */ - for (index = reader_data; index < reader_data + num_readers; index++) - pthread_kill(index->tid, SIGURCU); + /* + * pthread_kill has a cmm_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 cmm_smp_mc() to make sure the + * cache flush is enforced. + */ + cds_list_for_each_entry(index, ®istry, node) { + CMM_STORE_SHARED(index->need_mb, 1); + pthread_kill(index->tid, SIGRCU); + } /* * Wait for sighandler (and thus mb()) to execute on every thread. - * BUSY-LOOP. + * + * 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). */ - while (sig_done < num_readers) - barrier(); - mb(); /* read sig_done before ending the barrier */ + cds_list_for_each_entry(index, ®istry, node) { + while (CMM_LOAD_SHARED(index->need_mb)) { + pthread_kill(index->tid, SIGRCU); + poll(NULL, 0, 1); + } + } + cmm_smp_mb(); /* read ->need_mb before ending the barrier */ } -void wait_for_quiescent_state(int parity) +static void smp_mb_master(int group) { - struct reader_data *index; + force_mb_all_readers(); +} +#endif /* #ifdef RCU_SIGNAL */ - if (!reader_data) - return; - /* Wait for each thread urcu_active_readers count to become 0. +/* + * synchronize_rcu() waiting. Single thread. + */ +static void wait_gp(void) +{ + /* Read reader_gp before read futex */ + smp_mb_master(RCU_MB_GROUP); + if (uatomic_read(&gp_futex) == -1) + futex_async(&gp_futex, FUTEX_WAIT, -1, + NULL, NULL, 0); +} + +void update_counter_and_wait(void) +{ + CDS_LIST_HEAD(qsreaders); + int wait_loops = 0; + struct rcu_reader *index, *tmp; + + /* Switch parity: 0 -> 1, 1 -> 0 */ + CMM_STORE_SHARED(rcu_gp_ctr, rcu_gp_ctr ^ RCU_GP_CTR_PHASE); + + /* + * 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 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 each thread rcu_reader.ctr count to become 0. */ - for (index = reader_data; index < reader_data + num_readers; index++) { + for (;;) { + wait_loops++; + if (wait_loops == RCU_QS_ACTIVE_ATTEMPTS) { + uatomic_dec(&gp_futex); + /* Write futex before read reader_gp */ + smp_mb_master(RCU_MB_GROUP); + } + + cds_list_for_each_entry_safe(index, tmp, ®istry, node) { + if (!rcu_gp_ongoing(&index->ctr)) + cds_list_move(&index->node, &qsreaders); + } + +#ifndef HAS_INCOHERENT_CACHES + if (cds_list_empty(®istry)) { + if (wait_loops == RCU_QS_ACTIVE_ATTEMPTS) { + /* Read reader_gp before write futex */ + smp_mb_master(RCU_MB_GROUP); + uatomic_set(&gp_futex, 0); + } + break; + } else { + if (wait_loops == RCU_QS_ACTIVE_ATTEMPTS) + wait_gp(); + else + caa_cpu_relax(); + } +#else /* #ifndef HAS_INCOHERENT_CACHES */ /* - * BUSY-LOOP. + * BUSY-LOOP. Force the reader thread to commit its + * rcu_reader.ctr update to memory if we wait for too long. */ - while (index->urcu_active_readers[parity] != 0) - barrier(); + if (cds_list_empty(®istry)) { + if (wait_loops == RCU_QS_ACTIVE_ATTEMPTS) { + /* Read reader_gp before write futex */ + smp_mb_master(RCU_MB_GROUP); + 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: + smp_mb_master(RCU_MB_GROUP); + wait_loops = 0; + break; /* only escape switch */ + default: + caa_cpu_relax(); + } + } +#endif /* #else #ifndef HAS_INCOHERENT_CACHES */ } - /* - * Locally : read *index->urcu_active_readers before freeing old - * pointer. - * Remote (reader threads) : Order urcu_qparity update and other - * thread's quiescent state counter read. - */ - force_mb_all_threads(); + /* put back the reader list in the registry */ + cds_list_splice(&qsreaders, ®istry); } -/* - * Return old pointer, OK to free, no more reference exist. - * Called under rcu_write_lock. - */ -void *urcu_publish_content(void **ptr, void *new) +void synchronize_rcu(void) { - int ret, prev_parity; - void *oldptr; + mutex_lock(&rcu_gp_lock); + + if (cds_list_empty(®istry)) + goto out; + + /* All threads should read qparity before accessing data structure + * where new ptr points to. Must be done within rcu_gp_lock because it + * iterates on reader threads.*/ + /* Write new ptr before changing the qparity */ + smp_mb_master(RCU_MB_GROUP); /* - * We can publish the new pointer before we change the current qparity. - * Readers seeing the new pointer while being in the previous qparity - * window will make us wait until the end of the quiescent state before - * we release the unrelated memory area. However, given we hold the - * urcu_mutex, we are making sure that no further garbage collection can - * occur until we release the mutex, therefore we guarantee that this - * given reader will have completed its execution using the new pointer - * when the next quiescent state window will be over. + * Wait for previous parity to be empty of readers. */ - oldptr = *ptr; - *ptr = new; - /* All threads should read qparity before ptr */ - /* Write ptr before changing the qparity */ - force_mb_all_threads(); - prev_parity = switch_next_urcu_qparity(); + update_counter_and_wait(); /* 0 -> 1, wait readers in parity 0 */ /* - * Wait for previous parity to be empty of readers. + * Must finish waiting for quiescent state for parity 0 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 + * rcu_reader ctr before store to rcu_gp_ctr. */ - wait_for_quiescent_state(prev_parity); + cmm_barrier(); + /* - * Deleting old data is ok ! + * 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. */ - - return oldptr; -} + cmm_smp_mb(); -void urcu_add_reader(pthread_t id) -{ - struct reader_data *oldarray; + /* + * Wait for previous parity to be empty of readers. + */ + update_counter_and_wait(); /* 1 -> 0, wait readers in parity 1 */ - if (!reader_data) { - alloc_readers = INIT_NUM_THREADS; - num_readers = 0; - reader_data = - malloc(sizeof(struct reader_data) * alloc_readers); - } - if (alloc_readers < num_readers + 1) { - oldarray = reader_data; - reader_data = malloc(sizeof(struct reader_data) - * (alloc_readers << 1)); - memcpy(reader_data, oldarray, - sizeof(struct reader_data) * alloc_readers); - alloc_readers <<= 1; - free(oldarray); - } - reader_data[num_readers].tid = id; - /* reference to the TLS of _this_ reader thread. */ - reader_data[num_readers].urcu_active_readers = urcu_active_readers; - num_readers++; + /* Finish waiting for reader threads before letting the old ptr being + * freed. Must be done within rcu_gp_lock because it iterates on reader + * threads. */ + smp_mb_master(RCU_MB_GROUP); +out: + mutex_unlock(&rcu_gp_lock); } /* - * Never shrink (implementation limitation). - * This is O(nb threads). Eventually use a hash table. + * library wrappers to be used by non-LGPL compatible source code. */ -void urcu_remove_reader(pthread_t id) -{ - struct reader_data *index; - - assert(reader_data != NULL); - for (index = reader_data; index < reader_data + num_readers; index++) { - if (index->tid == id) { - memcpy(index, &reader_data[num_readers - 1], - sizeof(struct reader_data)); - reader_data[num_readers - 1].tid = 0; - reader_data[num_readers - 1].urcu_active_readers = NULL; - num_readers--; - return; - } - } - /* Hrm not found, forgot to register ? */ - assert(0); + +void rcu_read_lock(void) +{ + _rcu_read_lock(); +} + +void rcu_read_unlock(void) +{ + _rcu_read_unlock(); +} + +void rcu_register_thread(void) +{ + rcu_reader.tid = pthread_self(); + assert(rcu_reader.need_mb == 0); + assert(!(rcu_reader.ctr & RCU_GP_CTR_NEST_MASK)); + + mutex_lock(&rcu_gp_lock); + rcu_init(); /* In case gcc does not support constructor attribute */ + cds_list_add(&rcu_reader.node, ®istry); + mutex_unlock(&rcu_gp_lock); } -void urcu_register_thread(void) +void rcu_unregister_thread(void) { - rcu_write_lock(); - urcu_add_reader(pthread_self()); - rcu_write_unlock(); + mutex_lock(&rcu_gp_lock); + cds_list_del(&rcu_reader.node); + mutex_unlock(&rcu_gp_lock); } -void urcu_unregister_thread(void) +#ifdef RCU_MEMBARRIER +void rcu_init(void) { - pthread_t self = pthread_self(); - rcu_write_lock(); - urcu_remove_reader(pthread_self()); - rcu_write_unlock(); + if (init_done) + return; + init_done = 1; + if (!membarrier(MEMBARRIER_EXPEDITED | MEMBARRIER_QUERY)) + has_sys_membarrier = 1; } +#endif -void sigurcu_handler(int signo, siginfo_t *siginfo, void *context) +#ifdef RCU_SIGNAL +static void sigrcu_handler(int signo, siginfo_t *siginfo, void *context) { - mb(); - atomic_inc(&sig_done); + /* + * Executing this cmm_smp_mb() is the only purpose of this signal handler. + * It punctually promotes cmm_barrier() into cmm_smp_mb() on every thread it is + * executed on. + */ + cmm_smp_mb(); + _CMM_STORE_SHARED(rcu_reader.need_mb, 0); + cmm_smp_mb(); } -void __attribute__((constructor)) urcu_init(void) +/* + * rcu_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 rcu_gp_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 rcu_init(void) { struct sigaction act; int ret; - act.sa_sigaction = sigurcu_handler; - ret = sigaction(SIGURCU, &act, NULL); + if (init_done) + return; + init_done = 1; + + act.sa_sigaction = sigrcu_handler; + act.sa_flags = SA_SIGINFO | SA_RESTART; + sigemptyset(&act.sa_mask); + ret = sigaction(SIGRCU, &act, NULL); if (ret) { perror("Error in sigaction"); exit(-1); } } -void __attribute__((destructor)) urcu_exit(void) +void rcu_exit(void) { struct sigaction act; int ret; - ret = sigaction(SIGURCU, NULL, &act); + ret = sigaction(SIGRCU, NULL, &act); if (ret) { perror("Error in sigaction"); exit(-1); } - assert(act.sa_sigaction == sigurcu_handler); - free(reader_data); + assert(act.sa_sigaction == sigrcu_handler); + assert(cds_list_empty(®istry)); } + +#endif /* #ifdef RCU_SIGNAL */ + +DEFINE_RCU_FLAVOR() + +#include "urcu-call-rcu-impl.h" +#include "urcu-defer-impl.h"