ArrayBlockingQueue的实现思路简单描述，ArrayBlockingQueue的底对于互斥访问使用的一个锁。细节参考源码take和put方法：
import java.util.concurrent.TimeUnit; import java.util.concurrent.locks.*; import java.util.*; public class ArrayBlockingQueue<E> extends AbstractQueue<E> implements BlockingQueue<E>, java.io.Serializable { /** The queued items */ final Object[] items;//证明了java泛型是语法级别的泛型。 /** items index for next take, poll, peek or remove */ int takeIndex; /** items index for next put, offer, or add */ int putIndex; // 可以使用一个int变量计数原因是：ArrayBlockingQueue的实现只有一把锁，对count访问时候都是在锁的保护机制下实现互斥的。 /** Number of elements in the queue */ int count; /* * Concurrency control uses the classic two-condition algorithm found in any * textbook. */ // 使用一把锁 /** Main lock guarding all access */ final ReentrantLock lock; // 两个Condition对象 /** Condition for waiting takes */ private final Condition notEmpty; /** Condition for waiting puts */ private final Condition notFull; /** * Circularly decrement i. */ final int dec(int i) { return ((i == 0) ? items.length : i) - 1; } @SuppressWarnings("unchecked") static <E> E cast(Object item) { return (E) item; } /** * Returns item at index i. */ final E itemAt(int i) { return this.<E>cast(items[i]); } /** * Throws NullPointerException if argument is null. * * @param v * the element */ private static void checkNotNull(Object v) { if (v == null) throw new NullPointerException(); } /** * Deletes item at position i. Utility for remove and iterator.remove. Call * only when holding lock. */ void removeAt(int i) { final Object[] items = this.items; // if removing front item, just advance if (i == takeIndex) { items[takeIndex] = null; takeIndex = inc(takeIndex); } else { // slide over all others up through putIndex. for (;;) { int nexti = inc(i); if (nexti != putIndex) { items[i] = items[nexti]; i = nexti; } else { items[i] = null; putIndex = i; break; } } } --count; notFull.signal(); } /** * Creates an {@code ArrayBlockingQueue} with the given (fixed) capacity and * default access policy. * * @param capacity * the capacity of this queue * @throws IllegalArgumentException * if {@code capacity < 1} */ public ArrayBlockingQueue(int capacity) { this(capacity, false); } /** * Creates an {@code ArrayBlockingQueue} with the given (fixed) capacity and * the specified access policy. * * @param capacity * the capacity of this queue * @param fair * if {@code true} then queue accesses for threads blocked on * insertion or removal, are processed in FIFO order; if * {@code false} the access order is unspecified. * @throws IllegalArgumentException * if {@code capacity < 1} */ public ArrayBlockingQueue(int capacity, boolean fair) { if (capacity <= 0) throw new IllegalArgumentException(); this.items = new Object[capacity]; lock = new ReentrantLock(fair); notEmpty = lock.newCondition(); notFull = lock.newCondition(); } /** * Creates an {@code ArrayBlockingQueue} with the given (fixed) capacity, * the specified access policy and initially containing the elements of the * given collection, added in traversal order of the collection's iterator. * * @param capacity * the capacity of this queue * @param fair * if {@code true} then queue accesses for threads blocked on * insertion or removal, are processed in FIFO order; if * {@code false} the access order is unspecified. * @param c * the collection of elements to initially contain * @throws IllegalArgumentException * if {@code capacity} is less than {@code c.size()}, or less * than 1. * @throws NullPointerException * if the specified collection or any of its elements are null */ public ArrayBlockingQueue(int capacity, boolean fair, Collection<? extends E> c) { this(capacity, fair); final ReentrantLock lock = this.lock; lock.lock(); // Lock only for visibility, not mutual exclusion try { int i = 0; try { for (E e : c) { checkNotNull(e); items[i++] = e; } } catch (ArrayIndexOutOfBoundsException ex) { throw new IllegalArgumentException(); } count = i; putIndex = (i == capacity) ? 0 : i; } finally { lock.unlock(); } } /** * 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 throwing an {@code IllegalStateException} * if this queue is full. * * @param e * the element to add * @return {@code true} (as specified by {@link Collection#add}) * @throws IllegalStateException * if this queue is full * @throws NullPointerException * if the specified element is null */ public boolean add(E e) { return super.add(e); } /** * 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. This * method is generally preferable to method {@link #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) { checkNotNull(e); final ReentrantLock lock = this.lock; lock.lock(); try { if (count == items.length) return false; else { insert(e); return true; } } finally { lock.unlock(); } } /** * Inserts the specified element at the tail of this queue, waiting up to * the specified wait time for space to become available if the queue is * full. * * @throws InterruptedException * {@inheritDoc} * @throws NullPointerException * {@inheritDoc} */ public boolean offer(E e, long timeout, TimeUnit unit) throws InterruptedException { checkNotNull(e); long nanos = unit.toNanos(timeout); final ReentrantLock lock = this.lock; lock.lockInterruptibly(); try { while (count == items.length) { if (nanos <= 0) return false; nanos = notFull.awaitNanos(nanos); } insert(e); return true; } finally { lock.unlock(); } } public E poll() { final ReentrantLock lock = this.lock; lock.lock(); try { return (count == 0) ? null : extract(); } finally { lock.unlock(); } } public E poll(long timeout, TimeUnit unit) throws InterruptedException { long nanos = unit.toNanos(timeout); final ReentrantLock lock = this.lock; lock.lockInterruptibly(); try { while (count == 0) { if (nanos <= 0) return null; nanos = notEmpty.awaitNanos(nanos); } return extract(); } finally { lock.unlock(); } } public E peek() { final ReentrantLock lock = this.lock; lock.lock(); try { return (count == 0) ? null : itemAt(takeIndex); } finally { lock.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() { final ReentrantLock lock = this.lock; lock.lock(); try { return count; } finally { lock.unlock(); } } // 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. */ public int remainingCapacity() { final ReentrantLock lock = this.lock; lock.lock(); try { return items.length - count; } finally { lock.unlock(); } } /** * 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). * * <p> * Removal of interior elements in circular array based queues is an * intrinsically slow and disruptive operation, so should be undertaken only * in exceptional circumstances, ideally only when the queue is known not to * be accessible by other threads. * * @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; final Object[] items = this.items; final ReentrantLock lock = this.lock; lock.lock(); try { for (int i = takeIndex, k = count; k > 0; i = inc(i), k--) { if (o.equals(items[i])) { removeAt(i); return true; } } return false; } finally { lock.unlock(); } } /** * 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; final Object[] items = this.items; final ReentrantLock lock = this.lock; lock.lock(); try { for (int i = takeIndex, k = count; k > 0; i = inc(i), k--) if (o.equals(items[i])) return true; return false; } finally { lock.unlock(); } } /** * 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 */ public Object[] toArray() { final Object[] items = this.items; final ReentrantLock lock = this.lock; lock.lock(); try { final int count = this.count; Object[] a = new Object[count]; for (int i = takeIndex, k = 0; k < count; i = inc(i), k++) a[k] = items[i]; return a; } finally { lock.unlock(); } } /** * 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> * 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 */ @SuppressWarnings("unchecked") public <T> T[] toArray(T[] a) { final Object[] items = this.items; final ReentrantLock lock = this.lock; lock.lock(); try { final int count = this.count; final int len = a.length; if (len < count) a = (T[]) java.lang.reflect.Array.newInstance(a.getClass().getComponentType(), count); for (int i = takeIndex, k = 0; k < count; i = inc(i), k++) a[k] = (T) items[i]; if (len > count) a[count] = null; return a; } finally { lock.unlock(); } } public String toString() { final ReentrantLock lock = this.lock; lock.lock(); try { int k = count; if (k == 0) return "[]"; StringBuilder sb = new StringBuilder(); sb.append('['); for (int i = takeIndex;; i = inc(i)) { Object e = items[i]; sb.append(e == this ? "(this Collection)" : e); if (--k == 0) return sb.append(']').toString(); sb.append(',').append(' '); } } finally { lock.unlock(); } } /** * Atomically removes all of the elements from this queue. The queue will be * empty after this call returns. */ public void clear() { final Object[] items = this.items; final ReentrantLock lock = this.lock; lock.lock(); try { for (int i = takeIndex, k = count; k > 0; i = inc(i), k--) items[i] = null; count = 0; putIndex = 0; takeIndex = 0; notFull.signalAll(); } finally { lock.unlock(); } } /** * @throws UnsupportedOperationException * {@inheritDoc} * @throws ClassCastException * {@inheritDoc} * @throws NullPointerException * {@inheritDoc} * @throws IllegalArgumentException * {@inheritDoc} */ public int drainTo(Collection<? super E> c) { checkNotNull(c); if (c == this) throw new IllegalArgumentException(); final Object[] items = this.items; final ReentrantLock lock = this.lock; lock.lock(); try { int i = takeIndex; int n = 0; int max = count; while (n < max) { c.add(this.<E>cast(items[i])); items[i] = null; i = inc(i); ++n; } if (n > 0) { count = 0; putIndex = 0; takeIndex = 0; notFull.signalAll(); } return n; } finally { lock.unlock(); } } /** * @throws UnsupportedOperationException * {@inheritDoc} * @throws ClassCastException * {@inheritDoc} * @throws NullPointerException * {@inheritDoc} * @throws IllegalArgumentException * {@inheritDoc} */ public int drainTo(Collection<? super E> c, int maxElements) { checkNotNull(c); if (c == this) throw new IllegalArgumentException(); if (maxElements <= 0) return 0; final Object[] items = this.items; final ReentrantLock lock = this.lock; lock.lock(); try { int i = takeIndex; int n = 0; int max = (maxElements < count) ? maxElements : count; while (n < max) { c.add(this.<E>cast(items[i])); items[i] = null; i = inc(i); ++n; } if (n > 0) { count -= n; takeIndex = i; notFull.signalAll(); } return n; } finally { lock.unlock(); } } /** * 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 {@code Iterator} is a "weakly consistent" iterator that will * never throw {@link java.util.ConcurrentModificationException * ConcurrentModificationException}, and guarantees to traverse elements as * they existed upon construction of the iterator, and may (but is not * guaranteed to) reflect any modifications subsequent to construction. * * @return an iterator over the elements in this queue in proper sequence */ public Iterator<E> iterator() { return new Itr(); } /** * 重点分析方法: * * @return * @throws InterruptedException */ public E take() throws InterruptedException { final ReentrantLock lock = this.lock; lock.lockInterruptibly(); try { //解决伪唤醒 while (count == 0) notEmpty.await();//如果缓冲区为空的话，则阻塞 return extract(); } finally { //释放锁 lock.unlock(); } } /** * Extracts element at current take position, advances, and signals. Call * only when holding lock. */ private E extract() { final Object[] items = this.items; //takeIndexe为消费数据 E x = this.<E>cast(items[takeIndex]); items[takeIndex] = null; // 计算下一个消费数据的位置 takeIndex = inc(takeIndex); --count; //通知生产者生产数据 notFull.signal(); return x; } // Internal helper methods /** * Circularly increment i. */ final int inc(int i) { return (++i == items.length) ? 0 : i; } /** * 重点分析方法: * * Inserts the specified element at the tail of this queue, waiting for * space to become available if the queue is full. * * @throws InterruptedException * {@inheritDoc} * @throws NullPointerException * {@inheritDoc} */ public void put(E e) throws InterruptedException { checkNotNull(e); final ReentrantLock lock = this.lock; lock.lockInterruptibly(); try { //解决伪唤醒 while (count == items.length) notFull.await();//如果容器满了则阻塞此处 insert(e); } finally { // 释放锁 lock.unlock(); } } /** * Inserts element at current put position, advances, and signals. Call only * when holding lock. */ private void insert(E x) { items[putIndex] = x; putIndex = inc(putIndex); ++count; //唤醒消费者进行消费 notEmpty.signal(); } /** * Iterator for ArrayBlockingQueue. To maintain weak consistency with * respect to puts and takes, we (1) read ahead one slot, so as to not * report hasNext true but then not have an element to return -- however we * later recheck this slot to use the most current value; (2) ensure that * each array slot is traversed at most once (by tracking "remaining" * elements); (3) skip over null slots, which can occur if takes race ahead * of iterators. However, for circular array-based queues, we cannot rely on * any well established definition of what it means to be weakly consistent * with respect to interior removes since these may require slot overwrites * in the process of sliding elements to cover gaps. So we settle for * resiliency, operating on established apparent nexts, which may miss some * elements that have moved between calls to next. */ private class Itr implements Iterator<E> { private int remaining; // Number of elements yet to be returned private int nextIndex; // Index of element to be returned by next private E nextItem; // Element to be returned by next call to next private E lastItem; // Element returned by last call to next private int lastRet; // Index of last element returned, or -1 if none Itr() { final ReentrantLock lock = ArrayBlockingQueue.this.lock; lock.lock(); try { lastRet = -1; if ((remaining = count) > 0) nextItem = itemAt(nextIndex = takeIndex); } finally { lock.unlock(); } } public boolean hasNext() { return remaining > 0; } public E next() { final ReentrantLock lock = ArrayBlockingQueue.this.lock; lock.lock(); try { if (remaining <= 0) throw new NoSuchElementException(); lastRet = nextIndex; E x = itemAt(nextIndex); // check for fresher value if (x == null) { x = nextItem; // we are forced to report old value lastItem = null; // but ensure remove fails } else lastItem = x; while (--remaining > 0 && // skip over nulls (nextItem = itemAt(nextIndex = inc(nextIndex))) == null) ; return x; } finally { lock.unlock(); } } public void remove() { final ReentrantLock lock = ArrayBlockingQueue.this.lock; lock.lock(); try { int i = lastRet; if (i == -1) throw new IllegalStateException(); lastRet = -1; E x = lastItem; lastItem = null; // only remove if item still at index if (x != null && x == items[i]) { boolean removingHead = (i == takeIndex); removeAt(i); if (!removingHead) nextIndex = dec(nextIndex); } } finally { lock.unlock(); } } } }