[urcu.git] / urcu-qsbr.c

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

void __attribute__((constructor)) urcu_init(void);
void __attribute__((destructor)) urcu_exit(void);

int init_done;

pthread_mutex_t urcu_mutex = PTHREAD_MUTEX_INITIALIZER;

/*
 * Global grace period counter.
 */
long urcu_gp_ctr = 0;

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

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

struct reader_registry {
	pthread_t tid;
	long *urcu_active_readers;
	char *need_mb;
};

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

static struct reader_registry *registry;
static char __thread need_mb;
static int num_readers, alloc_readers;

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);
		}
		if (need_mb) {
			smp_mb();
			need_mb = 0;
			smp_mb();
		}
		poll(NULL,0,10);
	}
#endif /* #else #ifndef DISTRUST_SIGNALS_EXTREME */
}

void internal_urcu_unlock(void)
{
	int ret;

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

#ifdef DEBUG_FULL_MB
#ifdef HAS_INCOHERENT_CACHES
static void force_mb_single_thread(struct reader_registry *index)
{
	smp_mb();
}
#endif /* #ifdef HAS_INCOHERENT_CACHES */

static void force_mb_all_threads(void)
{
	smp_mb();
}
#else /* #ifdef DEBUG_FULL_MB */
#ifdef HAS_INCOHERENT_CACHES
static void force_mb_single_thread(struct reader_registry *index)
{
	assert(registry);
	/*
	 * pthread_kill has a smp_mb(). But beware, we assume it performs
	 * a cache flush on architectures with non-coherent cache. Let's play
	 * safe and don't assume anything : we use smp_mc() to make sure the
	 * cache flush is enforced.
	 */
	*index->need_mb = 1;
	smp_mc();	/* write ->need_mb before sending the signals */
	pthread_kill(index->tid, SIGURCU);
	smp_mb();
	/*
	 * Wait for sighandler (and thus mb()) to execute on every thread.
	 * BUSY-LOOP.
	 */
	while (*index->need_mb) {
		poll(NULL, 0, 1);
	}
	smp_mb();	/* read ->need_mb before ending the barrier */
}
#endif /* #ifdef HAS_INCOHERENT_CACHES */

static void force_mb_all_threads(void)
{
	struct reader_registry *index;
	/*
	 * Ask for each threads to execute a smp_mb() so we can consider the
	 * compiler barriers around rcu read lock as real memory barriers.
	 */
	if (!registry)
		return;
	/*
	 * pthread_kill has a smp_mb(). But beware, we assume it performs
	 * a cache flush on architectures with non-coherent cache. Let's play
	 * safe and don't assume anything : we use smp_mc() to make sure the
	 * cache flush is enforced.
	 */
	for (index = registry; index < registry + num_readers; index++) {
		*index->need_mb = 1;
		smp_mc();	/* write need_mb before sending the signal */
		pthread_kill(index->tid, SIGURCU);
	}
	/*
	 * Wait for sighandler (and thus mb()) to execute on every thread.
	 *
	 * Note that the pthread_kill() will never be executed on systems
	 * that correctly deliver signals in a timely manner.  However, it
	 * is not uncommon for kernels to have bugs that can result in
	 * lost or unduly delayed signals.
	 *
	 * If you are seeing the below pthread_kill() executing much at
	 * all, we suggest testing the underlying kernel and filing the
	 * relevant bug report.  For Linux kernels, we recommend getting
	 * the Linux Test Project (LTP).
	 */
	for (index = registry; index < registry + num_readers; index++) {
		while (*index->need_mb) {
			pthread_kill(index->tid, SIGURCU);
			poll(NULL, 0, 1);
		}
	}
	smp_mb();	/* read ->need_mb before ending the barrier */
}
#endif /* #else #ifdef DEBUG_FULL_MB */

void wait_for_quiescent_state(void)
{
	struct reader_registry *index;

	if (!registry)
		return;
	/*
	 * Wait for each thread urcu_active_readers count to become 0.
	 */
	for (index = registry; index < registry + num_readers; index++) {
#ifndef HAS_INCOHERENT_CACHES
		while (rcu_old_gp_ongoing(index->urcu_active_readers))
			cpu_relax();
#else /* #ifndef HAS_INCOHERENT_CACHES */
		int wait_loops = 0;
		/*
		 * BUSY-LOOP. Force the reader thread to commit its
		 * urcu_active_readers update to memory if we wait for too long.
		 */
		while (rcu_old_gp_ongoing(index->urcu_active_readers)) {
			if (wait_loops++ == KICK_READER_LOOPS) {
				force_mb_single_thread(index);
				wait_loops = 0;
			} else {
				cpu_relax();
			}
		}
#endif /* #else #ifndef HAS_INCOHERENT_CACHES */
	}
}

void synchronize_rcu(void)
{
	internal_urcu_lock();
	force_mb_all_threads();
	urcu_gp_ctr += 2;
	wait_for_quiescent_state();
	force_mb_all_threads();
	internal_urcu_unlock();
}

/*
 * 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_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;
}

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_active_readers = &urcu_active_readers;
	registry[num_readers].need_mb = &need_mb;
	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_active_readers = NULL;
			num_readers--;
			return;
		}
	}
	/* Hrm not found, forgot to register ? */
	assert(0);
}

void rcu_register_thread(void)
{
	internal_urcu_lock();
	urcu_init();	/* In case gcc does not support constructor attribute */
	rcu_add_reader(pthread_self());
	internal_urcu_unlock();
}

void rcu_unregister_thread(void)
{
	internal_urcu_lock();
	rcu_remove_reader(pthread_self());
	internal_urcu_unlock();
}

#ifndef DEBUG_FULL_MB
static void sigurcu_handler(int signo, siginfo_t *siginfo, void *context)
{
	/*
	 * Executing this smp_mb() is the only purpose of this signal handler.
	 * It punctually promotes barrier() into smp_mb() on every thread it is
	 * executed on.
	 */
	smp_mb();
	need_mb = 0;
	smp_mb();
}

/*
 * urcu_init constructor. Called when the library is linked, but also when
 * reader threads are calling rcu_register_thread().
 * Should only be called by a single thread at a given time. This is ensured by
 * holing the internal_urcu_lock() from rcu_register_thread() or by running at
 * library load time, which should not be executed by multiple threads nor
 * concurrently with rcu_register_thread() anyway.
 */
void urcu_init(void)
{
	struct sigaction act;
	int ret;

	if (init_done)
		return;
	init_done = 1;

	act.sa_sigaction = sigurcu_handler;
	ret = sigaction(SIGURCU, &act, NULL);
	if (ret) {
		perror("Error in sigaction");
		exit(-1);
	}
}

void urcu_exit(void)
{
	struct sigaction act;
	int ret;

	ret = sigaction(SIGURCU, NULL, &act);
	if (ret) {
		perror("Error in sigaction");
		exit(-1);
	}
	assert(act.sa_sigaction == sigurcu_handler);
	free(registry);
}
#endif /* #ifndef DEBUG_FULL_MB */
Commit	Line	Data
	1	/*
	2	* urcu.c
	3	*
	4	* Userspace RCU library
	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
	35	#include "urcu-static.h"
	36	/* Do not #define _LGPL_SOURCE to ensure we can emit the wrapper symbols */
	37	#include "urcu.h"
	38
	39	void __attribute__((constructor)) urcu_init(void);
	40	void __attribute__((destructor)) urcu_exit(void);
	41
	42	int init_done;
	43
	44	pthread_mutex_t urcu_mutex = PTHREAD_MUTEX_INITIALIZER;
	45
	46	/*
	47	* Global grace period counter.
	48	*/
	49	long urcu_gp_ctr = 0;
	50
	51	/*
	52	* Written to only by each individual reader. Read by both the reader and the
	53	* writers.
	54	*/
	55	long __thread urcu_active_readers;
	56
	57	/* Thread IDs of registered readers */
	58	#define INIT_NUM_THREADS 4
	59
	60	struct reader_registry {
	61	pthread_t tid;
	62	long *urcu_active_readers;
	63	char *need_mb;
	64	};
	65
	66	#ifdef DEBUG_YIELD
	67	unsigned int yield_active;
	68	unsigned int __thread rand_yield;
	69	#endif
	70
	71	static struct reader_registry *registry;
	72	static char __thread need_mb;
	73	static int num_readers, alloc_readers;
	74
	75	void internal_urcu_lock(void)
	76	{
	77	int ret;
	78
	79	#ifndef DISTRUST_SIGNALS_EXTREME
	80	ret = pthread_mutex_lock(&urcu_mutex);
	81	if (ret) {
	82	perror("Error in pthread mutex lock");
	83	exit(-1);
	84	}
	85	#else /* #ifndef DISTRUST_SIGNALS_EXTREME */
	86	while ((ret = pthread_mutex_trylock(&urcu_mutex)) != 0) {
	87	if (ret != EBUSY && ret != EINTR) {
	88	printf("ret = %d, errno = %d\n", ret, errno);
	89	perror("Error in pthread mutex lock");
	90	exit(-1);
	91	}
	92	if (need_mb) {
	93	smp_mb();
	94	need_mb = 0;
	95	smp_mb();
	96	}
	97	poll(NULL,0,10);
	98	}
	99	#endif /* #else #ifndef DISTRUST_SIGNALS_EXTREME */
	100	}
	101
	102	void internal_urcu_unlock(void)
	103	{
	104	int ret;
	105
	106	ret = pthread_mutex_unlock(&urcu_mutex);
	107	if (ret) {
	108	perror("Error in pthread mutex unlock");
	109	exit(-1);
	110	}
	111	}
	112
	113	#ifdef DEBUG_FULL_MB
	114	#ifdef HAS_INCOHERENT_CACHES
	115	static void force_mb_single_thread(struct reader_registry *index)
	116	{
	117	smp_mb();
	118	}
	119	#endif /* #ifdef HAS_INCOHERENT_CACHES */
	120
	121	static void force_mb_all_threads(void)
	122	{
	123	smp_mb();
	124	}
	125	#else /* #ifdef DEBUG_FULL_MB */
	126	#ifdef HAS_INCOHERENT_CACHES
	127	static void force_mb_single_thread(struct reader_registry *index)
	128	{
	129	assert(registry);
	130	/*
	131	* pthread_kill has a smp_mb(). But beware, we assume it performs
	132	* a cache flush on architectures with non-coherent cache. Let's play
	133	* safe and don't assume anything : we use smp_mc() to make sure the
	134	* cache flush is enforced.
	135	*/
	136	*index->need_mb = 1;
	137	smp_mc(); /* write ->need_mb before sending the signals */
	138	pthread_kill(index->tid, SIGURCU);
	139	smp_mb();
	140	/*
	141	* Wait for sighandler (and thus mb()) to execute on every thread.
	142	* BUSY-LOOP.
	143	*/
	144	while (*index->need_mb) {
	145	poll(NULL, 0, 1);
	146	}
	147	smp_mb(); /* read ->need_mb before ending the barrier */
	148	}
	149	#endif /* #ifdef HAS_INCOHERENT_CACHES */
	150
	151	static void force_mb_all_threads(void)
	152	{
	153	struct reader_registry *index;
	154	/*
	155	* Ask for each threads to execute a smp_mb() so we can consider the
	156	* compiler barriers around rcu read lock as real memory barriers.
	157	*/
	158	if (!registry)
	159	return;
	160	/*
	161	* pthread_kill has a smp_mb(). But beware, we assume it performs
	162	* a cache flush on architectures with non-coherent cache. Let's play
	163	* safe and don't assume anything : we use smp_mc() to make sure the
	164	* cache flush is enforced.
	165	*/
	166	for (index = registry; index < registry + num_readers; index++) {
	167	*index->need_mb = 1;
	168	smp_mc(); /* write need_mb before sending the signal */
	169	pthread_kill(index->tid, SIGURCU);
	170	}
	171	/*
	172	* Wait for sighandler (and thus mb()) to execute on every thread.
	173	*
	174	* Note that the pthread_kill() will never be executed on systems
	175	* that correctly deliver signals in a timely manner. However, it
	176	* is not uncommon for kernels to have bugs that can result in
	177	* lost or unduly delayed signals.
	178	*
	179	* If you are seeing the below pthread_kill() executing much at
	180	* all, we suggest testing the underlying kernel and filing the
	181	* relevant bug report. For Linux kernels, we recommend getting
	182	* the Linux Test Project (LTP).
	183	*/
	184	for (index = registry; index < registry + num_readers; index++) {
	185	while (*index->need_mb) {
	186	pthread_kill(index->tid, SIGURCU);
	187	poll(NULL, 0, 1);
	188	}
	189	}
	190	smp_mb(); /* read ->need_mb before ending the barrier */
	191	}
	192	#endif /* #else #ifdef DEBUG_FULL_MB */
	193
	194	void wait_for_quiescent_state(void)
	195	{
	196	struct reader_registry *index;
	197
	198	if (!registry)
	199	return;
	200	/*
	201	* Wait for each thread urcu_active_readers count to become 0.
	202	*/
	203	for (index = registry; index < registry + num_readers; index++) {
	204	#ifndef HAS_INCOHERENT_CACHES
	205	while (rcu_old_gp_ongoing(index->urcu_active_readers))
	206	cpu_relax();
	207	#else /* #ifndef HAS_INCOHERENT_CACHES */
	208	int wait_loops = 0;
	209	/*
	210	* BUSY-LOOP. Force the reader thread to commit its
	211	* urcu_active_readers update to memory if we wait for too long.
	212	*/
	213	while (rcu_old_gp_ongoing(index->urcu_active_readers)) {
	214	if (wait_loops++ == KICK_READER_LOOPS) {
	215	force_mb_single_thread(index);
	216	wait_loops = 0;
	217	} else {
	218	cpu_relax();
	219	}
	220	}
	221	#endif /* #else #ifndef HAS_INCOHERENT_CACHES */
	222	}
	223	}
	224
	225	void synchronize_rcu(void)
	226	{
	227	internal_urcu_lock();
	228	force_mb_all_threads();
	229	urcu_gp_ctr += 2;
	230	wait_for_quiescent_state();
	231	force_mb_all_threads();
	232	internal_urcu_unlock();
	233	}
	234
	235	/*
	236	* library wrappers to be used by non-LGPL compatible source code.
	237	*/
	238
	239	void rcu_read_lock(void)
	240	{
	241	_rcu_read_lock();
	242	}
	243
	244	void rcu_read_unlock(void)
	245	{
	246	_rcu_read_unlock();
	247	}
	248
	249	void rcu_dereference(void p)
	250	{
	251	return _rcu_dereference(p);
	252	}
	253
	254	void rcu_assign_pointer_sym(void p, void v)
	255	{
	256	wmb();
	257	return STORE_SHARED(p, v);
	258	}
	259
	260	void rcu_xchg_pointer_sym(void p, void v)
	261	{
	262	wmb();
	263	return xchg(p, v);
	264	}
	265
	266	void rcu_publish_content_sym(void p, void v)
	267	{
	268	void *oldptr;
	269
	270	oldptr = _rcu_xchg_pointer(p, v);
	271	synchronize_rcu();
	272	return oldptr;
	273	}
	274
	275	static void rcu_add_reader(pthread_t id)
	276	{
	277	struct reader_registry *oldarray;
	278
	279	if (!registry) {
	280	alloc_readers = INIT_NUM_THREADS;
	281	num_readers = 0;
	282	registry =
	283	malloc(sizeof(struct reader_registry) * alloc_readers);
	284	}
	285	if (alloc_readers < num_readers + 1) {
	286	oldarray = registry;
	287	registry = malloc(sizeof(struct reader_registry)
	288	* (alloc_readers << 1));
	289	memcpy(registry, oldarray,
	290	sizeof(struct reader_registry) * alloc_readers);
	291	alloc_readers <<= 1;
	292	free(oldarray);
	293	}
	294	registry[num_readers].tid = id;
	295	/* reference to the TLS of _this_ reader thread. */
	296	registry[num_readers].urcu_active_readers = &urcu_active_readers;
	297	registry[num_readers].need_mb = &need_mb;
	298	num_readers++;
	299	}
	300
	301	/*
	302	* Never shrink (implementation limitation).
	303	* This is O(nb threads). Eventually use a hash table.
	304	*/
	305	static void rcu_remove_reader(pthread_t id)
	306	{
	307	struct reader_registry *index;
	308
	309	assert(registry != NULL);
	310	for (index = registry; index < registry + num_readers; index++) {
	311	if (pthread_equal(index->tid, id)) {
	312	memcpy(index, &registry[num_readers - 1],
	313	sizeof(struct reader_registry));
	314	registry[num_readers - 1].tid = 0;
	315	registry[num_readers - 1].urcu_active_readers = NULL;
	316	num_readers--;
	317	return;
	318	}
	319	}
	320	/* Hrm not found, forgot to register ? */
	321	assert(0);
	322	}
	323
	324	void rcu_register_thread(void)
	325	{
	326	internal_urcu_lock();
	327	urcu_init(); /* In case gcc does not support constructor attribute */
	328	rcu_add_reader(pthread_self());
	329	internal_urcu_unlock();
	330	}
	331
	332	void rcu_unregister_thread(void)
	333	{
	334	internal_urcu_lock();
	335	rcu_remove_reader(pthread_self());
	336	internal_urcu_unlock();
	337	}
	338
	339	#ifndef DEBUG_FULL_MB
	340	static void sigurcu_handler(int signo, siginfo_t siginfo, void context)
	341	{
	342	/*
	343	* Executing this smp_mb() is the only purpose of this signal handler.
	344	* It punctually promotes barrier() into smp_mb() on every thread it is
	345	* executed on.
	346	*/
	347	smp_mb();
	348	need_mb = 0;
	349	smp_mb();
	350	}
	351
	352	/*
	353	* urcu_init constructor. Called when the library is linked, but also when
	354	* reader threads are calling rcu_register_thread().
	355	* Should only be called by a single thread at a given time. This is ensured by
	356	* holing the internal_urcu_lock() from rcu_register_thread() or by running at
	357	* library load time, which should not be executed by multiple threads nor
	358	* concurrently with rcu_register_thread() anyway.
	359	*/
	360	void urcu_init(void)
	361	{
	362	struct sigaction act;
	363	int ret;
	364
	365	if (init_done)
	366	return;
	367	init_done = 1;
	368
	369	act.sa_sigaction = sigurcu_handler;
	370	ret = sigaction(SIGURCU, &act, NULL);
	371	if (ret) {
	372	perror("Error in sigaction");
	373	exit(-1);
	374	}
	375	}
	376
	377	void urcu_exit(void)
	378	{
	379	struct sigaction act;
	380	int ret;
	381
	382	ret = sigaction(SIGURCU, NULL, &act);
	383	if (ret) {
	384	perror("Error in sigaction");
	385	exit(-1);
	386	}
	387	assert(act.sa_sigaction == sigurcu_handler);
	388	free(registry);
	389	}
	390	#endif /* #ifndef DEBUG_FULL_MB */