/* -*- tab-width: 4 -*-
*
* Electric(tm) VLSI Design System
*
* File: FCQueue.java
* Written by: Itai Incze, Tel-Aviv University
*
* Copyright (c) 2010, Oracle and/or its affiliates. All rights reserved.
*
* Electric(tm) is free software; you can redistribute it and/or modify
* it under the terms of the GNU General Public License as published by
* the Free Software Foundation; either version 3 of the License, or
* (at your option) any later version.
*
* Electric(tm) 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 General Public License for more details.
*
* You should have received a copy of the GNU General Public License
* along with Electric(tm); see the file COPYING. If not, write to
* the Free Software Foundation, Inc., 59 Temple Place, Suite 330,
* Boston, Mass 02111-1307, USA.
*/
package com.sun.electric.tool.util.concurrent.datastructures;
import java.util.concurrent.atomic.AtomicInteger;
import java.util.concurrent.atomic.AtomicReferenceFieldUpdater;
/**
*
* @author itai
*/
public class FCQueue<T> extends IStructure<T> {
// Maximum participating threads
final int MAX_THREADS = 512;
static class CombiningNode<T> {
volatile boolean is_linked;
int last_request_timestamp;
// comb_list_head CAS will perform the write for this
CombiningNode<T> next;
volatile boolean is_request_valid;
// membar on item and is_consumer is committed by a write to
// is_request_valid
boolean is_consumer;
T item;
CombiningNode() {
is_linked = false;
next = null;
is_request_valid = false;
}
}
AtomicInteger fc_lock;
// used to gather combined enqueued items
T[] combined_pushed_items;
volatile int current_timestamp = 0;
private ThreadLocal<CombiningNode<T>> combining_node = new ThreadLocal<CombiningNode<T>>() {
@Override
protected CombiningNode<T> initialValue() {
return new CombiningNode<T>();
}
};
volatile CombiningNode<T> comb_list_head;
// For compareAndSet on the _req_list_head
@SuppressWarnings("unchecked")
final private static AtomicReferenceFieldUpdater<FCQueue, CombiningNode> comb_list_head_updater = AtomicReferenceFieldUpdater
.newUpdater(FCQueue.class, CombiningNode.class, "comb_list_head");
static class QueueFatNode<T> {
T items[];
int items_left;
QueueFatNode<T> next;
}
volatile QueueFatNode<T> queue_head, queue_tail;
@SuppressWarnings("unchecked")
public FCQueue() {
combined_pushed_items = (T[]) new Object[MAX_THREADS];
fc_lock = new AtomicInteger(0);
queue_head = new QueueFatNode<T>();
queue_tail = queue_head;
queue_head.next = null;
queue_head.items_left = 0;
}
final int COMBINING_NODE_TIMEOUT = 10000;
final int COMBINING_NODE_TIMEOUT_CHECK_FREQUENCY = 100;
final int MAX_COMBINING_ROUNDS = 32;
@SuppressWarnings("unchecked")
void doFlatCombining(CombiningNode<T> combiner_thread_node) {
int combining_rounds = 0;
int num_pushed_items = 0;
CombiningNode<T> cur_comb_node = null;
CombiningNode<T> last_combining_node = null;
// advance timestamp and sample volatile variables to local variables
// for reading speed
int local_current_timestamp = ++current_timestamp;
QueueFatNode<T> local_queue_head = queue_head;
boolean check_timestamps = (local_current_timestamp
% COMBINING_NODE_TIMEOUT_CHECK_FREQUENCY == 0);
boolean have_work = false;
while (true) {
if(this.abort) {
return;
}
// initialize for a new round
num_pushed_items = 0;
cur_comb_node = comb_list_head;
last_combining_node = cur_comb_node;
have_work = false;
while (cur_comb_node != null) {
if (!cur_comb_node.is_request_valid) {
// After manipulating is_linked the owner thread can change
// next so we need to save it first
CombiningNode<T> next_node = cur_comb_node.next;
// take the node out if its not the first one
// (we're letting the first one go to avoid CASes)
if ((check_timestamps)
&& (cur_comb_node != comb_list_head)
&& (local_current_timestamp - cur_comb_node.last_request_timestamp > COMBINING_NODE_TIMEOUT)) {
last_combining_node.next = next_node;
cur_comb_node.is_linked = false;
}
cur_comb_node = next_node;
continue;
}
have_work = true;
// update combining node last use timestamp
cur_comb_node.last_request_timestamp = local_current_timestamp;
if (cur_comb_node.is_consumer) {
boolean consumer_satisfied = false;
// check queue first
while ((local_queue_head.next != null) && !consumer_satisfied) {
QueueFatNode<T> head_next = local_queue_head.next;
if (head_next.items_left == 0) {
local_queue_head = head_next;
} else {
head_next.items_left--;
cur_comb_node.item = head_next.items[head_next.items_left];
consumer_satisfied = true;
}
}
// if queue is empty, check current pass
if ((!consumer_satisfied) && (num_pushed_items > 0)) {
num_pushed_items--;
cur_comb_node.item = combined_pushed_items[num_pushed_items];
consumer_satisfied = true;
}
if (!consumer_satisfied) {
// queue empty
cur_comb_node.item = null;
}
} else {
combined_pushed_items[num_pushed_items] = cur_comb_node.item;
num_pushed_items++;
}
// requesting thread is released
cur_comb_node.is_request_valid = false;
// next node
last_combining_node = cur_comb_node;
cur_comb_node = cur_comb_node.next;
}
// pushed items needs to go into the queue
if (num_pushed_items > 0) {
QueueFatNode<T> new_node = new QueueFatNode<T>();
new_node.items_left = num_pushed_items;
new_node.items = (T[]) new Object[num_pushed_items];
System.arraycopy(combined_pushed_items, 0, new_node.items, 0, num_pushed_items);
new_node.next = null;
queue_tail.next = new_node;
queue_tail = new_node;
}
combining_rounds++;
if ((!have_work) || (combining_rounds >= MAX_COMBINING_ROUNDS)) {
// no more rounds needed
// Update queue_head.
// This membar flushes write queue so it also finalize changes
// made to the queue nodes
queue_head = local_queue_head;
return;
}
}
}
private void link_in_combining(CombiningNode<T> cn) {
while (true) {
if (abort) {
return;
}
// snapshot the list head
CombiningNode<T> cur_head = comb_list_head;
cn.next = cur_head;
// try to insert the node
if (comb_list_head == cur_head) {
if (comb_list_head_updater.compareAndSet(this, cn.next, cn)) {
return;
}
}
}
}
final int NUM_ROUNDS_IS_LINKED_CHECK_FREQUENCY = 100;
private void wait_until_fulfilled(CombiningNode<T> comb_node) {
int rounds = 0;
while (true) {
if (abort) {
return;
}
// make sure the combining node is in the list
if ((rounds % NUM_ROUNDS_IS_LINKED_CHECK_FREQUENCY == 0) && (!comb_node.is_linked)) {
comb_node.is_linked = true;
link_in_combining(comb_node);
}
if (fc_lock.get() == 0) {
if (fc_lock.compareAndSet(0, 1)) {
// combiner
doFlatCombining(comb_node);
fc_lock.set(0);
}
}
if (!comb_node.is_request_valid) {
return;
}
rounds++;
}
}
public void add(T value) {
CombiningNode<T> comb_node = combining_node.get();
comb_node.is_consumer = false;
comb_node.item = value;
comb_node.is_request_valid = true;
wait_until_fulfilled(comb_node);
}
public T remove() {
CombiningNode<T> comb_node = combining_node.get();
comb_node.is_consumer = true;
comb_node.is_request_valid = true;
wait_until_fulfilled(comb_node);
return comb_node.item;
}
public int size() {
return 0;
}
public String name() {
return this.getClass().toString();
}
/*
* (non-Javadoc)
*
* @see com.sun.electric.tool.util.IStructure#isEmpty()
*/
@Override
public boolean isEmpty() {
return false;
}
}