[userspace-rcu.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;

/*
 * 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.
 */
struct urcu_reader_status __thread urcu_reader_status;

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

struct reader_registry {
	pthread_t tid;
	struct urcu_reader_status *urcu_reader_status;
};

#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_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;

		index->urcu_reader_status->gp_waiting = 1;
		while (rcu_gp_ongoing(&index->urcu_reader_status->qs_gp)) {
			if (wait_loops++ == RCU_QS_ACTIVE_ATTEMPTS) {
				sched_yield();	/* ideally sched_yield_to() */
				wait_loops = 0;
			} else {
#ifndef HAS_INCOHERENT_CACHES
				cpu_relax();
#else /* #ifndef HAS_INCOHERENT_CACHES */
				smp_mb();
#endif /* #else #ifndef HAS_INCOHERENT_CACHES */
			}
		}
		index->urcu_reader_status->gp_waiting = 0;
	}
}

/*
 * 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 = urcu_reader_status.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(urcu_reader_status.qs_gp, 0);

	internal_urcu_lock();

	STORE_SHARED(urcu_gp_ctr, urcu_gp_ctr ^ RCU_GP_ONGOING);

	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 */

	STORE_SHARED(urcu_gp_ctr, urcu_gp_ctr ^ RCU_GP_ONGOING);

	internal_urcu_unlock();

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

	was_online = urcu_reader_status.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(urcu_reader_status.qs_gp, 0);

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

	if (was_online)
		_STORE_SHARED(urcu_reader_status.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].urcu_reader_status = &urcu_reader_status;
	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].urcu_reader_status = 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 MD	41
	42	/*
	43	* Global grace period counter.
	44	*/
ac258107	45	unsigned long urcu_gp_ctr = RCU_GP_ONLINE;
9f1621ca MD	46
	47	/*
	48	* Written to only by each individual reader. Read by both the reader and the
	49	* writers.
	50	*/
8b25e300	51	struct urcu_reader_status __thread urcu_reader_status;
9f1621ca MD	52
	53	/* Thread IDs of registered readers */
	54	#define INIT_NUM_THREADS 4
	55
	56	struct reader_registry {
	57	pthread_t tid;
8b25e300	58	struct urcu_reader_status *urcu_reader_status;
9f1621ca MD	59	};
	60
	61	#ifdef DEBUG_YIELD
	62	unsigned int yield_active;
	63	unsigned int __thread rand_yield;
	64	#endif
	65
	66	static struct reader_registry *registry;
9f1621ca MD	67	static int num_readers, alloc_readers;
9f1621ca MD	68
90c1618a	69	static void internal_urcu_lock(void)
9f1621ca MD	70	{
	71	int ret;
	72
	73	#ifndef DISTRUST_SIGNALS_EXTREME
	74	ret = pthread_mutex_lock(&urcu_mutex);
	75	if (ret) {
	76	perror("Error in pthread mutex lock");
	77	exit(-1);
	78	}
	79	#else /* #ifndef DISTRUST_SIGNALS_EXTREME */
	80	while ((ret = pthread_mutex_trylock(&urcu_mutex)) != 0) {
	81	if (ret != EBUSY && ret != EINTR) {
	82	printf("ret = %d, errno = %d\n", ret, errno);
	83	perror("Error in pthread mutex lock");
	84	exit(-1);
	85	}
9f1621ca MD	86	poll(NULL,0,10);
	87	}
	88	#endif /* #else #ifndef DISTRUST_SIGNALS_EXTREME */
	89	}
	90
90c1618a	91	static void internal_urcu_unlock(void)
9f1621ca MD	92	{
	93	int ret;
	94
	95	ret = pthread_mutex_unlock(&urcu_mutex);
	96	if (ret) {
	97	perror("Error in pthread mutex unlock");
	98	exit(-1);
	99	}
	100	}
	101
bc6c15bb MD	102	/*
	103	* synchronize_rcu() waiting. Single thread.
	104	*/
90c1618a	105	static void wait_for_quiescent_state(void)
9f1621ca MD	106	{
	107	struct reader_registry *index;
	108
	109	if (!registry)
	110	return;
	111	/*
8b25e300	112	* Wait for each thread rcu_reader qs_gp count to become 0.
9f1621ca MD	113	*/
9f1621ca MD	114	for (index = registry; index < registry + num_readers; index++) {
bc6c15bb MD	115	int wait_loops = 0;
bc6c15bb MD	116
8b25e300 MD	117	index->urcu_reader_status->gp_waiting = 1;
8b25e300 MD	118	while (rcu_gp_ongoing(&index->urcu_reader_status->qs_gp)) {
bc6c15bb	119	if (wait_loops++ == RCU_QS_ACTIVE_ATTEMPTS) {
ae62b5e8	120	sched_yield(); /* ideally sched_yield_to() */
b3c4dd1a	121	wait_loops = 0;
bc6c15bb	122	} else {
9f1621ca	123	#ifndef HAS_INCOHERENT_CACHES
bc6c15bb	124	cpu_relax();
9f1621ca	125	#else /* #ifndef HAS_INCOHERENT_CACHES */
bc6c15bb	126	smp_mb();
9f1621ca	127	#endif /* #else #ifndef HAS_INCOHERENT_CACHES */
bc6c15bb MD	128	}
bc6c15bb MD	129	}
8b25e300	130	index->urcu_reader_status->gp_waiting = 0;
9f1621ca MD	131	}
	132	}
	133
47d2f29e MD	134	/*
	135	* Using a two-subphases algorithm for architectures with smaller than 64-bit
	136	* long-size to ensure we do not encounter an overflow bug.
	137	*/
	138
	139	#if (BITS_PER_LONG < 64)
	140	/*
	141	* called with urcu_mutex held.
	142	*/
	143	static void switch_next_urcu_qparity(void)
	144	{
	145	STORE_SHARED(urcu_gp_ctr, urcu_gp_ctr ^ RCU_GP_CTR);
	146	}
	147
	148	void synchronize_rcu(void)
	149	{
bc49c323 MD	150	unsigned long was_online;
bc49c323 MD	151
8b25e300	152	was_online = urcu_reader_status.qs_gp;
bc49c323	153
47d2f29e MD	154	/* All threads should read qparity before accessing data structure
	155	* where new ptr points to.
	156	*/
	157	/* Write new ptr before changing the qparity */
	158	smp_mb();
	159
bc49c323 MD	160	/*
	161	* Mark the writer thread offline to make sure we don't wait for
	162	* our own quiescent state. This allows using synchronize_rcu() in
	163	* threads registered as readers.
	164	*/
	165	if (was_online)
8b25e300	166	STORE_SHARED(urcu_reader_status.qs_gp, 0);
bc49c323	167
47d2f29e MD	168	internal_urcu_lock();
47d2f29e MD	169
ae62b5e8 MD	170	STORE_SHARED(urcu_gp_ctr, urcu_gp_ctr ^ RCU_GP_ONGOING);
ae62b5e8 MD	171
47d2f29e MD	172	switch_next_urcu_qparity(); /* 0 -> 1 */
	173
	174	/*
	175	* Must commit qparity update to memory before waiting for parity
	176	* 0 quiescent state. Failure to do so could result in the writer
	177	* waiting forever while new readers are always accessing data (no
	178	* progress).
	179	* Ensured by STORE_SHARED and LOAD_SHARED.
	180	*/
	181
	182	/*
	183	* Wait for previous parity to be empty of readers.
	184	*/
	185	wait_for_quiescent_state(); /* Wait readers in parity 0 */
	186
	187	/*
	188	* Must finish waiting for quiescent state for parity 0 before
	189	* committing qparity update to memory. Failure to do so could result in
	190	* the writer waiting forever while new readers are always accessing
	191	* data (no progress).
	192	* Ensured by STORE_SHARED and LOAD_SHARED.
	193	*/
	194
	195	switch_next_urcu_qparity(); /* 1 -> 0 */
	196
	197	/*
	198	* Must commit qparity update to memory before waiting for parity
	199	* 1 quiescent state. Failure to do so could result in the writer
	200	* waiting forever while new readers are always accessing data (no
	201	* progress).
	202	* Ensured by STORE_SHARED and LOAD_SHARED.
	203	*/
	204
	205	/*
	206	* Wait for previous parity to be empty of readers.
	207	*/
	208	wait_for_quiescent_state(); /* Wait readers in parity 1 */
	209
ae62b5e8 MD	210	STORE_SHARED(urcu_gp_ctr, urcu_gp_ctr ^ RCU_GP_ONGOING);
ae62b5e8 MD	211
47d2f29e MD	212	internal_urcu_unlock();
47d2f29e MD	213
bc49c323 MD	214	/*
bc49c323 MD	215	* Finish waiting for reader threads before letting the old ptr being
47d2f29e MD	216	* freed.
47d2f29e MD	217	*/
bc49c323	218	if (was_online)
8b25e300 MD	219	_STORE_SHARED(urcu_reader_status.qs_gp,
8b25e300 MD	220	LOAD_SHARED(urcu_gp_ctr));
47d2f29e MD	221	smp_mb();
	222	}
	223	#else /* !(BITS_PER_LONG < 64) */
9f1621ca MD	224	void synchronize_rcu(void)
9f1621ca MD	225	{
f0f7dbdd	226	unsigned long was_online;
ff2f67a0	227
8b25e300	228	was_online = urcu_reader_status.qs_gp;
ff2f67a0 MD	229
	230	/*
	231	* Mark the writer thread offline to make sure we don't wait for
	232	* our own quiescent state. This allows using synchronize_rcu() in
	233	* threads registered as readers.
	234	*/
8f50d1ce	235	smp_mb();
ff2f67a0	236	if (was_online)
8b25e300	237	STORE_SHARED(urcu_reader_status.qs_gp, 0);
ff2f67a0	238
4e27f058	239	internal_urcu_lock();
ae62b5e8	240	STORE_SHARED(urcu_gp_ctr, urcu_gp_ctr ^ RCU_GP_ONGOING);
55570466	241	STORE_SHARED(urcu_gp_ctr, urcu_gp_ctr + RCU_GP_CTR);
9f1621ca	242	wait_for_quiescent_state();
ae62b5e8	243	STORE_SHARED(urcu_gp_ctr, urcu_gp_ctr ^ RCU_GP_ONGOING);
9f1621ca	244	internal_urcu_unlock();
ff2f67a0 MD	245
ff2f67a0 MD	246	if (was_online)
8b25e300 MD	247	_STORE_SHARED(urcu_reader_status.qs_gp,
8b25e300 MD	248	LOAD_SHARED(urcu_gp_ctr));
8f50d1ce	249	smp_mb();
9f1621ca	250	}
47d2f29e	251	#endif /* !(BITS_PER_LONG < 64) */
9f1621ca MD	252
	253	/*
	254	* library wrappers to be used by non-LGPL compatible source code.
	255	*/
	256
	257	void rcu_read_lock(void)
	258	{
	259	_rcu_read_lock();
	260	}
	261
	262	void rcu_read_unlock(void)
	263	{
	264	_rcu_read_unlock();
	265	}
	266
	267	void rcu_dereference(void p)
	268	{
	269	return _rcu_dereference(p);
	270	}
	271
	272	void rcu_assign_pointer_sym(void p, void v)
	273	{
	274	wmb();
	275	return STORE_SHARED(p, v);
	276	}
	277
4d1ce26f MD	278	void rcu_cmpxchg_pointer_sym(void p, void old, void *_new)
	279	{
	280	wmb();
	281	return cmpxchg(p, old, _new);
	282	}
	283
9f1621ca MD	284	void rcu_xchg_pointer_sym(void p, void v)
	285	{
	286	wmb();
	287	return xchg(p, v);
	288	}
	289
	290	void rcu_publish_content_sym(void p, void v)
	291	{
	292	void *oldptr;
	293
	294	oldptr = _rcu_xchg_pointer(p, v);
	295	synchronize_rcu();
	296	return oldptr;
	297	}
	298
7ac06cef MD	299	void rcu_quiescent_state(void)
	300	{
	301	_rcu_quiescent_state();
	302	}
	303
	304	void rcu_thread_offline(void)
	305	{
	306	_rcu_thread_offline();
	307	}
	308
	309	void rcu_thread_online(void)
	310	{
	311	_rcu_thread_online();
	312	}
	313
9f1621ca MD	314	static void rcu_add_reader(pthread_t id)
	315	{
	316	struct reader_registry *oldarray;
	317
	318	if (!registry) {
	319	alloc_readers = INIT_NUM_THREADS;
	320	num_readers = 0;
	321	registry =
	322	malloc(sizeof(struct reader_registry) * alloc_readers);
	323	}
	324	if (alloc_readers < num_readers + 1) {
	325	oldarray = registry;
	326	registry = malloc(sizeof(struct reader_registry)
	327	* (alloc_readers << 1));
	328	memcpy(registry, oldarray,
	329	sizeof(struct reader_registry) * alloc_readers);
	330	alloc_readers <<= 1;
	331	free(oldarray);
	332	}
	333	registry[num_readers].tid = id;
	334	/* reference to the TLS of _this_ reader thread. */
8b25e300	335	registry[num_readers].urcu_reader_status = &urcu_reader_status;
9f1621ca MD	336	num_readers++;
	337	}
	338
	339	/*
	340	* Never shrink (implementation limitation).
	341	* This is O(nb threads). Eventually use a hash table.
	342	*/
	343	static void rcu_remove_reader(pthread_t id)
	344	{
	345	struct reader_registry *index;
	346
	347	assert(registry != NULL);
	348	for (index = registry; index < registry + num_readers; index++) {
	349	if (pthread_equal(index->tid, id)) {
	350	memcpy(index, &registry[num_readers - 1],
	351	sizeof(struct reader_registry));
	352	registry[num_readers - 1].tid = 0;
8b25e300	353	registry[num_readers - 1].urcu_reader_status = NULL;
9f1621ca MD	354	num_readers--;
	355	return;
	356	}
	357	}
	358	/* Hrm not found, forgot to register ? */
	359	assert(0);
	360	}
	361
	362	void rcu_register_thread(void)
	363	{
	364	internal_urcu_lock();
9f1621ca MD	365	rcu_add_reader(pthread_self());
9f1621ca MD	366	internal_urcu_unlock();
5f373c84	367	_rcu_thread_online();
9f1621ca MD	368	}
	369
	370	void rcu_unregister_thread(void)
	371	{
76f3022f MD	372	/*
	373	* We have to make the thread offline otherwise we end up dealocking
	374	* with a waiting writer.
	375	*/
	376	_rcu_thread_offline();
9f1621ca MD	377	internal_urcu_lock();
	378	rcu_remove_reader(pthread_self());
	379	internal_urcu_unlock();
	380	}