X-Git-Url: http://git.liburcu.org/?p=userspace-rcu.git;a=blobdiff_plain;f=src%2Furcu-qsbr.c;fp=src%2Furcu-qsbr.c;h=e029ace86a383b22256e2bf6da61cdb0fa526e1c;hp=0000000000000000000000000000000000000000;hb=6893800a4d1cc14dff0395ddcd660a5138db183d;hpb=a59f39055b5ecb77b68cf78b9839aa9e8e4ec332

diff --git a/src/urcu-qsbr.c b/src/urcu-qsbr.c
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+/*
+ * 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(&registry))
+		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(&registry, &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, &registry);
+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(&registry))
+		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(&registry, NULL, &qsreaders);
+
+	/*
+	 * Put quiescent reader list back into registry.
+	 */
+	cds_list_splice(&qsreaders, &registry);
+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, &registry);
+	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(&registry));
+	 */
+}
+
+DEFINE_RCU_FLAVOR(rcu_flavor);
+
+#include "urcu-call-rcu-impl.h"
+#include "urcu-defer-impl.h"