线程池的大小如何设置（美团技术给出动态更改线程大小的方案）
线程池大小的设置一直是在开发中比较难的点，网上没有找到一个比较合适的设置的方案。
这个是美团技术整理一份关于网上比较多的一些线程设置方案。
按照网上的方案设置线程池的大小，基本都是对线程池的大小偏高。下面是美团大佬给出的方案。
Java线程池实现原理及其在美团业务中的实践
这篇博客，主要在这个方案下，写一下代码方面的如果改变比较关注的核心线程、最大线程数、队列长度的调整。这里在调整整个线程池大小的时候有两个需要注意点：
1、jdk 的BlockingQueue 的capacity 是final修饰的。
其实ThreadPoolExecutor提供设置最大线程池和核心线程的大小
executor.setMaximumPoolSize(20);
executor.setCorePoolSize(10);
但在队列长度设置的的key发现jdk设置容量的地方，
可以看到阻塞队列的长度是 final修饰的，无法改变其容量大小，因此为了改变容量大小。我们可以自定义阻塞队列，只需要改将阻塞队列改一个名字，并将其去掉final修饰。
2、在ThreadPoolExecutor#getTask的时候，如果当前工作线程大于核心最大线程，不能够获取到runnable任务。
如果当前工作线程大于核心最大线程，不能够获取到runnable任务，因此在设置最大线程数和核心线程的大小的时候，需要先设置最大线程数，再去设置核心线程数。
下面是代码的具体实现：
package com.yin.freemakeradd.utils;
import java.time.LocalDateTime;
import java.time.format.DateTimeFormatter;
import java.util.concurrent.*;
/**
* @author yin
* @Date 2020/4/25 16:51
* @Method
*/
public class DynamicThreadPool {
/**
* 构建一个普通线程池
* @return
*/
private static ThreadPoolExecutor buildThreadPoolExecutor(int corePoolSize,
int maximumPoolSize,
long keepAliveTime,
TimeUnit unit,
DynamicLinkedBlockingQueue workQueue,
String threadName){
return new ThreadPoolExecutor(corePoolSize, maximumPoolSize,
keepAliveTime,unit, workQueue, new ThreadFactory() {
@Override
public Thread newThread(Runnable r) {
Thread thread = new Thread(r);
thread.setName(threadName);
thread.setDaemon(true);
return thread;
}
});
}
public static void main(String[] args) throws InterruptedException {
dynamicThreadPool();
}
private static void dynamicThreadPool() throws InterruptedException {
ThreadPoolExecutor executor = buildThreadPoolExecutor(2, 5,
60, TimeUnit.SECONDS, new DynamicLinkedBlockingQueue<>(10), "dynamicPoolTestThread");
for (int i = 0; i < 15; i++) {
final int j = i;
executor.submit(()->{
printThreadPoolStatus(executor, "创建任务");
try {
TimeUnit.SECONDS.sleep(10+2*j);
} catch (InterruptedException e) {
e.printStackTrace();
}
});
}
sleepSeconds(1);
printThreadPoolStatus(executor, "完成任务创建");
DynamicLinkedBlockingQueue queue =(DynamicLinkedBlockingQueue) executor.getQueue();
queue.setCapacity(20);
executor.setMaximumPoolSize(20);
executor.setCorePoolSize(10);
sleepSeconds(1);
printThreadPoolStatus(executor, "改变设置之后");
Thread.currentThread().join();
}
private static void sleepSeconds(int time){
try {
TimeUnit.SECONDS.sleep(time);
} catch (InterruptedException e) {
e.printStackTrace();
}
}
private static DateTimeFormatter formatter = DateTimeFormatter.ofPattern("yyyy-MM-dd HH:mm:ss SSS");
private static void printThreadPoolStatus(ThreadPoolExecutor executor, String name) {
BlockingQueue queue = executor.getQueue();
System.out.println(formatter.format(LocalDateTime.now())+"::"+name + "::" + Thread.currentThread().getName() + "::" +
"核心线程数 ：" + executor.getCorePoolSize() +
"::最大线程数 ：" + executor.getMaximumPoolSize() +
"::活动线程数 ：" + executor.getActiveCount()+
"::任务完成数"+executor.getCompletedTaskCount()+
"::队列使用 ："+queue.size()+"::队列未使用 ："+queue.remainingCapacity()+"::队列总共大小 ："+(queue.size()+queue.remainingCapacity()));
}
}
自定义队列：
/*
* ORACLE PROPRIETARY/CONFIDENTIAL. Use is subject to license terms.
*
*
*
*
*
*
*
*
*
*
*
*
*
*
*
*
*
*
*
*
*/
/*
*
*
*
*
*
* Written by Doug Lea with assistance from members of JCP JSR-166
* Expert Group and released to the public domain, as explained at
* http://creativecommons.org/publicdomain/zero/1.0/
*/
import java.util.*;
import java.util.concurrent.BlockingQueue;
import java.util.concurrent.LinkedBlockingQueue;
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;
/**
* An optionally-bounded {@linkplain BlockingQueue blocking queue} based on
* linked nodes.
* This queue orders elements FIFO (first-in-first-out).
* The head of the queue is that element that has been on the
* queue the longest time.
* The tail 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.
*
* 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.
*
*
This class and its iterator implement all of the
* optional methods of the {@link Collection} and {@link
* Iterator} interfaces.
*
*
This class is a member of the
*
* Java Collections Framework.
*
* @param the type of elements held in this collection
* @author Doug Lea
* @since 1.5
*/
public class DynamicLinkedBlockingQueue extends AbstractQueue
implements BlockingQueue, 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 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 next;
Node(E x) {
item = x;
}
}
/**
* The capacity bound, or Integer.MAX_VALUE if none
*/
private volatile int capacity;
public int getCapacity() {
return capacity;
}
public void setCapacity(int capacity) {
this.capacity = capacity;
}
/**
* Current number of elements
*/
private final AtomicInteger count = new AtomicInteger();
/**
* Head of linked list.
* Invariant: head.item == null
*/
transient Node head;
/**
* Tail of linked list.
* Invariant: last.next == null
*/
private transient Node 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 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 h = head;
Node 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 LinkedBlockingQueue} with a capacity of
* {@link Integer#MAX_VALUE}.
*/
public DynamicLinkedBlockingQueue() {
this(Integer.MAX_VALUE);
}
/**
* Creates a {@code LinkedBlockingQueue} with the given (fixed) capacity.
*
* @param capacity the capacity of this queue
* @throws IllegalArgumentException if {@code capacity} is not greater
* than zero
*/
public DynamicLinkedBlockingQueue(int capacity) {
if (capacity <= 0) throw new IllegalArgumentException();
this.capacity = capacity;
last = head = new Node(null);
}
/**
* Creates a {@code LinkedBlockingQueue} 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 DynamicLinkedBlockingQueue(Collection 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));
++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
*/
public int size() {
return count.get();
}
// 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.
*
* Note that you cannot 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.
*/
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}
*/
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 node = new Node(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}
*/
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));
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
*/
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 node = new Node(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;
}
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;
}
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;
}
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;
}
public E peek() {
if (count.get() == 0)
return null;
final ReentrantLock takeLock = this.takeLock;
takeLock.lock();
try {
Node 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 p, Node 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
*/
public boolean remove(Object o) {
if (o == null) return false;
fullyLock();
try {
for (Node 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
*/
public boolean contains(Object o) {
if (o == null) return false;
fullyLock();
try {
for (Node 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.
*
* 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.
*
*
This method acts as bridge between array-based and collection-based
* APIs.
*
* @return an array containing all of the elements in this queue
*/
public Object[] toArray() {
fullyLock();
try {
int size = count.get();
Object[] a = new Object[size];
int k = 0;
for (Node 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.
*
* 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}.
*
*
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.
*
*
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}:
*
*
{@code String[] y = x.toArray(new String[0]);}
*
* 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
*/
@SuppressWarnings("unchecked")
public 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 p = head.next; p != null; p = p.next)
a[k++] = (T) p.item;
if (a.length > k)
a[k] = null;
return a;
} finally {
fullyUnlock();
}
}
public String toString() {
fullyLock();
try {
Node 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.
*/
public void clear() {
fullyLock();
try {
for (Node 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}
*/
public int drainTo(Collection c) {
return drainTo(c, Integer.MAX_VALUE);
}
/**
* @throws UnsupportedOperationException {@inheritDoc}
* @throws ClassCastException {@inheritDoc}
* @throws NullPointerException {@inheritDoc}
* @throws IllegalArgumentException {@inheritDoc}
*/
public int drainTo(Collection 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 h = head;
int i = 0;
try {
while (i < n) {
Node 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).
*
* The returned iterator is
* weakly consistent.
*
* @return an iterator over the elements in this queue in proper sequence
*/
public Iterator iterator() {
return new Itr();
}
private class Itr implements Iterator {
/*
* 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 current;
private Node lastRet;
private E currentElement;
Itr() {
fullyLock();
try {
current = head.next;
if (current != null)
currentElement = current.item;
} finally {
fullyUnlock();
}
}
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 nextNode(Node p) {
for (; ; ) {
Node s = p.next;
if (s == p)
return head.next;
if (s == null || s.item != null)
return s;
p = s;
}
}
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();
}
}
public void remove() {
if (lastRet == null)
throw new IllegalStateException();
fullyLock();
try {
Node node = lastRet;
lastRet = null;
for (Node 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 implements Spliterator {
static final int MAX_BATCH = 1 << 25; // max batch array size;
final DynamicLinkedBlockingQueue queue;
Node current; // current node; null until initialized
int batch; // batch size for splits
boolean exhausted; // true when no more nodes
long est; // size estimate
LBQSpliterator(DynamicLinkedBlockingQueue queue) {
this.queue = queue;
this.est = queue.size();
}
public long estimateSize() {
return est;
}
public Spliterator trySplit() {
Node h;
final DynamicLinkedBlockingQueue 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 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;
}
public void forEachRemaining(Consumer action) {
if (action == null) throw new NullPointerException();
final DynamicLinkedBlockingQueue q = this.queue;
if (!exhausted) {
exhausted = true;
Node 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);
}
}
public boolean tryAdvance(Consumer action) {
if (action == null) throw new NullPointerException();
final DynamicLinkedBlockingQueue 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;
}
public int characteristics() {
return Spliterator.ORDERED | Spliterator.NONNULL |
Spliterator.CONCURRENT;
}
}
/**
* Returns a {@link Spliterator} over the elements in this queue.
*
* The returned spliterator is
* weakly consistent.
*
*
The {@code Spliterator} reports {@link Spliterator#CONCURRENT},
* {@link Spliterator#ORDERED}, and {@link Spliterator#NONNULL}.
*
* @return a {@code Spliterator} over the elements in this queue
* @implNote The {@code Spliterator} implements {@code trySplit} to permit limited
* parallelism.
* @since 1.8
*/
public Spliterator spliterator() {
return new LBQSpliterator(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 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(null);
// Read in all elements and place in queue
for (; ; ) {
@SuppressWarnings("unchecked")
E item = (E) s.readObject();
if (item == null)
break;
add(item);
}
}
}
可以看到当改变设置之后：
