[urcu.git] / urcu-qsbr.c

/*
 * urcu-qsbr.c
 *
 * Userspace RCU QSBR library
 *
 * Copyright (c) 2009 Mathieu Desnoyers <mathieu.desnoyers@polymtl.ca>
 * 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 <stdio.h>
#include <pthread.h>
#include <signal.h>
#include <assert.h>
#include <stdlib.h>
#include <string.h>
#include <errno.h>
#include <poll.h>

#define BUILD_QSBR_LIB
#include "urcu-qsbr-static.h"
/* Do not #define _LGPL_SOURCE to ensure we can emit the wrapper symbols */
#include "urcu-qsbr.h"

static pthread_mutex_t urcu_mutex = PTHREAD_MUTEX_INITIALIZER;

int gp_futex;

/*
 * Global grace period counter.
 */
unsigned long urcu_gp_ctr = RCU_GP_ONLINE;

/*
 * Written to only by each individual reader. Read by both the reader and the
 * writers.
 */
unsigned long __thread rcu_reader_qs_gp;

/* Thread IDs of registered readers */
#define INIT_NUM_THREADS 4

struct reader_registry {
	pthread_t tid;
	unsigned long *rcu_reader_qs_gp;
};

#ifdef DEBUG_YIELD
unsigned int yield_active;
unsigned int __thread rand_yield;
#endif

static struct reader_registry *registry;
static int num_readers, alloc_readers;

static void internal_urcu_lock(void)
{
	int ret;

#ifndef DISTRUST_SIGNALS_EXTREME
	ret = pthread_mutex_lock(&urcu_mutex);
	if (ret) {
		perror("Error in pthread mutex lock");
		exit(-1);
	}
#else /* #ifndef DISTRUST_SIGNALS_EXTREME */
	while ((ret = pthread_mutex_trylock(&urcu_mutex)) != 0) {
		if (ret != EBUSY && ret != EINTR) {
			printf("ret = %d, errno = %d\n", ret, errno);
			perror("Error in pthread mutex lock");
			exit(-1);
		}
		poll(NULL,0,10);
	}
#endif /* #else #ifndef DISTRUST_SIGNALS_EXTREME */
}

static void internal_urcu_unlock(void)
{
	int ret;

	ret = pthread_mutex_unlock(&urcu_mutex);
	if (ret) {
		perror("Error in pthread mutex unlock");
		exit(-1);
	}
}

/*
 * synchronize_rcu() waiting. Single thread.
 */
static void wait_gp(struct reader_registry *index)
{
	atomic_dec(&gp_futex);
	smp_mb(); /* Write futex before read reader_gp */
	if (!rcu_gp_ongoing(index->rcu_reader_qs_gp)) {
		/* Read reader_gp before write futex */
		smp_mb();
		/* Callbacks are queued, don't wait. */
		atomic_set(&gp_futex, 0);
	} else {
		/* Read reader_gp before read futex */
		smp_rmb();
		if (atomic_read(&gp_futex) == -1)
			futex(&gp_futex, FUTEX_WAIT, -1,
			      NULL, NULL, 0);
	}
}

static void wait_for_quiescent_state(void)
{
	struct reader_registry *index;

	if (!registry)
		return;
	/*
	 * Wait for each thread rcu_reader_qs_gp count to become 0.
	 */
	for (index = registry; index < registry + num_readers; index++) {
		int wait_loops = 0;

		while (rcu_gp_ongoing(index->rcu_reader_qs_gp)) {
			if (wait_loops++ == RCU_QS_ACTIVE_ATTEMPTS) {
				wait_gp(index);
			} else {
#ifndef HAS_INCOHERENT_CACHES
				cpu_relax();
#else /* #ifndef HAS_INCOHERENT_CACHES */
				smp_mb();
#endif /* #else #ifndef HAS_INCOHERENT_CACHES */
			}
		}
	}
}

/*
 * Using a two-subphases algorithm for architectures with smaller than 64-bit
 * long-size to ensure we do not encounter an overflow bug.
 */

#if (BITS_PER_LONG < 64)
/*
 * called with urcu_mutex held.
 */
static void switch_next_urcu_qparity(void)
{
	STORE_SHARED(urcu_gp_ctr, urcu_gp_ctr ^ RCU_GP_CTR);
}

void synchronize_rcu(void)
{
	unsigned long was_online;

	was_online = rcu_reader_qs_gp;

	/* All threads should read qparity before accessing data structure
	 * where new ptr points to.
	 */
	/* Write new ptr before changing the qparity */
	smp_mb();

	/*
	 * 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)
		STORE_SHARED(rcu_reader_qs_gp, 0);

	internal_urcu_lock();

	switch_next_urcu_qparity();	/* 0 -> 1 */

	/*
	 * Must commit qparity update to memory before waiting for parity
	 * 0 quiescent state. Failure to do so could result in the writer
	 * waiting forever while new readers are always accessing data (no
	 * progress).
	 * Ensured by STORE_SHARED and LOAD_SHARED.
	 */

	/*
	 * Wait for previous parity to be empty of readers.
	 */
	wait_for_quiescent_state();	/* Wait readers in parity 0 */

	/*
	 * Must finish waiting for quiescent state for parity 0 before
	 * committing qparity update to memory. Failure to do so could result in
	 * the writer waiting forever while new readers are always accessing
	 * data (no progress).
	 * Ensured by STORE_SHARED and LOAD_SHARED.
	 */

	switch_next_urcu_qparity();	/* 1 -> 0 */

	/*
	 * Must commit qparity update to memory before waiting for parity
	 * 1 quiescent state. Failure to do so could result in the writer
	 * waiting forever while new readers are always accessing data (no
	 * progress).
	 * Ensured by STORE_SHARED and LOAD_SHARED.
	 */

	/*
	 * Wait for previous parity to be empty of readers.
	 */
	wait_for_quiescent_state();	/* Wait readers in parity 1 */

	internal_urcu_unlock();

	/*
	 * Finish waiting for reader threads before letting the old ptr being
	 * freed.
	 */
	if (was_online)
		_STORE_SHARED(rcu_reader_qs_gp, LOAD_SHARED(urcu_gp_ctr));
	smp_mb();
}
#else /* !(BITS_PER_LONG < 64) */
void synchronize_rcu(void)
{
	unsigned long was_online;

	was_online = rcu_reader_qs_gp;

	/*
	 * 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.
	 */
	smp_mb();
	if (was_online)
		STORE_SHARED(rcu_reader_qs_gp, 0);

	internal_urcu_lock();
	STORE_SHARED(urcu_gp_ctr, urcu_gp_ctr + RCU_GP_CTR);
	wait_for_quiescent_state();
	internal_urcu_unlock();

	if (was_online)
		_STORE_SHARED(rcu_reader_qs_gp, LOAD_SHARED(urcu_gp_ctr));
	smp_mb();
}
#endif  /* !(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();
}

void *rcu_dereference(void *p)
{
	return _rcu_dereference(p);
}

void *rcu_assign_pointer_sym(void **p, void *v)
{
	wmb();
	return STORE_SHARED(p, v);
}

void *rcu_cmpxchg_pointer_sym(void **p, void *old, void *_new)
{
	wmb();
	return cmpxchg(p, old, _new);
}

void *rcu_xchg_pointer_sym(void **p, void *v)
{
	wmb();
	return xchg(p, v);
}

void *rcu_publish_content_sym(void **p, void *v)
{
	void *oldptr;

	oldptr = _rcu_xchg_pointer(p, v);
	synchronize_rcu();
	return oldptr;
}

void rcu_quiescent_state(void)
{
	_rcu_quiescent_state();
}

void rcu_thread_offline(void)
{
	_rcu_thread_offline();
}

void rcu_thread_online(void)
{
	_rcu_thread_online();
}

static void rcu_add_reader(pthread_t id)
{
	struct reader_registry *oldarray;

	if (!registry) {
		alloc_readers = INIT_NUM_THREADS;
		num_readers = 0;
		registry =
			malloc(sizeof(struct reader_registry) * alloc_readers);
	}
	if (alloc_readers < num_readers + 1) {
		oldarray = registry;
		registry = malloc(sizeof(struct reader_registry)
				* (alloc_readers << 1));
		memcpy(registry, oldarray,
			sizeof(struct reader_registry) * alloc_readers);
		alloc_readers <<= 1;
		free(oldarray);
	}
	registry[num_readers].tid = id;
	/* reference to the TLS of _this_ reader thread. */
	registry[num_readers].rcu_reader_qs_gp = &rcu_reader_qs_gp;
	num_readers++;
}

/*
 * Never shrink (implementation limitation).
 * This is O(nb threads). Eventually use a hash table.
 */
static void rcu_remove_reader(pthread_t id)
{
	struct reader_registry *index;

	assert(registry != NULL);
	for (index = registry; index < registry + num_readers; index++) {
		if (pthread_equal(index->tid, id)) {
			memcpy(index, &registry[num_readers - 1],
				sizeof(struct reader_registry));
			registry[num_readers - 1].tid = 0;
			registry[num_readers - 1].rcu_reader_qs_gp = NULL;
			num_readers--;
			return;
		}
	}
	/* Hrm not found, forgot to register ? */
	assert(0);
}

void rcu_register_thread(void)
{
	internal_urcu_lock();
	rcu_add_reader(pthread_self());
	internal_urcu_unlock();
	_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();
	internal_urcu_lock();
	rcu_remove_reader(pthread_self());
	internal_urcu_unlock();
}
Commit	Line	Data
9f1621ca	1	/*
7ac06cef	2	* urcu-qsbr.c
9f1621ca	3	*
7ac06cef	4	* Userspace RCU QSBR library
9f1621ca MD	5	*
	6	* Copyright (c) 2009 Mathieu Desnoyers <mathieu.desnoyers@polymtl.ca>
	7	* Copyright (c) 2009 Paul E. McKenney, IBM Corporation.
	8	*
	9	* This library is free software; you can redistribute it and/or
	10	* modify it under the terms of the GNU Lesser General Public
	11	* License as published by the Free Software Foundation; either
	12	* version 2.1 of the License, or (at your option) any later version.
	13	*
	14	* This library is distributed in the hope that it will be useful,
	15	* but WITHOUT ANY WARRANTY; without even the implied warranty of
	16	* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
	17	* Lesser General Public License for more details.
	18	*
	19	* You should have received a copy of the GNU Lesser General Public
	20	* License along with this library; if not, write to the Free Software
	21	* Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA
	22	*
	23	* IBM's contributions to this file may be relicensed under LGPLv2 or later.
	24	*/
	25
	26	#include <stdio.h>
	27	#include <pthread.h>
	28	#include <signal.h>
	29	#include <assert.h>
	30	#include <stdlib.h>
	31	#include <string.h>
	32	#include <errno.h>
	33	#include <poll.h>
	34
727f819d	35	#define BUILD_QSBR_LIB
7ac06cef	36	#include "urcu-qsbr-static.h"
9f1621ca	37	/* Do not #define _LGPL_SOURCE to ensure we can emit the wrapper symbols */
7ac06cef	38	#include "urcu-qsbr.h"
9f1621ca	39
81d1f1f5	40	static pthread_mutex_t urcu_mutex = PTHREAD_MUTEX_INITIALIZER;
9f1621ca	41
bc6c15bb MD	42	int gp_futex;
bc6c15bb MD	43
9f1621ca MD	44	/*
	45	* Global grace period counter.
	46	*/
ac258107	47	unsigned long urcu_gp_ctr = RCU_GP_ONLINE;
9f1621ca MD	48
	49	/*
	50	* Written to only by each individual reader. Read by both the reader and the
	51	* writers.
	52	*/
f0f7dbdd	53	unsigned long __thread rcu_reader_qs_gp;
9f1621ca MD	54
	55	/* Thread IDs of registered readers */
	56	#define INIT_NUM_THREADS 4
	57
	58	struct reader_registry {
	59	pthread_t tid;
f0f7dbdd	60	unsigned long *rcu_reader_qs_gp;
9f1621ca MD	61	};
	62
	63	#ifdef DEBUG_YIELD
	64	unsigned int yield_active;
	65	unsigned int __thread rand_yield;
	66	#endif
	67
	68	static struct reader_registry *registry;
9f1621ca MD	69	static int num_readers, alloc_readers;
9f1621ca MD	70
90c1618a	71	static void internal_urcu_lock(void)
9f1621ca MD	72	{
	73	int ret;
	74
	75	#ifndef DISTRUST_SIGNALS_EXTREME
	76	ret = pthread_mutex_lock(&urcu_mutex);
	77	if (ret) {
	78	perror("Error in pthread mutex lock");
	79	exit(-1);
	80	}
	81	#else /* #ifndef DISTRUST_SIGNALS_EXTREME */
	82	while ((ret = pthread_mutex_trylock(&urcu_mutex)) != 0) {
	83	if (ret != EBUSY && ret != EINTR) {
	84	printf("ret = %d, errno = %d\n", ret, errno);
	85	perror("Error in pthread mutex lock");
	86	exit(-1);
	87	}
9f1621ca MD	88	poll(NULL,0,10);
	89	}
	90	#endif /* #else #ifndef DISTRUST_SIGNALS_EXTREME */
	91	}
	92
90c1618a	93	static void internal_urcu_unlock(void)
9f1621ca MD	94	{
	95	int ret;
	96
	97	ret = pthread_mutex_unlock(&urcu_mutex);
	98	if (ret) {
	99	perror("Error in pthread mutex unlock");
	100	exit(-1);
	101	}
	102	}
	103
bc6c15bb MD	104	/*
	105	* synchronize_rcu() waiting. Single thread.
	106	*/
	107	static void wait_gp(struct reader_registry *index)
	108	{
	109	atomic_dec(&gp_futex);
	110	smp_mb(); /* Write futex before read reader_gp */
	111	if (!rcu_gp_ongoing(index->rcu_reader_qs_gp)) {
	112	/* Read reader_gp before write futex */
	113	smp_mb();
	114	/* Callbacks are queued, don't wait. */
	115	atomic_set(&gp_futex, 0);
	116	} else {
	117	/* Read reader_gp before read futex */
	118	smp_rmb();
	119	if (atomic_read(&gp_futex) == -1)
	120	futex(&gp_futex, FUTEX_WAIT, -1,
	121	NULL, NULL, 0);
	122	}
	123	}
	124
90c1618a	125	static void wait_for_quiescent_state(void)
9f1621ca MD	126	{
	127	struct reader_registry *index;
	128
	129	if (!registry)
	130	return;
	131	/*
3395d46c	132	* Wait for each thread rcu_reader_qs_gp count to become 0.
9f1621ca MD	133	*/
9f1621ca MD	134	for (index = registry; index < registry + num_readers; index++) {
bc6c15bb MD	135	int wait_loops = 0;
	136
	137	while (rcu_gp_ongoing(index->rcu_reader_qs_gp)) {
	138	if (wait_loops++ == RCU_QS_ACTIVE_ATTEMPTS) {
	139	wait_gp(index);
	140	} else {
9f1621ca	141	#ifndef HAS_INCOHERENT_CACHES
bc6c15bb	142	cpu_relax();
9f1621ca	143	#else /* #ifndef HAS_INCOHERENT_CACHES */
bc6c15bb	144	smp_mb();
9f1621ca	145	#endif /* #else #ifndef HAS_INCOHERENT_CACHES */
bc6c15bb MD	146	}
bc6c15bb MD	147	}
9f1621ca MD	148	}
	149	}
	150
47d2f29e MD	151	/*
	152	* Using a two-subphases algorithm for architectures with smaller than 64-bit
	153	* long-size to ensure we do not encounter an overflow bug.
	154	*/
	155
	156	#if (BITS_PER_LONG < 64)
	157	/*
	158	* called with urcu_mutex held.
	159	*/
	160	static void switch_next_urcu_qparity(void)
	161	{
	162	STORE_SHARED(urcu_gp_ctr, urcu_gp_ctr ^ RCU_GP_CTR);
	163	}
	164
	165	void synchronize_rcu(void)
	166	{
bc49c323 MD	167	unsigned long was_online;
	168
	169	was_online = rcu_reader_qs_gp;
	170
47d2f29e MD	171	/* All threads should read qparity before accessing data structure
	172	* where new ptr points to.
	173	*/
	174	/* Write new ptr before changing the qparity */
	175	smp_mb();
	176
bc49c323 MD	177	/*
	178	* Mark the writer thread offline to make sure we don't wait for
	179	* our own quiescent state. This allows using synchronize_rcu() in
	180	* threads registered as readers.
	181	*/
	182	if (was_online)
	183	STORE_SHARED(rcu_reader_qs_gp, 0);
	184
47d2f29e MD	185	internal_urcu_lock();
	186
	187	switch_next_urcu_qparity(); /* 0 -> 1 */
	188
	189	/*
	190	* Must commit qparity update to memory before waiting for parity
	191	* 0 quiescent state. Failure to do so could result in the writer
	192	* waiting forever while new readers are always accessing data (no
	193	* progress).
	194	* Ensured by STORE_SHARED and LOAD_SHARED.
	195	*/
	196
	197	/*
	198	* Wait for previous parity to be empty of readers.
	199	*/
	200	wait_for_quiescent_state(); /* Wait readers in parity 0 */
	201
	202	/*
	203	* Must finish waiting for quiescent state for parity 0 before
	204	* committing qparity update to memory. Failure to do so could result in
	205	* the writer waiting forever while new readers are always accessing
	206	* data (no progress).
	207	* Ensured by STORE_SHARED and LOAD_SHARED.
	208	*/
	209
	210	switch_next_urcu_qparity(); /* 1 -> 0 */
	211
	212	/*
	213	* Must commit qparity update to memory before waiting for parity
	214	* 1 quiescent state. Failure to do so could result in the writer
	215	* waiting forever while new readers are always accessing data (no
	216	* progress).
	217	* Ensured by STORE_SHARED and LOAD_SHARED.
	218	*/
	219
	220	/*
	221	* Wait for previous parity to be empty of readers.
	222	*/
	223	wait_for_quiescent_state(); /* Wait readers in parity 1 */
	224
	225	internal_urcu_unlock();
	226
bc49c323 MD	227	/*
bc49c323 MD	228	* Finish waiting for reader threads before letting the old ptr being
47d2f29e MD	229	* freed.
47d2f29e MD	230	*/
bc49c323 MD	231	if (was_online)
bc49c323 MD	232	_STORE_SHARED(rcu_reader_qs_gp, LOAD_SHARED(urcu_gp_ctr));
47d2f29e MD	233	smp_mb();
	234	}
	235	#else /* !(BITS_PER_LONG < 64) */
9f1621ca MD	236	void synchronize_rcu(void)
9f1621ca MD	237	{
f0f7dbdd	238	unsigned long was_online;
ff2f67a0	239
ab179a17	240	was_online = rcu_reader_qs_gp;
ff2f67a0 MD	241
	242	/*
	243	* Mark the writer thread offline to make sure we don't wait for
	244	* our own quiescent state. This allows using synchronize_rcu() in
	245	* threads registered as readers.
	246	*/
8f50d1ce	247	smp_mb();
ff2f67a0	248	if (was_online)
8f50d1ce	249	STORE_SHARED(rcu_reader_qs_gp, 0);
ff2f67a0	250
4e27f058	251	internal_urcu_lock();
55570466	252	STORE_SHARED(urcu_gp_ctr, urcu_gp_ctr + RCU_GP_CTR);
9f1621ca	253	wait_for_quiescent_state();
9f1621ca	254	internal_urcu_unlock();
ff2f67a0 MD	255
ff2f67a0 MD	256	if (was_online)
ab179a17	257	_STORE_SHARED(rcu_reader_qs_gp, LOAD_SHARED(urcu_gp_ctr));
8f50d1ce	258	smp_mb();
9f1621ca	259	}
47d2f29e	260	#endif /* !(BITS_PER_LONG < 64) */
9f1621ca MD	261
	262	/*
	263	* library wrappers to be used by non-LGPL compatible source code.
	264	*/
	265
	266	void rcu_read_lock(void)
	267	{
	268	_rcu_read_lock();
	269	}
	270
	271	void rcu_read_unlock(void)
	272	{
	273	_rcu_read_unlock();
	274	}
	275
	276	void rcu_dereference(void p)
	277	{
	278	return _rcu_dereference(p);
	279	}
	280
	281	void rcu_assign_pointer_sym(void p, void v)
	282	{
	283	wmb();
	284	return STORE_SHARED(p, v);
	285	}
	286
4d1ce26f MD	287	void rcu_cmpxchg_pointer_sym(void p, void old, void *_new)
	288	{
	289	wmb();
	290	return cmpxchg(p, old, _new);
	291	}
	292
9f1621ca MD	293	void rcu_xchg_pointer_sym(void p, void v)
	294	{
	295	wmb();
	296	return xchg(p, v);
	297	}
	298
	299	void rcu_publish_content_sym(void p, void v)
	300	{
	301	void *oldptr;
	302
	303	oldptr = _rcu_xchg_pointer(p, v);
	304	synchronize_rcu();
	305	return oldptr;
	306	}
	307
7ac06cef MD	308	void rcu_quiescent_state(void)
	309	{
	310	_rcu_quiescent_state();
	311	}
	312
	313	void rcu_thread_offline(void)
	314	{
	315	_rcu_thread_offline();
	316	}
	317
	318	void rcu_thread_online(void)
	319	{
	320	_rcu_thread_online();
	321	}
	322
9f1621ca MD	323	static void rcu_add_reader(pthread_t id)
	324	{
	325	struct reader_registry *oldarray;
	326
	327	if (!registry) {
	328	alloc_readers = INIT_NUM_THREADS;
	329	num_readers = 0;
	330	registry =
	331	malloc(sizeof(struct reader_registry) * alloc_readers);
	332	}
	333	if (alloc_readers < num_readers + 1) {
	334	oldarray = registry;
	335	registry = malloc(sizeof(struct reader_registry)
	336	* (alloc_readers << 1));
	337	memcpy(registry, oldarray,
	338	sizeof(struct reader_registry) * alloc_readers);
	339	alloc_readers <<= 1;
	340	free(oldarray);
	341	}
	342	registry[num_readers].tid = id;
	343	/* reference to the TLS of _this_ reader thread. */
3395d46c	344	registry[num_readers].rcu_reader_qs_gp = &rcu_reader_qs_gp;
9f1621ca MD	345	num_readers++;
	346	}
	347
	348	/*
	349	* Never shrink (implementation limitation).
	350	* This is O(nb threads). Eventually use a hash table.
	351	*/
	352	static void rcu_remove_reader(pthread_t id)
	353	{
	354	struct reader_registry *index;
	355
	356	assert(registry != NULL);
	357	for (index = registry; index < registry + num_readers; index++) {
	358	if (pthread_equal(index->tid, id)) {
	359	memcpy(index, &registry[num_readers - 1],
	360	sizeof(struct reader_registry));
	361	registry[num_readers - 1].tid = 0;
3395d46c	362	registry[num_readers - 1].rcu_reader_qs_gp = NULL;
9f1621ca MD	363	num_readers--;
	364	return;
	365	}
	366	}
	367	/* Hrm not found, forgot to register ? */
	368	assert(0);
	369	}
	370
	371	void rcu_register_thread(void)
	372	{
	373	internal_urcu_lock();
9f1621ca MD	374	rcu_add_reader(pthread_self());
9f1621ca MD	375	internal_urcu_unlock();
5f373c84	376	_rcu_thread_online();
9f1621ca MD	377	}
	378
	379	void rcu_unregister_thread(void)
	380	{
76f3022f MD	381	/*
	382	* We have to make the thread offline otherwise we end up dealocking
	383	* with a waiting writer.
	384	*/
	385	_rcu_thread_offline();
9f1621ca MD	386	internal_urcu_lock();
	387	rcu_remove_reader(pthread_self());
	388	internal_urcu_unlock();
	389	}