[urcu.git] / urcu-defer.c

/*
 * urcu-defer.c
 *
 * Userspace RCU library - batch memory reclamation
 *
 * Copyright (c) 2009 Mathieu Desnoyers <mathieu.desnoyers@polymtl.ca>
 *
 * 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
 */

#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 <linux/futex.h>
#include <sys/time.h>
#include <syscall.h>
#include <unistd.h>

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

#define futex(...)	syscall(__NR_futex, __VA_ARGS__)

void __attribute__((destructor)) urcu_defer_exit(void);

extern void synchronize_rcu(void);

/*
 * urcu_defer_mutex nests inside defer_thread_mutex.
 */
static pthread_mutex_t urcu_defer_mutex = PTHREAD_MUTEX_INITIALIZER;
static pthread_mutex_t defer_thread_mutex = PTHREAD_MUTEX_INITIALIZER;

int defer_thread_futex;

/*
 * Written to only by each individual deferer. Read by both the deferer and
 * the reclamation tread.
 */
struct defer_queue __thread defer_queue;

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

struct deferer_registry {
	pthread_t tid;
	struct defer_queue *defer_queue;
	unsigned long last_head;
};

static struct deferer_registry *registry;
static int num_deferers, alloc_deferers;

static pthread_t tid_defer;

/*
 * Wake-up any waiting defer thread. Called from many concurrent threads.
 */
static void wake_up_defer(void)
{
	if (unlikely(atomic_read(&defer_thread_futex) == -1))
		atomic_set(&defer_thread_futex, 0);
		futex(&defer_thread_futex, FUTEX_WAKE,
		      0, NULL, NULL, 0);
}

/*
 * Defer thread waiting. Single thread.
 */
static void wait_defer(void)
{
	atomic_dec(&defer_thread_futex);
	if (atomic_read(&defer_thread_futex) == -1)
		futex(&defer_thread_futex, FUTEX_WAIT, -1,
		      NULL, NULL, 0);
}

static void internal_urcu_lock(pthread_mutex_t *mutex)
{
	int ret;

#ifndef DISTRUST_SIGNALS_EXTREME
	ret = pthread_mutex_lock(mutex);
	if (ret) {
		perror("Error in pthread mutex lock");
		exit(-1);
	}
#else /* #ifndef DISTRUST_SIGNALS_EXTREME */
	while ((ret = pthread_mutex_trylock(mutex)) != 0) {
		if (ret != EBUSY && ret != EINTR) {
			printf("ret = %d, errno = %d\n", ret, errno);
			perror("Error in pthread mutex lock");
			exit(-1);
		}
		pthread_testcancel();
		poll(NULL,0,10);
	}
#endif /* #else #ifndef DISTRUST_SIGNALS_EXTREME */
}

static void internal_urcu_unlock(pthread_mutex_t *mutex)
{
	int ret;

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

/*
 * Must be called after Q.S. is reached.
 */
static void rcu_defer_barrier_queue(struct defer_queue *queue,
				    unsigned long head)
{
	unsigned long i;
	void (*fct)(void *p);
	void *p;

	/*
	 * Tail is only modified when lock is held.
	 * Head is only modified by owner thread.
	 */

	for (i = queue->tail; i != head;) {
		smp_rmb();       /* read head before q[]. */
		p = LOAD_SHARED(queue->q[i++ & DEFER_QUEUE_MASK]);
		if (unlikely(DQ_IS_FCT_BIT(p))) {
			DQ_CLEAR_FCT_BIT(p);
			queue->last_fct_out = p;
			p = LOAD_SHARED(queue->q[i++ & DEFER_QUEUE_MASK]);
		} else if (unlikely(p == DQ_FCT_MARK)) {
			p = LOAD_SHARED(queue->q[i++ & DEFER_QUEUE_MASK]);
			queue->last_fct_out = p;
			p = LOAD_SHARED(queue->q[i++ & DEFER_QUEUE_MASK]);
		}
		fct = queue->last_fct_out;
		fct(p);
	}
	smp_mb();	/* push tail after having used q[] */
	STORE_SHARED(queue->tail, i);
}

static void _rcu_defer_barrier_thread(void)
{
	unsigned long head, num_items;

	head = defer_queue.head;
	num_items = head - defer_queue.tail;
	if (unlikely(!num_items))
		return;
	synchronize_rcu();
	rcu_defer_barrier_queue(&defer_queue, head);
}


void rcu_defer_barrier_thread(void)
{
	internal_urcu_lock(&urcu_defer_mutex);
	_rcu_defer_barrier_thread();
	internal_urcu_unlock(&urcu_defer_mutex);
}

/*
 * rcu_defer_barrier - Execute all queued rcu callbacks.
 *
 * Execute all RCU callbacks queued before rcu_defer_barrier() execution.
 * All callbacks queued on the local thread prior to a rcu_defer_barrier() call
 * are guaranteed to be executed.
 * Callbacks queued by other threads concurrently with rcu_defer_barrier()
 * execution are not guaranteed to be executed in the current batch (could
 * be left for the next batch). These callbacks queued by other threads are only
 * guaranteed to be executed if there is explicit synchronization between
 * the thread adding to the queue and the thread issuing the defer_barrier call.
 */

void rcu_defer_barrier(void)
{
	struct deferer_registry *index;
	unsigned long num_items = 0;

	if (!registry)
		return;

	internal_urcu_lock(&urcu_defer_mutex);
	for (index = registry; index < registry + num_deferers; index++) {
		index->last_head = LOAD_SHARED(index->defer_queue->head);
		num_items += index->last_head - index->defer_queue->tail;
	}
	if (likely(!num_items)) {
		/*
		 * We skip the grace period because there are no queued
		 * callbacks to execute.
		 */
		goto end;
	}
	synchronize_rcu();
	for (index = registry; index < registry + num_deferers; index++)
		rcu_defer_barrier_queue(index->defer_queue,
					  index->last_head);
end:
	internal_urcu_unlock(&urcu_defer_mutex);
}

/*
 * _rcu_defer_queue - Queue a RCU callback.
 */
void _rcu_defer_queue(void (*fct)(void *p), void *p)
{
	unsigned long head, tail;

	/*
	 * Head is only modified by ourself. Tail can be modified by reclamation
	 * thread.
	 */
	head = defer_queue.head;
	tail = LOAD_SHARED(defer_queue.tail);

	/*
	 * If queue is full, empty it ourself.
	 * Worse-case: must allow 2 supplementary entries for fct pointer.
	 */
	if (unlikely(head - tail >= DEFER_QUEUE_SIZE - 2)) {
		assert(head - tail <= DEFER_QUEUE_SIZE);
		rcu_defer_barrier_thread();
		assert(head - LOAD_SHARED(defer_queue.tail) == 0);
	}

	if (unlikely(defer_queue.last_fct_in != fct)) {
		defer_queue.last_fct_in = fct;
		if (unlikely(DQ_IS_FCT_BIT(fct) || fct == DQ_FCT_MARK)) {
			/*
			 * If the function to encode is not aligned or the
			 * marker, write DQ_FCT_MARK followed by the function
			 * pointer.
			 */
			_STORE_SHARED(defer_queue.q[head++ & DEFER_QUEUE_MASK],
				      DQ_FCT_MARK);
			_STORE_SHARED(defer_queue.q[head++ & DEFER_QUEUE_MASK],
				      fct);
		} else {
			DQ_SET_FCT_BIT(fct);
			_STORE_SHARED(defer_queue.q[head++ & DEFER_QUEUE_MASK],
				      fct);
		}
	} else {
		if (unlikely(DQ_IS_FCT_BIT(p) || p == DQ_FCT_MARK)) {
			/*
			 * If the data to encode is not aligned or the marker,
			 * write DQ_FCT_MARK followed by the function pointer.
			 */
			_STORE_SHARED(defer_queue.q[head++ & DEFER_QUEUE_MASK],
				      DQ_FCT_MARK);
			_STORE_SHARED(defer_queue.q[head++ & DEFER_QUEUE_MASK],
				      fct);
		}
	}
	_STORE_SHARED(defer_queue.q[head++ & DEFER_QUEUE_MASK], p);
	smp_wmb();	/* Publish new pointer before head */
			/* Write q[] before head. */
	STORE_SHARED(defer_queue.head, head);
	/*
	 * Wake-up any waiting defer thread.
	 */
	wake_up_defer();
}

void *thr_defer(void *args)
{
	for (;;) {
		pthread_testcancel();
		/*
		 * "Be green". Don't wake up the CPU if there is no RCU work
		 * to perform whatsoever. Aims at saving laptop battery life by
		 * leaving the processor in sleep state when idle.
		 */
		wait_defer();
		/* Sleeping after wait_defer to let many callbacks enqueue */
		poll(NULL,0,100);	/* wait for 100ms */
		rcu_defer_barrier();
	}

	return NULL;
}

/*
 * library wrappers to be used by non-LGPL compatible source code.
 */

void rcu_defer_queue(void (*fct)(void *p), void *p)
{
	_rcu_defer_queue(fct, p);
}

static void rcu_add_deferer(pthread_t id)
{
	struct deferer_registry *oldarray;

	if (!registry) {
		alloc_deferers = INIT_NUM_THREADS;
		num_deferers = 0;
		registry =
			malloc(sizeof(struct deferer_registry) * alloc_deferers);
	}
	if (alloc_deferers < num_deferers + 1) {
		oldarray = registry;
		registry = malloc(sizeof(struct deferer_registry)
				* (alloc_deferers << 1));
		memcpy(registry, oldarray,
			sizeof(struct deferer_registry) * alloc_deferers);
		alloc_deferers <<= 1;
		free(oldarray);
	}
	registry[num_deferers].tid = id;
	/* reference to the TLS of _this_ deferer thread. */
	registry[num_deferers].defer_queue = &defer_queue;
	registry[num_deferers].last_head = 0;
	num_deferers++;
}

/*
 * Never shrink (implementation limitation).
 * This is O(nb threads). Eventually use a hash table.
 */
static void rcu_remove_deferer(pthread_t id)
{
	struct deferer_registry *index;

	assert(registry != NULL);
	for (index = registry; index < registry + num_deferers; index++) {
		if (pthread_equal(index->tid, id)) {
			memcpy(index, &registry[num_deferers - 1],
				sizeof(struct deferer_registry));
			registry[num_deferers - 1].tid = 0;
			registry[num_deferers - 1].defer_queue = NULL;
			registry[num_deferers - 1].last_head = 0;
			num_deferers--;
			return;
		}
	}
	/* Hrm not found, forgot to register ? */
	assert(0);
}

static void start_defer_thread(void)
{
	int ret;

	ret = pthread_create(&tid_defer, NULL, thr_defer,
		NULL);
	assert(!ret);
}

static void stop_defer_thread(void)
{
	int ret;
	void *tret;

	pthread_cancel(tid_defer);
	wake_up_defer();
	ret = pthread_join(tid_defer, &tret);
	assert(!ret);
}

void rcu_defer_register_thread(void)
{
	int deferers;

	internal_urcu_lock(&defer_thread_mutex);
	internal_urcu_lock(&urcu_defer_mutex);
	defer_queue.q = malloc(sizeof(void *) * DEFER_QUEUE_SIZE);
	rcu_add_deferer(pthread_self());
	deferers = num_deferers;
	internal_urcu_unlock(&urcu_defer_mutex);

	if (deferers == 1)
		start_defer_thread();
	internal_urcu_unlock(&defer_thread_mutex);
}

void rcu_defer_unregister_thread(void)
{
	int deferers;

	internal_urcu_lock(&defer_thread_mutex);
	internal_urcu_lock(&urcu_defer_mutex);
	rcu_remove_deferer(pthread_self());
	_rcu_defer_barrier_thread();
	free(defer_queue.q);
	defer_queue.q = NULL;
	deferers = num_deferers;
	internal_urcu_unlock(&urcu_defer_mutex);

	if (deferers == 0)
		stop_defer_thread();
	internal_urcu_unlock(&defer_thread_mutex);
}

void urcu_defer_exit(void)
{
	free(registry);
}
Commit	Line	Data
786ee85b MD	1	/*
	2	* urcu-defer.c
	3	*
	4	* Userspace RCU library - batch memory reclamation
	5	*
	6	* Copyright (c) 2009 Mathieu Desnoyers <mathieu.desnoyers@polymtl.ca>
	7	*
	8	* This library is free software; you can redistribute it and/or
	9	* modify it under the terms of the GNU Lesser General Public
	10	* License as published by the Free Software Foundation; either
	11	* version 2.1 of the License, or (at your option) any later version.
	12	*
	13	* This library is distributed in the hope that it will be useful,
	14	* but WITHOUT ANY WARRANTY; without even the implied warranty of
	15	* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
	16	* Lesser General Public License for more details.
	17	*
	18	* You should have received a copy of the GNU Lesser General Public
	19	* License along with this library; if not, write to the Free Software
	20	* Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA
	21	*/
	22
	23	#include <stdio.h>
	24	#include <pthread.h>
	25	#include <signal.h>
	26	#include <assert.h>
	27	#include <stdlib.h>
	28	#include <string.h>
	29	#include <errno.h>
	30	#include <poll.h>
4ce9e4f2 MD	31	#include <linux/futex.h>
	32	#include <sys/time.h>
	33	#include <syscall.h>
	34	#include <unistd.h>
786ee85b MD	35
	36	#include "urcu-defer-static.h"
	37	/* Do not #define _LGPL_SOURCE to ensure we can emit the wrapper symbols */
	38	#include "urcu-defer.h"
	39
4ce9e4f2 MD	40	#define futex(...) syscall(__NR_futex, __VA_ARGS__)
4ce9e4f2 MD	41
786ee85b MD	42	void __attribute__((destructor)) urcu_defer_exit(void);
	43
	44	extern void synchronize_rcu(void);
	45
	46	/*
	47	* urcu_defer_mutex nests inside defer_thread_mutex.
	48	*/
	49	static pthread_mutex_t urcu_defer_mutex = PTHREAD_MUTEX_INITIALIZER;
	50	static pthread_mutex_t defer_thread_mutex = PTHREAD_MUTEX_INITIALIZER;
	51
4ce9e4f2 MD	52	int defer_thread_futex;
4ce9e4f2 MD	53
786ee85b MD	54	/*
	55	* Written to only by each individual deferer. Read by both the deferer and
	56	* the reclamation tread.
	57	*/
	58	struct defer_queue __thread defer_queue;
	59
	60	/* Thread IDs of registered deferers */
	61	#define INIT_NUM_THREADS 4
	62
	63	struct deferer_registry {
	64	pthread_t tid;
	65	struct defer_queue *defer_queue;
	66	unsigned long last_head;
	67	};
	68
	69	static struct deferer_registry *registry;
	70	static int num_deferers, alloc_deferers;
	71
	72	static pthread_t tid_defer;
4ce9e4f2 MD	73
	74	/*
	75	* Wake-up any waiting defer thread. Called from many concurrent threads.
	76	*/
2c22932b	77	static void wake_up_defer(void)
4ce9e4f2 MD	78	{
	79	if (unlikely(atomic_read(&defer_thread_futex) == -1))
	80	atomic_set(&defer_thread_futex, 0);
	81	futex(&defer_thread_futex, FUTEX_WAKE,
	82	0, NULL, NULL, 0);
	83	}
	84
	85	/*
	86	* Defer thread waiting. Single thread.
	87	*/
	88	static void wait_defer(void)
	89	{
	90	atomic_dec(&defer_thread_futex);
	91	if (atomic_read(&defer_thread_futex) == -1)
	92	futex(&defer_thread_futex, FUTEX_WAIT, -1,
	93	NULL, NULL, 0);
	94	}
786ee85b MD	95
	96	static void internal_urcu_lock(pthread_mutex_t *mutex)
	97	{
	98	int ret;
	99
	100	#ifndef DISTRUST_SIGNALS_EXTREME
	101	ret = pthread_mutex_lock(mutex);
	102	if (ret) {
	103	perror("Error in pthread mutex lock");
	104	exit(-1);
	105	}
	106	#else /* #ifndef DISTRUST_SIGNALS_EXTREME */
	107	while ((ret = pthread_mutex_trylock(mutex)) != 0) {
	108	if (ret != EBUSY && ret != EINTR) {
	109	printf("ret = %d, errno = %d\n", ret, errno);
	110	perror("Error in pthread mutex lock");
	111	exit(-1);
	112	}
4ce9e4f2	113	pthread_testcancel();
786ee85b MD	114	poll(NULL,0,10);
	115	}
	116	#endif /* #else #ifndef DISTRUST_SIGNALS_EXTREME */
	117	}
	118
	119	static void internal_urcu_unlock(pthread_mutex_t *mutex)
	120	{
	121	int ret;
	122
	123	ret = pthread_mutex_unlock(mutex);
	124	if (ret) {
	125	perror("Error in pthread mutex unlock");
	126	exit(-1);
	127	}
	128	}
	129
	130	/*
	131	* Must be called after Q.S. is reached.
	132	*/
	133	static void rcu_defer_barrier_queue(struct defer_queue *queue,
804b4375	134	unsigned long head)
786ee85b MD	135	{
786ee85b MD	136	unsigned long i;
804b4375 MD	137	void (fct)(void p);
804b4375 MD	138	void *p;
786ee85b MD	139
	140	/*
	141	* Tail is only modified when lock is held.
	142	* Head is only modified by owner thread.
	143	*/
	144
804b4375	145	for (i = queue->tail; i != head;) {
786ee85b	146	smp_rmb(); /* read head before q[]. */
804b4375 MD	147	p = LOAD_SHARED(queue->q[i++ & DEFER_QUEUE_MASK]);
804b4375 MD	148	if (unlikely(DQ_IS_FCT_BIT(p))) {
804b4375 MD	149	DQ_CLEAR_FCT_BIT(p);
	150	queue->last_fct_out = p;
	151	p = LOAD_SHARED(queue->q[i++ & DEFER_QUEUE_MASK]);
	152	} else if (unlikely(p == DQ_FCT_MARK)) {
804b4375 MD	153	p = LOAD_SHARED(queue->q[i++ & DEFER_QUEUE_MASK]);
	154	queue->last_fct_out = p;
	155	p = LOAD_SHARED(queue->q[i++ & DEFER_QUEUE_MASK]);
29cdb8d8	156	}
804b4375	157	fct = queue->last_fct_out;
804b4375	158	fct(p);
786ee85b MD	159	}
	160	smp_mb(); /* push tail after having used q[] */
	161	STORE_SHARED(queue->tail, i);
	162	}
	163
	164	static void _rcu_defer_barrier_thread(void)
	165	{
0d0e6c21	166	unsigned long head, num_items;
786ee85b MD	167
786ee85b MD	168	head = defer_queue.head;
0d0e6c21 MD	169	num_items = head - defer_queue.tail;
	170	if (unlikely(!num_items))
	171	return;
786ee85b MD	172	synchronize_rcu();
	173	rcu_defer_barrier_queue(&defer_queue, head);
	174	}
	175
	176
	177	void rcu_defer_barrier_thread(void)
	178	{
	179	internal_urcu_lock(&urcu_defer_mutex);
	180	_rcu_defer_barrier_thread();
	181	internal_urcu_unlock(&urcu_defer_mutex);
	182	}
	183
0d0e6c21 MD	184	/*
	185	* rcu_defer_barrier - Execute all queued rcu callbacks.
	186	*
	187	* Execute all RCU callbacks queued before rcu_defer_barrier() execution.
	188	* All callbacks queued on the local thread prior to a rcu_defer_barrier() call
	189	* are guaranteed to be executed.
	190	* Callbacks queued by other threads concurrently with rcu_defer_barrier()
	191	* execution are not guaranteed to be executed in the current batch (could
	192	* be left for the next batch). These callbacks queued by other threads are only
	193	* guaranteed to be executed if there is explicit synchronization between
	194	* the thread adding to the queue and the thread issuing the defer_barrier call.
	195	*/
	196
786ee85b MD	197	void rcu_defer_barrier(void)
	198	{
	199	struct deferer_registry *index;
0d0e6c21	200	unsigned long num_items = 0;
786ee85b MD	201
	202	if (!registry)
	203	return;
	204
	205	internal_urcu_lock(&urcu_defer_mutex);
0d0e6c21	206	for (index = registry; index < registry + num_deferers; index++) {
786ee85b	207	index->last_head = LOAD_SHARED(index->defer_queue->head);
0d0e6c21 MD	208	num_items += index->last_head - index->defer_queue->tail;
	209	}
	210	if (likely(!num_items)) {
	211	/*
	212	* We skip the grace period because there are no queued
	213	* callbacks to execute.
	214	*/
	215	goto end;
	216	}
786ee85b MD	217	synchronize_rcu();
	218	for (index = registry; index < registry + num_deferers; index++)
	219	rcu_defer_barrier_queue(index->defer_queue,
	220	index->last_head);
0d0e6c21	221	end:
786ee85b MD	222	internal_urcu_unlock(&urcu_defer_mutex);
	223	}
	224
2c22932b MD	225	/*
	226	* _rcu_defer_queue - Queue a RCU callback.
	227	*/
	228	void _rcu_defer_queue(void (fct)(void p), void *p)
	229	{
	230	unsigned long head, tail;
	231
	232	/*
	233	* Head is only modified by ourself. Tail can be modified by reclamation
	234	* thread.
	235	*/
	236	head = defer_queue.head;
	237	tail = LOAD_SHARED(defer_queue.tail);
	238
	239	/*
	240	* If queue is full, empty it ourself.
	241	* Worse-case: must allow 2 supplementary entries for fct pointer.
	242	*/
	243	if (unlikely(head - tail >= DEFER_QUEUE_SIZE - 2)) {
	244	assert(head - tail <= DEFER_QUEUE_SIZE);
	245	rcu_defer_barrier_thread();
	246	assert(head - LOAD_SHARED(defer_queue.tail) == 0);
	247	}
	248
	249	if (unlikely(defer_queue.last_fct_in != fct)) {
	250	defer_queue.last_fct_in = fct;
	251	if (unlikely(DQ_IS_FCT_BIT(fct) \|\| fct == DQ_FCT_MARK)) {
	252	/*
	253	* If the function to encode is not aligned or the
	254	* marker, write DQ_FCT_MARK followed by the function
	255	* pointer.
	256	*/
	257	_STORE_SHARED(defer_queue.q[head++ & DEFER_QUEUE_MASK],
	258	DQ_FCT_MARK);
	259	_STORE_SHARED(defer_queue.q[head++ & DEFER_QUEUE_MASK],
	260	fct);
	261	} else {
	262	DQ_SET_FCT_BIT(fct);
	263	_STORE_SHARED(defer_queue.q[head++ & DEFER_QUEUE_MASK],
	264	fct);
	265	}
	266	} else {
	267	if (unlikely(DQ_IS_FCT_BIT(p) \|\| p == DQ_FCT_MARK)) {
	268	/*
	269	* If the data to encode is not aligned or the marker,
	270	* write DQ_FCT_MARK followed by the function pointer.
	271	*/
	272	_STORE_SHARED(defer_queue.q[head++ & DEFER_QUEUE_MASK],
	273	DQ_FCT_MARK);
	274	_STORE_SHARED(defer_queue.q[head++ & DEFER_QUEUE_MASK],
	275	fct);
	276	}
	277	}
	278	_STORE_SHARED(defer_queue.q[head++ & DEFER_QUEUE_MASK], p);
	279	smp_wmb(); /* Publish new pointer before head */
	280	/* Write q[] before head. */
	281	STORE_SHARED(defer_queue.head, head);
	282	/*
	283	* Wake-up any waiting defer thread.
	284	*/
	285	wake_up_defer();
	286	}
	287
786ee85b MD	288	void thr_defer(void args)
	289	{
	290	for (;;) {
4ce9e4f2	291	pthread_testcancel();
4ce9e4f2 MD	292	/*
	293	* "Be green". Don't wake up the CPU if there is no RCU work
	294	* to perform whatsoever. Aims at saving laptop battery life by
	295	* leaving the processor in sleep state when idle.
	296	*/
4ce9e4f2	297	wait_defer();
4ce9e4f2	298	/* Sleeping after wait_defer to let many callbacks enqueue */
71df5ef4	299	poll(NULL,0,100); /* wait for 100ms */
786ee85b MD	300	rcu_defer_barrier();
	301	}
	302
	303	return NULL;
	304	}
	305
	306	/*
	307	* library wrappers to be used by non-LGPL compatible source code.
	308	*/
	309
804b4375	310	void rcu_defer_queue(void (fct)(void p), void *p)
786ee85b	311	{
804b4375	312	_rcu_defer_queue(fct, p);
786ee85b MD	313	}
	314
	315	static void rcu_add_deferer(pthread_t id)
	316	{
	317	struct deferer_registry *oldarray;
	318
	319	if (!registry) {
	320	alloc_deferers = INIT_NUM_THREADS;
	321	num_deferers = 0;
	322	registry =
	323	malloc(sizeof(struct deferer_registry) * alloc_deferers);
	324	}
	325	if (alloc_deferers < num_deferers + 1) {
	326	oldarray = registry;
	327	registry = malloc(sizeof(struct deferer_registry)
	328	* (alloc_deferers << 1));
	329	memcpy(registry, oldarray,
	330	sizeof(struct deferer_registry) * alloc_deferers);
	331	alloc_deferers <<= 1;
	332	free(oldarray);
	333	}
	334	registry[num_deferers].tid = id;
	335	/* reference to the TLS of _this_ deferer thread. */
	336	registry[num_deferers].defer_queue = &defer_queue;
804b4375	337	registry[num_deferers].last_head = 0;
786ee85b MD	338	num_deferers++;
	339	}
	340
	341	/*
	342	* Never shrink (implementation limitation).
	343	* This is O(nb threads). Eventually use a hash table.
	344	*/
	345	static void rcu_remove_deferer(pthread_t id)
	346	{
	347	struct deferer_registry *index;
	348
	349	assert(registry != NULL);
	350	for (index = registry; index < registry + num_deferers; index++) {
	351	if (pthread_equal(index->tid, id)) {
	352	memcpy(index, &registry[num_deferers - 1],
	353	sizeof(struct deferer_registry));
	354	registry[num_deferers - 1].tid = 0;
	355	registry[num_deferers - 1].defer_queue = NULL;
804b4375	356	registry[num_deferers - 1].last_head = 0;
786ee85b MD	357	num_deferers--;
	358	return;
	359	}
	360	}
	361	/* Hrm not found, forgot to register ? */
	362	assert(0);
	363	}
	364
	365	static void start_defer_thread(void)
	366	{
	367	int ret;
	368
	369	ret = pthread_create(&tid_defer, NULL, thr_defer,
	370	NULL);
	371	assert(!ret);
	372	}
	373
	374	static void stop_defer_thread(void)
	375	{
	376	int ret;
	377	void *tret;
	378
4ce9e4f2 MD	379	pthread_cancel(tid_defer);
4ce9e4f2 MD	380	wake_up_defer();
786ee85b MD	381	ret = pthread_join(tid_defer, &tret);
	382	assert(!ret);
	383	}
	384
	385	void rcu_defer_register_thread(void)
	386	{
	387	int deferers;
	388
	389	internal_urcu_lock(&defer_thread_mutex);
	390	internal_urcu_lock(&urcu_defer_mutex);
	391	defer_queue.q = malloc(sizeof(void ) DEFER_QUEUE_SIZE);
	392	rcu_add_deferer(pthread_self());
	393	deferers = num_deferers;
	394	internal_urcu_unlock(&urcu_defer_mutex);
	395
	396	if (deferers == 1)
	397	start_defer_thread();
	398	internal_urcu_unlock(&defer_thread_mutex);
	399	}
	400
	401	void rcu_defer_unregister_thread(void)
	402	{
	403	int deferers;
	404
	405	internal_urcu_lock(&defer_thread_mutex);
	406	internal_urcu_lock(&urcu_defer_mutex);
	407	rcu_remove_deferer(pthread_self());
	408	_rcu_defer_barrier_thread();
	409	free(defer_queue.q);
	410	defer_queue.q = NULL;
	411	deferers = num_deferers;
	412	internal_urcu_unlock(&urcu_defer_mutex);
	413
	414	if (deferers == 0)
	415	stop_defer_thread();
	416	internal_urcu_unlock(&defer_thread_mutex);
	417	}
	418
	419	void urcu_defer_exit(void)
	420	{
	421	free(registry);
	422	}