X-Git-Url: http://git.liburcu.org/?p=userspace-rcu.git;a=blobdiff_plain;f=src%2Furcu-defer-impl.h;fp=src%2Furcu-defer-impl.h;h=f96553365ba4f51035f427798edd2ac4eb981f13;hp=0000000000000000000000000000000000000000;hb=6893800a4d1cc14dff0395ddcd660a5138db183d;hpb=a59f39055b5ecb77b68cf78b9839aa9e8e4ec332

diff --git a/src/urcu-defer-impl.h b/src/urcu-defer-impl.h
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+#ifndef _URCU_DEFER_IMPL_H
+#define _URCU_DEFER_IMPL_H
+
+/*
+ * urcu-defer-impl.h
+ *
+ * Userspace RCU header - memory reclamation.
+ *
+ * TO BE INCLUDED ONLY FROM URCU LIBRARY CODE. See urcu-defer.h for linking
+ * dynamically with the userspace rcu reclamation 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.
+ */
+
+#include <stdlib.h>
+#include <pthread.h>
+#include <stdio.h>
+#include <signal.h>
+#include <assert.h>
+#include <string.h>
+#include <errno.h>
+#include <poll.h>
+#include <sys/time.h>
+#include <unistd.h>
+#include <stdint.h>
+
+#include "urcu/futex.h"
+
+#include <urcu/compiler.h>
+#include <urcu/arch.h>
+#include <urcu/uatomic.h>
+#include <urcu/list.h>
+#include <urcu/system.h>
+#include <urcu/tls-compat.h>
+#include "urcu-die.h"
+
+/*
+ * Number of entries in the per-thread defer queue. Must be power of 2.
+ */
+#define DEFER_QUEUE_SIZE	(1 << 12)
+#define DEFER_QUEUE_MASK	(DEFER_QUEUE_SIZE - 1)
+
+/*
+ * Typically, data is aligned at least on the architecture size.
+ * Use lowest bit to indicate that the current callback is changing.
+ * Assumes that (void *)-2L is not used often. Used to encode non-aligned
+ * functions and non-aligned data using extra space.
+ * We encode the (void *)-2L fct as: -2L, fct, data.
+ * We encode the (void *)-2L data as either:
+ *   fct | DQ_FCT_BIT, data (if fct is aligned), or
+ *   -2L, fct, data (if fct is not aligned).
+ * Here, DQ_FCT_MARK == ~DQ_FCT_BIT. Required for the test order.
+ */
+#define DQ_FCT_BIT		(1 << 0)
+#define DQ_IS_FCT_BIT(x)	((unsigned long)(x) & DQ_FCT_BIT)
+#define DQ_SET_FCT_BIT(x)	\
+	(x = (void *)((unsigned long)(x) | DQ_FCT_BIT))
+#define DQ_CLEAR_FCT_BIT(x)	\
+	(x = (void *)((unsigned long)(x) & ~DQ_FCT_BIT))
+#define DQ_FCT_MARK		((void *)(~DQ_FCT_BIT))
+
+/*
+ * This code section can only be included in LGPL 2.1 compatible source code.
+ * See below for the function call wrappers which can be used in code meant to
+ * be only linked with the Userspace RCU library. This comes with a small
+ * performance degradation on the read-side due to the added function calls.
+ * This is required to permit relinking with newer versions of the library.
+ */
+
+/*
+ * defer queue.
+ * Contains pointers. Encoded to save space when same callback is often used.
+ * When looking up the next item:
+ * - if DQ_FCT_BIT is set, set the current callback to DQ_CLEAR_FCT_BIT(ptr)
+ *   - next element contains pointer to data.
+ * - else if item == DQ_FCT_MARK
+ *   - set the current callback to next element ptr
+ *   - following next element contains pointer to data.
+ * - else current element contains data
+ */
+struct defer_queue {
+	unsigned long head;	/* add element at head */
+	void *last_fct_in;	/* last fct pointer encoded */
+	unsigned long tail;	/* next element to remove at tail */
+	void *last_fct_out;	/* last fct pointer encoded */
+	void **q;
+	/* registry information */
+	unsigned long last_head;
+	struct cds_list_head list;	/* list of thread queues */
+};
+
+/* Do not #define _LGPL_SOURCE to ensure we can emit the wrapper symbols */
+#include "urcu-defer.h"
+
+void __attribute__((destructor)) rcu_defer_exit(void);
+
+extern void synchronize_rcu(void);
+
+/*
+ * rcu_defer_mutex nests inside defer_thread_mutex.
+ */
+static pthread_mutex_t rcu_defer_mutex = PTHREAD_MUTEX_INITIALIZER;
+static pthread_mutex_t defer_thread_mutex = PTHREAD_MUTEX_INITIALIZER;
+
+static int32_t defer_thread_futex;
+static int32_t defer_thread_stop;
+
+/*
+ * Written to only by each individual deferer. Read by both the deferer and
+ * the reclamation tread.
+ */
+static DEFINE_URCU_TLS(struct defer_queue, defer_queue);
+static CDS_LIST_HEAD(registry_defer);
+static pthread_t tid_defer;
+
+static void mutex_lock_defer(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);
+		(void) poll(NULL,0,10);
+	}
+#endif /* #else #ifndef DISTRUST_SIGNALS_EXTREME */
+}
+
+/*
+ * Wake-up any waiting defer thread. Called from many concurrent threads.
+ */
+static void wake_up_defer(void)
+{
+	if (caa_unlikely(uatomic_read(&defer_thread_futex) == -1)) {
+		uatomic_set(&defer_thread_futex, 0);
+		if (futex_noasync(&defer_thread_futex, FUTEX_WAKE, 1,
+				NULL, NULL, 0) < 0)
+			urcu_die(errno);
+	}
+}
+
+static unsigned long rcu_defer_num_callbacks(void)
+{
+	unsigned long num_items = 0, head;
+	struct defer_queue *index;
+
+	mutex_lock_defer(&rcu_defer_mutex);
+	cds_list_for_each_entry(index, &registry_defer, list) {
+		head = CMM_LOAD_SHARED(index->head);
+		num_items += head - index->tail;
+	}
+	mutex_unlock(&rcu_defer_mutex);
+	return num_items;
+}
+
+/*
+ * Defer thread waiting. Single thread.
+ */
+static void wait_defer(void)
+{
+	uatomic_dec(&defer_thread_futex);
+	/* Write futex before read queue */
+	/* Write futex before read defer_thread_stop */
+	cmm_smp_mb();
+	if (_CMM_LOAD_SHARED(defer_thread_stop)) {
+		uatomic_set(&defer_thread_futex, 0);
+		pthread_exit(0);
+	}
+	if (rcu_defer_num_callbacks()) {
+		cmm_smp_mb();	/* Read queue before write futex */
+		/* Callbacks are queued, don't wait. */
+		uatomic_set(&defer_thread_futex, 0);
+	} else {
+		cmm_smp_rmb();	/* Read queue before read futex */
+		if (uatomic_read(&defer_thread_futex) != -1)
+			return;
+		while (futex_noasync(&defer_thread_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);
+			}
+		}
+	}
+}
+
+/*
+ * Must be called after Q.S. is reached.
+ */
+static void rcu_defer_barrier_queue(struct defer_queue *queue,
+				    unsigned long head)
+{
+	unsigned long i;
+	void (*fct)(void *p);
+	void *p;
+
+	/*
+	 * Tail is only modified when lock is held.
+	 * Head is only modified by owner thread.
+	 */
+
+	for (i = queue->tail; i != head;) {
+		cmm_smp_rmb();       /* read head before q[]. */
+		p = CMM_LOAD_SHARED(queue->q[i++ & DEFER_QUEUE_MASK]);
+		if (caa_unlikely(DQ_IS_FCT_BIT(p))) {
+			DQ_CLEAR_FCT_BIT(p);
+			queue->last_fct_out = p;
+			p = CMM_LOAD_SHARED(queue->q[i++ & DEFER_QUEUE_MASK]);
+		} else if (caa_unlikely(p == DQ_FCT_MARK)) {
+			p = CMM_LOAD_SHARED(queue->q[i++ & DEFER_QUEUE_MASK]);
+			queue->last_fct_out = p;
+			p = CMM_LOAD_SHARED(queue->q[i++ & DEFER_QUEUE_MASK]);
+		}
+		fct = queue->last_fct_out;
+		fct(p);
+	}
+	cmm_smp_mb();	/* push tail after having used q[] */
+	CMM_STORE_SHARED(queue->tail, i);
+}
+
+static void _rcu_defer_barrier_thread(void)
+{
+	unsigned long head, num_items;
+
+	head = URCU_TLS(defer_queue).head;
+	num_items = head - URCU_TLS(defer_queue).tail;
+	if (caa_unlikely(!num_items))
+		return;
+	synchronize_rcu();
+	rcu_defer_barrier_queue(&URCU_TLS(defer_queue), head);
+}
+
+void rcu_defer_barrier_thread(void)
+{
+	mutex_lock_defer(&rcu_defer_mutex);
+	_rcu_defer_barrier_thread();
+	mutex_unlock(&rcu_defer_mutex);
+}
+
+/*
+ * rcu_defer_barrier - Execute all queued rcu callbacks.
+ *
+ * Execute all RCU callbacks queued before rcu_defer_barrier() execution.
+ * All callbacks queued on the local thread prior to a rcu_defer_barrier() call
+ * are guaranteed to be executed.
+ * Callbacks queued by other threads concurrently with rcu_defer_barrier()
+ * execution are not guaranteed to be executed in the current batch (could
+ * be left for the next batch). These callbacks queued by other threads are only
+ * guaranteed to be executed if there is explicit synchronization between
+ * the thread adding to the queue and the thread issuing the defer_barrier call.
+ */
+
+void rcu_defer_barrier(void)
+{
+	struct defer_queue *index;
+	unsigned long num_items = 0;
+
+	if (cds_list_empty(&registry_defer))
+		return;
+
+	mutex_lock_defer(&rcu_defer_mutex);
+	cds_list_for_each_entry(index, &registry_defer, list) {
+		index->last_head = CMM_LOAD_SHARED(index->head);
+		num_items += index->last_head - index->tail;
+	}
+	if (caa_likely(!num_items)) {
+		/*
+		 * We skip the grace period because there are no queued
+		 * callbacks to execute.
+		 */
+		goto end;
+	}
+	synchronize_rcu();
+	cds_list_for_each_entry(index, &registry_defer, list)
+		rcu_defer_barrier_queue(index, index->last_head);
+end:
+	mutex_unlock(&rcu_defer_mutex);
+}
+
+/*
+ * _defer_rcu - Queue a RCU callback.
+ */
+static void _defer_rcu(void (*fct)(void *p), void *p)
+{
+	unsigned long head, tail;
+
+	/*
+	 * Head is only modified by ourself. Tail can be modified by reclamation
+	 * thread.
+	 */
+	head = URCU_TLS(defer_queue).head;
+	tail = CMM_LOAD_SHARED(URCU_TLS(defer_queue).tail);
+
+	/*
+	 * If queue is full, or reached threshold. Empty queue ourself.
+	 * Worse-case: must allow 2 supplementary entries for fct pointer.
+	 */
+	if (caa_unlikely(head - tail >= DEFER_QUEUE_SIZE - 2)) {
+		assert(head - tail <= DEFER_QUEUE_SIZE);
+		rcu_defer_barrier_thread();
+		assert(head - CMM_LOAD_SHARED(URCU_TLS(defer_queue).tail) == 0);
+	}
+
+	/*
+	 * Encode:
+	 * if the function is not changed and the data is aligned and it is
+	 * not the marker:
+	 *	store the data
+	 * otherwise if the function is aligned and its not the marker:
+	 *	store the function with DQ_FCT_BIT
+	 *	store the data
+	 * otherwise:
+	 *	store the marker (DQ_FCT_MARK)
+	 *	store the function
+	 *	store the data
+	 *
+	 * Decode: see the comments before 'struct defer_queue'
+	 *         or the code in rcu_defer_barrier_queue().
+	 */
+	if (caa_unlikely(URCU_TLS(defer_queue).last_fct_in != fct
+			|| DQ_IS_FCT_BIT(p)
+			|| p == DQ_FCT_MARK)) {
+		URCU_TLS(defer_queue).last_fct_in = fct;
+		if (caa_unlikely(DQ_IS_FCT_BIT(fct) || fct == DQ_FCT_MARK)) {
+			_CMM_STORE_SHARED(URCU_TLS(defer_queue).q[head++ & DEFER_QUEUE_MASK],
+				      DQ_FCT_MARK);
+			_CMM_STORE_SHARED(URCU_TLS(defer_queue).q[head++ & DEFER_QUEUE_MASK],
+				      fct);
+		} else {
+			DQ_SET_FCT_BIT(fct);
+			_CMM_STORE_SHARED(URCU_TLS(defer_queue).q[head++ & DEFER_QUEUE_MASK],
+				      fct);
+		}
+	}
+	_CMM_STORE_SHARED(URCU_TLS(defer_queue).q[head++ & DEFER_QUEUE_MASK], p);
+	cmm_smp_wmb();	/* Publish new pointer before head */
+			/* Write q[] before head. */
+	CMM_STORE_SHARED(URCU_TLS(defer_queue).head, head);
+	cmm_smp_mb();	/* Write queue head before read futex */
+	/*
+	 * Wake-up any waiting defer thread.
+	 */
+	wake_up_defer();
+}
+
+static void *thr_defer(void *args)
+{
+	for (;;) {
+		/*
+		 * "Be green". Don't wake up the CPU if there is no RCU work
+		 * to perform whatsoever. Aims at saving laptop battery life by
+		 * leaving the processor in sleep state when idle.
+		 */
+		wait_defer();
+		/* Sleeping after wait_defer to let many callbacks enqueue */
+		(void) poll(NULL,0,100);	/* wait for 100ms */
+		rcu_defer_barrier();
+	}
+
+	return NULL;
+}
+
+/*
+ * library wrappers to be used by non-LGPL compatible source code.
+ */
+
+void defer_rcu(void (*fct)(void *p), void *p)
+{
+	_defer_rcu(fct, p);
+}
+
+static void start_defer_thread(void)
+{
+	int ret;
+
+	ret = pthread_create(&tid_defer, NULL, thr_defer, NULL);
+	assert(!ret);
+}
+
+static void stop_defer_thread(void)
+{
+	int ret;
+	void *tret;
+
+	_CMM_STORE_SHARED(defer_thread_stop, 1);
+	/* Store defer_thread_stop before testing futex */
+	cmm_smp_mb();
+	wake_up_defer();
+
+	ret = pthread_join(tid_defer, &tret);
+	assert(!ret);
+
+	CMM_STORE_SHARED(defer_thread_stop, 0);
+	/* defer thread should always exit when futex value is 0 */
+	assert(uatomic_read(&defer_thread_futex) == 0);
+}
+
+int rcu_defer_register_thread(void)
+{
+	int was_empty;
+
+	assert(URCU_TLS(defer_queue).last_head == 0);
+	assert(URCU_TLS(defer_queue).q == NULL);
+	URCU_TLS(defer_queue).q = malloc(sizeof(void *) * DEFER_QUEUE_SIZE);
+	if (!URCU_TLS(defer_queue).q)
+		return -ENOMEM;
+
+	mutex_lock_defer(&defer_thread_mutex);
+	mutex_lock_defer(&rcu_defer_mutex);
+	was_empty = cds_list_empty(&registry_defer);
+	cds_list_add(&URCU_TLS(defer_queue).list, &registry_defer);
+	mutex_unlock(&rcu_defer_mutex);
+
+	if (was_empty)
+		start_defer_thread();
+	mutex_unlock(&defer_thread_mutex);
+	return 0;
+}
+
+void rcu_defer_unregister_thread(void)
+{
+	int is_empty;
+
+	mutex_lock_defer(&defer_thread_mutex);
+	mutex_lock_defer(&rcu_defer_mutex);
+	cds_list_del(&URCU_TLS(defer_queue).list);
+	_rcu_defer_barrier_thread();
+	free(URCU_TLS(defer_queue).q);
+	URCU_TLS(defer_queue).q = NULL;
+	is_empty = cds_list_empty(&registry_defer);
+	mutex_unlock(&rcu_defer_mutex);
+
+	if (is_empty)
+		stop_defer_thread();
+	mutex_unlock(&defer_thread_mutex);
+}
+
+void rcu_defer_exit(void)
+{
+	assert(cds_list_empty(&registry_defer));
+}
+
+#endif /* _URCU_DEFER_IMPL_H */