[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 <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__)
#define FUTEX_WAIT		0
#define FUTEX_WAKE		1

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;

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);
	}
}

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

static unsigned long rcu_defer_num_callbacks(void)
{
	unsigned long num_items = 0, head;
	struct deferer_registry *index;

	internal_urcu_lock(&urcu_defer_mutex);
	for (index = registry; index < registry + num_deferers; index++) {
		head = LOAD_SHARED(index->defer_queue->head);
		num_items += head - index->defer_queue->tail;
	}
	internal_urcu_unlock(&urcu_defer_mutex);
	return num_items;
}

/*
 * Defer thread waiting. Single thread.
 */
static void wait_defer(void)
{
	uatomic_dec(&defer_thread_futex);
	smp_mb();	/* Write futex before read queue */
	if (rcu_defer_num_callbacks()) {
		smp_mb();	/* Read queue before write futex */
		/* Callbacks are queued, don't wait. */
		uatomic_set(&defer_thread_futex, 0);
	} else {
		smp_rmb();	/* Read queue before read futex */
		if (uatomic_read(&defer_thread_futex) == -1)
			futex(&defer_thread_futex, FUTEX_WAIT, -1,
			      NULL, NULL, 0);
	}
}

/*
 * 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);
	smp_mb();	/* Write queue head before read futex */
	/*
	 * 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 <sys/time.h>
	32	#include <syscall.h>
	33	#include <unistd.h>
786ee85b MD	34
	35	#include "urcu-defer-static.h"
	36	/* Do not #define _LGPL_SOURCE to ensure we can emit the wrapper symbols */
	37	#include "urcu-defer.h"
	38
4ce9e4f2	39	#define futex(...) syscall(__NR_futex, __VA_ARGS__)
80cca311 MD	40	#define FUTEX_WAIT 0
80cca311 MD	41	#define FUTEX_WAKE 1
4ce9e4f2	42
786ee85b MD	43	void __attribute__((destructor)) urcu_defer_exit(void);
	44
	45	extern void synchronize_rcu(void);
	46
	47	/*
	48	* urcu_defer_mutex nests inside defer_thread_mutex.
	49	*/
	50	static pthread_mutex_t urcu_defer_mutex = PTHREAD_MUTEX_INITIALIZER;
	51	static pthread_mutex_t defer_thread_mutex = PTHREAD_MUTEX_INITIALIZER;
	52
3dce4bfa	53	static int defer_thread_futex;
4ce9e4f2	54
786ee85b MD	55	/*
	56	* Written to only by each individual deferer. Read by both the deferer and
	57	* the reclamation tread.
	58	*/
3dce4bfa	59	static struct defer_queue __thread defer_queue;
786ee85b MD	60
	61	/* Thread IDs of registered deferers */
	62	#define INIT_NUM_THREADS 4
	63
	64	struct deferer_registry {
	65	pthread_t tid;
	66	struct defer_queue *defer_queue;
	67	unsigned long last_head;
	68	};
	69
	70	static struct deferer_registry *registry;
	71	static int num_deferers, alloc_deferers;
	72
	73	static pthread_t tid_defer;
4ce9e4f2	74
786ee85b MD	75	static void internal_urcu_lock(pthread_mutex_t *mutex)
	76	{
	77	int ret;
	78
	79	#ifndef DISTRUST_SIGNALS_EXTREME
	80	ret = pthread_mutex_lock(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(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	}
4ce9e4f2	92	pthread_testcancel();
786ee85b MD	93	poll(NULL,0,10);
	94	}
	95	#endif /* #else #ifndef DISTRUST_SIGNALS_EXTREME */
	96	}
	97
	98	static void internal_urcu_unlock(pthread_mutex_t *mutex)
	99	{
	100	int ret;
	101
	102	ret = pthread_mutex_unlock(mutex);
	103	if (ret) {
	104	perror("Error in pthread mutex unlock");
	105	exit(-1);
	106	}
	107	}
	108
04eb9c4f MD	109	/*
	110	* Wake-up any waiting defer thread. Called from many concurrent threads.
	111	*/
	112	static void wake_up_defer(void)
	113	{
ec4e58a3 MD	114	if (unlikely(uatomic_read(&defer_thread_futex) == -1)) {
ec4e58a3 MD	115	uatomic_set(&defer_thread_futex, 0);
8fd3b219	116	futex(&defer_thread_futex, FUTEX_WAKE, 1,
04eb9c4f MD	117	NULL, NULL, 0);
	118	}
	119	}
	120
	121	static unsigned long rcu_defer_num_callbacks(void)
	122	{
	123	unsigned long num_items = 0, head;
	124	struct deferer_registry *index;
	125
	126	internal_urcu_lock(&urcu_defer_mutex);
	127	for (index = registry; index < registry + num_deferers; index++) {
	128	head = LOAD_SHARED(index->defer_queue->head);
	129	num_items += head - index->defer_queue->tail;
	130	}
	131	internal_urcu_unlock(&urcu_defer_mutex);
	132	return num_items;
	133	}
	134
	135	/*
	136	* Defer thread waiting. Single thread.
	137	*/
	138	static void wait_defer(void)
	139	{
ec4e58a3	140	uatomic_dec(&defer_thread_futex);
04eb9c4f MD	141	smp_mb(); /* Write futex before read queue */
	142	if (rcu_defer_num_callbacks()) {
	143	smp_mb(); /* Read queue before write futex */
	144	/* Callbacks are queued, don't wait. */
ec4e58a3	145	uatomic_set(&defer_thread_futex, 0);
04eb9c4f MD	146	} else {
04eb9c4f MD	147	smp_rmb(); /* Read queue before read futex */
ec4e58a3	148	if (uatomic_read(&defer_thread_futex) == -1)
04eb9c4f MD	149	futex(&defer_thread_futex, FUTEX_WAIT, -1,
	150	NULL, NULL, 0);
	151	}
	152	}
	153
786ee85b MD	154	/*
	155	* Must be called after Q.S. is reached.
	156	*/
	157	static void rcu_defer_barrier_queue(struct defer_queue *queue,
804b4375	158	unsigned long head)
786ee85b MD	159	{
786ee85b MD	160	unsigned long i;
804b4375 MD	161	void (fct)(void p);
804b4375 MD	162	void *p;
786ee85b MD	163
	164	/*
	165	* Tail is only modified when lock is held.
	166	* Head is only modified by owner thread.
	167	*/
	168
804b4375	169	for (i = queue->tail; i != head;) {
786ee85b	170	smp_rmb(); /* read head before q[]. */
804b4375 MD	171	p = LOAD_SHARED(queue->q[i++ & DEFER_QUEUE_MASK]);
804b4375 MD	172	if (unlikely(DQ_IS_FCT_BIT(p))) {
804b4375 MD	173	DQ_CLEAR_FCT_BIT(p);
	174	queue->last_fct_out = p;
	175	p = LOAD_SHARED(queue->q[i++ & DEFER_QUEUE_MASK]);
	176	} else if (unlikely(p == DQ_FCT_MARK)) {
804b4375 MD	177	p = LOAD_SHARED(queue->q[i++ & DEFER_QUEUE_MASK]);
	178	queue->last_fct_out = p;
	179	p = LOAD_SHARED(queue->q[i++ & DEFER_QUEUE_MASK]);
29cdb8d8	180	}
804b4375	181	fct = queue->last_fct_out;
804b4375	182	fct(p);
786ee85b MD	183	}
	184	smp_mb(); /* push tail after having used q[] */
	185	STORE_SHARED(queue->tail, i);
	186	}
	187
	188	static void _rcu_defer_barrier_thread(void)
	189	{
0d0e6c21	190	unsigned long head, num_items;
786ee85b MD	191
786ee85b MD	192	head = defer_queue.head;
0d0e6c21 MD	193	num_items = head - defer_queue.tail;
	194	if (unlikely(!num_items))
	195	return;
786ee85b MD	196	synchronize_rcu();
	197	rcu_defer_barrier_queue(&defer_queue, head);
	198	}
	199
	200
	201	void rcu_defer_barrier_thread(void)
	202	{
	203	internal_urcu_lock(&urcu_defer_mutex);
	204	_rcu_defer_barrier_thread();
	205	internal_urcu_unlock(&urcu_defer_mutex);
	206	}
	207
0d0e6c21 MD	208	/*
	209	* rcu_defer_barrier - Execute all queued rcu callbacks.
	210	*
	211	* Execute all RCU callbacks queued before rcu_defer_barrier() execution.
	212	* All callbacks queued on the local thread prior to a rcu_defer_barrier() call
	213	* are guaranteed to be executed.
	214	* Callbacks queued by other threads concurrently with rcu_defer_barrier()
	215	* execution are not guaranteed to be executed in the current batch (could
	216	* be left for the next batch). These callbacks queued by other threads are only
	217	* guaranteed to be executed if there is explicit synchronization between
	218	* the thread adding to the queue and the thread issuing the defer_barrier call.
	219	*/
	220
786ee85b MD	221	void rcu_defer_barrier(void)
	222	{
	223	struct deferer_registry *index;
0d0e6c21	224	unsigned long num_items = 0;
786ee85b MD	225
	226	if (!registry)
	227	return;
	228
	229	internal_urcu_lock(&urcu_defer_mutex);
0d0e6c21	230	for (index = registry; index < registry + num_deferers; index++) {
786ee85b	231	index->last_head = LOAD_SHARED(index->defer_queue->head);
0d0e6c21 MD	232	num_items += index->last_head - index->defer_queue->tail;
	233	}
	234	if (likely(!num_items)) {
	235	/*
	236	* We skip the grace period because there are no queued
	237	* callbacks to execute.
	238	*/
	239	goto end;
	240	}
786ee85b MD	241	synchronize_rcu();
	242	for (index = registry; index < registry + num_deferers; index++)
	243	rcu_defer_barrier_queue(index->defer_queue,
	244	index->last_head);
0d0e6c21	245	end:
786ee85b MD	246	internal_urcu_unlock(&urcu_defer_mutex);
	247	}
	248
2c22932b MD	249	/*
	250	* _rcu_defer_queue - Queue a RCU callback.
	251	*/
	252	void _rcu_defer_queue(void (fct)(void p), void *p)
	253	{
	254	unsigned long head, tail;
	255
	256	/*
	257	* Head is only modified by ourself. Tail can be modified by reclamation
	258	* thread.
	259	*/
	260	head = defer_queue.head;
	261	tail = LOAD_SHARED(defer_queue.tail);
	262
	263	/*
	264	* If queue is full, empty it ourself.
	265	* Worse-case: must allow 2 supplementary entries for fct pointer.
	266	*/
	267	if (unlikely(head - tail >= DEFER_QUEUE_SIZE - 2)) {
	268	assert(head - tail <= DEFER_QUEUE_SIZE);
	269	rcu_defer_barrier_thread();
	270	assert(head - LOAD_SHARED(defer_queue.tail) == 0);
	271	}
	272
	273	if (unlikely(defer_queue.last_fct_in != fct)) {
	274	defer_queue.last_fct_in = fct;
	275	if (unlikely(DQ_IS_FCT_BIT(fct) \|\| fct == DQ_FCT_MARK)) {
	276	/*
	277	* If the function to encode is not aligned or the
	278	* marker, write DQ_FCT_MARK followed by the function
	279	* pointer.
	280	*/
	281	_STORE_SHARED(defer_queue.q[head++ & DEFER_QUEUE_MASK],
	282	DQ_FCT_MARK);
	283	_STORE_SHARED(defer_queue.q[head++ & DEFER_QUEUE_MASK],
	284	fct);
	285	} else {
	286	DQ_SET_FCT_BIT(fct);
	287	_STORE_SHARED(defer_queue.q[head++ & DEFER_QUEUE_MASK],
	288	fct);
	289	}
	290	} else {
	291	if (unlikely(DQ_IS_FCT_BIT(p) \|\| p == DQ_FCT_MARK)) {
	292	/*
	293	* If the data to encode is not aligned or the marker,
	294	* write DQ_FCT_MARK followed by the function pointer.
	295	*/
	296	_STORE_SHARED(defer_queue.q[head++ & DEFER_QUEUE_MASK],
	297	DQ_FCT_MARK);
	298	_STORE_SHARED(defer_queue.q[head++ & DEFER_QUEUE_MASK],
	299	fct);
	300	}
	301	}
	302	_STORE_SHARED(defer_queue.q[head++ & DEFER_QUEUE_MASK], p);
	303	smp_wmb(); /* Publish new pointer before head */
	304	/* Write q[] before head. */
	305	STORE_SHARED(defer_queue.head, head);
04eb9c4f	306	smp_mb(); /* Write queue head before read futex */
2c22932b MD	307	/*
	308	* Wake-up any waiting defer thread.
	309	*/
	310	wake_up_defer();
	311	}
	312
786ee85b MD	313	void thr_defer(void args)
	314	{
	315	for (;;) {
4ce9e4f2	316	pthread_testcancel();
4ce9e4f2 MD	317	/*
	318	* "Be green". Don't wake up the CPU if there is no RCU work
	319	* to perform whatsoever. Aims at saving laptop battery life by
	320	* leaving the processor in sleep state when idle.
	321	*/
4ce9e4f2	322	wait_defer();
4ce9e4f2	323	/* Sleeping after wait_defer to let many callbacks enqueue */
71df5ef4	324	poll(NULL,0,100); /* wait for 100ms */
786ee85b MD	325	rcu_defer_barrier();
	326	}
	327
	328	return NULL;
	329	}
	330
	331	/*
	332	* library wrappers to be used by non-LGPL compatible source code.
	333	*/
	334
804b4375	335	void rcu_defer_queue(void (fct)(void p), void *p)
786ee85b	336	{
804b4375	337	_rcu_defer_queue(fct, p);
786ee85b MD	338	}
	339
	340	static void rcu_add_deferer(pthread_t id)
	341	{
	342	struct deferer_registry *oldarray;
	343
	344	if (!registry) {
	345	alloc_deferers = INIT_NUM_THREADS;
	346	num_deferers = 0;
	347	registry =
	348	malloc(sizeof(struct deferer_registry) * alloc_deferers);
	349	}
	350	if (alloc_deferers < num_deferers + 1) {
	351	oldarray = registry;
	352	registry = malloc(sizeof(struct deferer_registry)
	353	* (alloc_deferers << 1));
	354	memcpy(registry, oldarray,
	355	sizeof(struct deferer_registry) * alloc_deferers);
	356	alloc_deferers <<= 1;
	357	free(oldarray);
	358	}
	359	registry[num_deferers].tid = id;
	360	/* reference to the TLS of _this_ deferer thread. */
	361	registry[num_deferers].defer_queue = &defer_queue;
804b4375	362	registry[num_deferers].last_head = 0;
786ee85b MD	363	num_deferers++;
	364	}
	365
	366	/*
	367	* Never shrink (implementation limitation).
	368	* This is O(nb threads). Eventually use a hash table.
	369	*/
	370	static void rcu_remove_deferer(pthread_t id)
	371	{
	372	struct deferer_registry *index;
	373
	374	assert(registry != NULL);
	375	for (index = registry; index < registry + num_deferers; index++) {
	376	if (pthread_equal(index->tid, id)) {
	377	memcpy(index, &registry[num_deferers - 1],
	378	sizeof(struct deferer_registry));
	379	registry[num_deferers - 1].tid = 0;
	380	registry[num_deferers - 1].defer_queue = NULL;
804b4375	381	registry[num_deferers - 1].last_head = 0;
786ee85b MD	382	num_deferers--;
	383	return;
	384	}
	385	}
	386	/* Hrm not found, forgot to register ? */
	387	assert(0);
	388	}
	389
	390	static void start_defer_thread(void)
	391	{
	392	int ret;
	393
	394	ret = pthread_create(&tid_defer, NULL, thr_defer,
	395	NULL);
	396	assert(!ret);
	397	}
	398
	399	static void stop_defer_thread(void)
	400	{
	401	int ret;
	402	void *tret;
	403
4ce9e4f2 MD	404	pthread_cancel(tid_defer);
4ce9e4f2 MD	405	wake_up_defer();
786ee85b MD	406	ret = pthread_join(tid_defer, &tret);
	407	assert(!ret);
	408	}
	409
	410	void rcu_defer_register_thread(void)
	411	{
	412	int deferers;
	413
	414	internal_urcu_lock(&defer_thread_mutex);
	415	internal_urcu_lock(&urcu_defer_mutex);
	416	defer_queue.q = malloc(sizeof(void ) DEFER_QUEUE_SIZE);
	417	rcu_add_deferer(pthread_self());
	418	deferers = num_deferers;
	419	internal_urcu_unlock(&urcu_defer_mutex);
	420
	421	if (deferers == 1)
	422	start_defer_thread();
	423	internal_urcu_unlock(&defer_thread_mutex);
	424	}
	425
	426	void rcu_defer_unregister_thread(void)
	427	{
	428	int deferers;
	429
	430	internal_urcu_lock(&defer_thread_mutex);
	431	internal_urcu_lock(&urcu_defer_mutex);
	432	rcu_remove_deferer(pthread_self());
	433	_rcu_defer_barrier_thread();
	434	free(defer_queue.q);
	435	defer_queue.q = NULL;
	436	deferers = num_deferers;
	437	internal_urcu_unlock(&urcu_defer_mutex);
	438
	439	if (deferers == 0)
	440	stop_defer_thread();
	441	internal_urcu_unlock(&defer_thread_mutex);
	442	}
	443
	444	void urcu_defer_exit(void)
	445	{
	446	free(registry);
	447	}