一、前言
我们为什么需要动态修改线程池的参数？因为线程池参数的设置虽然有参考的方向，但是具体的值是根据业务的发展会动态变化的，我们需要一个能够动态设置线程池的方案。
二、实现思路
2.1 springboot启动的时候把你关注的线程池的属性存起来
目的：因为如果修改线程池参数的文件被删除了，我们要复原线程池原本的参数，当然如果我们认为不需要复原，这一步就是不必要的。
2.2 监听配置中心要修改的线程池的属性变化
大多数的商业项目都会有配置中心来进行动态修改项目的某些值。这里的配置中心开源的有Apollo这样的框架。里面提供了如何获取配置中心key value的方法和监听值变化的方法。
2.3 用VariableLinkedBlockingQueue来替代LinkedBlockingQueue
用了VariableLinkedBlockingQueue可变队列来处理我们常用LinkedBlockingQueue来设置线程池队列，但是这个队列不可变，不能再设置的问题。我们用VariableLinkedBlockingQueue来替代LinkedBlockingQueue，如果你的LinkedBlockingQueue那就没办法改变队列长度了。
2.4 主流程伪代码实现
2.4.1 定义线程池动作枚举类 规范方法执行
import lombok.AllArgsConstructor;
import lombok.Getter;
import lombok.extern.slf4j.Slf4j;
import org.apache.commons.lang3.math.NumberUtils;
import java.util.Arrays;
import java.util.Objects;
import java.util.concurrent.ThreadPoolExecutor;
import java.util.concurrent.TimeUnit;
/**
* 支持修改线程池的参数
*/
@AllArgsConstructor
@Getter
@Slf4j
public enum ThreadSupportChangePropertyEnum {
CORE_POOL_THREAD("corePoolSize"){
@Override
public long getValue(ThreadPoolExecutor threadPoolExecutor) {
return threadPoolExecutor.getCorePoolSize();
}
@Override
public void apply(String latest, ThreadPoolExecutor threadPoolExecutor) {
threadPoolExecutor.setCorePoolSize(NumberUtils.toInt(latest, threadPoolExecutor.getCorePoolSize()));
}
@Override
public void apply(Long value, ThreadPoolExecutor threadPoolExecutor) {
threadPoolExecutor.setCorePoolSize(value.intValue());
}
},
MAXIMUM_POOL_THREAD("maximumPoolSize"){
@Override
public long getValue(ThreadPoolExecutor threadPoolExecutor) {
return threadPoolExecutor.getMaximumPoolSize();
}
@Override
public void apply(String latest, ThreadPoolExecutor threadPoolExecutor) {
threadPoolExecutor.setMaximumPoolSize(NumberUtils.toInt(latest, threadPoolExecutor.getMaximumPoolSize()));
}
@Override
public void apply(Long value, ThreadPoolExecutor threadPoolExecutor) {
threadPoolExecutor.setMaximumPoolSize(value.intValue());
}
},
KEEP_ALIVE_TIME("keepAliveTime"){
@Override
public long getValue(ThreadPoolExecutor threadPoolExecutor) {
return threadPoolExecutor.getKeepAliveTime(TimeUnit.MILLISECONDS);
}
@Override
public void apply(String latest, ThreadPoolExecutor threadPoolExecutor) {
threadPoolExecutor.setKeepAliveTime(NumberUtils.toLong(latest, threadPoolExecutor.getKeepAliveTime(TimeUnit.MILLISECONDS)), TimeUnit.MILLISECONDS);
}
@Override
public void apply(Long value, ThreadPoolExecutor threadPoolExecutor) {
threadPoolExecutor.setKeepAliveTime(value, TimeUnit.MILLISECONDS);
}
},
/**
* 仅支持 VariableLinkedBlockingQueue 类型线程池队列支持修改队列长度
*/
CAPACITY("capacity") {
@Override
public long getValue(ThreadPoolExecutor threadPoolExecutor) {
return threadPoolExecutor.getQueue().size();
}
@Override
public void apply(String value, ThreadPoolExecutor threadPoolExecutor) {
if (!threadPoolExecutor.getQueue().getClass().isAssignableFrom(VariableLinkedBlockingQueue.class)) {
log.warn("不支持修改的线程池队列类型，仅支持 VariableLinkedBlockingQueue.class 类型的线程阻塞队列修改线程池队列大小");
return;
}
((VariableLinkedBlockingQueue)threadPoolExecutor.getQueue()).setCapacity(NumberUtils.toInt(value, threadPoolExecutor.getQueue().size()));
}
@Override
public void apply(Long value, ThreadPoolExecutor threadPoolExecutor) {
if (!threadPoolExecutor.getQueue().getClass().isAssignableFrom(VariableLinkedBlockingQueue.class)) {
log.warn("不支持修改的线程池队列类型，仅支持 VariableLinkedBlockingQueue.class 类型的线程阻塞队列修改线程池队列大小");
return;
}
((VariableLinkedBlockingQueue)threadPoolExecutor.getQueue()).setCapacity(value.intValue());
}
}
;
private String name;
private static ThreadSupportChangePropertyEnum[] ENUMS = ThreadSupportChangePropertyEnum.values();
public static ThreadSupportChangePropertyEnum of(String key) {
return Arrays.stream(ENUMS).filter(property -> Objects.equals(property.getName(), key)).findFirst()
.orElseThrow(() -> new IllegalArgumentException("不支持修改的属性: " + key));
}
public abstract long getValue(ThreadPoolExecutor threadPoolExecutor);
/**
* 处理配置中心String类型的监听值
* @param value
* @param threadPoolExecutor
*/
public abstract void apply(String value, ThreadPoolExecutor threadPoolExecutor);
/**
* 处理配置中心Long类型的监听值
* @param value
* @param threadPoolExecutor
*/
public abstract void apply(Long value, ThreadPoolExecutor threadPoolExecutor);
}
2.4.2 主流程代码
import lombok.extern.slf4j.Slf4j;
import org.apache.commons.collections4.MapUtils;
import org.apache.commons.lang3.StringUtils;
import org.springframework.beans.BeansException;
import org.springframework.context.ApplicationContext;
import org.springframework.context.ApplicationContextAware;
import org.springframework.stereotype.Component;
import java.util.Arrays;
import java.util.HashMap;
import java.util.Map;
import java.util.Objects;
import java.util.concurrent.ExecutorService;
import java.util.concurrent.ThreadPoolExecutor;
@Component
@Slf4j
public class DynamicThreadPoolChangeListener implements ApplicationContextAware {
// key:包了Trace的线程池名字 value:对应的线程池
private Map<String, ExecutorService> traceThreadPoolExecutorMap;
// key:线程池名字+属性 value:初始值
private Map<String, Long> originThreadPoolKeyValueMap = new HashMap<>();
// 只监听配置中心 "threadpool.properties"这个文件的配置
private static final String LISTEN_FILE = "threadpool.properties";
private ConfigService configService;
/**
* PS：这里要换成你们使用的配置中心提供的监听key变化的api
*
* key:配置中心配置的key
* latest:修改后的值
* old:修改前的值
*/
KeyListener keyListener = (key, latest, old) -> {
String beanName = getThreadPoolBeanName(key);
String propertyName = getChangedPropertyName(key);
log.info("config change key:{}, old:{} -> latest:{}, beanName:{}, propertyName:{}", key, old, latest, beanName, propertyName);
if (StringUtils.isBlank(latest)) {
latest = String.valueOf(originThreadPoolKeyValueMap.get(key));
}
// 我们的业务线程池做了一些自定义，所以是用自定义的TraceThreadPoolExecutor.class实现的，大家可以换成ThreadPoolExecutor.class
ExecutorService executorService = traceThreadPoolExecutorMap.get(beanName);
if (Objects.isNull(executorService) || !executorService.getClass().isAssignableFrom(TraceThreadPoolExecutor.class)) {
log.warn("仅支持动态修改 TraceThreadPoolExecutor 类型的线程池参数, key:{}", key);
return;
}
ThreadPoolExecutor executor = (ThreadPoolExecutor)executorService;
ThreadSupportChangePropertyEnum.of(propertyName).apply(latest, executor);
};
@Override
public void setApplicationContext(ApplicationContext applicationContext) throws BeansException {
try {
log.info("config service watch {} init", LISTEN_FILE);
traceThreadPoolExecutorMap = applicationContext.getBeansOfType(ExecutorService.class);
if (MapUtils.isEmpty(traceThreadPoolExecutorMap)) {
return;
}
traceThreadPoolExecutorMap.forEach((beanName, executorService) -> {
if (!executorService.getClass().isAssignableFrom(TraceThreadPoolExecutor.class)) {
return;
}
Arrays.stream(ThreadSupportChangePropertyEnum.values())
.forEach(propertyNameEnum -> {
String property = propertyNameEnum.getName();
Long originValue = null;
Long configCenterValue = null;
try {
ThreadPoolExecutor threadPoolExecutor = (ThreadPoolExecutor)executorService;
String key = beanName + "." + property;
originValue = propertyNameEnum.getValue(threadPoolExecutor);
originThreadPoolKeyValueMap.put(key, originValue);
configCenterValue = com.ctrip.framework.apollo.ConfigService.getConfig(LISTEN_FILE).getLongProperty(key, originValue);
if (Objects.nonNull(configCenterValue)) {
TraceThreadPoolExecutor executor = (TraceThreadPoolExecutor) executorService;
propertyNameEnum.apply(configCenterValue, executor);
}
} catch (Exception e) {
log.error("init TraceThreadPoolExecutor origin values exception, beanName:{}, property:{}, value:{} configValue:{}", beanName, property, originValue, configCenterValue, e);
}
});
});
log.info("origin keyValue:{}", originThreadPoolKeyValueMap);
log.info("trace thread pool:{}",traceThreadPoolExecutorMap);
configService = applicationContext.getBean(ConfigService.class);
// 监听某个文件的全部key
configService.watch(LISTEN_FILE)
.keyListener(ForWatch.KEYS_ALL, keyListener)
.start();
log.info("config service watch {}.", LISTEN_FILE);
} catch (Exception ignore) {
}
}
/**
* 配置中心threadpool.properties里的配置
* 按照xxx.xxx的方式配置 第一个xxx使用线程池的beanName 第二个xxx是线程池的属性
*
* @param key
* @return 第二个xxx是线程池的属性
*/
private String getChangedPropertyName(String key) {
if (StringUtils.isBlank(key)) {
return StringUtils.EMPTY;
}
int index = key.indexOf(".") + 1;
if(index <= 0) {
return StringUtils.EMPTY;
}
return key.substring(index);
}
/**
* 配置中心threadpool.properties里的配置
* 按照xxx.xxx的方式配置 第一个xxx使用线程池的beanName 第二个xxx是线程池的属性
*
* @param key
* @return 这里获取的第一个xxx 线程池的beanName
*/
private String getThreadPoolBeanName(String key) {
if (StringUtils.isBlank(key)) {
return StringUtils.EMPTY;
}
int index = key.indexOf(".");
if(index <= 0) {
return StringUtils.EMPTY;
}
return key.substring(0, index);
}
}
实现VariableLinkedBlockingQueue代码
/*
* Licensed to the Apache Software Foundation (ASF) under one or more
* contributor license agreements. See the NOTICE file distributed with
* this work for additional information regarding copyright ownership.
* The ASF licenses this file to You under the Apache License, Version 2.0
* (the "License"); you may not use this file except in compliance with
* the License. You may obtain a copy of the License at
*
* http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS,
* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
* See the License for the specific language governing permissions and
* limitations under the License.
*/
// Copyright (c) 2007-2020 VMware, Inc. or its affiliates. All rights reserved.
//
// This software, the RabbitMQ Java client library, is triple-licensed under the
// Mozilla Public License 2.0 ("MPL"), the GNU General Public License version 2
// ("GPL") and the Apache License version 2 ("ASL"). For the MPL, please see
// LICENSE-MPL-RabbitMQ. For the GPL, please see LICENSE-GPL2. For the ASL,
// please see LICENSE-APACHE2.
//
// This software is distributed on an "AS IS" basis, WITHOUT WARRANTY OF ANY KIND,
// either express or implied. See the LICENSE file for specific language governing
// rights and limitations of this software.
//
// If you have any questions regarding licensing, please contact us at
// info@rabbitmq.com.
/*
* Modifications Copyright 2015-2020 VMware, Inc. or its affiliates. and licenced as per
* the rest of the RabbitMQ Java client.
*/
/*
* Written by Doug Lea with assistance from members of JCP JSR-166
* Expert Group and released to the public domain, as explained at
* https://creativecommons.org/licenses/publicdomain
*/
package com.allawn.framework.common;
import java.util.*;
import java.util.concurrent.BlockingQueue;
import java.util.concurrent.TimeUnit;
import java.util.concurrent.atomic.AtomicInteger;
import java.util.concurrent.locks.Condition;
import java.util.concurrent.locks.ReentrantLock;
import java.util.function.Consumer;
/**
* A clone of {@linkplain java.util.concurrent.LinkedBlockingQueue}
* with the addition of a {@link #setCapacity(int)} method, allowing us to
* change the capacity of the queue while it is in use.<p>
*
* The documentation for LinkedBlockingQueue follows...<p>
*
* An optionally-bounded {@linkplain BlockingQueue blocking queue} based on
* linked nodes.
* This queue orders elements FIFO (first-in-first-out).
* The <em>head</em> of the queue is that element that has been on the
* queue the longest time.
* The <em>tail</em> of the queue is that element that has been on the
* queue the shortest time. New elements
* are inserted at the tail of the queue, and the queue retrieval
* operations obtain elements at the head of the queue.
* Linked queues typically have higher throughput than array-based queues but
* less predictable performance in most concurrent applications.
*
* <p> The optional capacity bound constructor argument serves as a
* way to prevent excessive queue expansion. The capacity, if unspecified,
* is equal to {@link Integer#MAX_VALUE}. Linked nodes are
* dynamically created upon each insertion unless this would bring the
* queue above capacity.
*
* <p>This class implements all of the <em>optional</em> methods
* of the {@link Collection} and {@link Iterator} interfaces.
*
* <p>This class is a member of the
* <a href="{@docRoot}/../guide/collections/index.html">
* Java Collections Framework</a>.
*
* @since 1.5
* @author Doug Lea
* @param <E> the type of elements held in this collection
*
**/
public class VariableLinkedBlockingQueue<E> extends AbstractQueue<E>
implements BlockingQueue<E>, java.io.Serializable {
private static final long serialVersionUID = -6903933977591709194L;
/*
* A variant of the "two lock queue" algorithm. The putLock gates
* entry to put (and offer), and has an associated condition for
* waiting puts. Similarly for the takeLock. The "count" field
* that they both rely on is maintained as an atomic to avoid
* needing to get both locks in most cases. Also, to minimize need
* for puts to get takeLock and vice-versa, cascading notifies are
* used. When a put notices that it has enabled at least one take,
* it signals taker. That taker in turn signals others if more
* items have been entered since the signal. And symmetrically for
* takes signalling puts. Operations such as remove(Object) and
* iterators acquire both locks.
*
* Visibility between writers and readers is provided as follows:
*
* Whenever an element is enqueued, the putLock is acquired and
* count updated. A subsequent reader guarantees visibility to the
* enqueued Node by either acquiring the putLock (via fullyLock)
* or by acquiring the takeLock, and then reading n = count.get();
* this gives visibility to the first n items.
*
* To implement weakly consistent iterators, it appears we need to
* keep all Nodes GC-reachable from a predecessor dequeued Node.
* That would cause two problems:
* - allow a rogue Iterator to cause unbounded memory retention
* - cause cross-generational linking of old Nodes to new Nodes if
* a Node was tenured while live, which generational GCs have a
* hard time dealing with, causing repeated major collections.
* However, only non-deleted Nodes need to be reachable from
* dequeued Nodes, and reachability does not necessarily have to
* be of the kind understood by the GC. We use the trick of
* linking a Node that has just been dequeued to itself. Such a
* self-link implicitly means to advance to head.next.
*/
/**
* Linked list node class
*/
static class Node<E> {
E item;
/**
* One of:
* - the real successor Node
* - this Node, meaning the successor is head.next
* - null, meaning there is no successor (this is the last node)
*/
Node<E> next;
Node(E x) {
item = x;
}
}
/** The capacity bound, or Integer.MAX_VALUE if none */
private int capacity;
/** Current number of elements */
private final AtomicInteger count = new AtomicInteger();
/**
* Head of linked list.
* Invariant: head.item == null
*/
transient Node<E> head;
/**
* Tail of linked list.
* Invariant: last.next == null
*/
private transient Node<E> last;
/** Lock held by take, poll, etc */
private final ReentrantLock takeLock = new ReentrantLock();
/** Wait queue for waiting takes */
private final Condition notEmpty = takeLock.newCondition();
/** Lock held by put, offer, etc */
private final ReentrantLock putLock = new ReentrantLock();
/** Wait queue for waiting puts */
private final Condition notFull = putLock.newCondition();
/**
* Signals a waiting take. Called only from put/offer (which do not
* otherwise ordinarily lock takeLock.)
*/
private void signalNotEmpty() {
final ReentrantLock takeLock = this.takeLock;
takeLock.lock();
try {
notEmpty.signal();
} finally {
takeLock.unlock();
}
}
/**
* Signals a waiting put. Called only from take/poll.
*/
private void signalNotFull() {
final ReentrantLock putLock = this.putLock;
putLock.lock();
try {
notFull.signal();
} finally {
putLock.unlock();
}
}
/**
* Links node at end of queue.
*
* @param node the node
*/
private void enqueue(Node<E> node) {
// assert putLock.isHeldByCurrentThread();
// assert last.next == null;
last = last.next = node;
}
/**
* Removes a node from head of queue.
*
* @return the node
*/
private E dequeue() {
// assert takeLock.isHeldByCurrentThread();
// assert head.item == null;
Node<E> h = head;
Node<E> first = h.next;
h.next = h; // help GC
head = first;
E x = first.item;
first.item = null;
return x;
}
/**
* Locks to prevent both puts and takes.
*/
void fullyLock() {
putLock.lock();
takeLock.lock();
}
/**
* Unlocks to allow both puts and takes.
*/
void fullyUnlock() {
takeLock.unlock();
putLock.unlock();
}
// /**
// * Tells whether both locks are held by current thread.
// */
// boolean isFullyLocked() {
// return (putLock.isHeldByCurrentThread() &&
// takeLock.isHeldByCurrentThread());
// }
/**
* Creates a {@code VariableLinkedBlockingQueue} with a capacity of
* {@link Integer#MAX_VALUE}.
*/
public VariableLinkedBlockingQueue() {
this(Integer.MAX_VALUE);
}
/**
* Creates a {@code VariableLinkedBlockingQueue} with the given (fixed) capacity.
*
* @param capacity the capacity of this queue
* @throws IllegalArgumentException if {@code capacity} is not greater
* than zero
*/
public VariableLinkedBlockingQueue(int capacity) {
if (capacity <= 0) {
throw new IllegalArgumentException();
}
this.capacity = capacity;
last = head = new Node<E>(null);
}
/**
* Creates a {@code VariableLinkedBlockingQueue} with a capacity of
* {@link Integer#MAX_VALUE}, initially containing the elements of the
* given collection,
* added in traversal order of the collection's iterator.
*
* @param c the collection of elements to initially contain
* @throws NullPointerException if the specified collection or any
* of its elements are null
*/
public VariableLinkedBlockingQueue(Collection<? extends E> c) {
this(Integer.MAX_VALUE);
final ReentrantLock putLock = this.putLock;
putLock.lock(); // Never contended, but necessary for visibility
try {
int n = 0;
for (E e : c) {
if (e == null) {
throw new NullPointerException();
}
if (n == capacity) {
throw new IllegalStateException("Queue full");
}
enqueue(new Node<E>(e));
++n;
}
count.set(n);
} finally {
putLock.unlock();
}
}
// this doc comment is overridden to remove the reference to collections
// greater in size than Integer.MAX_VALUE
/**
* Returns the number of elements in this queue.
*
* @return the number of elements in this queue
*/
@Override
public int size() {
return count.get();
}
/**
* Set a new capacity for the queue. Increasing the capacity can
* cause any waiting {@link #put(Object)} invocations to succeed if the new
* capacity is larger than the queue.
* @param capacity the new capacity for the queue
*/
public void setCapacity(int capacity) {
final int oldCapacity = this.capacity;
this.capacity = capacity;
final int size = count.get();
if (capacity > size && size >= oldCapacity) {
signalNotFull();
}
}
// this doc comment is a modified copy of the inherited doc comment,
// without the reference to unlimited queues.
/**
* Returns the number of additional elements that this queue can ideally
* (in the absence of memory or resource constraints) accept without
* blocking. This is always equal to the initial capacity of this queue
* less the current {@code size} of this queue.
*
* <p>Note that you <em>cannot</em> always tell if an attempt to insert
* an element will succeed by inspecting {@code remainingCapacity}
* because it may be the case that another thread is about to
* insert or remove an element.
*/
@Override
public int remainingCapacity() {
return capacity - count.get();
}
/**
* Inserts the specified element at the tail of this queue, waiting if
* necessary for space to become available.
*
* @throws InterruptedException {@inheritDoc}
* @throws NullPointerException {@inheritDoc}
*/
@Override
public void put(E e) throws InterruptedException {
if (e == null) {
throw new NullPointerException();
}
// Note: convention in all put/take/etc is to preset local var
// holding count negative to indicate failure unless set.
int c = -1;
Node<E> node = new Node<E>(e);
final ReentrantLock putLock = this.putLock;
final AtomicInteger count = this.count;
putLock.lockInterruptibly();
try {
/*
* Note that count is used in wait guard even though it is
* not protected by lock. This works because count can
* only decrease at this point (all other puts are shut
* out by lock), and we (or some other waiting put) are
* signalled if it ever changes from capacity. Similarly
* for all other uses of count in other wait guards.
*/
while (count.get() >= capacity) {
notFull.await();
}
enqueue(node);
c = count.getAndIncrement();
if (c + 1 < capacity) {
notFull.signal();
}
} finally {
putLock.unlock();
}
if (c == 0) {
signalNotEmpty();
}
}
/**
* Inserts the specified element at the tail of this queue, waiting if
* necessary up to the specified wait time for space to become available.
*
* @return {@code true} if successful, or {@code false} if
* the specified waiting time elapses before space is available
* @throws InterruptedException {@inheritDoc}
* @throws NullPointerException {@inheritDoc}
*/
@Override
public boolean offer(E e, long timeout, TimeUnit unit)
throws InterruptedException {
if (e == null) {
throw new NullPointerException();
}
long nanos = unit.toNanos(timeout);
int c = -1;
final ReentrantLock putLock = this.putLock;
final AtomicInteger count = this.count;
putLock.lockInterruptibly();
try {
while (count.get() >= capacity) {
if (nanos <= 0) {
return false;
}
nanos = notFull.awaitNanos(nanos);
}
enqueue(new Node<E>(e));
c = count.getAndIncrement();
if (c + 1 < capacity) {
notFull.signal();
}
} finally {
putLock.unlock();
}
if (c == 0) {
signalNotEmpty();
}
return true;
}
/**
* Inserts the specified element at the tail of this queue if it is
* possible to do so immediately without exceeding the queue's capacity,
* returning {@code true} upon success and {@code false} if this queue
* is full.
* When using a capacity-restricted queue, this method is generally
* preferable to method {@link BlockingQueue#add add}, which can fail to
* insert an element only by throwing an exception.
*
* @throws NullPointerException if the specified element is null
*/
@Override
public boolean offer(E e) {
if (e == null) {
throw new NullPointerException();
}
final AtomicInteger count = this.count;
if (count.get() >= capacity) {
return false;
}
int c = -1;
Node<E> node = new Node<E>(e);
final ReentrantLock putLock = this.putLock;
putLock.lock();
try {
if (count.get() < capacity) {
enqueue(node);
c = count.getAndIncrement();
if (c + 1 < capacity) {
notFull.signal();
}
}
} finally {
putLock.unlock();
}
if (c == 0) {
signalNotEmpty();
}
return c >= 0;
}
@Override
public E take() throws InterruptedException {
E x;
int c = -1;
final AtomicInteger count = this.count;
final ReentrantLock takeLock = this.takeLock;
takeLock.lockInterruptibly();
try {
while (count.get() == 0) {
notEmpty.await();
}
x = dequeue();
c = count.getAndDecrement();
if (c > 1) {
notEmpty.signal();
}
} finally {
takeLock.unlock();
}
if (c >= capacity) {
signalNotFull();
}
return x;
}
@Override
public E poll(long timeout, TimeUnit unit) throws InterruptedException {
E x = null;
int c = -1;
long nanos = unit.toNanos(timeout);
final AtomicInteger count = this.count;
final ReentrantLock takeLock = this.takeLock;
takeLock.lockInterruptibly();
try {
while (count.get() == 0) {
if (nanos <= 0) {
return null;
}
nanos = notEmpty.awaitNanos(nanos);
}
x = dequeue();
c = count.getAndDecrement();
if (c > 1) {
notEmpty.signal();
}
} finally {
takeLock.unlock();
}
if (c >= capacity) {
signalNotFull();
}
return x;
}
@Override
public E poll() {
final AtomicInteger count = this.count;
if (count.get() == 0) {
return null;
}
E x = null;
int c = -1;
final ReentrantLock takeLock = this.takeLock;
takeLock.lock();
try {
if (count.get() > 0) {
x = dequeue();
c = count.getAndDecrement();
if (c > 1) {
notEmpty.signal();
}
}
} finally {
takeLock.unlock();
}
if (c >= capacity) {
signalNotFull();
}
return x;
}
@Override
public E peek() {
if (count.get() == 0) {
return null;
}
final ReentrantLock takeLock = this.takeLock;
takeLock.lock();
try {
Node<E> first = head.next;
if (first == null) {
return null;
} else {
return first.item;
}
} finally {
takeLock.unlock();
}
}
/**
* Unlinks interior Node p with predecessor trail.
*/
void unlink(Node<E> p, Node<E> trail) {
// assert isFullyLocked();
// p.next is not changed, to allow iterators that are
// traversing p to maintain their weak-consistency guarantee.
p.item = null;
trail.next = p.next;
if (last == p) {
last = trail;
}
if (count.getAndDecrement() >= capacity) {
notFull.signal();
}
}
/**
* Removes a single instance of the specified element from this queue,
* if it is present. More formally, removes an element {@code e} such
* that {@code o.equals(e)}, if this queue contains one or more such
* elements.
* Returns {@code true} if this queue contained the specified element
* (or equivalently, if this queue changed as a result of the call).
*
* @param o element to be removed from this queue, if present
* @return {@code true} if this queue changed as a result of the call
*/
@Override
public boolean remove(Object o) {
if (o == null) {
return false;
}
fullyLock();
try {
for (Node<E> trail = head, p = trail.next;
p != null;
trail = p, p = p.next) {
if (o.equals(p.item)) {
unlink(p, trail);
return true;
}
}
return false;
} finally {
fullyUnlock();
}
}
/**
* Returns {@code true} if this queue contains the specified element.
* More formally, returns {@code true} if and only if this queue contains
* at least one element {@code e} such that {@code o.equals(e)}.
*
* @param o object to be checked for containment in this queue
* @return {@code true} if this queue contains the specified element
*/
@Override
public boolean contains(Object o) {
if (o == null) {
return false;
}
fullyLock();
try {
for (Node<E> p = head.next; p != null; p = p.next) {
if (o.equals(p.item)) {
return true;
}
}
return false;
} finally {
fullyUnlock();
}
}
/**
* Returns an array containing all of the elements in this queue, in
* proper sequence.
*
* <p>The returned array will be "safe" in that no references to it are
* maintained by this queue. (In other words, this method must allocate
* a new array). The caller is thus free to modify the returned array.
*
* <p>This method acts as bridge between array-based and collection-based
* APIs.
*
* @return an array containing all of the elements in this queue
*/
@Override
public Object[] toArray() {
fullyLock();
try {
int size = count.get();
Object[] a = new Object[size];
int k = 0;
for (Node<E> p = head.next; p != null; p = p.next) {
a[k++] = p.item;
}
return a;
} finally {
fullyUnlock();
}
}
/**
* Returns an array containing all of the elements in this queue, in
* proper sequence; the runtime type of the returned array is that of
* the specified array. If the queue fits in the specified array, it
* is returned therein. Otherwise, a new array is allocated with the
* runtime type of the specified array and the size of this queue.
*
* <p>If this queue fits in the specified array with room to spare
* (i.e., the array has more elements than this queue), the element in
* the array immediately following the end of the queue is set to
* {@code null}.
*
* <p>Like the {@link #toArray()} method, this method acts as bridge between
* array-based and collection-based APIs. Further, this method allows
* precise control over the runtime type of the output array, and may,
* under certain circumstances, be used to save allocation costs.
*
* <p>Suppose {@code x} is a queue known to contain only strings.
* The following code can be used to dump the queue into a newly
* allocated array of {@code String}:
*
* <pre> {@code String[] y = x.toArray(new String[0]);}</pre>
*
* Note that {@code toArray(new Object[0])} is identical in function to
* {@code toArray()}.
*
* @param a the array into which the elements of the queue are to
* be stored, if it is big enough; otherwise, a new array of the
* same runtime type is allocated for this purpose
* @return an array containing all of the elements in this queue
* @throws ArrayStoreException if the runtime type of the specified array
* is not a supertype of the runtime type of every element in
* this queue
* @throws NullPointerException if the specified array is null
*/
@Override
@SuppressWarnings("unchecked")
public <T> T[] toArray(T[] a) {
fullyLock();
try {
int size = count.get();
if (a.length < size) {
a = (T[]) java.lang.reflect.Array.newInstance(a.getClass().getComponentType(), size);
}
int k = 0;
for (Node<E> p = head.next; p != null; p = p.next) {
a[k++] = (T) p.item;
}
if (a.length > k) {
a[k] = null;
}
return a;
} finally {
fullyUnlock();
}
}
@Override
public String toString() {
fullyLock();
try {
Node<E> p = head.next;
if (p == null) {
return "[]";
}
StringBuilder sb = new StringBuilder();
sb.append('[');
for (;;) {
E e = p.item;
sb.append(e == this ? "(this Collection)" : e);
p = p.next;
if (p == null) {
return sb.append(']').toString();
}
sb.append(',').append(' ');
}
} finally {
fullyUnlock();
}
}
/**
* Atomically removes all of the elements from this queue.
* The queue will be empty after this call returns.
*/
@Override
public void clear() {
fullyLock();
try {
for (Node<E> p, h = head; (p = h.next) != null; h = p) {
h.next = h;
p.item = null;
}
head = last;
// assert head.item == null && head.next == null;
if (count.getAndSet(0) >= capacity) {
notFull.signal();
}
} finally {
fullyUnlock();
}
}
/**
* @throws UnsupportedOperationException {@inheritDoc}
* @throws ClassCastException {@inheritDoc}
* @throws NullPointerException {@inheritDoc}
* @throws IllegalArgumentException {@inheritDoc}
*/
@Override
public int drainTo(Collection<? super E> c) {
return drainTo(c, Integer.MAX_VALUE);
}
/**
* @throws UnsupportedOperationException {@inheritDoc}
* @throws ClassCastException {@inheritDoc}
* @throws NullPointerException {@inheritDoc}
* @throws IllegalArgumentException {@inheritDoc}
*/
@Override
public int drainTo(Collection<? super E> c, int maxElements) {
if (c == null) {
throw new NullPointerException();
}
if (c == this) {
throw new IllegalArgumentException();
}
if (maxElements <= 0) {
return 0;
}
boolean signalNotFull = false;
final ReentrantLock takeLock = this.takeLock;
takeLock.lock();
try {
int n = Math.min(maxElements, count.get());
// count.get provides visibility to first n Nodes
Node<E> h = head;
int i = 0;
try {
while (i < n) {
Node<E> p = h.next;
c.add(p.item);
p.item = null;
h.next = h;
h = p;
++i;
}
return n;
} finally {
// Restore invariants even if c.add() threw
if (i > 0) {
// assert h.item == null;
head = h;
signalNotFull = (count.getAndAdd(-i) >= capacity);
}
}
} finally {
takeLock.unlock();
if (signalNotFull) {
signalNotFull();
}
}
}
/**
* Returns an iterator over the elements in this queue in proper sequence.
* The elements will be returned in order from first (head) to last (tail).
*
* <p>The returned iterator is
* <a href="package-summary.html#Weakly"><i>weakly consistent</i></a>.
*
* @return an iterator over the elements in this queue in proper sequence
*/
@Override
public Iterator<E> iterator() {
return new Itr();
}
private class Itr implements Iterator<E> {
/*
* Basic weakly-consistent iterator. At all times hold the next
* item to hand out so that if hasNext() reports true, we will
* still have it to return even if lost race with a take etc.
*/
private Node<E> current;
private Node<E> lastRet;
private E currentElement;
Itr() {
fullyLock();
try {
current = head.next;
if (current != null) {
currentElement = current.item;
}
} finally {
fullyUnlock();
}
}
@Override
public boolean hasNext() {
return current != null;
}
/**
* Returns the next live successor of p, or null if no such.
*
* Unlike other traversal methods, iterators need to handle both:
* - dequeued nodes (p.next == p)
* - (possibly multiple) interior removed nodes (p.item == null)
*/
private Node<E> nextNode(Node<E> p) {
for (;;) {
Node<E> s = p.next;
if (s == p) {
return head.next;
}
if (s == null || s.item != null) {
return s;
}
p = s;
}
}
@Override
public E next() {
fullyLock();
try {
if (current == null) {
throw new NoSuchElementException();
}
E x = currentElement;
lastRet = current;
current = nextNode(current);
currentElement = (current == null) ? null : current.item;
return x;
} finally {
fullyUnlock();
}
}
@Override
public void remove() {
if (lastRet == null) {
throw new IllegalStateException();
}
fullyLock();
try {
Node<E> node = lastRet;
lastRet = null;
for (Node<E> trail = head, p = trail.next;
p != null;
trail = p, p = p.next) {
if (p == node) {
unlink(p, trail);
break;
}
}
} finally {
fullyUnlock();
}
}
}
/** A customized variant of Spliterators.IteratorSpliterator */
static final class LBQSpliterator<E> implements Spliterator<E> {
static final int MAX_BATCH = 1 << 25; // max batch array size;
final VariableLinkedBlockingQueue<E> queue;
Node<E> current; // current node; null until initialized
int batch; // batch size for splits
boolean exhausted; // true when no more nodes
long est; // size estimate
LBQSpliterator(VariableLinkedBlockingQueue<E> queue) {
this.queue = queue;
this.est = queue.size();
}
@Override
public long estimateSize() {
return est;
}
@Override
public Spliterator<E> trySplit() {
Node<E> h;
final VariableLinkedBlockingQueue<E> q = this.queue;
int b = batch;
int n = (b <= 0) ? 1 : (b >= MAX_BATCH) ? MAX_BATCH : b + 1;
if (!exhausted &&
((h = current) != null || (h = q.head.next) != null) &&
h.next != null) {
Object[] a = new Object[n];
int i = 0;
Node<E> p = current;
q.fullyLock();
try {
if (p != null || (p = q.head.next) != null) {
do {
if ((a[i] = p.item) != null) {
++i;
}
} while ((p = p.next) != null && i < n);
}
} finally {
q.fullyUnlock();
}
if ((current = p) == null) {
est = 0L;
exhausted = true;
} else if ((est -= i) < 0L) {
est = 0L;
}
if (i > 0) {
batch = i;
return Spliterators.spliterator(a, 0, i, Spliterator.ORDERED | Spliterator.NONNULL |
Spliterator.CONCURRENT);
}
}
return null;
}
@Override
public void forEachRemaining(Consumer<? super E> action) {
if (action == null) {
throw new NullPointerException();
}
final VariableLinkedBlockingQueue<E> q = this.queue;
if (!exhausted) {
exhausted = true;
Node<E> p = current;
do {
E e = null;
q.fullyLock();
try {
if (p == null) {
p = q.head.next;
}
while (p != null) {
e = p.item;
p = p.next;
if (e != null) {
break;
}
}
} finally {
q.fullyUnlock();
}
if (e != null) {
action.accept(e);
}
} while (p != null);
}
}
@Override
public boolean tryAdvance(Consumer<? super E> action) {
if (action == null) {
throw new NullPointerException();
}
final VariableLinkedBlockingQueue<E> q = this.queue;
if (!exhausted) {
E e = null;
q.fullyLock();
try {
if (current == null) {
current = q.head.next;
}
while (current != null) {
e = current.item;
current = current.next;
if (e != null) {
break;
}
}
} finally {
q.fullyUnlock();
}
if (current == null) {
exhausted = true;
}
if (e != null) {
action.accept(e);
return true;
}
}
return false;
}
@Override
public int characteristics() {
return Spliterator.ORDERED | Spliterator.NONNULL |
Spliterator.CONCURRENT;
}
}
/**
* Returns a {@link Spliterator} over the elements in this queue.
*
* <p>The returned spliterator is
* <a href="package-summary.html#Weakly"><i>weakly consistent</i></a>.
*
* <p>The {@code Spliterator} reports {@link Spliterator#CONCURRENT},
* {@link Spliterator#ORDERED}, and {@link Spliterator#NONNULL}.
*
* The {@code Spliterator} implements {@code trySplit} to permit limited
* parallelism.
*
* @return a {@code Spliterator} over the elements in this queue
* @since 1.8
*/
@Override
public Spliterator<E> spliterator() {
return new LBQSpliterator<E>(this);
}
/**
* Saves this queue to a stream (that is, serializes it).
*
* @param s the stream
* @throws java.io.IOException if an I/O error occurs
* @serialData The capacity is emitted (int), followed by all of
* its elements (each an {@code Object}) in the proper order,
* followed by a null
*/
private void writeObject(java.io.ObjectOutputStream s)
throws java.io.IOException {
fullyLock();
try {
// Write out any hidden stuff, plus capacity
s.defaultWriteObject();
// Write out all elements in the proper order.
for (Node<E> p = head.next; p != null; p = p.next) {
s.writeObject(p.item);
}
// Use trailing null as sentinel
s.writeObject(null);
} finally {
fullyUnlock();
}
}
/**
* Reconstitutes this queue from a stream (that is, deserializes it).
* @param s the stream
* @throws ClassNotFoundException if the class of a serialized object
* could not be found
* @throws java.io.IOException if an I/O error occurs
*/
private void readObject(java.io.ObjectInputStream s)
throws java.io.IOException, ClassNotFoundException {
// Read in capacity, and any hidden stuff
s.defaultReadObject();
count.set(0);
last = head = new Node<E>(null);
// Read in all elements and place in queue
for (;;) {
@SuppressWarnings("unchecked")
E item = (E) s.readObject();
if (item == null) {
break;
}
add(item);
}
}
}
