[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;

static int defer_thread_futex;

/*
 * Written to only by each individual deferer. Read by both the deferer and
 * the reclamation tread.
 */
static 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
3dce4bfa	52	static int defer_thread_futex;
4ce9e4f2	53
786ee85b MD	54	/*
	55	* Written to only by each individual deferer. Read by both the deferer and
	56	* the reclamation tread.
	57	*/
3dce4bfa	58	static struct defer_queue __thread defer_queue;
786ee85b MD	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	78	{
3dce4bfa	79	if (unlikely(atomic_read(&defer_thread_futex) == -1)) {
4ce9e4f2	80	atomic_set(&defer_thread_futex, 0);
3dce4bfa MD	81	futex(&defer_thread_futex, FUTEX_WAKE, 0,
	82	NULL, NULL, 0);
	83	}
4ce9e4f2 MD	84	}
	85
	86	/*
	87	* Defer thread waiting. Single thread.
	88	*/
	89	static void wait_defer(void)
	90	{
	91	atomic_dec(&defer_thread_futex);
	92	if (atomic_read(&defer_thread_futex) == -1)
	93	futex(&defer_thread_futex, FUTEX_WAIT, -1,
	94	NULL, NULL, 0);
	95	}
786ee85b MD	96
	97	static void internal_urcu_lock(pthread_mutex_t *mutex)
	98	{
	99	int ret;
	100
	101	#ifndef DISTRUST_SIGNALS_EXTREME
	102	ret = pthread_mutex_lock(mutex);
	103	if (ret) {
	104	perror("Error in pthread mutex lock");
	105	exit(-1);
	106	}
	107	#else /* #ifndef DISTRUST_SIGNALS_EXTREME */
	108	while ((ret = pthread_mutex_trylock(mutex)) != 0) {
	109	if (ret != EBUSY && ret != EINTR) {
	110	printf("ret = %d, errno = %d\n", ret, errno);
	111	perror("Error in pthread mutex lock");
	112	exit(-1);
	113	}
4ce9e4f2	114	pthread_testcancel();
786ee85b MD	115	poll(NULL,0,10);
	116	}
	117	#endif /* #else #ifndef DISTRUST_SIGNALS_EXTREME */
	118	}
	119
	120	static void internal_urcu_unlock(pthread_mutex_t *mutex)
	121	{
	122	int ret;
	123
	124	ret = pthread_mutex_unlock(mutex);
	125	if (ret) {
	126	perror("Error in pthread mutex unlock");
	127	exit(-1);
	128	}
	129	}
	130
	131	/*
	132	* Must be called after Q.S. is reached.
	133	*/
	134	static void rcu_defer_barrier_queue(struct defer_queue *queue,
804b4375	135	unsigned long head)
786ee85b MD	136	{
786ee85b MD	137	unsigned long i;
804b4375 MD	138	void (fct)(void p);
804b4375 MD	139	void *p;
786ee85b MD	140
	141	/*
	142	* Tail is only modified when lock is held.
	143	* Head is only modified by owner thread.
	144	*/
	145
804b4375	146	for (i = queue->tail; i != head;) {
786ee85b	147	smp_rmb(); /* read head before q[]. */
804b4375 MD	148	p = LOAD_SHARED(queue->q[i++ & DEFER_QUEUE_MASK]);
804b4375 MD	149	if (unlikely(DQ_IS_FCT_BIT(p))) {
804b4375 MD	150	DQ_CLEAR_FCT_BIT(p);
	151	queue->last_fct_out = p;
	152	p = LOAD_SHARED(queue->q[i++ & DEFER_QUEUE_MASK]);
	153	} else if (unlikely(p == DQ_FCT_MARK)) {
804b4375 MD	154	p = LOAD_SHARED(queue->q[i++ & DEFER_QUEUE_MASK]);
	155	queue->last_fct_out = p;
	156	p = LOAD_SHARED(queue->q[i++ & DEFER_QUEUE_MASK]);
29cdb8d8	157	}
804b4375	158	fct = queue->last_fct_out;
804b4375	159	fct(p);
786ee85b MD	160	}
	161	smp_mb(); /* push tail after having used q[] */
	162	STORE_SHARED(queue->tail, i);
	163	}
	164
	165	static void _rcu_defer_barrier_thread(void)
	166	{
0d0e6c21	167	unsigned long head, num_items;
786ee85b MD	168
786ee85b MD	169	head = defer_queue.head;
0d0e6c21 MD	170	num_items = head - defer_queue.tail;
	171	if (unlikely(!num_items))
	172	return;
786ee85b MD	173	synchronize_rcu();
	174	rcu_defer_barrier_queue(&defer_queue, head);
	175	}
	176
	177
	178	void rcu_defer_barrier_thread(void)
	179	{
	180	internal_urcu_lock(&urcu_defer_mutex);
	181	_rcu_defer_barrier_thread();
	182	internal_urcu_unlock(&urcu_defer_mutex);
	183	}
	184
0d0e6c21 MD	185	/*
	186	* rcu_defer_barrier - Execute all queued rcu callbacks.
	187	*
	188	* Execute all RCU callbacks queued before rcu_defer_barrier() execution.
	189	* All callbacks queued on the local thread prior to a rcu_defer_barrier() call
	190	* are guaranteed to be executed.
	191	* Callbacks queued by other threads concurrently with rcu_defer_barrier()
	192	* execution are not guaranteed to be executed in the current batch (could
	193	* be left for the next batch). These callbacks queued by other threads are only
	194	* guaranteed to be executed if there is explicit synchronization between
	195	* the thread adding to the queue and the thread issuing the defer_barrier call.
	196	*/
	197
786ee85b MD	198	void rcu_defer_barrier(void)
	199	{
	200	struct deferer_registry *index;
0d0e6c21	201	unsigned long num_items = 0;
786ee85b MD	202
	203	if (!registry)
	204	return;
	205
	206	internal_urcu_lock(&urcu_defer_mutex);
0d0e6c21	207	for (index = registry; index < registry + num_deferers; index++) {
786ee85b	208	index->last_head = LOAD_SHARED(index->defer_queue->head);
0d0e6c21 MD	209	num_items += index->last_head - index->defer_queue->tail;
	210	}
	211	if (likely(!num_items)) {
	212	/*
	213	* We skip the grace period because there are no queued
	214	* callbacks to execute.
	215	*/
	216	goto end;
	217	}
786ee85b MD	218	synchronize_rcu();
	219	for (index = registry; index < registry + num_deferers; index++)
	220	rcu_defer_barrier_queue(index->defer_queue,
	221	index->last_head);
0d0e6c21	222	end:
786ee85b MD	223	internal_urcu_unlock(&urcu_defer_mutex);
	224	}
	225
2c22932b MD	226	/*
	227	* _rcu_defer_queue - Queue a RCU callback.
	228	*/
	229	void _rcu_defer_queue(void (fct)(void p), void *p)
	230	{
	231	unsigned long head, tail;
	232
	233	/*
	234	* Head is only modified by ourself. Tail can be modified by reclamation
	235	* thread.
	236	*/
	237	head = defer_queue.head;
	238	tail = LOAD_SHARED(defer_queue.tail);
	239
	240	/*
	241	* If queue is full, empty it ourself.
	242	* Worse-case: must allow 2 supplementary entries for fct pointer.
	243	*/
	244	if (unlikely(head - tail >= DEFER_QUEUE_SIZE - 2)) {
	245	assert(head - tail <= DEFER_QUEUE_SIZE);
	246	rcu_defer_barrier_thread();
	247	assert(head - LOAD_SHARED(defer_queue.tail) == 0);
	248	}
	249
	250	if (unlikely(defer_queue.last_fct_in != fct)) {
	251	defer_queue.last_fct_in = fct;
	252	if (unlikely(DQ_IS_FCT_BIT(fct) \|\| fct == DQ_FCT_MARK)) {
	253	/*
	254	* If the function to encode is not aligned or the
	255	* marker, write DQ_FCT_MARK followed by the function
	256	* pointer.
	257	*/
	258	_STORE_SHARED(defer_queue.q[head++ & DEFER_QUEUE_MASK],
	259	DQ_FCT_MARK);
	260	_STORE_SHARED(defer_queue.q[head++ & DEFER_QUEUE_MASK],
	261	fct);
	262	} else {
	263	DQ_SET_FCT_BIT(fct);
	264	_STORE_SHARED(defer_queue.q[head++ & DEFER_QUEUE_MASK],
	265	fct);
	266	}
	267	} else {
	268	if (unlikely(DQ_IS_FCT_BIT(p) \|\| p == DQ_FCT_MARK)) {
	269	/*
	270	* If the data to encode is not aligned or the marker,
	271	* write DQ_FCT_MARK followed by the function pointer.
	272	*/
	273	_STORE_SHARED(defer_queue.q[head++ & DEFER_QUEUE_MASK],
	274	DQ_FCT_MARK);
	275	_STORE_SHARED(defer_queue.q[head++ & DEFER_QUEUE_MASK],
	276	fct);
	277	}
	278	}
	279	_STORE_SHARED(defer_queue.q[head++ & DEFER_QUEUE_MASK], p);
	280	smp_wmb(); /* Publish new pointer before head */
	281	/* Write q[] before head. */
	282	STORE_SHARED(defer_queue.head, head);
	283	/*
	284	* Wake-up any waiting defer thread.
	285	*/
	286	wake_up_defer();
	287	}
	288
786ee85b MD	289	void thr_defer(void args)
	290	{
	291	for (;;) {
4ce9e4f2	292	pthread_testcancel();
4ce9e4f2 MD	293	/*
	294	* "Be green". Don't wake up the CPU if there is no RCU work
	295	* to perform whatsoever. Aims at saving laptop battery life by
	296	* leaving the processor in sleep state when idle.
	297	*/
4ce9e4f2	298	wait_defer();
4ce9e4f2	299	/* Sleeping after wait_defer to let many callbacks enqueue */
71df5ef4	300	poll(NULL,0,100); /* wait for 100ms */
786ee85b MD	301	rcu_defer_barrier();
	302	}
	303
	304	return NULL;
	305	}
	306
	307	/*
	308	* library wrappers to be used by non-LGPL compatible source code.
	309	*/
	310
804b4375	311	void rcu_defer_queue(void (fct)(void p), void *p)
786ee85b	312	{
804b4375	313	_rcu_defer_queue(fct, p);
786ee85b MD	314	}
	315
	316	static void rcu_add_deferer(pthread_t id)
	317	{
	318	struct deferer_registry *oldarray;
	319
	320	if (!registry) {
	321	alloc_deferers = INIT_NUM_THREADS;
	322	num_deferers = 0;
	323	registry =
	324	malloc(sizeof(struct deferer_registry) * alloc_deferers);
	325	}
	326	if (alloc_deferers < num_deferers + 1) {
	327	oldarray = registry;
	328	registry = malloc(sizeof(struct deferer_registry)
	329	* (alloc_deferers << 1));
	330	memcpy(registry, oldarray,
	331	sizeof(struct deferer_registry) * alloc_deferers);
	332	alloc_deferers <<= 1;
	333	free(oldarray);
	334	}
	335	registry[num_deferers].tid = id;
	336	/* reference to the TLS of _this_ deferer thread. */
	337	registry[num_deferers].defer_queue = &defer_queue;
804b4375	338	registry[num_deferers].last_head = 0;
786ee85b MD	339	num_deferers++;
	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_deferer(pthread_t id)
	347	{
	348	struct deferer_registry *index;
	349
	350	assert(registry != NULL);
	351	for (index = registry; index < registry + num_deferers; index++) {
	352	if (pthread_equal(index->tid, id)) {
	353	memcpy(index, &registry[num_deferers - 1],
	354	sizeof(struct deferer_registry));
	355	registry[num_deferers - 1].tid = 0;
	356	registry[num_deferers - 1].defer_queue = NULL;
804b4375	357	registry[num_deferers - 1].last_head = 0;
786ee85b MD	358	num_deferers--;
	359	return;
	360	}
	361	}
	362	/* Hrm not found, forgot to register ? */
	363	assert(0);
	364	}
	365
	366	static void start_defer_thread(void)
	367	{
	368	int ret;
	369
	370	ret = pthread_create(&tid_defer, NULL, thr_defer,
	371	NULL);
	372	assert(!ret);
	373	}
	374
	375	static void stop_defer_thread(void)
	376	{
	377	int ret;
	378	void *tret;
	379
4ce9e4f2 MD	380	pthread_cancel(tid_defer);
4ce9e4f2 MD	381	wake_up_defer();
786ee85b MD	382	ret = pthread_join(tid_defer, &tret);
	383	assert(!ret);
	384	}
	385
	386	void rcu_defer_register_thread(void)
	387	{
	388	int deferers;
	389
	390	internal_urcu_lock(&defer_thread_mutex);
	391	internal_urcu_lock(&urcu_defer_mutex);
	392	defer_queue.q = malloc(sizeof(void ) DEFER_QUEUE_SIZE);
	393	rcu_add_deferer(pthread_self());
	394	deferers = num_deferers;
	395	internal_urcu_unlock(&urcu_defer_mutex);
	396
	397	if (deferers == 1)
	398	start_defer_thread();
	399	internal_urcu_unlock(&defer_thread_mutex);
	400	}
	401
	402	void rcu_defer_unregister_thread(void)
	403	{
	404	int deferers;
	405
	406	internal_urcu_lock(&defer_thread_mutex);
	407	internal_urcu_lock(&urcu_defer_mutex);
	408	rcu_remove_deferer(pthread_self());
	409	_rcu_defer_barrier_thread();
	410	free(defer_queue.q);
	411	defer_queue.q = NULL;
	412	deferers = num_deferers;
	413	internal_urcu_unlock(&urcu_defer_mutex);
	414
	415	if (deferers == 0)
	416	stop_defer_thread();
	417	internal_urcu_unlock(&defer_thread_mutex);
	418	}
	419
	420	void urcu_defer_exit(void)
	421	{
	422	free(registry);
	423	}