edu.emory.mathcs.backport.java.util.concurrent

Class LinkedBlockingDeque

Implemented Interfaces:
BlockingDeque, BlockingQueue, Collection, Deque, Queue, java.io.Serializable

public class LinkedBlockingDeque
extends AbstractQueue
implements BlockingDeque, java.io.Serializable

An optionally-bounded blocking deque based on linked nodes.

The optional capacity bound constructor argument serves as a way to prevent excessive expansion. The capacity, if unspecified, is equal to Integer.MAX_VALUE. Linked nodes are dynamically created upon each insertion unless this would bring the deque above capacity.

Most operations run in constant time (ignoring time spent blocking). Exceptions include remove, removeFirstOccurrence, removeLastOccurrence, contains, iterator.remove(), and the bulk operations, all of which run in linear time.

This class and its iterator implement all of the optional methods of the Collection and Iterator interfaces.

This class is a member of the ../../../../../../../../guide/collections/index.html"> Java Collections Framework.

Author:
Doug Lea
Since:
1.6
See Also:
Serialized Form

Constructor Summary

LinkedBlockingDeque()
Creates a LinkedBlockingDeque with a capacity of Integer.MAX_VALUE.
LinkedBlockingDeque(Collection c)
Creates a LinkedBlockingDeque with a capacity of Integer.MAX_VALUE, initially containing the elements of the given collection, added in traversal order of the collection's iterator.
LinkedBlockingDeque(int capacity)
Creates a LinkedBlockingDeque with the given (fixed) capacity.

Method Summary

boolean
add(Object e)
Inserts the specified element at the end of this deque unless it would violate capacity restrictions.
void
addFirst(Object e)
void
addLast(Object e)
void
clear()
Atomically removes all of the elements from this deque.
boolean
contains(Object o)
Returns true if this deque contains the specified element.
Iterator
descendingIterator()
Returns an iterator over the elements in this deque in reverse sequential order.
int
drainTo(Collection c)
int
drainTo(Collection c, int maxElements)
Object
element()
Retrieves, but does not remove, the head of the queue represented by this deque.
Object
getFirst()
Object
getLast()
Iterator
iterator()
Returns an iterator over the elements in this deque in proper sequence.
boolean
offer(Object e)
boolean
offer(Object e, long timeout, TimeUnit unit)
boolean
offerFirst(Object e)
boolean
offerFirst(Object e, long timeout, TimeUnit unit)
boolean
offerLast(Object e)
boolean
offerLast(Object e, long timeout, TimeUnit unit)
Object
peek()
Retrieves, but does not remove, the head of the queue represented by this deque (in other words, the first element of this deque), or returns null if this deque is empty.
Object
peekFirst()
Retrieves, but does not remove, the first element of this deque, or returns null if this deque is empty.
Object
peekLast()
Retrieves, but does not remove, the last element of this deque, or returns null if this deque is empty.
Object
poll()
Retrieves and removes the head of the queue represented by this deque (in other words, the first element of this deque), or returns null if this deque is empty.
Object
poll(long timeout, TimeUnit unit)
Object
pollFirst()
Retrieves and removes the first element of this deque, or returns null if this deque is empty.
Object
pollFirst(long timeout, TimeUnit unit)
Object
pollLast()
Retrieves and removes the last element of this deque, or returns null if this deque is empty.
Object
pollLast(long timeout, TimeUnit unit)
Object
pop()
void
push(Object e)
void
put(Object e)
void
putFirst(Object e)
void
putLast(Object e)
int
remainingCapacity()
Returns the number of additional elements that this deque can ideally (in the absence of memory or resource constraints) accept without blocking.
Object
remove()
Retrieves and removes the head of the queue represented by this deque.
boolean
remove(Object o)
Removes the first occurrence of the specified element from this deque.
Object
removeFirst()
boolean
removeFirstOccurrence(Object o)
Removes the first occurrence of the specified element from this deque.
Object
removeLast()
boolean
removeLastOccurrence(Object o)
Removes the last occurrence of the specified element from this deque.
int
size()
Returns the number of elements in this deque.
Object
take()
Object
takeFirst()
Object
takeLast()
Object[]
toArray()
Returns an array containing all of the elements in this deque, in proper sequence (from first to last element).
Object[]
toArray(Object[] a)
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.
String
toString()

Methods inherited from class edu.emory.mathcs.backport.java.util.AbstractQueue

add, addAll, clear, element, remove

Methods inherited from class edu.emory.mathcs.backport.java.util.AbstractCollection

toArray, toArray

Constructor Details

LinkedBlockingDeque

public LinkedBlockingDeque()
Creates a LinkedBlockingDeque with a capacity of Integer.MAX_VALUE.

LinkedBlockingDeque

public LinkedBlockingDeque(Collection c)
Creates a LinkedBlockingDeque with a capacity of Integer.MAX_VALUE, initially containing the elements of the given collection, added in traversal order of the collection's iterator.
Parameters:
c - the collection of elements to initially contain

LinkedBlockingDeque

public LinkedBlockingDeque(int capacity)
Creates a LinkedBlockingDeque with the given (fixed) capacity.
Parameters:
capacity - the capacity of this deque

Method Details

add

public boolean add(Object e)
Specified by:
add in interface BlockingDeque
add in interface BlockingQueue
add in interface Queue
add in interface Deque
Overrides:
add in interface AbstractQueue

addFirst

public void addFirst(Object e)
Specified by:
addFirst in interface BlockingDeque
addFirst in interface Deque

addLast

public void addLast(Object e)
Specified by:
addLast in interface BlockingDeque
addLast in interface Deque

clear

public void clear()
Atomically removes all of the elements from this deque. The deque will be empty after this call returns.
Overrides:
clear in interface AbstractQueue

contains

public boolean contains(Object o)
Returns true if this deque contains the specified element. More formally, returns true if and only if this deque contains at least one element e such that o.equals(e).
Specified by:
contains in interface BlockingDeque
contains in interface BlockingQueue
contains in interface Deque
Parameters:
o - object to be checked for containment in this deque
Returns:
true if this deque contains the specified element

descendingIterator

public Iterator descendingIterator()
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 a "weakly consistent" iterator that will never throw java.util.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.
Specified by:
descendingIterator in interface Deque

drainTo

public int drainTo(Collection c)
Specified by:
drainTo in interface BlockingQueue

drainTo

public int drainTo(Collection c,
                   int maxElements)
Specified by:
drainTo in interface BlockingQueue

element

public Object element()
Retrieves, but does not remove, the head of the queue represented by this deque. This method differs from peek only in that it throws an exception if this deque is empty.

This method is equivalent to getFirst.

Specified by:
element in interface BlockingDeque
element in interface Queue
element in interface Deque
Overrides:
element in interface AbstractQueue
Returns:
the head of the queue represented by this deque

getFirst

public Object getFirst()
Specified by:
getFirst in interface Deque

getLast

public Object getLast()
Specified by:
getLast in interface Deque

iterator

public Iterator iterator()
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 a "weakly consistent" iterator that will never throw java.util.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.
Specified by:
iterator in interface BlockingDeque
iterator in interface Deque
Returns:
an iterator over the elements in this deque in proper sequence

offer

public boolean offer(Object e)
Specified by:
offer in interface BlockingDeque
offer in interface BlockingQueue
offer in interface Queue
offer in interface Deque

offer

public boolean offer(Object e,
                     long timeout,
                     TimeUnit unit)
            throws InterruptedException
Specified by:
offer in interface BlockingDeque
offer in interface BlockingQueue

offerFirst

public boolean offerFirst(Object e)
Specified by:
offerFirst in interface BlockingDeque
offerFirst in interface Deque

offerFirst

public boolean offerFirst(Object e,
                          long timeout,
                          TimeUnit unit)
            throws InterruptedException
Specified by:
offerFirst in interface BlockingDeque

offerLast

public boolean offerLast(Object e)
Specified by:
offerLast in interface BlockingDeque
offerLast in interface Deque

offerLast

public boolean offerLast(Object e,
                         long timeout,
                         TimeUnit unit)
            throws InterruptedException
Specified by:
offerLast in interface BlockingDeque

peek

public Object peek()
Specified by:
peek in interface BlockingDeque
peek in interface Queue
peek in interface Deque
Returns:
the head of the queue represented by this deque, or null if this deque is empty

peekFirst

public Object peekFirst()
Retrieves, but does not remove, the first element of this deque, or returns null if this deque is empty.
Specified by:
peekFirst in interface Deque
Returns:
the head of this deque, or null if this deque is empty

peekLast

public Object peekLast()
Retrieves, but does not remove, the last element of this deque, or returns null if this deque is empty.
Specified by:
peekLast in interface Deque
Returns:
the tail of this deque, or null if this deque is empty

poll

public Object poll()
Specified by:
poll in interface BlockingDeque
poll in interface Queue
poll in interface Deque
Returns:
the first element of this deque, or null if this deque is empty

poll

public Object poll(long timeout,
                   TimeUnit unit)
            throws InterruptedException
Specified by:
poll in interface BlockingDeque
poll in interface BlockingQueue

pollFirst

public Object pollFirst()
Retrieves and removes the first element of this deque, or returns null if this deque is empty.
Specified by:
pollFirst in interface Deque
Returns:
the head of this deque, or null if this deque is empty

pollFirst

public Object pollFirst(long timeout,
                        TimeUnit unit)
            throws InterruptedException
Specified by:
pollFirst in interface BlockingDeque

pollLast

public Object pollLast()
Retrieves and removes the last element of this deque, or returns null if this deque is empty.
Specified by:
pollLast in interface Deque
Returns:
the tail of this deque, or null if this deque is empty

pollLast

public Object pollLast(long timeout,
                       TimeUnit unit)
            throws InterruptedException
Specified by:
pollLast in interface BlockingDeque

pop

public Object pop()
Specified by:
pop in interface Deque

push

public void push(Object e)
Specified by:
push in interface BlockingDeque
push in interface Deque

put

public void put(Object e)
            throws InterruptedException
Specified by:
put in interface BlockingDeque
put in interface BlockingQueue

putFirst

public void putFirst(Object e)
            throws InterruptedException
Specified by:
putFirst in interface BlockingDeque

putLast

public void putLast(Object e)
            throws InterruptedException
Specified by:
putLast in interface BlockingDeque

remainingCapacity

public int remainingCapacity()
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 size of this deque.

Note that you cannot always tell if an attempt to insert an element will succeed by inspecting remainingCapacity because it may be the case that another thread is about to insert or remove an element.

Specified by:
remainingCapacity in interface BlockingQueue

remove

public Object remove()
Specified by:
remove in interface BlockingDeque
remove in interface Queue
remove in interface Deque
Overrides:
remove in interface AbstractQueue
Returns:
the head of the queue represented by this deque

remove

public boolean remove(Object o)
Specified by:
remove in interface BlockingDeque
remove in interface BlockingQueue
remove in interface Deque
Parameters:
o - element to be removed from this deque, if present
Returns:
true if this deque changed as a result of the call

removeFirst

public Object removeFirst()
Specified by:
removeFirst in interface Deque

removeFirstOccurrence

public boolean removeFirstOccurrence(Object o)
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 e such that (o==null ? e==null : o.equals(e)) (if such an element exists). Returns true if this deque contained the specified element (or equivalently, if this deque changed as a result of the call).
Specified by:
removeFirstOccurrence in interface BlockingDeque
removeFirstOccurrence in interface Deque
Parameters:
o - element to be removed from this deque, if present
Returns:
true if an element was removed as a result of this call

removeLast

public Object removeLast()
Specified by:
removeLast in interface Deque

removeLastOccurrence

public boolean removeLastOccurrence(Object o)
Removes the last occurrence of the specified element from this deque. If the deque does not contain the element, it is unchanged. More formally, removes the last element e such that (o==null ? e==null : o.equals(e)) (if such an element exists). Returns true if this deque contained the specified element (or equivalently, if this deque changed as a result of the call).
Specified by:
removeLastOccurrence in interface BlockingDeque
removeLastOccurrence in interface Deque
Parameters:
o - element to be removed from this deque, if present
Returns:
true if an element was removed as a result of this call

size

public int size()
Returns the number of elements in this deque.
Specified by:
size in interface BlockingDeque
size in interface Deque
Returns:
the number of elements in this deque

take

public Object take()
            throws InterruptedException
Specified by:
take in interface BlockingDeque
take in interface BlockingQueue

takeFirst

public Object takeFirst()
            throws InterruptedException
Specified by:
takeFirst in interface BlockingDeque

takeLast

public Object takeLast()
            throws InterruptedException
Specified by:
takeLast in interface BlockingDeque

toArray

public Object[] toArray()
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.

Overrides:
toArray in interface AbstractCollection
Returns:
an array containing all of the elements in this deque

toArray

public Object[] toArray(Object[] a)
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 null.

Like the 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 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 String:

     String[] y = x.toArray(new String[0]);
Note that toArray(new Object[0]) is identical in function to toArray().
Overrides:
toArray in interface AbstractCollection
Parameters:
a - the array into which the elements of the deque are to be stored, if it is big enough; otherwise, a new array of the same runtime type is allocated for this purpose
Returns:
an array containing all of the elements in this deque

toString

public String toString()