--- /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 _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 / userspace-rcu.git / blobdiff