[urcu.git] / urcu.c

/*
 * urcu.c
 *
 * Userspace RCU library
 *
 * Copyright February 2009 - Mathieu Desnoyers <mathieu.desnoyers@polymtl.ca>
 *
 * Distributed under GPLv2
 *
 * 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.h"

pthread_mutex_t urcu_mutex = PTHREAD_MUTEX_INITIALIZER;

/*
 * Global grace period counter.
 * Contains the current RCU_GP_CTR_BIT.
 * Also has a RCU_GP_CTR_BIT of 1, to accelerate the reader fast path.
 * Written to only by writer with mutex taken. Read by both writer and readers.
 */
long urcu_gp_ctr = RCU_GP_COUNT;

/*
 * 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);
	}
}

/*
 * called with urcu_mutex held.
 */
static void switch_next_urcu_qparity(void)
{
	STORE_SHARED(urcu_gp_ctr, urcu_gp_ctr ^ RCU_GP_CTR_BIT);
}

#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();

	/* All threads should read qparity before accessing data structure
	 * where new ptr points to. Must be done within internal_urcu_lock
	 * because it iterates on reader threads.*/
	/* Write new ptr before changing the qparity */
	force_mb_all_threads();

	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 */

	/* Finish waiting for reader threads before letting the old ptr being
	 * freed. Must be done within internal_urcu_lock because it iterates on
	 * reader threads. */
	force_mb_all_threads();

	internal_urcu_unlock();
}

void urcu_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.
 */
void urcu_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 urcu_register_thread(void)
{
	internal_urcu_lock();
	urcu_add_reader(pthread_self());
	internal_urcu_unlock();
}

void urcu_unregister_thread(void)
{
	internal_urcu_lock();
	urcu_remove_reader(pthread_self());
	internal_urcu_unlock();
}

#ifndef DEBUG_FULL_MB
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();
}

void __attribute__((constructor)) urcu_init(void)
{
	struct sigaction act;
	int ret;

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

void __attribute__((destructor)) 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 February 2009 - Mathieu Desnoyers <mathieu.desnoyers@polymtl.ca>
	7	*
	8	* Distributed under GPLv2
	9	*
	10	* IBM's contributions to this file may be relicensed under LGPLv2 or later.
	11	*/
	12
	13	#include <stdio.h>
	14	#include <pthread.h>
	15	#include <signal.h>
	16	#include <assert.h>
	17	#include <stdlib.h>
	18	#include <string.h>
	19	#include <errno.h>
	20	#include <poll.h>
	21
	22	#include "urcu.h"
	23
	24	pthread_mutex_t urcu_mutex = PTHREAD_MUTEX_INITIALIZER;
	25
	26	/*
	27	* Global grace period counter.
	28	* Contains the current RCU_GP_CTR_BIT.
	29	* Also has a RCU_GP_CTR_BIT of 1, to accelerate the reader fast path.
	30	* Written to only by writer with mutex taken. Read by both writer and readers.
	31	*/
	32	long urcu_gp_ctr = RCU_GP_COUNT;
	33
	34	/*
	35	* Written to only by each individual reader. Read by both the reader and the
	36	* writers.
	37	*/
	38	long __thread urcu_active_readers;
	39
	40	/* Thread IDs of registered readers */
	41	#define INIT_NUM_THREADS 4
	42
	43	struct reader_registry {
	44	pthread_t tid;
	45	long *urcu_active_readers;
	46	char *need_mb;
	47	};
	48
	49	#ifdef DEBUG_YIELD
	50	unsigned int yield_active;
	51	unsigned int __thread rand_yield;
	52	#endif
	53
	54	static struct reader_registry *registry;
	55	static char __thread need_mb;
	56	static int num_readers, alloc_readers;
	57
	58	void internal_urcu_lock(void)
	59	{
	60	int ret;
	61
	62	#ifndef DISTRUST_SIGNALS_EXTREME
	63	ret = pthread_mutex_lock(&urcu_mutex);
	64	if (ret) {
	65	perror("Error in pthread mutex lock");
	66	exit(-1);
	67	}
	68	#else /* #ifndef DISTRUST_SIGNALS_EXTREME */
	69	while ((ret = pthread_mutex_trylock(&urcu_mutex)) != 0) {
	70	if (ret != EBUSY && ret != EINTR) {
	71	printf("ret = %d, errno = %d\n", ret, errno);
	72	perror("Error in pthread mutex lock");
	73	exit(-1);
	74	}
	75	if (need_mb) {
	76	smp_mb();
	77	need_mb = 0;
	78	smp_mb();
	79	}
	80	poll(NULL,0,10);
	81	}
	82	#endif /* #else #ifndef DISTRUST_SIGNALS_EXTREME */
	83	}
	84
	85	void internal_urcu_unlock(void)
	86	{
	87	int ret;
	88
	89	ret = pthread_mutex_unlock(&urcu_mutex);
	90	if (ret) {
	91	perror("Error in pthread mutex unlock");
	92	exit(-1);
	93	}
	94	}
	95
	96	/*
	97	* called with urcu_mutex held.
	98	*/
	99	static void switch_next_urcu_qparity(void)
	100	{
	101	STORE_SHARED(urcu_gp_ctr, urcu_gp_ctr ^ RCU_GP_CTR_BIT);
	102	}
	103
	104	#ifdef DEBUG_FULL_MB
	105	#ifdef HAS_INCOHERENT_CACHES
	106	static void force_mb_single_thread(struct reader_registry *index)
	107	{
	108	smp_mb();
	109	}
	110	#endif /* #ifdef HAS_INCOHERENT_CACHES */
	111
	112	static void force_mb_all_threads(void)
	113	{
	114	smp_mb();
	115	}
	116	#else /* #ifdef DEBUG_FULL_MB */
	117	#ifdef HAS_INCOHERENT_CACHES
	118	static void force_mb_single_thread(struct reader_registry *index)
	119	{
	120	assert(registry);
	121	/*
	122	* pthread_kill has a smp_mb(). But beware, we assume it performs
	123	* a cache flush on architectures with non-coherent cache. Let's play
	124	* safe and don't assume anything : we use smp_mc() to make sure the
	125	* cache flush is enforced.
	126	*/
	127	*index->need_mb = 1;
	128	smp_mc(); /* write ->need_mb before sending the signals */
	129	pthread_kill(index->tid, SIGURCU);
	130	smp_mb();
	131	/*
	132	* Wait for sighandler (and thus mb()) to execute on every thread.
	133	* BUSY-LOOP.
	134	*/
	135	while (*index->need_mb) {
	136	poll(NULL, 0, 1);
	137	}
	138	smp_mb(); /* read ->need_mb before ending the barrier */
	139	}
	140	#endif /* #ifdef HAS_INCOHERENT_CACHES */
	141
	142	static void force_mb_all_threads(void)
	143	{
	144	struct reader_registry *index;
	145	/*
	146	* Ask for each threads to execute a smp_mb() so we can consider the
	147	* compiler barriers around rcu read lock as real memory barriers.
	148	*/
	149	if (!registry)
	150	return;
	151	/*
	152	* pthread_kill has a smp_mb(). But beware, we assume it performs
	153	* a cache flush on architectures with non-coherent cache. Let's play
	154	* safe and don't assume anything : we use smp_mc() to make sure the
	155	* cache flush is enforced.
	156	*/
	157	for (index = registry; index < registry + num_readers; index++) {
	158	*index->need_mb = 1;
	159	smp_mc(); /* write need_mb before sending the signal */
	160	pthread_kill(index->tid, SIGURCU);
	161	}
	162	/*
	163	* Wait for sighandler (and thus mb()) to execute on every thread.
	164	*
	165	* Note that the pthread_kill() will never be executed on systems
	166	* that correctly deliver signals in a timely manner. However, it
	167	* is not uncommon for kernels to have bugs that can result in
	168	* lost or unduly delayed signals.
	169	*
	170	* If you are seeing the below pthread_kill() executing much at
	171	* all, we suggest testing the underlying kernel and filing the
	172	* relevant bug report. For Linux kernels, we recommend getting
	173	* the Linux Test Project (LTP).
	174	*/
	175	for (index = registry; index < registry + num_readers; index++) {
	176	while (*index->need_mb) {
	177	pthread_kill(index->tid, SIGURCU);
	178	poll(NULL, 0, 1);
	179	}
	180	}
	181	smp_mb(); /* read ->need_mb before ending the barrier */
	182	}
	183	#endif /* #else #ifdef DEBUG_FULL_MB */
	184
	185	void wait_for_quiescent_state(void)
	186	{
	187	struct reader_registry *index;
	188
	189	if (!registry)
	190	return;
	191	/*
	192	* Wait for each thread urcu_active_readers count to become 0.
	193	*/
	194	for (index = registry; index < registry + num_readers; index++) {
	195	#ifndef HAS_INCOHERENT_CACHES
	196	while (rcu_old_gp_ongoing(index->urcu_active_readers))
	197	cpu_relax();
	198	#else /* #ifndef HAS_INCOHERENT_CACHES */
	199	int wait_loops = 0;
	200	/*
	201	* BUSY-LOOP. Force the reader thread to commit its
	202	* urcu_active_readers update to memory if we wait for too long.
	203	*/
	204	while (rcu_old_gp_ongoing(index->urcu_active_readers)) {
	205	if (wait_loops++ == KICK_READER_LOOPS) {
	206	force_mb_single_thread(index);
	207	wait_loops = 0;
	208	} else {
	209	cpu_relax();
	210	}
	211	}
	212	#endif /* #else #ifndef HAS_INCOHERENT_CACHES */
	213	}
	214	}
	215
	216	void synchronize_rcu(void)
	217	{
	218	internal_urcu_lock();
	219
	220	/* All threads should read qparity before accessing data structure
	221	* where new ptr points to. Must be done within internal_urcu_lock
	222	* because it iterates on reader threads.*/
	223	/* Write new ptr before changing the qparity */
	224	force_mb_all_threads();
	225
	226	switch_next_urcu_qparity(); /* 0 -> 1 */
	227
	228	/*
	229	* Must commit qparity update to memory before waiting for parity
	230	* 0 quiescent state. Failure to do so could result in the writer
	231	* waiting forever while new readers are always accessing data (no
	232	* progress).
	233	* Ensured by STORE_SHARED and LOAD_SHARED.
	234	*/
	235
	236	/*
	237	* Wait for previous parity to be empty of readers.
	238	*/
	239	wait_for_quiescent_state(); /* Wait readers in parity 0 */
	240
	241	/*
	242	* Must finish waiting for quiescent state for parity 0 before
	243	* committing qparity update to memory. Failure to do so could result in
	244	* the writer waiting forever while new readers are always accessing
	245	* data (no progress).
	246	* Ensured by STORE_SHARED and LOAD_SHARED.
	247	*/
	248
	249	switch_next_urcu_qparity(); /* 1 -> 0 */
	250
	251	/*
	252	* Must commit qparity update to memory before waiting for parity
	253	* 1 quiescent state. Failure to do so could result in the writer
	254	* waiting forever while new readers are always accessing data (no
	255	* progress).
	256	* Ensured by STORE_SHARED and LOAD_SHARED.
	257	*/
	258
	259	/*
	260	* Wait for previous parity to be empty of readers.
	261	*/
	262	wait_for_quiescent_state(); /* Wait readers in parity 1 */
	263
	264	/* Finish waiting for reader threads before letting the old ptr being
	265	* freed. Must be done within internal_urcu_lock because it iterates on
	266	* reader threads. */
	267	force_mb_all_threads();
	268
	269	internal_urcu_unlock();
	270	}
	271
	272	void urcu_add_reader(pthread_t id)
	273	{
	274	struct reader_registry *oldarray;
	275
	276	if (!registry) {
	277	alloc_readers = INIT_NUM_THREADS;
	278	num_readers = 0;
	279	registry =
	280	malloc(sizeof(struct reader_registry) * alloc_readers);
	281	}
	282	if (alloc_readers < num_readers + 1) {
	283	oldarray = registry;
	284	registry = malloc(sizeof(struct reader_registry)
	285	* (alloc_readers << 1));
	286	memcpy(registry, oldarray,
	287	sizeof(struct reader_registry) * alloc_readers);
	288	alloc_readers <<= 1;
	289	free(oldarray);
	290	}
	291	registry[num_readers].tid = id;
	292	/* reference to the TLS of _this_ reader thread. */
	293	registry[num_readers].urcu_active_readers = &urcu_active_readers;
	294	registry[num_readers].need_mb = &need_mb;
	295	num_readers++;
	296	}
	297
	298	/*
	299	* Never shrink (implementation limitation).
	300	* This is O(nb threads). Eventually use a hash table.
	301	*/
	302	void urcu_remove_reader(pthread_t id)
	303	{
	304	struct reader_registry *index;
	305
	306	assert(registry != NULL);
	307	for (index = registry; index < registry + num_readers; index++) {
	308	if (pthread_equal(index->tid, id)) {
	309	memcpy(index, &registry[num_readers - 1],
	310	sizeof(struct reader_registry));
	311	registry[num_readers - 1].tid = 0;
	312	registry[num_readers - 1].urcu_active_readers = NULL;
	313	num_readers--;
	314	return;
	315	}
	316	}
	317	/* Hrm not found, forgot to register ? */
	318	assert(0);
	319	}
	320
	321	void urcu_register_thread(void)
	322	{
	323	internal_urcu_lock();
	324	urcu_add_reader(pthread_self());
	325	internal_urcu_unlock();
	326	}
	327
	328	void urcu_unregister_thread(void)
	329	{
	330	internal_urcu_lock();
	331	urcu_remove_reader(pthread_self());
	332	internal_urcu_unlock();
	333	}
	334
	335	#ifndef DEBUG_FULL_MB
	336	void sigurcu_handler(int signo, siginfo_t siginfo, void context)
	337	{
	338	/*
	339	* Executing this smp_mb() is the only purpose of this signal handler.
	340	* It punctually promotes barrier() into smp_mb() on every thread it is
	341	* executed on.
	342	*/
	343	smp_mb();
	344	need_mb = 0;
	345	smp_mb();
	346	}
	347
	348	void __attribute__((constructor)) urcu_init(void)
	349	{
	350	struct sigaction act;
	351	int ret;
	352
	353	act.sa_sigaction = sigurcu_handler;
	354	ret = sigaction(SIGURCU, &act, NULL);
	355	if (ret) {
	356	perror("Error in sigaction");
	357	exit(-1);
	358	}
	359	}
	360
	361	void __attribute__((destructor)) urcu_exit(void)
	362	{
	363	struct sigaction act;
	364	int ret;
	365
	366	ret = sigaction(SIGURCU, NULL, &act);
	367	if (ret) {
	368	perror("Error in sigaction");
	369	exit(-1);
	370	}
	371	assert(act.sa_sigaction == sigurcu_handler);
	372	free(registry);
	373	}
	374	#endif /* #ifndef DEBUG_FULL_MB */