/*
* ORACLE PROPRIETARY/CONFIDENTIAL. Use is subject to license terms.
*
*
*
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*
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*/
/*
*
*
*
*
*
* 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.concurrent.atomic.
AtomicInteger;
import java.util.concurrent.locks.
Condition;
import java.util.concurrent.locks.
ReentrantLock;
import java.util.
AbstractQueue;
import java.util.
Collection;
import java.util.
Iterator;
import java.util.
NoSuchElementException;
import java.util.
Spliterator;
import java.util.
Spliterators;
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 <em>head</em> of the queue is that element that has been on the
* queue the longest time.
* The <em>tail</em> 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.
*
* <p>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.
*
* <p>This class and its iterator implement all of the
* <em>optional</em> methods of the {@link Collection} and {@link
* Iterator} interfaces.
*
* <p>This class 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 class
LinkedBlockingQueue<E> extends
AbstractQueue<E>
implements
BlockingQueue<E>, 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> {
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<E>
next;
Node(E
x) {
item =
x; }
}
/** The capacity bound, or Integer.MAX_VALUE if none */
private final int
capacity;
/** Current number of elements */
private final
AtomicInteger count = new
AtomicInteger();
/**
* Head of linked list.
* Invariant: head.item == null
*/
transient
Node<E>
head;
/**
* Tail of linked list.
* Invariant: last.next == null
*/
private transient
Node<E>
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<E>
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<E>
h =
head;
Node<E>
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
LinkedBlockingQueue() {
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
LinkedBlockingQueue(int
capacity) {
if (
capacity <= 0) throw new
IllegalArgumentException();
this.
capacity =
capacity;
last =
head = new
Node<E>(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
LinkedBlockingQueue(
Collection<? extends E>
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>(
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.
*
* <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() {
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<E>
node = new
Node<E>(
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>(
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<E>
node = new
Node<E>(
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<E>
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<E>
p,
Node<E>
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<E>
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<E>
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.
*
* <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() {
fullyLock();
try {
int
size =
count.
get();
Object[]
a = new
Object[
size];
int
k = 0;
for (
Node<E>
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.
*
* <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> {@code 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) {
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<E>
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<E>
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<E>
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<? super E>
c) {
return
drainTo(
c,
Integer.
MAX_VALUE);
}
/**
* @throws UnsupportedOperationException {@inheritDoc}
* @throws ClassCastException {@inheritDoc}
* @throws NullPointerException {@inheritDoc}
* @throws IllegalArgumentException {@inheritDoc}
*/
public int
drainTo(
Collection<? super E>
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<E>
h =
head;
int
i = 0;
try {
while (
i <
n) {
Node<E>
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).
*
* <p>The returned iterator is
* <a href="package-summary.html#Weakly"><i>weakly consistent</i></a>.
*
* @return an iterator over the elements in this queue in proper sequence
*/
public
Iterator<E>
iterator() {
return new
Itr();
}
private class
Itr implements
Iterator<E> {
/*
* 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<E>
current;
private
Node<E>
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<E>
nextNode(
Node<E>
p) {
for (;;) {
Node<E>
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<E>
node =
lastRet;
lastRet = null;
for (
Node<E>
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<E> implements
Spliterator<E> {
static final int
MAX_BATCH = 1 << 25; // max batch array size;
final
LinkedBlockingQueue<E>
queue;
Node<E>
current; // current node; null until initialized
int
batch; // batch size for splits
boolean
exhausted; // true when no more nodes
long
est; // size estimate
LBQSpliterator(
LinkedBlockingQueue<E>
queue) {
this.
queue =
queue;
this.
est =
queue.
size();
}
public long
estimateSize() { return
est; }
public
Spliterator<E>
trySplit() {
Node<E>
h;
final
LinkedBlockingQueue<E>
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<E>
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<? super E>
action) {
if (
action == null) throw new
NullPointerException();
final
LinkedBlockingQueue<E>
q = this.
queue;
if (!
exhausted) {
exhausted = true;
Node<E>
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<? super E>
action) {
if (
action == null) throw new
NullPointerException();
final
LinkedBlockingQueue<E>
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.
*
* <p>The returned spliterator is
* <a href="package-summary.html#Weakly"><i>weakly consistent</i></a>.
*
* <p>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 queue
* @since 1.8
*/
public
Spliterator<E>
spliterator() {
return new
LBQSpliterator<E>(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<E>
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<E>(null);
// Read in all elements and place in queue
for (;;) {
@
SuppressWarnings("unchecked")
E
item = (E)
s.
readObject();
if (
item == null)
break;
add(
item);
}
}
}