[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>
#include <unistd.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) {
				/* adapted wait time, in us */
				usleep(LOAD_SHARED(index->urcu_reader_status->qs_time_delta_usec) / 4);
				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>
ee72ef6e	34	#include <unistd.h>
9f1621ca	35
727f819d	36	#define BUILD_QSBR_LIB
7ac06cef	37	#include "urcu-qsbr-static.h"
9f1621ca	38	/* Do not #define _LGPL_SOURCE to ensure we can emit the wrapper symbols */
7ac06cef	39	#include "urcu-qsbr.h"
9f1621ca	40
81d1f1f5	41	static pthread_mutex_t urcu_mutex = PTHREAD_MUTEX_INITIALIZER;
9f1621ca MD	42
	43	/*
	44	* Global grace period counter.
	45	*/
ac258107	46	unsigned long urcu_gp_ctr = RCU_GP_ONLINE;
9f1621ca MD	47
	48	/*
	49	* Written to only by each individual reader. Read by both the reader and the
	50	* writers.
	51	*/
8b25e300	52	struct urcu_reader_status __thread urcu_reader_status;
9f1621ca MD	53
	54	/* Thread IDs of registered readers */
	55	#define INIT_NUM_THREADS 4
	56
	57	struct reader_registry {
	58	pthread_t tid;
8b25e300	59	struct urcu_reader_status *urcu_reader_status;
9f1621ca MD	60	};
	61
	62	#ifdef DEBUG_YIELD
	63	unsigned int yield_active;
	64	unsigned int __thread rand_yield;
	65	#endif
	66
	67	static struct reader_registry *registry;
9f1621ca MD	68	static int num_readers, alloc_readers;
9f1621ca MD	69
90c1618a	70	static void internal_urcu_lock(void)
9f1621ca MD	71	{
	72	int ret;
	73
	74	#ifndef DISTRUST_SIGNALS_EXTREME
	75	ret = pthread_mutex_lock(&urcu_mutex);
	76	if (ret) {
	77	perror("Error in pthread mutex lock");
	78	exit(-1);
	79	}
	80	#else /* #ifndef DISTRUST_SIGNALS_EXTREME */
	81	while ((ret = pthread_mutex_trylock(&urcu_mutex)) != 0) {
	82	if (ret != EBUSY && ret != EINTR) {
	83	printf("ret = %d, errno = %d\n", ret, errno);
	84	perror("Error in pthread mutex lock");
	85	exit(-1);
	86	}
9f1621ca MD	87	poll(NULL,0,10);
	88	}
	89	#endif /* #else #ifndef DISTRUST_SIGNALS_EXTREME */
	90	}
	91
90c1618a	92	static void internal_urcu_unlock(void)
9f1621ca MD	93	{
	94	int ret;
	95
	96	ret = pthread_mutex_unlock(&urcu_mutex);
	97	if (ret) {
	98	perror("Error in pthread mutex unlock");
	99	exit(-1);
	100	}
	101	}
	102
bc6c15bb MD	103	/*
	104	* synchronize_rcu() waiting. Single thread.
	105	*/
90c1618a	106	static void wait_for_quiescent_state(void)
9f1621ca MD	107	{
	108	struct reader_registry *index;
	109
	110	if (!registry)
	111	return;
	112	/*
8b25e300	113	* Wait for each thread rcu_reader qs_gp count to become 0.
9f1621ca MD	114	*/
9f1621ca MD	115	for (index = registry; index < registry + num_readers; index++) {
bc6c15bb MD	116	int wait_loops = 0;
bc6c15bb MD	117
69915897 MD	118	if (likely(!rcu_gp_ongoing(&index->urcu_reader_status->qs_gp)))
	119	continue;
	120
8b25e300 MD	121	index->urcu_reader_status->gp_waiting = 1;
8b25e300 MD	122	while (rcu_gp_ongoing(&index->urcu_reader_status->qs_gp)) {
bc6c15bb	123	if (wait_loops++ == RCU_QS_ACTIVE_ATTEMPTS) {
ee72ef6e	124	/* adapted wait time, in us */
539718ae	125	usleep(LOAD_SHARED(index->urcu_reader_status->qs_time_delta_usec) / 4);
b3c4dd1a	126	wait_loops = 0;
bc6c15bb	127	} else {
9f1621ca	128	#ifndef HAS_INCOHERENT_CACHES
bc6c15bb	129	cpu_relax();
9f1621ca	130	#else /* #ifndef HAS_INCOHERENT_CACHES */
bc6c15bb	131	smp_mb();
9f1621ca	132	#endif /* #else #ifndef HAS_INCOHERENT_CACHES */
bc6c15bb MD	133	}
bc6c15bb MD	134	}
8b25e300	135	index->urcu_reader_status->gp_waiting = 0;
9f1621ca MD	136	}
	137	}
	138
47d2f29e MD	139	/*
	140	* Using a two-subphases algorithm for architectures with smaller than 64-bit
	141	* long-size to ensure we do not encounter an overflow bug.
	142	*/
	143
	144	#if (BITS_PER_LONG < 64)
	145	/*
	146	* called with urcu_mutex held.
	147	*/
	148	static void switch_next_urcu_qparity(void)
	149	{
	150	STORE_SHARED(urcu_gp_ctr, urcu_gp_ctr ^ RCU_GP_CTR);
	151	}
	152
	153	void synchronize_rcu(void)
	154	{
bc49c323 MD	155	unsigned long was_online;
bc49c323 MD	156
8b25e300	157	was_online = urcu_reader_status.qs_gp;
bc49c323	158
47d2f29e MD	159	/* All threads should read qparity before accessing data structure
	160	* where new ptr points to.
	161	*/
	162	/* Write new ptr before changing the qparity */
	163	smp_mb();
	164
bc49c323 MD	165	/*
	166	* Mark the writer thread offline to make sure we don't wait for
	167	* our own quiescent state. This allows using synchronize_rcu() in
	168	* threads registered as readers.
	169	*/
	170	if (was_online)
8b25e300	171	STORE_SHARED(urcu_reader_status.qs_gp, 0);
bc49c323	172
47d2f29e MD	173	internal_urcu_lock();
47d2f29e MD	174
ae62b5e8 MD	175	STORE_SHARED(urcu_gp_ctr, urcu_gp_ctr ^ RCU_GP_ONGOING);
ae62b5e8 MD	176
47d2f29e MD	177	switch_next_urcu_qparity(); /* 0 -> 1 */
	178
	179	/*
	180	* Must commit qparity update to memory before waiting for parity
	181	* 0 quiescent state. Failure to do so could result in the writer
	182	* waiting forever while new readers are always accessing data (no
	183	* progress).
	184	* Ensured by STORE_SHARED and LOAD_SHARED.
	185	*/
	186
	187	/*
	188	* Wait for previous parity to be empty of readers.
	189	*/
	190	wait_for_quiescent_state(); /* Wait readers in parity 0 */
	191
	192	/*
	193	* Must finish waiting for quiescent state for parity 0 before
	194	* committing qparity update to memory. Failure to do so could result in
	195	* the writer waiting forever while new readers are always accessing
	196	* data (no progress).
	197	* Ensured by STORE_SHARED and LOAD_SHARED.
	198	*/
	199
	200	switch_next_urcu_qparity(); /* 1 -> 0 */
	201
	202	/*
	203	* Must commit qparity update to memory before waiting for parity
	204	* 1 quiescent state. Failure to do so could result in the writer
	205	* waiting forever while new readers are always accessing data (no
	206	* progress).
	207	* Ensured by STORE_SHARED and LOAD_SHARED.
	208	*/
	209
	210	/*
	211	* Wait for previous parity to be empty of readers.
	212	*/
	213	wait_for_quiescent_state(); /* Wait readers in parity 1 */
	214
ae62b5e8 MD	215	STORE_SHARED(urcu_gp_ctr, urcu_gp_ctr ^ RCU_GP_ONGOING);
ae62b5e8 MD	216
47d2f29e MD	217	internal_urcu_unlock();
47d2f29e MD	218
bc49c323 MD	219	/*
bc49c323 MD	220	* Finish waiting for reader threads before letting the old ptr being
47d2f29e MD	221	* freed.
47d2f29e MD	222	*/
bc49c323	223	if (was_online)
8b25e300 MD	224	_STORE_SHARED(urcu_reader_status.qs_gp,
8b25e300 MD	225	LOAD_SHARED(urcu_gp_ctr));
47d2f29e MD	226	smp_mb();
	227	}
	228	#else /* !(BITS_PER_LONG < 64) */
9f1621ca MD	229	void synchronize_rcu(void)
9f1621ca MD	230	{
f0f7dbdd	231	unsigned long was_online;
ff2f67a0	232
8b25e300	233	was_online = urcu_reader_status.qs_gp;
ff2f67a0 MD	234
	235	/*
	236	* Mark the writer thread offline to make sure we don't wait for
	237	* our own quiescent state. This allows using synchronize_rcu() in
	238	* threads registered as readers.
	239	*/
8f50d1ce	240	smp_mb();
ff2f67a0	241	if (was_online)
8b25e300	242	STORE_SHARED(urcu_reader_status.qs_gp, 0);
ff2f67a0	243
4e27f058	244	internal_urcu_lock();
ae62b5e8	245	STORE_SHARED(urcu_gp_ctr, urcu_gp_ctr ^ RCU_GP_ONGOING);
55570466	246	STORE_SHARED(urcu_gp_ctr, urcu_gp_ctr + RCU_GP_CTR);
9f1621ca	247	wait_for_quiescent_state();
ae62b5e8	248	STORE_SHARED(urcu_gp_ctr, urcu_gp_ctr ^ RCU_GP_ONGOING);
9f1621ca	249	internal_urcu_unlock();
ff2f67a0 MD	250
ff2f67a0 MD	251	if (was_online)
8b25e300 MD	252	_STORE_SHARED(urcu_reader_status.qs_gp,
8b25e300 MD	253	LOAD_SHARED(urcu_gp_ctr));
8f50d1ce	254	smp_mb();
9f1621ca	255	}
47d2f29e	256	#endif /* !(BITS_PER_LONG < 64) */
9f1621ca MD	257
	258	/*
	259	* library wrappers to be used by non-LGPL compatible source code.
	260	*/
	261
	262	void rcu_read_lock(void)
	263	{
	264	_rcu_read_lock();
	265	}
	266
	267	void rcu_read_unlock(void)
	268	{
	269	_rcu_read_unlock();
	270	}
	271
	272	void rcu_dereference(void p)
	273	{
	274	return _rcu_dereference(p);
	275	}
	276
	277	void rcu_assign_pointer_sym(void p, void v)
	278	{
	279	wmb();
	280	return STORE_SHARED(p, v);
	281	}
	282
4d1ce26f MD	283	void rcu_cmpxchg_pointer_sym(void p, void old, void *_new)
	284	{
	285	wmb();
	286	return cmpxchg(p, old, _new);
	287	}
	288
9f1621ca MD	289	void rcu_xchg_pointer_sym(void p, void v)
	290	{
	291	wmb();
	292	return xchg(p, v);
	293	}
	294
	295	void rcu_publish_content_sym(void p, void v)
	296	{
	297	void *oldptr;
	298
	299	oldptr = _rcu_xchg_pointer(p, v);
	300	synchronize_rcu();
	301	return oldptr;
	302	}
	303
7ac06cef MD	304	void rcu_quiescent_state(void)
	305	{
	306	_rcu_quiescent_state();
	307	}
	308
	309	void rcu_thread_offline(void)
	310	{
	311	_rcu_thread_offline();
	312	}
	313
	314	void rcu_thread_online(void)
	315	{
	316	_rcu_thread_online();
	317	}
	318
9f1621ca MD	319	static void rcu_add_reader(pthread_t id)
	320	{
	321	struct reader_registry *oldarray;
	322
	323	if (!registry) {
	324	alloc_readers = INIT_NUM_THREADS;
	325	num_readers = 0;
	326	registry =
	327	malloc(sizeof(struct reader_registry) * alloc_readers);
	328	}
	329	if (alloc_readers < num_readers + 1) {
	330	oldarray = registry;
	331	registry = malloc(sizeof(struct reader_registry)
	332	* (alloc_readers << 1));
	333	memcpy(registry, oldarray,
	334	sizeof(struct reader_registry) * alloc_readers);
	335	alloc_readers <<= 1;
	336	free(oldarray);
	337	}
	338	registry[num_readers].tid = id;
	339	/* reference to the TLS of _this_ reader thread. */
8b25e300	340	registry[num_readers].urcu_reader_status = &urcu_reader_status;
9f1621ca MD	341	num_readers++;
	342	}
	343
	344	/*
	345	* Never shrink (implementation limitation).
	346	* This is O(nb threads). Eventually use a hash table.
	347	*/
	348	static void rcu_remove_reader(pthread_t id)
	349	{
	350	struct reader_registry *index;
	351
	352	assert(registry != NULL);
	353	for (index = registry; index < registry + num_readers; index++) {
	354	if (pthread_equal(index->tid, id)) {
	355	memcpy(index, &registry[num_readers - 1],
	356	sizeof(struct reader_registry));
	357	registry[num_readers - 1].tid = 0;
8b25e300	358	registry[num_readers - 1].urcu_reader_status = NULL;
9f1621ca MD	359	num_readers--;
	360	return;
	361	}
	362	}
	363	/* Hrm not found, forgot to register ? */
	364	assert(0);
	365	}
	366
	367	void rcu_register_thread(void)
	368	{
	369	internal_urcu_lock();
9f1621ca MD	370	rcu_add_reader(pthread_self());
9f1621ca MD	371	internal_urcu_unlock();
5f373c84	372	_rcu_thread_online();
9f1621ca MD	373	}
	374
	375	void rcu_unregister_thread(void)
	376	{
76f3022f MD	377	/*
	378	* We have to make the thread offline otherwise we end up dealocking
	379	* with a waiting writer.
	380	*/
	381	_rcu_thread_offline();
9f1621ca MD	382	internal_urcu_lock();
	383	rcu_remove_reader(pthread_self());
	384	internal_urcu_unlock();
	385	}