+++ /dev/null
-/*
- * urcu.c
- *
- * Userspace RCU library
- *
- * Copyright (c) 2009 Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
- * 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 _GNU_SOURCE
-#define _LGPL_SOURCE
-#define _DEFAULT_SOURCE
-#include <stdio.h>
-#include <pthread.h>
-#include <signal.h>
-#include <assert.h>
-#include <stdlib.h>
-#include <stdint.h>
-#include <string.h>
-#include <errno.h>
-#include <poll.h>
-
-#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"
projects / urcu.git / blobdiff