--- /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