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/*
* Copyright 2011-2015 Samy Al Bahra.
* Copyright 2011 David Joseph.
* All rights reserved.
*
* Redistribution and use in source and binary forms, with or without
* modification, are permitted provided that the following conditions
* are met:
* 1. Redistributions of source code must retain the above copyright
* notice, this list of conditions and the following disclaimer.
* 2. Redistributions in binary form must reproduce the above copyright
* notice, this list of conditions and the following disclaimer in the
* documentation and/or other materials provided with the distribution.
*
* THIS SOFTWARE IS PROVIDED BY THE AUTHOR AND CONTRIBUTORS ``AS IS'' AND
* ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
* IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
* ARE DISCLAIMED. IN NO EVENT SHALL THE AUTHOR OR CONTRIBUTORS BE LIABLE
* FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
* DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
* OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
* HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
* LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
* OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
* SUCH DAMAGE.
*/
#include <ck_barrier.h>
#include <ck_cc.h>
#include <ck_pr.h>
#include <ck_spinlock.h>
struct ck_barrier_combining_queue {
struct ck_barrier_combining_group *head;
struct ck_barrier_combining_group *tail;
};
static struct ck_barrier_combining_group *
ck_barrier_combining_queue_dequeue(struct ck_barrier_combining_queue *queue)
{
struct ck_barrier_combining_group *front = NULL;
if (queue->head != NULL) {
front = queue->head;
queue->head = queue->head->next;
}
return front;
}
static void
ck_barrier_combining_insert(struct ck_barrier_combining_group *parent,
struct ck_barrier_combining_group *tnode,
struct ck_barrier_combining_group **child)
{
*child = tnode;
tnode->parent = parent;
/*
* After inserting, we must increment the parent group's count for
* number of threads expected to reach it; otherwise, the
* barrier may end prematurely.
*/
parent->k++;
return;
}
/*
* This implementation of software combining tree barriers
* uses level order traversal to insert new thread groups
* into the barrier's tree. We use a queue to implement this
* traversal.
*/
static void
ck_barrier_combining_queue_enqueue(struct ck_barrier_combining_queue *queue,
struct ck_barrier_combining_group *node_value)
{
node_value->next = NULL;
if (queue->head == NULL) {
queue->head = queue->tail = node_value;
return;
}
queue->tail->next = node_value;
queue->tail = node_value;
return;
}
void
ck_barrier_combining_group_init(struct ck_barrier_combining *root,
struct ck_barrier_combining_group *tnode,
unsigned int nthr)
{
struct ck_barrier_combining_group *node;
struct ck_barrier_combining_queue queue;
queue.head = queue.tail = NULL;
tnode->k = nthr;
tnode->count = 0;
tnode->sense = 0;
tnode->left = tnode->right = NULL;
/*
* Finds the first available node for linkage into the combining
* tree. The use of a spinlock is excusable as this is a one-time
* initialization cost.
*/
ck_spinlock_fas_lock(&root->mutex);
ck_barrier_combining_queue_enqueue(&queue, root->root);
while (queue.head != NULL) {
node = ck_barrier_combining_queue_dequeue(&queue);
/* If the left child is free, link the group there. */
if (node->left == NULL) {
ck_barrier_combining_insert(node, tnode, &node->left);
goto leave;
}
/* If the right child is free, link the group there. */
if (node->right == NULL) {
ck_barrier_combining_insert(node, tnode, &node->right);
goto leave;
}
/*
* If unsuccessful, try inserting as a child of the children of the
* current node.
*/
ck_barrier_combining_queue_enqueue(&queue, node->left);
ck_barrier_combining_queue_enqueue(&queue, node->right);
}
leave:
ck_spinlock_fas_unlock(&root->mutex);
return;
}
void
ck_barrier_combining_init(struct ck_barrier_combining *root,
struct ck_barrier_combining_group *init_root)
{
init_root->k = 0;
init_root->count = 0;
init_root->sense = 0;
init_root->parent = init_root->left = init_root->right = NULL;
ck_spinlock_fas_init(&root->mutex);
root->root = init_root;
return;
}
static void
ck_barrier_combining_aux(struct ck_barrier_combining *barrier,
struct ck_barrier_combining_group *tnode,
unsigned int sense)
{
/*
* If this is the last thread in the group, it moves on to the parent group.
* Otherwise, it spins on this group's sense.
*/
if (ck_pr_faa_uint(&tnode->count, 1) == tnode->k - 1) {
/*
* If we are and will be the last thread entering the barrier for the
* current group then signal the parent group if one exists.
*/
if (tnode->parent != NULL)
ck_barrier_combining_aux(barrier, tnode->parent, sense);
/*
* Once the thread returns from its parent(s), it reinitializes the group's
* arrival count and signals other threads to continue by flipping the group
* sense. Order of these operations is not important since we assume a static
* number of threads are members of a barrier for the lifetime of the barrier.
* Since count is explicitly reinitialized, it is guaranteed that at any point
* tnode->count is equivalent to tnode->k if and only if that many threads
* are at the barrier.
*/
ck_pr_store_uint(&tnode->count, 0);
ck_pr_fence_store();
ck_pr_store_uint(&tnode->sense, ~tnode->sense);
} else {
while (sense != ck_pr_load_uint(&tnode->sense))
ck_pr_stall();
}
ck_pr_fence_memory();
return;
}
void
ck_barrier_combining(struct ck_barrier_combining *barrier,
struct ck_barrier_combining_group *tnode,
struct ck_barrier_combining_state *state)
{
ck_barrier_combining_aux(barrier, tnode, state->sense);
/* Reverse the execution context's sense for the next barrier. */
state->sense = ~state->sense;
return;
}
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