+++ /dev/null
-/*
- * urcu-qsbr.c
- *
- * Userspace RCU QSBR 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 _GNU_SOURCE
-#define _LGPL_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/wfcqueue.h"
-#include "urcu/map/urcu-qsbr.h"
-#define BUILD_QSBR_LIB
-#include "urcu/static/urcu-qsbr.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-qsbr.h"
-#define _LGPL_SOURCE
-
-void __attribute__((destructor)) rcu_exit(void);
-
-/*
- * 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_ONLINE };
-
-/*
- * Active attempts to check for reader Q.S. before calling futex().
- */
-#define RCU_QS_ACTIVE_ATTEMPTS 100
-
-/*
- * 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);
- 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);
-}
-
-/*
- * synchronize_rcu() waiting. Single thread.
- */
-static void wait_gp(void)
-{
- /* Read reader_gp before read futex */
- cmm_smp_rmb();
- if (uatomic_read(&rcu_gp.futex) != -1)
- return;
- while (futex_noasync(&rcu_gp.futex, FUTEX_WAIT, -1,
- NULL, NULL, 0)) {
- switch (errno) {
- case EWOULDBLOCK:
- /* Value already changed. */
- return;
- case EINTR:
- /* Retry if interrupted by signal. */
- break; /* Get out of switch. */
- default:
- /* Unexpected error. */
- urcu_die(errno);
- }
- }
-}
-
-/*
- * 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;
-
- /*
- * Wait for each thread URCU_TLS(rcu_reader).ctr to either
- * indicate quiescence (offline), or for them to 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_set(&rcu_gp.futex, -1);
- /*
- * Write futex before write waiting (the other side
- * reads them in the opposite order).
- */
- cmm_smp_wmb();
- cds_list_for_each_entry(index, input_readers, node) {
- _CMM_STORE_SHARED(index->waiting, 1);
- }
- /* Write futex before read reader_gp */
- cmm_smp_mb();
- }
- 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;
- }
- }
-
- if (cds_list_empty(input_readers)) {
- if (wait_loops >= RCU_QS_ACTIVE_ATTEMPTS) {
- /* Read reader_gp before write futex */
- cmm_smp_mb();
- uatomic_set(&rcu_gp.futex, 0);
- }
- break;
- } else {
- /* Temporarily unlock the registry lock. */
- mutex_unlock(&rcu_registry_lock);
- if (wait_loops >= RCU_QS_ACTIVE_ATTEMPTS) {
- wait_gp();
- } else {
-#ifndef HAS_INCOHERENT_CACHES
- caa_cpu_relax();
-#else /* #ifndef HAS_INCOHERENT_CACHES */
- cmm_smp_mb();
-#endif /* #else #ifndef HAS_INCOHERENT_CACHES */
- }
- /* Re-lock the registry lock before the next loop. */
- mutex_lock(&rcu_registry_lock);
- }
- }
-}
-
-/*
- * Using a two-subphases algorithm for architectures with smaller than 64-bit
- * long-size to ensure we do not encounter an overflow bug.
- */
-
-#if (CAA_BITS_PER_LONG < 64)
-void synchronize_rcu(void)
-{
- CDS_LIST_HEAD(cur_snap_readers);
- CDS_LIST_HEAD(qsreaders);
- unsigned long was_online;
- DEFINE_URCU_WAIT_NODE(wait, URCU_WAIT_WAITING);
- struct urcu_waiters waiters;
-
- was_online = rcu_read_ongoing();
-
- /* All threads should read qparity before accessing data structure
- * where new ptr points to. In the "then" case, rcu_thread_offline
- * includes a memory barrier.
- *
- * Mark the writer thread offline to make sure we don't wait for
- * our own quiescent state. This allows using synchronize_rcu()
- * in threads registered as readers.
- */
- if (was_online)
- rcu_thread_offline();
- else
- cmm_smp_mb();
-
- /*
- * 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.
- */
- if (urcu_wait_add(&gp_waiters, &wait) != 0) {
- /* Not first in queue: will be awakened by another thread. */
- urcu_adaptative_busy_wait(&wait);
- goto gp_end;
- }
- /* 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;
-
- /*
- * 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);
-
- /*
- * 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 URCU_TLS(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);
-out:
- mutex_unlock(&rcu_registry_lock);
- mutex_unlock(&rcu_gp_lock);
- urcu_wake_all_waiters(&waiters);
-gp_end:
- /*
- * Finish waiting for reader threads before letting the old ptr being
- * freed.
- */
- if (was_online)
- rcu_thread_online();
- else
- cmm_smp_mb();
-}
-#else /* !(CAA_BITS_PER_LONG < 64) */
-void synchronize_rcu(void)
-{
- CDS_LIST_HEAD(qsreaders);
- unsigned long was_online;
- DEFINE_URCU_WAIT_NODE(wait, URCU_WAIT_WAITING);
- struct urcu_waiters waiters;
-
- was_online = rcu_read_ongoing();
-
- /*
- * Mark the writer thread offline to make sure we don't wait for
- * our own quiescent state. This allows using synchronize_rcu()
- * in threads registered as readers.
- */
- if (was_online)
- rcu_thread_offline();
- else
- cmm_smp_mb();
-
- /*
- * 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.
- */
- if (urcu_wait_add(&gp_waiters, &wait) != 0) {
- /* Not first in queue: will be awakened by another thread. */
- urcu_adaptative_busy_wait(&wait);
- goto gp_end;
- }
- /* 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;
-
- /* Increment current G.P. */
- CMM_STORE_SHARED(rcu_gp.ctr, rcu_gp.ctr + RCU_GP_CTR);
-
- /*
- * 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 URCU_TLS(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 count of be quiescent.
- * wait_for_readers() can release and grab again rcu_registry_lock
- * interally.
- */
- wait_for_readers(®istry, NULL, &qsreaders);
-
- /*
- * Put quiescent reader list back into registry.
- */
- cds_list_splice(&qsreaders, ®istry);
-out:
- mutex_unlock(&rcu_registry_lock);
- mutex_unlock(&rcu_gp_lock);
- urcu_wake_all_waiters(&waiters);
-gp_end:
- if (was_online)
- rcu_thread_online();
- else
- cmm_smp_mb();
-}
-#endif /* !(CAA_BITS_PER_LONG < 64) */
-
-/*
- * 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_quiescent_state(void)
-{
- _rcu_quiescent_state();
-}
-
-void rcu_thread_offline(void)
-{
- _rcu_thread_offline();
-}
-
-void rcu_thread_online(void)
-{
- _rcu_thread_online();
-}
-
-void rcu_register_thread(void)
-{
- URCU_TLS(rcu_reader).tid = pthread_self();
- assert(URCU_TLS(rcu_reader).ctr == 0);
-
- mutex_lock(&rcu_registry_lock);
- assert(!URCU_TLS(rcu_reader).registered);
- URCU_TLS(rcu_reader).registered = 1;
- cds_list_add(&URCU_TLS(rcu_reader).node, ®istry);
- mutex_unlock(&rcu_registry_lock);
- _rcu_thread_online();
-}
-
-void rcu_unregister_thread(void)
-{
- /*
- * We have to make the thread offline otherwise we end up dealocking
- * with a waiting writer.
- */
- _rcu_thread_offline();
- assert(URCU_TLS(rcu_reader).registered);
- URCU_TLS(rcu_reader).registered = 0;
- mutex_lock(&rcu_registry_lock);
- cds_list_del(&URCU_TLS(rcu_reader).node);
- mutex_unlock(&rcu_registry_lock);
-}
-
-void rcu_exit(void)
-{
- /*
- * Assertion disabled because call_rcu threads are now rcu
- * readers, and left running at exit.
- * assert(cds_list_empty(®istry));
- */
-}
-
-DEFINE_RCU_FLAVOR(rcu_flavor);
-
-#include "urcu-call-rcu-impl.h"
-#include "urcu-defer-impl.h"
projects / urcu.git / blobdiff