阻塞队列（4）LinkedBlockingDeque源码详解( 二 ) 问题LinkedBlockingDeque是什么？优

prev;/*** One of:* - the real successor Node* - this Node, meaning the successor is head* - null, meaning there is no successor*/Node next;Node(E x) {item = x;}}基础属性/** * Pointer to first node. * Invariant: (first == null /** * Pointer to last node. * Invariant: (first == null /** Number of items in the deque */private transient int count;/** Maximum number of items in the deque */private final int capacity;/** Main lock guarding all access */final ReentrantLock lock = new ReentrantLock();/** Condition for waiting takes */private final Condition notEmpty = lock.newCondition();/** Condition for waiting puts */private final Condition notFull = lock.newCondition();构造器/*** Creates a {@code LinkedBlockingDeque} with a capacity of* {@link Integer#MAX_VALUE}.*/public LinkedBlockingDeque() {this(Integer.MAX_VALUE);}/*** Creates a {@code LinkedBlockingDeque} with the given (fixed) capacity.** @param capacity the capacity of this deque* @throws IllegalArgumentException if {@code capacity} is less than 1*/public LinkedBlockingDeque(int capacity) {if (capacity <= 0) throw new IllegalArgumentException();this.capacity = capacity;}/*** Creates a {@code LinkedBlockingDeque} 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 LinkedBlockingDeque(Collection c) {this(Integer.MAX_VALUE);final ReentrantLock lock = this.lock;lock.lock(); // Never contended, but necessary for visibilitytry {for (E e : c) {if (e == null)throw new NullPointerException();if (!linkLast(new Node(e)))throw new IllegalStateException("Deque full");}} finally {lock.unlock();}}吐槽默认竟然构造成最大整数，真是令人费解？
初始化线程安全保证使用了 ReentrantLock 可互斥锁，来保证线程安全性。
看的出来，如果有元素为空，会直接抛出异常。
添加元素/*** @throws IllegalStateException if this deque is full* @throws NullPointerException {@inheritDoc}*/public void addFirst(E e) {if (!offerFirst(e))throw new IllegalStateException("Deque full");}/*** @throws IllegalStateException if this deque is full* @throws NullPointerException{@inheritDoc}*/public void addLast(E e) {if (!offerLast(e))throw new IllegalStateException("Deque full");}/*** @throws NullPointerException {@inheritDoc}*/public boolean offerFirst(E e) {if (e == null) throw new NullPointerException();Node node = new Node(e);final ReentrantLock lock = this.lock;lock.lock();try {return linkFirst(node);} finally {lock.unlock();}}/*** @throws NullPointerException {@inheritDoc}*/public boolean offerLast(E e) {if (e == null) throw new NullPointerException();Node node = new Node(e);final ReentrantLock lock = this.lock;lock.lock();try {return linkLast(node);} finally {lock.unlock();}}/*** @throws NullPointerException {@inheritDoc}* @throws InterruptedException {@inheritDoc}*/public void putFirst(E e) throws InterruptedException {if (e == null) throw new NullPointerException();Node node = new Node(e);final ReentrantLock lock = this.lock;lock.lock();try {while (!linkFirst(node))notFull.await();} finally {lock.unlock();}}/*** @throws NullPointerException {@inheritDoc}* @throws InterruptedException {@inheritDoc}*/public void putLast(E e) throws InterruptedException {if (e == null) throw new NullPointerException();Node node = new Node(e);final ReentrantLock lock = this.lock;lock.lock();try {while (!linkLast(node))notFull.await();} finally {lock.unlock();}}/*** @throws NullPointerException {@inheritDoc}* @throws InterruptedException {@inheritDoc}*/public boolean offerFirst(E e, long timeout, TimeUnit unit)throws InterruptedException {if (e == null) throw new NullPointerException();Node node = new Node(e);long nanos = unit.toNanos(timeout);// 有没有想过为什么不是直接使用 this.lock.lockInterruptibly?// 在默认的 HotSpot 中，局部变量是存储在局部线程存储区中的，在这里将共享区中的变量复制到局部线程存储区中是为了加速变量的访问速度。final ReentrantLock lock = this.lock;lock.lockInterruptibly();try {while (!linkFirst(node)) {if (nanos <= 0)return false;nanos = notFull.awaitNanos(nanos);}return true;} finally {lock.unlock();}}/*** @throws NullPointerException {@inheritDoc}* @throws InterruptedException {@inheritDoc}*/public boolean offerLast(E e, long timeout, TimeUnit unit)throws InterruptedException {if (e == null) throw new NullPointerException();Node node = new Node(e);long nanos = unit.toNanos(timeout);final ReentrantLock lock = this.lock;lock.lockInterruptibly();try {while (!linkLast(node)) {if (nanos <= 0)return false;nanos = notFull.awaitNanos(nanos);}return true;} finally {lock.unlock();}}linkFirst--tt-darkmode-color: #A3A3A3;">这里使用了 Condition 类来保证队列阻塞。