Java并发包下BlockingQueue源码解析

废话不多说，源码及其注释直接搞起：

/*
 * 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/
 */

package java.util.concurrent;

import java.util.Collection;
import java.util.Queue;

/**
 * A {@link java.util.Queue} that additionally supports operations
 * that wait for the queue to become non-empty when retrieving an
 * element, and wait for space to become available in the queue when
 * storing an element.
 * 
 * BlockingQueue是这样一种队列：在执行检索操作时，等待队列变为非空的时间内，允许执行一些额外的操作，
 * 当存储一个元素时，等待队列中有空间释放出来。
 * 
 * <p><tt>BlockingQueue</tt> methods come in four forms, with different ways
 * of handling operations that cannot be satisfied immediately, but may be
 * satisfied at some point in the future:
 * one throws an exception, the second returns a special value (either
 * <tt>null</tt> or <tt>false</tt>, depending on the operation), the third
 * blocks the current thread indefinitely until the operation can succeed,
 * and the fourth blocks for only a given maximum time limit before giving
 * up.  These methods are summarized in the following table:
 * BlockingQueue的方法有四种形式：处理操作不会立刻返回，而是在未来一个时间点返回：
 * 1.抛出异常
 * 2.返回特殊值：null或者false
 * 3.无限期阻塞，直到操作执行完成
 * 4.经过一个最大的阻塞时间后放弃执行
 *
 * <p>
 * <table BORDER CELLPADDING=3 CELLSPACING=1>
 *  <tr>
 *    <td></td>
 *    <td ALIGN=CENTER><em>Throws exception</em></td>
 *    <td ALIGN=CENTER><em>Special value</em></td>
 *    <td ALIGN=CENTER><em>Blocks</em></td>
 *    <td ALIGN=CENTER><em>Times out</em></td>
 *  </tr>
 *  <tr>
 *    <td><b>Insert</b></td>
 *    <td>{@link #add add(e)}</td>
 *    <td>{@link #offer offer(e)}</td>
 *    <td>{@link #put put(e)}</td>
 *    <td>{@link #offer(Object, long, TimeUnit) offer(e, time, unit)}</td>
 *  </tr>
 *  <tr>
 *    <td><b>Remove</b></td>
 *    <td>{@link #remove remove()}</td>
 *    <td>{@link #poll poll()}</td>
 *    <td>{@link #take take()}</td>
 *    <td>{@link #poll(long, TimeUnit) poll(time, unit)}</td>
 *  </tr>
 *  <tr>
 *    <td><b>Examine</b></td>
 *    <td>{@link #element element()}</td>
 *    <td>{@link #peek peek()}</td>
 *    <td><em>not applicable</em></td>
 *    <td><em>not applicable</em></td>
 *  </tr>
 * </table>
 *
 * <p>A <tt>BlockingQueue</tt> does not accept <tt>null</tt> elements.
 * Implementations throw <tt>NullPointerException</tt> on attempts
 * to <tt>add</tt>, <tt>put</tt> or <tt>offer</tt> a <tt>null</tt>.  A
 * <tt>null</tt> is used as a sentinel value to indicate failure of
 * <tt>poll</tt> operations.
 *
 * BlockingQueue不接受null元素。add，put，offer方法加入一个null值的时候会抛出NullPointerException。
 * 当poll操作失败的时候，null作为一个标记被返回。
 * 
 * <p>A <tt>BlockingQueue</tt> may be capacity bounded. At any given
 * time it may have a <tt>remainingCapacity</tt> beyond which no
 * additional elements can be <tt>put</tt> without blocking.
 * A <tt>BlockingQueue</tt> without any intrinsic capacity constraints always
 * reports a remaining capacity of <tt>Integer.MAX_VALUE</tt>.
 *
 * BlockingQueue是一个有界队列。在任何给定的时间，它可能有一个剩余的容量，
 * 超过这个容量不会有其他元素无阻塞进入队列。
 *
 * <p> <tt>BlockingQueue</tt> implementations are designed to be used
 * primarily for producer-consumer queues, but additionally support
 * the {@link java.util.Collection} interface.  So, for example, it is
 * possible to remove an arbitrary element from a queue using
 * <tt>remove(x)</tt>. However, such operations are in general
 * <em>not</em> performed very efficiently, and are intended for only
 * occasional use, such as when a queued message is cancelled.
 *
 * BlockingQueue的实现是为了用户生产者-消费者队列。因此可以用remove从队列中删除任意元素。
 * 然而这些操作并不是很高效，并且只能偶尔使用，比如队列的消息被取消的时候使用。
 *
 * <p> <tt>BlockingQueue</tt> implementations are thread-safe.  All
 * queuing methods achieve their effects atomically using internal
 * locks or other forms of concurrency control. However, the
 * <em>bulk</em> Collection operations <tt>addAll</tt>,
 * <tt>containsAll</tt>, <tt>retainAll</tt> and <tt>removeAll</tt> are
 * <em>not</em> necessarily performed atomically unless specified
 * otherwise in an implementation. So it is possible, for example, for
 * <tt>addAll(c)</tt> to fail (throwing an exception) after adding
 * only some of the elements in <tt>c</tt>.
 * 
 * BlockingQueue的实现是线程安全的。队列中的所有的方法都是使用内部锁或者其他并发控制达到原子性。
 * 然而，批量操作addAll，containsAl，retainAll和removeAll不一定是以原子方式执行，除非在实现中另有指定。
 *
 * <p>A <tt>BlockingQueue</tt> does <em>not</em> intrinsically support
 * any kind of "close" or "shutdown" operation to
 * indicate that no more items will be added.  The needs and usage of
 * such features tend to be implementation-dependent. For example, a
 * common tactic is for producers to insert special
 * <em>end-of-stream</em> or <em>poison</em> objects, that are
 * interpreted accordingly when taken by consumers.
 *
 * BlockingQueue本质上不支持close或者shutdown这样的操作表明不能再向队列中加入元素。
 * 这些需求和使用取决于具体的实现。一种常见的策略是生产者插入特殊的流结束或标记，并在消费者采取相应的解释时予以解释。
 * 
 * <p>
 * Usage example, based on a typical producer-consumer scenario.
 * Note that a <tt>BlockingQueue</tt> can safely be used with multiple
 * producers and multiple consumers.
 * <pre>
 * 使用范例，基于一个典型的生产者-消费者场景
 * 注意:BlockingQueue可以被多个生产者和多个消费者安全的使用
 *
 * class Producer implements Runnable {
 *   private final BlockingQueue queue;
 *   Producer(BlockingQueue q) { queue = q; }
 *   public void run() {
 *     try {
 *       while (true) { queue.put(produce()); }
 *     } catch (InterruptedException ex) { ... handle ...}
 *   }
 *   Object produce() { ... }
 * }
 *
 * class Consumer implements Runnable {
 *   private final BlockingQueue queue;
 *   Consumer(BlockingQueue q) { queue = q; }
 *   public void run() {
 *     try {
 *       while (true) { consume(queue.take()); }
 *     } catch (InterruptedException ex) { ... handle ...}
 *   }
 *   void consume(Object x) { ... }
 * }
 *
 * class Setup {
 *   void main() {
 *     BlockingQueue q = new SomeQueueImplementation();
 *     Producer p = new Producer(q);
 *     Consumer c1 = new Consumer(q);
 *     Consumer c2 = new Consumer(q);
 *     new Thread(p).start();
 *     new Thread(c1).start();
 *     new Thread(c2).start();
 *   }
 * }
 * </pre>
 *
 * <p>Memory consistency effects: As with other concurrent
 * collections, actions in a thread prior to placing an object into a
 * {@code BlockingQueue}
 * <a href="package-summary.html#MemoryVisibility"><i>happen-before</i></a>
 * actions subsequent to the access or removal of that element from
 * the {@code BlockingQueue} in another thread.
 *
 * <p>This interface is a member of the
 * <a href="{@docRoot}/../technotes/guides/collections/index.html">
 * Java Collections Framework</a>.
 *
 * @since 1.5
 * @author Doug Lea
 * @param <E> the type of elements held in this collection
 */
public interface BlockingQueue<E> extends Queue<E> {
    /**
     * Inserts the specified element into this queue if it is possible to do
     * so immediately without violating capacity restrictions, returning
     * <tt>true</tt> upon success and throwing an
     * <tt>IllegalStateException</tt> if no space is currently available.
     * When using a capacity-restricted queue, it is generally preferable to
     * use {@link #offer(Object) offer}.
     *
     * 如果可以立即执行而不违反容量限制，则将指定的元素插入此队列中。如果插入成功返回true。如果
     * 空间不足，抛出IllegalStateException。当使用的是限制容量的队列时，最好使用offer方法。
     *
     * @param e the element to add
     * @return <tt>true</tt> (as specified by {@link Collection#add})
     * @throws IllegalStateException if the element cannot be added at this
     *         time due to capacity restrictions
     * @throws ClassCastException if the class of the specified element
     *         prevents it from being added to this queue
     * @throws NullPointerException if the specified element is null
     * @throws IllegalArgumentException if some property of the specified
     *         element prevents it from being added to this queue
     */
    boolean add(E e);

    /**
     * Inserts the specified element into this queue if it is possible to do
     * so immediately without violating capacity restrictions, returning
     * <tt>true</tt> upon success and <tt>false</tt> if no space is currently
     * available.  When using a capacity-restricted queue, this method is
     * generally preferable to {@link #add}, which can fail to insert an
     * element only by throwing an exception.
     * 
     * 如果可以立即执行而不违反容量限制，则将指定的元素插入此队列中。如果插入成功返回true，如果
     * 空间不足，返回false。当使用的是限制容量的队列时，该方法比插入失败时抛出异常的add方法更好。
     *
     * @param e the element to add
     * @return <tt>true</tt> if the element was added to this queue, else
     *         <tt>false</tt>
     * @throws ClassCastException if the class of the specified element
     *         prevents it from being added to this queue
     * @throws NullPointerException if the specified element is null
     * @throws IllegalArgumentException if some property of the specified
     *         element prevents it from being added to this queue
     */
    boolean offer(E e);

    /**
     * Inserts the specified element into this queue, waiting if necessary
     * for space to become available.
     *
     * 向队列插入一个元素，如果空间不足就等待。
     *
     * @param e the element to add
     * @throws InterruptedException if interrupted while waiting
     * @throws ClassCastException if the class of the specified element
     *         prevents it from being added to this queue
     * @throws NullPointerException if the specified element is null
     * @throws IllegalArgumentException if some property of the specified
     *         element prevents it from being added to this queue
     */
    void put(E e) throws InterruptedException;

    /**
     * Inserts the specified element into this queue, waiting up to the
     * specified wait time if necessary for space to become available.
     * 
     * 向队列插入一个元素，如果空间不足就等待指定的时候以得到可用的空间。
     *
     * @param e the element to add
     * @param timeout how long to wait before giving up, in units of
     *        <tt>unit</tt>
     * @param unit a <tt>TimeUnit</tt> determining how to interpret the
     *        <tt>timeout</tt> parameter
     * @return <tt>true</tt> if successful, or <tt>false</tt> if
     *         the specified waiting time elapses before space is available
     * @throws InterruptedException if interrupted while waiting
     * @throws ClassCastException if the class of the specified element
     *         prevents it from being added to this queue
     * @throws NullPointerException if the specified element is null
     * @throws IllegalArgumentException if some property of the specified
     *         element prevents it from being added to this queue
     */
    boolean offer(E e, long timeout, TimeUnit unit)
        throws InterruptedException;

    /**
     * Retrieves and removes the head of this queue, waiting if necessary
     * until an element becomes available.
     * 
     * 检索并删除队列头部元素，如果队列中没有元素就等待。
     *
     * @return the head of this queue
     * @throws InterruptedException if interrupted while waiting
     */
    E take() throws InterruptedException;

    /**
     * Retrieves and removes the head of this queue, waiting up to the
     * specified wait time if necessary for an element to become available.
     *
     * 检索并删除队列头部元素，如果队列中没有元素就等待指定时间。
     *
     * @param timeout how long to wait before giving up, in units of
     *        <tt>unit</tt>
     * @param unit a <tt>TimeUnit</tt> determining how to interpret the
     *        <tt>timeout</tt> parameter
     * @return the head of this queue, or <tt>null</tt> if the
     *         specified waiting time elapses before an element is available
     * @throws InterruptedException if interrupted while waiting
     */
    E poll(long timeout, TimeUnit unit)
        throws InterruptedException;

    /**
     * Returns the number of additional elements that this queue can ideally
     * (in the absence of memory or resource constraints) accept without
     * blocking, or <tt>Integer.MAX_VALUE</tt> if there is no intrinsic
     * limit.
     *
     * 返回这个队列在理想状态下可以非阻塞接收的元素的个数。如果没有明确指定队列容量，那么就返回Integer.MAX_VALUE
     *
     * <p>Note that you <em>cannot</em> always tell if an attempt to insert
     * an element will succeed by inspecting <tt>remainingCapacity</tt>
     * because it may be the case that another thread is about to
     * insert or remove an element.
     *
     * @return the remaining capacity
     */
    int remainingCapacity();

    /**
     * Removes a single instance of the specified element from this queue,
     * if it is present.  More formally, removes an element <tt>e</tt> such
     * that <tt>o.equals(e)</tt>, if this queue contains one or more such
     * elements.
     * Returns <tt>true</tt> if this queue contained the specified element
     * (or equivalently, if this queue changed as a result of the call).
     * 
     * 如果元素存在，从队列中删除这个元素。如果队列中含有o.equals(e)的元素，则删除。
     * 如果队列中含有指定的元素，则返回true
     *
     * @param o element to be removed from this queue, if present
     * @return <tt>true</tt> if this queue changed as a result of the call
     * @throws ClassCastException if the class of the specified element
     *         is incompatible with this queue
     *         (<a href="../Collection.html#optional-restrictions">optional</a>)
     * @throws NullPointerException if the specified element is null
     *         (<a href="../Collection.html#optional-restrictions">optional</a>)
     */
    boolean remove(Object o);

    /**
     * Returns <tt>true</tt> if this queue contains the specified element.
     * More formally, returns <tt>true</tt> if and only if this queue contains
     * at least one element <tt>e</tt> such that <tt>o.equals(e)</tt>.
     *
     * 返回队列是否包含指定元素。更准确的说，如果队列中至少有一个元素，满足o.equals(e)将返回true
     *
     * @param o object to be checked for containment in this queue
     * @return <tt>true</tt> if this queue contains the specified element
     * @throws ClassCastException if the class of the specified element
     *         is incompatible with this queue
     *         (<a href="../Collection.html#optional-restrictions">optional</a>)
     * @throws NullPointerException if the specified element is null
     *         (<a href="../Collection.html#optional-restrictions">optional</a>)
     */
    public boolean contains(Object o);

    /**
     * Removes all available elements from this queue and adds them
     * to the given collection.  This operation may be more
     * efficient than repeatedly polling this queue.  A failure
     * encountered while attempting to add elements to
     * collection <tt>c</tt> may result in elements being in neither,
     * either or both collections when the associated exception is
     * thrown.  Attempts to drain a queue to itself result in
     * <tt>IllegalArgumentException</tt>. Further, the behavior of
     * this operation is undefined if the specified collection is
     * modified while the operation is in progress.
     *
     * 将队列中的所有的元素删除，并把队列中的元素保存到指定的集合中。此方法比重复的从队列中执行poll更高效。
     * 当相关的异常抛出时，可能会导致将元素添加到集合c的过程中该元素不在任何一个集合中。尝试将一个队列中的
     * 元素批量保存到队列本身会抛出IllegalArgumentException。当在执行drainTo的过程中如果指定的集合c被
     * 修改了，那么这种情况产生的结果是未知的。
     *
     * @param c the collection to transfer elements into
     * @return the number of elements transferred
     * @throws UnsupportedOperationException if addition of elements
     *         is not supported by the specified collection
     * @throws ClassCastException if the class of an element of this queue
     *         prevents it from being added to the specified collection
     * @throws NullPointerException if the specified collection is null
     * @throws IllegalArgumentException if the specified collection is this
     *         queue, or some property of an element of this queue prevents
     *         it from being added to the specified collection
     */
    int drainTo(Collection<? super E> c);

    /**
     * Removes at most the given number of available elements from
     * this queue and adds them to the given collection.  A failure
     * encountered while attempting to add elements to
     * collection <tt>c</tt> may result in elements being in neither,
     * either or both collections when the associated exception is
     * thrown.  Attempts to drain a queue to itself result in
     * <tt>IllegalArgumentException</tt>. Further, the behavior of
     * this operation is undefined if the specified collection is
     * modified while the operation is in progress.
     *
     * 将指定数量的元素从队列中删除，并保存到指定的集合中。
     * 当相关的异常抛出时，可能会导致将元素添加到集合c的过程中该元素不在任何一个集合中。
     * 尝试将一个队列中的元素批量保存到队列本身会抛出IllegalArgumentException。
     * 当在执行drainTo的过程中如果指定的集合c被修改了，那么这种情况产生的结果是未知的。
     * 
     * @param c the collection to transfer elements into
     * @param maxElements the maximum number of elements to transfer
     * @return the number of elements transferred
     * @throws UnsupportedOperationException if addition of elements
     *         is not supported by the specified collection
     * @throws ClassCastException if the class of an element of this queue
     *         prevents it from being added to the specified collection
     * @throws NullPointerException if the specified collection is null
     * @throws IllegalArgumentException if the specified collection is this
     *         queue, or some property of an element of this queue prevents
     *         it from being added to the specified collection
     */
    int drainTo(Collection<? super E> c, int maxElements);
}