package source.java.util.concurrent;
import java.util.AbstractQueue;
import java.util.Collection;
import java.util.Iterator;
import java.util.NoSuchElementException;
import java.util.Objects;
import java.util.Spliterator;
import java.util.Spliterators;
import java.util.concurrent.BlockingDeque;
import java.util.concurrent.TimeUnit;
import java.util.concurrent.locks.Condition;
import java.util.concurrent.locks.ReentrantLock;
import java.util.function.Consumer;
import java.util.function.Predicate;
import com.sun.deploy.ref.Helpers;
/**
LinkedBlockingDeque 是基于链表实现的，可以选择有界或无界的双端阻塞队列。
*/
public class LinkedBlockingDequeprivate static final long serialVersionUID = -387911632671998426L;
/** 双向链表节点 */
static final class Node/** * One of: * - the real predecessor Node * - this Node, meaning the predecessor is tail * - null, meaning there is no predecessor */ Node<E> prev; /** * One of: * - the real successor Node * - this Node, meaning the successor is head * - null, meaning there is no successor */ Node<E> next; Node(E x) { item = x; }}
/**- 头结点
- Invariant: (first == null && last == null) ||
*/(first.prev == null && first.item != null)
transient Node
- 尾节点
- Invariant: (first == null && last == null) ||
*/(last.next == null && last.item != null)
transient Node
/** 双端队列中的元素总数 */
private transient int count;/** 双端队列的容量 */
private final int capacity;/** 控制访问的锁 */
final ReentrantLock lock = new ReentrantLock();扫描二维码关注公众号，回复： 4398480 查看本文章
/** 队列为空时，用于阻塞执行 take 操作的线程的非空条件 */
private final Condition notEmpty = lock.newCondition();/** 队列已满时，用于阻塞执行 put 操作的线程的非满条件 */
/**
private final Condition notFull = lock.newCondition();- 创建一个容量为 Integer.MAX_VALUE 的双端阻塞队列
*/
public LinkedBlockingDeque() {
this(Integer.MAX_VALUE);
}
- 创建一个容量为 capacity 的双端阻塞队列
*/
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<? extends E> c) {
this(Integer.MAX_VALUE);
addAll(c);
}
private boolean linkFirst(Node
private boolean linkLast(Node
/**- Removes and returns first element, or null if empty.
*/
private E unlinkFirst() {
// assert lock.isHeldByCurrentThread();
final Node
- Removes and returns last element, or null if empty.
*/
private E unlinkLast() {
// assert lock.isHeldByCurrentThread();
final Node
- Unlinks x.
*/
void unlink(Node
// BlockingDeque methods
/**- @throws IllegalStateException if this deque is full
- @throws NullPointerException {@inheritDoc}
*/
@Override
public void addFirst(E e) {
if (!offerFirst(e)) {
throw new IllegalStateException("Deque full");
}
}
- @throws IllegalStateException if this deque is full
- @throws NullPointerException {@inheritDoc}
*/
@Override
public void addLast(E e) {
if (!offerLast(e)) {
throw new IllegalStateException("Deque full");
}
}
- 如果队列已满，则直接返回 false，否则将目标元素 e 添加到队列头部
*/
@Override
public boolean offerFirst(E e) {
if (e == null) {
throw new NullPointerException();
}
final Node
- 如果队列已满，则直接返回 false，否则将目标元素 e 添加到队列尾部
*/
@Override
public boolean offerLast(E e) {
if (e == null) {
throw new NullPointerException();
}
final Node
- 将目标元素 e 添加到队列头部，如果队列已满，则阻塞等待有可用空间后重试
*/
@Override
public void putFirst(E e) throws InterruptedException {
if (e == null) {
throw new NullPointerException();
}
final Node
- 将目标元素 e 添加到队列尾部，如果队列已满，则阻塞等待有可用空间后重试
*/
@Override
public void putLast(E e) throws InterruptedException {
if (e == null) {
throw new NullPointerException();
}
final Node
- 在指定的超时时间内尝试将目标元素 e 添加到队列头部，成功则返回 true
*/
@Override
public boolean offerFirst(E e, long timeout, TimeUnit unit)
throws InterruptedException {
if (e == null) {
throw new NullPointerException();
}
final Node
- 在指定的超时时间内尝试将目标元素 e 添加到队列尾部，成功则返回 true
*/
@Override
public boolean offerLast(E e, long timeout, TimeUnit unit)
throws InterruptedException {
if (e == null) {
throw new NullPointerException();
}
final Node
- @throws NoSuchElementException {@inheritDoc}
*/
@Override
public E removeFirst() {
final E x = pollFirst();
if (x == null) {
throw new NoSuchElementException();
}
return x;
}
- @throws NoSuchElementException {@inheritDoc}
*/
@Override
public E removeLast() {
final E x = pollLast();
if (x == null) {
throw new NoSuchElementException();
}
return x;
}
- 如果队列为空，则立即返回 null，否则移除并返回头部元素
- created by ZXD at 6 Dec 2018 T 21:03:40
- @return
*/
@Override
public E pollFirst() {
final ReentrantLock lock = this.lock;
lock.lock();
try {
return unlinkFirst();
} finally {
lock.unlock();
}
}
- 如果队列为空，则立即返回 null，否则移除并返回尾部元素
- created by ZXD at 6 Dec 2018 T 21:04:43
- @return
*/
@Override
public E pollLast() {
final ReentrantLock lock = this.lock;
lock.lock();
try {
return unlinkLast();
} finally {
lock.unlock();
}
}
- 移除并返回头部节点，如果队列为空，则阻塞等待有可用元素之后重试
- created by ZXD at 6 Dec 2018 T 21:00:25
- @return
- @throws InterruptedException
*/
@Override
public E takeFirst() throws InterruptedException {
final ReentrantLock lock = this.lock;
lock.lock();
try {
E x;
// 尝试移除并返回头部节点
while ( (x = unlinkFirst()) == null) {
// 队列为空，则阻塞等待有可用元素之后重试
notEmpty.await();
}
return x;
} finally {
lock.unlock();
}
}
- 移除并返回尾部节点，如果队列为空，则阻塞等待有可用元素之后重试
- created by ZXD at 6 Dec 2018 T 21:02:04
- @return
- @throws InterruptedException
*/
@Override
public E takeLast() throws InterruptedException {
final ReentrantLock lock = this.lock;
lock.lock();
try {
E x;
// 尝试移除并返回尾部节点
while ( (x = unlinkLast()) == null) {
// 队列为空，则阻塞等待有可用元素之后重试
notEmpty.await();
}
return x;
} finally {
lock.unlock();
}
}
- 在指定的超时时间内尝试移除并返回头部元素，如果已经超时，则返回 null
- created by ZXD at 6 Dec 2018 T 21:05:21
- @param timeout
- @param unit
- @return
- @throws InterruptedException
*/
@Override
public E pollFirst(long timeout, TimeUnit unit)
throws InterruptedException {
long nanos = unit.toNanos(timeout);
final ReentrantLock lock = this.lock;
lock.lockInterruptibly();
try {
E x;
// 尝试移除并返回头部元素
while ( (x = unlinkFirst()) == null) {
// 已经超时则返回 null
if (nanos <= 0L) {
return null;
}
// 当前线程在非空条件上阻塞等待，被唤醒后进行重试
nanos = notEmpty.awaitNanos(nanos);
}
// 移除成功则直接返回头部元素
return x;
} finally {
lock.unlock();
}
}
- created by ZXD at 6 Dec 2018 T 21:08:24
- @param timeout
- @param unit
- @return
- @throws InterruptedException
*/
@Override
public E pollLast(long timeout, TimeUnit unit)
throws InterruptedException {
long nanos = unit.toNanos(timeout);
final ReentrantLock lock = this.lock;
lock.lockInterruptibly();
try {
E x;
// 尝试移除并返回尾部元素
while ( (x = unlinkLast()) == null) {
// 已经超时则返回 null
if (nanos <= 0L) {
return null;
}
// 当前线程在非空条件上阻塞等待，被唤醒后进行重试
nanos = notEmpty.awaitNanos(nanos);
}
// 移除成功则直接返回尾部元素
return x;
} finally {
lock.unlock();
}
}
- @throws NoSuchElementException {@inheritDoc}
*/
@Override
public E getFirst() {
final E x = peekFirst();
if (x == null) {
throw new NoSuchElementException();
}
return x;
}
- @throws NoSuchElementException {@inheritDoc}
*/
@Override
public E getLast() {
final E x = peekLast();
if (x == null) {
throw new NoSuchElementException();
}
return x;
}
@Override
public E peekFirst() {
final ReentrantLock lock = this.lock;
lock.lock();
try {
return first == null ? null : first.item;
} finally {
lock.unlock();
}
}@Override
public E peekLast() {
final ReentrantLock lock = this.lock;
lock.lock();
try {
return last == null ? null : last.item;
} finally {
lock.unlock();
}
}@Override
public boolean removeFirstOccurrence(Object o) {
if (o == null) {
return false;
}
final ReentrantLock lock = this.lock;
lock.lock();
try {
for (Node@Override
public boolean removeLastOccurrence(Object o) {
if (o == null) {
return false;
}
final ReentrantLock lock = this.lock;
lock.lock();
try {
for (Node// BlockingQueue methods
/**- Inserts the specified element at the end of this deque unless it would
- violate capacity restrictions. When using a capacity-restricted deque,
- it is generally preferable to use method {@link #offer(Object) offer}.
This method is equivalent to {@link #addLast}.
- @throws IllegalStateException if this deque is full
- @throws NullPointerException if the specified element is null
*/
@Override
public boolean add(E e) {
addLast(e);
return true;
}
- @throws NullPointerException if the specified element is null
*/
@Override
public boolean offer(E e) {
return offerLast(e);
}
- @throws NullPointerException {@inheritDoc}
- @throws InterruptedException {@inheritDoc}
*/
@Override
public void put(E e) throws InterruptedException {
putLast(e);
}
- @throws NullPointerException {@inheritDoc}
- @throws InterruptedException {@inheritDoc}
*/
@Override
public boolean offer(E e, long timeout, TimeUnit unit)
throws InterruptedException {
return offerLast(e, timeout, unit);
}
- Retrieves and removes the head of the queue represented by this deque.
- This method differs from {@link #poll() poll()} only in that it throws an
- exception if this deque is empty.
This method is equivalent to {@link #removeFirst() removeFirst}.
- @return the head of the queue represented by this deque
- @throws NoSuchElementException if this deque is empty
*/
@Override
public E remove() {
return removeFirst();
}
@Override
public E poll() {
return pollFirst();
}@Override
public E take() throws InterruptedException {
return takeFirst();
}@Override
/**
public E poll(long timeout, TimeUnit unit) throws InterruptedException {
return pollFirst(timeout, unit);
}- Retrieves, but does not remove, the head of the queue represented by
- this deque. This method differs from {@link #peek() peek()} only in that
- it throws an exception if this deque is empty.
This method is equivalent to {@link #getFirst() getFirst}.
- @return the head of the queue represented by this deque
- @throws NoSuchElementException if this deque is empty
*/
@Override
public E element() {
return getFirst();
}
@Override
/**
public E peek() {
return peekFirst();
}- Returns the number of additional elements that this deque can ideally
- (in the absence of memory or resource constraints) accept without
- blocking. This is always equal to the initial capacity of this deque
- less the current {@code size} of this deque.
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.
*/
@Override
public int remainingCapacity() {
final ReentrantLock lock = this.lock;
lock.lock();
try {
return capacity - count;
} finally {
lock.unlock();
}
}
- @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) {
Objects.requireNonNull(c);
if (c == this) {
throw new IllegalArgumentException();
}
if (maxElements <= 0) {
return 0;
}
final ReentrantLock lock = this.lock;
lock.lock();
try {
final int n = Math.min(maxElements, count);
for (int i = 0; i < n; i++) {
c.add(first.item); // In this order, in case add() throws.
unlinkFirst();
}
return n;
} finally {
lock.unlock();
}
}
// Stack methods
/**- @throws IllegalStateException if this deque is full
- @throws NullPointerException {@inheritDoc}
*/
@Override
public void push(E e) {
addFirst(e);
}
- @throws NoSuchElementException {@inheritDoc}
*/
@Override
public E pop() {
return removeFirst();
}
// Collection methods
/**- Removes the first occurrence of the specified element from this deque.
- If the deque does not contain the element, it is unchanged.
- More formally, removes the first element {@code e} such that
- {@code o.equals(e)} (if such an element exists).
- Returns {@code true} if this deque contained the specified element
- (or equivalently, if this deque changed as a result of the call).
This method is equivalent to
- {@link #removeFirstOccurrence(Object) removeFirstOccurrence}.
- @param o element to be removed from this deque, if present
- @return {@code true} if this deque changed as a result of the call
*/
@Override
public boolean remove(Object o) {
return removeFirstOccurrence(o);
}
- Returns the number of elements in this deque.
- @return the number of elements in this deque
*/
@Override
public int size() {
final ReentrantLock lock = this.lock;
lock.lock();
try {
return count;
} finally {
lock.unlock();
}
}
- Returns {@code true} if this deque contains the specified element.
- More formally, returns {@code true} if and only if this deque contains
- at least one element {@code e} such that {@code o.equals(e)}.
- @param o object to be checked for containment in this deque
- @return {@code true} if this deque contains the specified element
*/
@Override
public boolean contains(Object o) {
if (o == null) {
return false;
}
final ReentrantLock lock = this.lock;
lock.lock();
try {
for (Node
- Appends all of the elements in the specified collection to the end of
- this deque, in the order that they are returned by the specified
- collection's iterator. Attempts to {@code addAll} of a deque to
- itself result in {@code IllegalArgumentException}.
- @param c the elements to be inserted into this deque
- @return {@code true} if this deque changed as a result of the call
- @throws NullPointerException if the specified collection or any
of its elements are null- @throws IllegalArgumentException if the collection is this deque
- @throws IllegalStateException if this deque is full
@see #add(Object)
*/
@Override
public boolean addAll(Collection<? extends E> c) {
if (c == this) {
// As historically specified in AbstractQueue#addAll
throw new IllegalArgumentException();
}// Copy c into a private chain of Nodes
Node// Atomically append the chain at the end
final ReentrantLock lock = this.lock;
lock.lock();
try {
if (count + n <= capacity) {
beg.prev = last;
if (first == null) {
first = beg;
} else {
last.next = beg;
}
last = end;
count += n;
notEmpty.signalAll();
return true;
}
} finally {
lock.unlock();
}
// Fall back to historic non-atomic implementation, failing
// with IllegalStateException when the capacity is exceeded.
return super.addAll(c);
}
- Returns an array containing all of the elements in this deque, in
- proper sequence (from first to last element).
The returned array will be "safe" in that no references to it are
- maintained by this deque. (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 deque
*/
@Override
@SuppressWarnings("unchecked")
public Object[] toArray() {
final ReentrantLock lock = this.lock;
lock.lock();
try {
final Object[] a = new Object[count];
int k = 0;
for (Node
- Returns an array containing all of the elements in this deque, in
- proper sequence; the runtime type of the returned array is that of
- the specified array. If the deque 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 deque.
If this deque fits in the specified array with room to spare
- (i.e., the array has more elements than this deque), the element in
- the array immediately following the end of the deque 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 deque known to contain only strings.
- The following code can be used to dump the deque 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 deque are to
be stored, if it is big enough; otherwise, a new array of thesame runtime type is allocated for this purpose- @return an array containing all of the elements in this deque
- @throws ArrayStoreException if the runtime type of the specified array
is not a supertype of the runtime type of every element inthis deque@throws NullPointerException if the specified array is null
*/
@Override
@SuppressWarnings("unchecked")
publicint k = 0; for (Node<E> p = first; p != null; p = p.next) { a[k++] = (T)p.item; } if (a.length > k) { a[k] = null; } return a;} finally {
lock.unlock();
}
}
@Override
/**
public String toString() {
return Helpers.collectionToString(this);
}- Atomically removes all of the elements from this deque.
- The deque will be empty after this call returns.
*/
@Override
public void clear() {
final ReentrantLock lock = this.lock;
lock.lock();
try {
for (Node
- Used for any element traversal that is not entirely under lock.
- Such traversals must handle both:
-
- dequeued nodes (p.next == p)
-
- (possibly multiple) interior removed nodes (p.item == null)
*/
Node
- (possibly multiple) interior removed nodes (p.item == null)
- Returns an iterator over the elements in this deque 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 deque in proper sequence
*/
@Override
public Iterator
- Returns an iterator over the elements in this deque in reverse
- sequential order. The elements will be returned in order from
- last (tail) to first (head).
The returned iterator is
- weakly consistent.
- @return an iterator over the elements in this deque in reverse order
*/
@Override
public Iterator
- Base class for LinkedBlockingDeque iterators.
*/
private abstract class AbstractItr implements Iterator
/** Forward iterator */
private class Itr extends AbstractItr {
Itr() {} // prevent access constructor creation
@Override
Node/** Descending iterator */
/**
private class DescendingItr extends AbstractItr {
DescendingItr() {} // prevent access constructor creation
@Override
Node- A customized variant of Spliterators.IteratorSpliterator.
Keep this class in sync with (very similar) LBQSpliterator.
*/
private final class LBDSpliterator implements SpliteratorLBDSpliterator() {}
@Override
public long estimateSize() { return est; }@Override
public Spliterator@Override
public boolean tryAdvance(Consumer<? super E> action) {
Objects.requireNonNull(action);
if (!exhausted) {
E e = null;
final ReentrantLock lock = LinkedBlockingDeque.this.lock;
lock.lock();
try {
Node@Override
public void forEachRemaining(Consumer<? super E> action) {
Objects.requireNonNull(action);
if (!exhausted) {
exhausted = true;
final Node@Override
public int characteristics() {
return Spliterator.ORDERED |
Spliterator.NONNULL |
Spliterator.CONCURRENT;
}
}
- Returns a {@link Spliterator} over the elements in this deque.
The returned spliterator is
- weakly consistent.
The {@code Spliterator} reports {@link Spliterator#CONCURRENT},
- {@link Spliterator#ORDERED}, and {@link Spliterator#NONNULL}.
- @implNote
- The {@code Spliterator} implements {@code trySplit} to permit limited
- parallelism.
- @return a {@code Spliterator} over the elements in this deque
- @since 1.8
*/
@Override
public Spliterator
- @throws NullPointerException {@inheritDoc}
*/
@Override
public void forEach(Consumer<? super E> action) {
Objects.requireNonNull(action);
forEachFrom(action, null);
}
- Runs action on each element found during a traversal starting at p.
- If p is null, traversal starts at head.
*/
void forEachFrom(Consumer<? super E> action, Node
- @throws NullPointerException {@inheritDoc}
*/
@Override
public boolean removeIf(Predicate<? super E> filter) {
Objects.requireNonNull(filter);
return bulkRemove(filter);
}
- @throws NullPointerException {@inheritDoc}
*/
@Override
public boolean removeAll(Collection<?> c) {
Objects.requireNonNull(c);
return bulkRemove(e -> c.contains(e));
}
- @throws NullPointerException {@inheritDoc}
*/
@Override
public boolean retainAll(Collection<?> c) {
Objects.requireNonNull(c);
return bulkRemove(e -> !c.contains(e));
}
/** Implementation of bulk remove methods. */
@SuppressWarnings("unchecked")
private boolean bulkRemove(Predicate<? super E> filter) {
boolean removed = false;
Node// 2. Run the filter on the elements while lock is free. for (int i = 0; i < n; i++) { final E e; if ((e = nodes[i].item) != null && filter.test(e)) { deathRow |= 1L << i; } } // 3. Remove any filtered elements while holding the lock. if (deathRow != 0) { lock.lock(); try { for (int i = 0; i < n; i++) { final Node<E> q; if ((deathRow & 1L << i) != 0L && (q = nodes[i]).item != null) { unlink(q); removed = true; } } } finally { lock.unlock(); } } } while (n > 0 && p != null); return removed;}
/**- Saves this deque to a stream (that is, serializes it).
- @param s the stream
- @throws java.io.IOException if an I/O error occurs
- @serialData The capacity (int), followed by elements (each an
- {@code Object}) in the proper order, followed by a null
*/
private void writeObject(java.io.ObjectOutputStream s)
throws java.io.IOException {
final ReentrantLock lock = this.lock;
lock.lock();
try {
// Write out capacity and any hidden stuff
s.defaultWriteObject();
// Write out all elements in the proper order.
for (Node
- Reconstitutes this deque 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 {
s.defaultReadObject();
count = 0;
first = null;
last = null;
// Read in all elements and place in queue
for (;;) {
@SuppressWarnings("unchecked")
final E item = (E)s.readObject();
if (item == null) {
break;
}
add(item);
}
}
void checkInvariants() {
// assert lock.isHeldByCurrentThread();
// Nodes may get self-linked or lose their item, but only
// after being unlinked and becoming unreachable from first.
for (Node
}