X-Git-Url: http://git.liburcu.org/?p=urcu.git;a=blobdiff_plain;f=src%2Furcu.c;fp=src%2Furcu.c;h=ccd9706dda6fe6a8b6bfcba2fced7893054cf3ae;hp=0000000000000000000000000000000000000000;hb=6893800a4d1cc14dff0395ddcd660a5138db183d;hpb=a59f39055b5ecb77b68cf78b9839aa9e8e4ec332 diff --git a/src/urcu.c b/src/urcu.c new file mode 100644 index 0000000..ccd9706 --- /dev/null +++ b/src/urcu.c @@ -0,0 +1,604 @@ +/* + * 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. + */ + +#define _BSD_SOURCE +#define _LGPL_SOURCE +#define _DEFAULT_SOURCE +#include +#include +#include +#include +#include +#include +#include +#include +#include + +#include "urcu/arch.h" +#include "urcu/wfcqueue.h" +#include "urcu/map/urcu.h" +#include "urcu/static/urcu.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 */ +#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 10 loops waiting for it. + */ +#define KICK_READER_LOOPS 10 + +/* + * Active attempts to check for reader Q.S. before calling futex(). + */ +#define RCU_QS_ACTIVE_ATTEMPTS 100 + +/* If the headers do not support membarrier system call, fall back on RCU_MB */ +#ifdef __NR_membarrier +# define membarrier(...) syscall(__NR_membarrier, __VA_ARGS__) +#else +# define membarrier(...) -ENOSYS +#endif + +enum membarrier_cmd { + MEMBARRIER_CMD_QUERY = 0, + MEMBARRIER_CMD_SHARED = (1 << 0), +}; + +#ifdef RCU_MEMBARRIER +static int init_done; +int rcu_has_sys_membarrier; + +void __attribute__((constructor)) rcu_init(void); +#endif + +#ifdef RCU_MB +void rcu_init(void) +{ +} +#endif + +#ifdef RCU_SIGNAL +static int init_done; + +void __attribute__((constructor)) rcu_init(void); +void __attribute__((destructor)) rcu_exit(void); +#endif + +/* + * 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_COUNT }; + +/* + * Written to only by each individual reader. Read by both the reader and the + * writers. + */ +DEFINE_URCU_TLS(struct rcu_reader, rcu_reader); + +static CDS_LIST_HEAD(registry); + +/* + * Queue keeping threads awaiting to wait for a grace period. Contains + * struct gp_waiters_thread objects. + */ +static DEFINE_URCU_WAIT_QUEUE(gp_waiters); + +static void mutex_lock(pthread_mutex_t *mutex) +{ + int ret; + +#ifndef DISTRUST_SIGNALS_EXTREME + ret = pthread_mutex_lock(mutex); + if (ret) + urcu_die(ret); +#else /* #ifndef DISTRUST_SIGNALS_EXTREME */ + while ((ret = pthread_mutex_trylock(mutex)) != 0) { + if (ret != EBUSY && ret != EINTR) + urcu_die(ret); + if (CMM_LOAD_SHARED(URCU_TLS(rcu_reader).need_mb)) { + cmm_smp_mb(); + _CMM_STORE_SHARED(URCU_TLS(rcu_reader).need_mb, 0); + cmm_smp_mb(); + } + (void) poll(NULL, 0, 10); + } +#endif /* #else #ifndef DISTRUST_SIGNALS_EXTREME */ +} + +static void mutex_unlock(pthread_mutex_t *mutex) +{ + int ret; + + ret = pthread_mutex_unlock(mutex); + if (ret) + urcu_die(ret); +} + +#ifdef RCU_MEMBARRIER +static void smp_mb_master(void) +{ + if (caa_likely(rcu_has_sys_membarrier)) + (void) membarrier(MEMBARRIER_CMD_SHARED, 0); + else + cmm_smp_mb(); +} +#endif + +#ifdef RCU_MB +static void smp_mb_master(void) +{ + cmm_smp_mb(); +} +#endif + +#ifdef RCU_SIGNAL +static void force_mb_all_readers(void) +{ + struct rcu_reader *index; + + /* + * 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 (cds_list_empty(®istry)) + return; + /* + * 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. + * + * 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). + */ + cds_list_for_each_entry(index, ®istry, node) { + while (CMM_LOAD_SHARED(index->need_mb)) { + pthread_kill(index->tid, SIGRCU); + (void) poll(NULL, 0, 1); + } + } + cmm_smp_mb(); /* read ->need_mb before ending the barrier */ +} + +static void smp_mb_master(void) +{ + force_mb_all_readers(); +} +#endif /* #ifdef RCU_SIGNAL */ + +/* + * synchronize_rcu() waiting. Single thread. + * Always called with rcu_registry lock held. Releases this lock and + * grabs it again. Holds the lock when it returns. + */ +static void wait_gp(void) +{ + /* + * Read reader_gp before read futex. smp_mb_master() needs to + * be called with the rcu registry lock held in RCU_SIGNAL + * flavor. + */ + smp_mb_master(); + /* Temporarily unlock the registry lock. */ + mutex_unlock(&rcu_registry_lock); + if (uatomic_read(&rcu_gp.futex) != -1) + goto end; + while (futex_async(&rcu_gp.futex, FUTEX_WAIT, -1, + NULL, NULL, 0)) { + switch (errno) { + case EWOULDBLOCK: + /* Value already changed. */ + goto end; + case EINTR: + /* Retry if interrupted by signal. */ + break; /* Get out of switch. */ + default: + /* Unexpected error. */ + urcu_die(errno); + } + } +end: + /* + * Re-lock the registry lock before the next loop. + */ + mutex_lock(&rcu_registry_lock); +} + +/* + * 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) +{ + unsigned int wait_loops = 0; + struct rcu_reader *index, *tmp; +#ifdef HAS_INCOHERENT_CACHES + unsigned int wait_gp_loops = 0; +#endif /* HAS_INCOHERENT_CACHES */ + + /* + * Wait for each thread URCU_TLS(rcu_reader).ctr to either + * indicate quiescence (not nested), or observe the current + * rcu_gp.ctr value. + */ + for (;;) { + if (wait_loops < RCU_QS_ACTIVE_ATTEMPTS) + wait_loops++; + if (wait_loops >= RCU_QS_ACTIVE_ATTEMPTS) { + uatomic_dec(&rcu_gp.futex); + /* Write futex before read reader_gp */ + smp_mb_master(); + } + + 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; + } + } + +#ifndef HAS_INCOHERENT_CACHES + if (cds_list_empty(input_readers)) { + if (wait_loops >= RCU_QS_ACTIVE_ATTEMPTS) { + /* Read reader_gp before write futex */ + smp_mb_master(); + uatomic_set(&rcu_gp.futex, 0); + } + break; + } else { + if (wait_loops >= RCU_QS_ACTIVE_ATTEMPTS) { + /* wait_gp unlocks/locks registry lock. */ + wait_gp(); + } else { + /* Temporarily unlock the registry lock. */ + mutex_unlock(&rcu_registry_lock); + caa_cpu_relax(); + /* + * Re-lock the registry lock before the + * next loop. + */ + mutex_lock(&rcu_registry_lock); + } + } +#else /* #ifndef HAS_INCOHERENT_CACHES */ + /* + * BUSY-LOOP. Force the reader thread to commit its + * URCU_TLS(rcu_reader).ctr update to memory if we wait + * for too long. + */ + if (cds_list_empty(input_readers)) { + if (wait_loops >= RCU_QS_ACTIVE_ATTEMPTS) { + /* Read reader_gp before write futex */ + smp_mb_master(); + uatomic_set(&rcu_gp.futex, 0); + } + break; + } else { + if (wait_gp_loops == KICK_READER_LOOPS) { + smp_mb_master(); + wait_gp_loops = 0; + } + if (wait_loops >= RCU_QS_ACTIVE_ATTEMPTS) { + /* wait_gp unlocks/locks registry lock. */ + wait_gp(); + wait_gp_loops++; + } else { + /* Temporarily unlock the registry lock. */ + mutex_unlock(&rcu_registry_lock); + caa_cpu_relax(); + /* + * Re-lock the registry lock before the + * next loop. + */ + mutex_lock(&rcu_registry_lock); + } + } +#endif /* #else #ifndef HAS_INCOHERENT_CACHES */ + } +} + +void synchronize_rcu(void) +{ + CDS_LIST_HEAD(cur_snap_readers); + CDS_LIST_HEAD(qsreaders); + DEFINE_URCU_WAIT_NODE(wait, URCU_WAIT_WAITING); + struct urcu_waiters waiters; + + /* + * 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. + * The implicit memory barrier before urcu_wait_add() + * orders prior memory accesses of threads put into the wait + * queue before their insertion into the wait queue. + */ + if (urcu_wait_add(&gp_waiters, &wait) != 0) { + /* Not first in queue: will be awakened by another thread. */ + urcu_adaptative_busy_wait(&wait); + /* Order following memory accesses after grace period. */ + cmm_smp_mb(); + return; + } + /* 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; + + /* + * All threads should read qparity before accessing data structure + * where new ptr points to. Must be done within rcu_registry_lock + * because it iterates on reader threads. + */ + /* Write new ptr before changing the qparity */ + smp_mb_master(); + + /* + * 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_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 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); + + /* + * Finish waiting for reader threads before letting the old ptr + * being freed. Must be done within rcu_registry_lock because it + * iterates on reader threads. + */ + smp_mb_master(); +out: + mutex_unlock(&rcu_registry_lock); + mutex_unlock(&rcu_gp_lock); + + /* + * Wakeup waiters only after we have completed the grace period + * and have ensured the memory barriers at the end of the grace + * period have been issued. + */ + urcu_wake_all_waiters(&waiters); +} + +/* + * 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(); +} + +int rcu_read_ongoing(void) +{ + return _rcu_read_ongoing(); +} + +void rcu_register_thread(void) +{ + URCU_TLS(rcu_reader).tid = pthread_self(); + assert(URCU_TLS(rcu_reader).need_mb == 0); + assert(!(URCU_TLS(rcu_reader).ctr & RCU_GP_CTR_NEST_MASK)); + + mutex_lock(&rcu_registry_lock); + assert(!URCU_TLS(rcu_reader).registered); + URCU_TLS(rcu_reader).registered = 1; + rcu_init(); /* In case gcc does not support constructor attribute */ + cds_list_add(&URCU_TLS(rcu_reader).node, ®istry); + mutex_unlock(&rcu_registry_lock); +} + +void rcu_unregister_thread(void) +{ + mutex_lock(&rcu_registry_lock); + assert(URCU_TLS(rcu_reader).registered); + URCU_TLS(rcu_reader).registered = 0; + cds_list_del(&URCU_TLS(rcu_reader).node); + mutex_unlock(&rcu_registry_lock); +} + +#ifdef RCU_MEMBARRIER +void rcu_init(void) +{ + int ret; + + if (init_done) + return; + init_done = 1; + ret = membarrier(MEMBARRIER_CMD_QUERY, 0); + if (ret >= 0 && (ret & MEMBARRIER_CMD_SHARED)) { + rcu_has_sys_membarrier = 1; + } +} +#endif + +#ifdef RCU_SIGNAL +static void sigrcu_handler(int signo, siginfo_t *siginfo, void *context) +{ + /* + * 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(URCU_TLS(rcu_reader).need_mb, 0); + cmm_smp_mb(); +} + +/* + * 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_registry_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; + + 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) + urcu_die(errno); +} + +void rcu_exit(void) +{ + /* + * Don't unregister the SIGRCU signal handler anymore, because + * call_rcu threads could still be using it shortly before the + * application exits. + * Assertion disabled because call_rcu threads are now rcu + * readers, and left running at exit. + * assert(cds_list_empty(®istry)); + */ +} + +#endif /* #ifdef RCU_SIGNAL */ + +DEFINE_RCU_FLAVOR(rcu_flavor); + +#include "urcu-call-rcu-impl.h" +#include "urcu-defer-impl.h"