+++ /dev/null
-#ifndef _URCU_DEFER_IMPL_H
-#define _URCU_DEFER_IMPL_H
-
-/*
- * urcu-defer-impl.h
- *
- * Userspace RCU header - memory reclamation.
- *
- * TO BE INCLUDED ONLY FROM URCU LIBRARY CODE. See urcu-defer.h for linking
- * dynamically with the userspace rcu reclamation library.
- *
- * Copyright (c) 2009 Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
- * Copyright (c) 2009 Paul E. McKenney, IBM Corporation.
- *
- * This library is free software; you can redistribute it and/or
- * modify it under the terms of the GNU Lesser General Public
- * License as published by the Free Software Foundation; either
- * version 2.1 of the License, or (at your option) any later version.
- *
- * This library is distributed in the hope that it will be useful,
- * but WITHOUT ANY WARRANTY; without even the implied warranty of
- * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
- * Lesser General Public License for more details.
- *
- * You should have received a copy of the GNU Lesser General Public
- * License along with this library; if not, write to the Free Software
- * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA
- *
- * IBM's contributions to this file may be relicensed under LGPLv2 or later.
- */
-
-#include <stdlib.h>
-#include <pthread.h>
-#include <stdio.h>
-#include <signal.h>
-#include <assert.h>
-#include <string.h>
-#include <errno.h>
-#include <poll.h>
-#include <sys/time.h>
-#include <unistd.h>
-#include <stdint.h>
-
-#include "urcu/futex.h"
-
-#include <urcu/compiler.h>
-#include <urcu/arch.h>
-#include <urcu/uatomic.h>
-#include <urcu/list.h>
-#include <urcu/system.h>
-#include <urcu/tls-compat.h>
-#include "urcu-die.h"
-
-/*
- * Number of entries in the per-thread defer queue. Must be power of 2.
- */
-#define DEFER_QUEUE_SIZE (1 << 12)
-#define DEFER_QUEUE_MASK (DEFER_QUEUE_SIZE - 1)
-
-/*
- * Typically, data is aligned at least on the architecture size.
- * Use lowest bit to indicate that the current callback is changing.
- * Assumes that (void *)-2L is not used often. Used to encode non-aligned
- * functions and non-aligned data using extra space.
- * We encode the (void *)-2L fct as: -2L, fct, data.
- * We encode the (void *)-2L data as either:
- * fct | DQ_FCT_BIT, data (if fct is aligned), or
- * -2L, fct, data (if fct is not aligned).
- * Here, DQ_FCT_MARK == ~DQ_FCT_BIT. Required for the test order.
- */
-#define DQ_FCT_BIT (1 << 0)
-#define DQ_IS_FCT_BIT(x) ((unsigned long)(x) & DQ_FCT_BIT)
-#define DQ_SET_FCT_BIT(x) \
- (x = (void *)((unsigned long)(x) | DQ_FCT_BIT))
-#define DQ_CLEAR_FCT_BIT(x) \
- (x = (void *)((unsigned long)(x) & ~DQ_FCT_BIT))
-#define DQ_FCT_MARK ((void *)(~DQ_FCT_BIT))
-
-/*
- * This code section can only be included in LGPL 2.1 compatible source code.
- * See below for the function call wrappers which can be used in code meant to
- * be only linked with the Userspace RCU library. This comes with a small
- * performance degradation on the read-side due to the added function calls.
- * This is required to permit relinking with newer versions of the library.
- */
-
-/*
- * defer queue.
- * Contains pointers. Encoded to save space when same callback is often used.
- * When looking up the next item:
- * - if DQ_FCT_BIT is set, set the current callback to DQ_CLEAR_FCT_BIT(ptr)
- * - next element contains pointer to data.
- * - else if item == DQ_FCT_MARK
- * - set the current callback to next element ptr
- * - following next element contains pointer to data.
- * - else current element contains data
- */
-struct defer_queue {
- unsigned long head; /* add element at head */
- void *last_fct_in; /* last fct pointer encoded */
- unsigned long tail; /* next element to remove at tail */
- void *last_fct_out; /* last fct pointer encoded */
- void **q;
- /* registry information */
- unsigned long last_head;
- struct cds_list_head list; /* list of thread queues */
-};
-
-/* Do not #define _LGPL_SOURCE to ensure we can emit the wrapper symbols */
-#include "urcu-defer.h"
-
-void __attribute__((destructor)) rcu_defer_exit(void);
-
-extern void synchronize_rcu(void);
-
-/*
- * rcu_defer_mutex nests inside defer_thread_mutex.
- */
-static pthread_mutex_t rcu_defer_mutex = PTHREAD_MUTEX_INITIALIZER;
-static pthread_mutex_t defer_thread_mutex = PTHREAD_MUTEX_INITIALIZER;
-
-static int32_t defer_thread_futex;
-static int32_t defer_thread_stop;
-
-/*
- * Written to only by each individual deferer. Read by both the deferer and
- * the reclamation tread.
- */
-static DEFINE_URCU_TLS(struct defer_queue, defer_queue);
-static CDS_LIST_HEAD(registry_defer);
-static pthread_t tid_defer;
-
-static void mutex_lock_defer(pthread_mutex_t *mutex)
-{
- int ret;
-
-#ifndef DISTRUST_SIGNALS_EXTREME
- ret = pthread_mutex_lock(mutex);
- if (ret)
- urcu_die(ret);
-#else /* #ifndef DISTRUST_SIGNALS_EXTREME */
- while ((ret = pthread_mutex_trylock(mutex)) != 0) {
- if (ret != EBUSY && ret != EINTR)
- urcu_die(ret);
- (void) poll(NULL,0,10);
- }
-#endif /* #else #ifndef DISTRUST_SIGNALS_EXTREME */
-}
-
-/*
- * Wake-up any waiting defer thread. Called from many concurrent threads.
- */
-static void wake_up_defer(void)
-{
- if (caa_unlikely(uatomic_read(&defer_thread_futex) == -1)) {
- uatomic_set(&defer_thread_futex, 0);
- if (futex_noasync(&defer_thread_futex, FUTEX_WAKE, 1,
- NULL, NULL, 0) < 0)
- urcu_die(errno);
- }
-}
-
-static unsigned long rcu_defer_num_callbacks(void)
-{
- unsigned long num_items = 0, head;
- struct defer_queue *index;
-
- mutex_lock_defer(&rcu_defer_mutex);
- cds_list_for_each_entry(index, ®istry_defer, list) {
- head = CMM_LOAD_SHARED(index->head);
- num_items += head - index->tail;
- }
- mutex_unlock(&rcu_defer_mutex);
- return num_items;
-}
-
-/*
- * Defer thread waiting. Single thread.
- */
-static void wait_defer(void)
-{
- uatomic_dec(&defer_thread_futex);
- /* Write futex before read queue */
- /* Write futex before read defer_thread_stop */
- cmm_smp_mb();
- if (_CMM_LOAD_SHARED(defer_thread_stop)) {
- uatomic_set(&defer_thread_futex, 0);
- pthread_exit(0);
- }
- if (rcu_defer_num_callbacks()) {
- cmm_smp_mb(); /* Read queue before write futex */
- /* Callbacks are queued, don't wait. */
- uatomic_set(&defer_thread_futex, 0);
- } else {
- cmm_smp_rmb(); /* Read queue before read futex */
- if (uatomic_read(&defer_thread_futex) != -1)
- return;
- while (futex_noasync(&defer_thread_futex, FUTEX_WAIT, -1,
- NULL, NULL, 0)) {
- switch (errno) {
- case EWOULDBLOCK:
- /* Value already changed. */
- return;
- case EINTR:
- /* Retry if interrupted by signal. */
- break; /* Get out of switch. */
- default:
- /* Unexpected error. */
- urcu_die(errno);
- }
- }
- }
-}
-
-/*
- * 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;) {
- cmm_smp_rmb(); /* read head before q[]. */
- p = CMM_LOAD_SHARED(queue->q[i++ & DEFER_QUEUE_MASK]);
- if (caa_unlikely(DQ_IS_FCT_BIT(p))) {
- DQ_CLEAR_FCT_BIT(p);
- queue->last_fct_out = p;
- p = CMM_LOAD_SHARED(queue->q[i++ & DEFER_QUEUE_MASK]);
- } else if (caa_unlikely(p == DQ_FCT_MARK)) {
- p = CMM_LOAD_SHARED(queue->q[i++ & DEFER_QUEUE_MASK]);
- queue->last_fct_out = p;
- p = CMM_LOAD_SHARED(queue->q[i++ & DEFER_QUEUE_MASK]);
- }
- fct = queue->last_fct_out;
- fct(p);
- }
- cmm_smp_mb(); /* push tail after having used q[] */
- CMM_STORE_SHARED(queue->tail, i);
-}
-
-static void _rcu_defer_barrier_thread(void)
-{
- unsigned long head, num_items;
-
- head = URCU_TLS(defer_queue).head;
- num_items = head - URCU_TLS(defer_queue).tail;
- if (caa_unlikely(!num_items))
- return;
- synchronize_rcu();
- rcu_defer_barrier_queue(&URCU_TLS(defer_queue), head);
-}
-
-void rcu_defer_barrier_thread(void)
-{
- mutex_lock_defer(&rcu_defer_mutex);
- _rcu_defer_barrier_thread();
- mutex_unlock(&rcu_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 defer_queue *index;
- unsigned long num_items = 0;
-
- if (cds_list_empty(®istry_defer))
- return;
-
- mutex_lock_defer(&rcu_defer_mutex);
- cds_list_for_each_entry(index, ®istry_defer, list) {
- index->last_head = CMM_LOAD_SHARED(index->head);
- num_items += index->last_head - index->tail;
- }
- if (caa_likely(!num_items)) {
- /*
- * We skip the grace period because there are no queued
- * callbacks to execute.
- */
- goto end;
- }
- synchronize_rcu();
- cds_list_for_each_entry(index, ®istry_defer, list)
- rcu_defer_barrier_queue(index, index->last_head);
-end:
- mutex_unlock(&rcu_defer_mutex);
-}
-
-/*
- * _defer_rcu - Queue a RCU callback.
- */
-static void _defer_rcu(void (*fct)(void *p), void *p)
-{
- unsigned long head, tail;
-
- /*
- * Head is only modified by ourself. Tail can be modified by reclamation
- * thread.
- */
- head = URCU_TLS(defer_queue).head;
- tail = CMM_LOAD_SHARED(URCU_TLS(defer_queue).tail);
-
- /*
- * If queue is full, or reached threshold. Empty queue ourself.
- * Worse-case: must allow 2 supplementary entries for fct pointer.
- */
- if (caa_unlikely(head - tail >= DEFER_QUEUE_SIZE - 2)) {
- assert(head - tail <= DEFER_QUEUE_SIZE);
- rcu_defer_barrier_thread();
- assert(head - CMM_LOAD_SHARED(URCU_TLS(defer_queue).tail) == 0);
- }
-
- /*
- * Encode:
- * if the function is not changed and the data is aligned and it is
- * not the marker:
- * store the data
- * otherwise if the function is aligned and its not the marker:
- * store the function with DQ_FCT_BIT
- * store the data
- * otherwise:
- * store the marker (DQ_FCT_MARK)
- * store the function
- * store the data
- *
- * Decode: see the comments before 'struct defer_queue'
- * or the code in rcu_defer_barrier_queue().
- */
- if (caa_unlikely(URCU_TLS(defer_queue).last_fct_in != fct
- || DQ_IS_FCT_BIT(p)
- || p == DQ_FCT_MARK)) {
- URCU_TLS(defer_queue).last_fct_in = fct;
- if (caa_unlikely(DQ_IS_FCT_BIT(fct) || fct == DQ_FCT_MARK)) {
- _CMM_STORE_SHARED(URCU_TLS(defer_queue).q[head++ & DEFER_QUEUE_MASK],
- DQ_FCT_MARK);
- _CMM_STORE_SHARED(URCU_TLS(defer_queue).q[head++ & DEFER_QUEUE_MASK],
- fct);
- } else {
- DQ_SET_FCT_BIT(fct);
- _CMM_STORE_SHARED(URCU_TLS(defer_queue).q[head++ & DEFER_QUEUE_MASK],
- fct);
- }
- }
- _CMM_STORE_SHARED(URCU_TLS(defer_queue).q[head++ & DEFER_QUEUE_MASK], p);
- cmm_smp_wmb(); /* Publish new pointer before head */
- /* Write q[] before head. */
- CMM_STORE_SHARED(URCU_TLS(defer_queue).head, head);
- cmm_smp_mb(); /* Write queue head before read futex */
- /*
- * Wake-up any waiting defer thread.
- */
- wake_up_defer();
-}
-
-static void *thr_defer(void *args)
-{
- for (;;) {
- /*
- * "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 */
- (void) poll(NULL,0,100); /* wait for 100ms */
- rcu_defer_barrier();
- }
-
- return NULL;
-}
-
-/*
- * library wrappers to be used by non-LGPL compatible source code.
- */
-
-void defer_rcu(void (*fct)(void *p), void *p)
-{
- _defer_rcu(fct, p);
-}
-
-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;
-
- _CMM_STORE_SHARED(defer_thread_stop, 1);
- /* Store defer_thread_stop before testing futex */
- cmm_smp_mb();
- wake_up_defer();
-
- ret = pthread_join(tid_defer, &tret);
- assert(!ret);
-
- CMM_STORE_SHARED(defer_thread_stop, 0);
- /* defer thread should always exit when futex value is 0 */
- assert(uatomic_read(&defer_thread_futex) == 0);
-}
-
-int rcu_defer_register_thread(void)
-{
- int was_empty;
-
- assert(URCU_TLS(defer_queue).last_head == 0);
- assert(URCU_TLS(defer_queue).q == NULL);
- URCU_TLS(defer_queue).q = malloc(sizeof(void *) * DEFER_QUEUE_SIZE);
- if (!URCU_TLS(defer_queue).q)
- return -ENOMEM;
-
- mutex_lock_defer(&defer_thread_mutex);
- mutex_lock_defer(&rcu_defer_mutex);
- was_empty = cds_list_empty(®istry_defer);
- cds_list_add(&URCU_TLS(defer_queue).list, ®istry_defer);
- mutex_unlock(&rcu_defer_mutex);
-
- if (was_empty)
- start_defer_thread();
- mutex_unlock(&defer_thread_mutex);
- return 0;
-}
-
-void rcu_defer_unregister_thread(void)
-{
- int is_empty;
-
- mutex_lock_defer(&defer_thread_mutex);
- mutex_lock_defer(&rcu_defer_mutex);
- cds_list_del(&URCU_TLS(defer_queue).list);
- _rcu_defer_barrier_thread();
- free(URCU_TLS(defer_queue).q);
- URCU_TLS(defer_queue).q = NULL;
- is_empty = cds_list_empty(®istry_defer);
- mutex_unlock(&rcu_defer_mutex);
-
- if (is_empty)
- stop_defer_thread();
- mutex_unlock(&defer_thread_mutex);
-}
-
-void rcu_defer_exit(void)
-{
- assert(cds_list_empty(®istry_defer));
-}
-
-#endif /* _URCU_DEFER_IMPL_H */
projects / userspace-rcu.git / blobdiff