[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;

/*
 * 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;

		if (likely(!rcu_gp_ongoing(&index->urcu_reader_status->qs_gp)))
			continue;
	
		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
2b7f706f MD	117	if (likely(!rcu_gp_ongoing(&index->urcu_reader_status->qs_gp)))
	118	continue;
	119
8b25e300 MD	120	index->urcu_reader_status->gp_waiting = 1;
8b25e300 MD	121	while (rcu_gp_ongoing(&index->urcu_reader_status->qs_gp)) {
bc6c15bb	122	if (wait_loops++ == RCU_QS_ACTIVE_ATTEMPTS) {
ae62b5e8	123	sched_yield(); /* ideally sched_yield_to() */
b3c4dd1a	124	wait_loops = 0;
bc6c15bb	125	} else {
9f1621ca	126	#ifndef HAS_INCOHERENT_CACHES
bc6c15bb	127	cpu_relax();
9f1621ca	128	#else /* #ifndef HAS_INCOHERENT_CACHES */
bc6c15bb	129	smp_mb();
9f1621ca	130	#endif /* #else #ifndef HAS_INCOHERENT_CACHES */
bc6c15bb MD	131	}
bc6c15bb MD	132	}
8b25e300	133	index->urcu_reader_status->gp_waiting = 0;
9f1621ca MD	134	}
	135	}
	136
47d2f29e MD	137	/*
	138	* Using a two-subphases algorithm for architectures with smaller than 64-bit
	139	* long-size to ensure we do not encounter an overflow bug.
	140	*/
	141
	142	#if (BITS_PER_LONG < 64)
	143	/*
	144	* called with urcu_mutex held.
	145	*/
	146	static void switch_next_urcu_qparity(void)
	147	{
	148	STORE_SHARED(urcu_gp_ctr, urcu_gp_ctr ^ RCU_GP_CTR);
	149	}
	150
	151	void synchronize_rcu(void)
	152	{
bc49c323 MD	153	unsigned long was_online;
bc49c323 MD	154
8b25e300	155	was_online = urcu_reader_status.qs_gp;
bc49c323	156
47d2f29e MD	157	/* All threads should read qparity before accessing data structure
	158	* where new ptr points to.
	159	*/
	160	/* Write new ptr before changing the qparity */
	161	smp_mb();
	162
bc49c323 MD	163	/*
	164	* Mark the writer thread offline to make sure we don't wait for
	165	* our own quiescent state. This allows using synchronize_rcu() in
	166	* threads registered as readers.
	167	*/
	168	if (was_online)
8b25e300	169	STORE_SHARED(urcu_reader_status.qs_gp, 0);
bc49c323	170
47d2f29e MD	171	internal_urcu_lock();
47d2f29e MD	172
ae62b5e8 MD	173	STORE_SHARED(urcu_gp_ctr, urcu_gp_ctr ^ RCU_GP_ONGOING);
ae62b5e8 MD	174
47d2f29e MD	175	switch_next_urcu_qparity(); /* 0 -> 1 */
	176
	177	/*
	178	* Must commit qparity update to memory before waiting for parity
	179	* 0 quiescent state. Failure to do so could result in the writer
	180	* waiting forever while new readers are always accessing data (no
	181	* progress).
	182	* Ensured by STORE_SHARED and LOAD_SHARED.
	183	*/
	184
	185	/*
	186	* Wait for previous parity to be empty of readers.
	187	*/
	188	wait_for_quiescent_state(); /* Wait readers in parity 0 */
	189
	190	/*
	191	* Must finish waiting for quiescent state for parity 0 before
	192	* committing qparity update to memory. Failure to do so could result in
	193	* the writer waiting forever while new readers are always accessing
	194	* data (no progress).
	195	* Ensured by STORE_SHARED and LOAD_SHARED.
	196	*/
	197
	198	switch_next_urcu_qparity(); /* 1 -> 0 */
	199
	200	/*
	201	* Must commit qparity update to memory before waiting for parity
	202	* 1 quiescent state. Failure to do so could result in the writer
	203	* waiting forever while new readers are always accessing data (no
	204	* progress).
	205	* Ensured by STORE_SHARED and LOAD_SHARED.
	206	*/
	207
	208	/*
	209	* Wait for previous parity to be empty of readers.
	210	*/
	211	wait_for_quiescent_state(); /* Wait readers in parity 1 */
	212
ae62b5e8 MD	213	STORE_SHARED(urcu_gp_ctr, urcu_gp_ctr ^ RCU_GP_ONGOING);
ae62b5e8 MD	214
47d2f29e MD	215	internal_urcu_unlock();
47d2f29e MD	216
bc49c323 MD	217	/*
bc49c323 MD	218	* Finish waiting for reader threads before letting the old ptr being
47d2f29e MD	219	* freed.
47d2f29e MD	220	*/
bc49c323	221	if (was_online)
8b25e300 MD	222	_STORE_SHARED(urcu_reader_status.qs_gp,
8b25e300 MD	223	LOAD_SHARED(urcu_gp_ctr));
47d2f29e MD	224	smp_mb();
	225	}
	226	#else /* !(BITS_PER_LONG < 64) */
9f1621ca MD	227	void synchronize_rcu(void)
9f1621ca MD	228	{
f0f7dbdd	229	unsigned long was_online;
ff2f67a0	230
8b25e300	231	was_online = urcu_reader_status.qs_gp;
ff2f67a0 MD	232
	233	/*
	234	* Mark the writer thread offline to make sure we don't wait for
	235	* our own quiescent state. This allows using synchronize_rcu() in
	236	* threads registered as readers.
	237	*/
8f50d1ce	238	smp_mb();
ff2f67a0	239	if (was_online)
8b25e300	240	STORE_SHARED(urcu_reader_status.qs_gp, 0);
ff2f67a0	241
4e27f058	242	internal_urcu_lock();
ae62b5e8	243	STORE_SHARED(urcu_gp_ctr, urcu_gp_ctr ^ RCU_GP_ONGOING);
55570466	244	STORE_SHARED(urcu_gp_ctr, urcu_gp_ctr + RCU_GP_CTR);
9f1621ca	245	wait_for_quiescent_state();
ae62b5e8	246	STORE_SHARED(urcu_gp_ctr, urcu_gp_ctr ^ RCU_GP_ONGOING);
9f1621ca	247	internal_urcu_unlock();
ff2f67a0 MD	248
ff2f67a0 MD	249	if (was_online)
8b25e300 MD	250	_STORE_SHARED(urcu_reader_status.qs_gp,
8b25e300 MD	251	LOAD_SHARED(urcu_gp_ctr));
8f50d1ce	252	smp_mb();
9f1621ca	253	}
47d2f29e	254	#endif /* !(BITS_PER_LONG < 64) */
9f1621ca MD	255
	256	/*
	257	* library wrappers to be used by non-LGPL compatible source code.
	258	*/
	259
	260	void rcu_read_lock(void)
	261	{
	262	_rcu_read_lock();
	263	}
	264
	265	void rcu_read_unlock(void)
	266	{
	267	_rcu_read_unlock();
	268	}
	269
	270	void rcu_dereference(void p)
	271	{
	272	return _rcu_dereference(p);
	273	}
	274
	275	void rcu_assign_pointer_sym(void p, void v)
	276	{
	277	wmb();
	278	return STORE_SHARED(p, v);
	279	}
	280
4d1ce26f MD	281	void rcu_cmpxchg_pointer_sym(void p, void old, void *_new)
	282	{
	283	wmb();
	284	return cmpxchg(p, old, _new);
	285	}
	286
9f1621ca MD	287	void rcu_xchg_pointer_sym(void p, void v)
	288	{
	289	wmb();
	290	return xchg(p, v);
	291	}
	292
	293	void rcu_publish_content_sym(void p, void v)
	294	{
	295	void *oldptr;
	296
	297	oldptr = _rcu_xchg_pointer(p, v);
	298	synchronize_rcu();
	299	return oldptr;
	300	}
	301
7ac06cef MD	302	void rcu_quiescent_state(void)
	303	{
	304	_rcu_quiescent_state();
	305	}
	306
	307	void rcu_thread_offline(void)
	308	{
	309	_rcu_thread_offline();
	310	}
	311
	312	void rcu_thread_online(void)
	313	{
	314	_rcu_thread_online();
	315	}
	316
9f1621ca MD	317	static void rcu_add_reader(pthread_t id)
	318	{
	319	struct reader_registry *oldarray;
	320
	321	if (!registry) {
	322	alloc_readers = INIT_NUM_THREADS;
	323	num_readers = 0;
	324	registry =
	325	malloc(sizeof(struct reader_registry) * alloc_readers);
	326	}
	327	if (alloc_readers < num_readers + 1) {
	328	oldarray = registry;
	329	registry = malloc(sizeof(struct reader_registry)
	330	* (alloc_readers << 1));
	331	memcpy(registry, oldarray,
	332	sizeof(struct reader_registry) * alloc_readers);
	333	alloc_readers <<= 1;
	334	free(oldarray);
	335	}
	336	registry[num_readers].tid = id;
	337	/* reference to the TLS of _this_ reader thread. */
8b25e300	338	registry[num_readers].urcu_reader_status = &urcu_reader_status;
9f1621ca MD	339	num_readers++;
	340	}
	341
	342	/*
	343	* Never shrink (implementation limitation).
	344	* This is O(nb threads). Eventually use a hash table.
	345	*/
	346	static void rcu_remove_reader(pthread_t id)
	347	{
	348	struct reader_registry *index;
	349
	350	assert(registry != NULL);
	351	for (index = registry; index < registry + num_readers; index++) {
	352	if (pthread_equal(index->tid, id)) {
	353	memcpy(index, &registry[num_readers - 1],
	354	sizeof(struct reader_registry));
	355	registry[num_readers - 1].tid = 0;
8b25e300	356	registry[num_readers - 1].urcu_reader_status = NULL;
9f1621ca MD	357	num_readers--;
	358	return;
	359	}
	360	}
	361	/* Hrm not found, forgot to register ? */
	362	assert(0);
	363	}
	364
	365	void rcu_register_thread(void)
	366	{
	367	internal_urcu_lock();
9f1621ca MD	368	rcu_add_reader(pthread_self());
9f1621ca MD	369	internal_urcu_unlock();
5f373c84	370	_rcu_thread_online();
9f1621ca MD	371	}
	372
	373	void rcu_unregister_thread(void)
	374	{
76f3022f MD	375	/*
	376	* We have to make the thread offline otherwise we end up dealocking
	377	* with a waiting writer.
	378	*/
	379	_rcu_thread_offline();
9f1621ca MD	380	internal_urcu_lock();
	381	rcu_remove_reader(pthread_self());
	382	internal_urcu_unlock();
	383	}