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

Interface BlockingDeque

All Superinterfaces:
BlockingQueue, Collection, Deque, Queue
Known Implementing Classes:
LinkedBlockingDeque

public interface BlockingDeque
extends BlockingQueue, Deque

A Deque that additionally supports blocking operations that wait for the deque to become non-empty when retrieving an element, and wait for space to become available in the deque when storing an element.

BlockingDeque 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 null or false, 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:

First Element (Head)
Throws exceptionSpecial valueBlocksTimes out
InsertaddFirst(e)offerFirst(e)putFirst(e)offerFirst(e, time, unit)
RemoveremoveFirst()pollFirst()takeFirst()pollFirst(time, unit)
ExaminegetFirst()peekFirst()not applicablenot applicable
Last Element (Tail)
Throws exceptionSpecial valueBlocksTimes out
InsertaddLast(e)offerLast(e)putLast(e)offerLast(e, time, unit)
RemoveremoveLast()pollLast()takeLast()pollLast(time, unit)
ExaminegetLast()peekLast()not applicablenot applicable

Like any BlockingQueue, a BlockingDeque is thread safe, does not permit null elements, and may (or may not) be capacity-constrained.

A BlockingDeque implementation may be used directly as a FIFO BlockingQueue. The methods inherited from the BlockingQueue interface are precisely equivalent to BlockingDeque methods as indicated in the following table:

BlockingQueue Method Equivalent BlockingDeque Method
Insert
add(e)addLast(e)
offer(e)offerLast(e)
put(e)putLast(e)
offer(e, time, unit)offerLast(e, time, unit)
Remove
remove()removeFirst()
poll()pollFirst()
take()takeFirst()
poll(time, unit)pollFirst(time, unit)
Examine
element()getFirst()
peek()peekFirst()

Memory consistency effects: As with other concurrent collections, actions in a thread prior to placing an object into a BlockingDeque happen-before actions subsequent to the access or removal of that element from the BlockingDeque in another thread.

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

Author:
Doug Lea
Since:
1.6

Method Summary

boolean
add(Object e)
Inserts the specified element into the queue represented by this deque (in other words, at the tail of this deque) if it is possible to do so immediately without violating capacity restrictions, returning true upon success and throwing an IllegalStateException if no space is currently available.
void
addFirst(Object e)
Inserts the specified element at the front of this deque if it is possible to do so immediately without violating capacity restrictions, throwing an IllegalStateException if no space is currently available.
void
addLast(Object e)
Inserts the specified element at the end of this deque if it is possible to do so immediately without violating capacity restrictions, throwing an IllegalStateException if no space is currently available.
boolean
contains(Object o)
Returns true if this deque contains the specified element.
Object
element()
Retrieves, but does not remove, the head of the queue represented by this deque (in other words, the first element of this deque).
Iterator
iterator()
Returns an iterator over the elements in this deque in proper sequence.
boolean
offer(Object e)
Inserts the specified element into the queue represented by this deque (in other words, at the tail of this deque) if it is possible to do so immediately without violating capacity restrictions, returning true upon success and false if no space is currently available.
boolean
offer(Object e, long timeout, TimeUnit unit)
Inserts the specified element into the queue represented by this deque (in other words, at the tail of this deque), waiting up to the specified wait time if necessary for space to become available.
boolean
offerFirst(Object e)
Inserts the specified element at the front of this deque if it is possible to do so immediately without violating capacity restrictions, returning true upon success and false if no space is currently available.
boolean
offerFirst(Object e, long timeout, TimeUnit unit)
Inserts the specified element at the front of this deque, waiting up to the specified wait time if necessary for space to become available.
boolean
offerLast(Object e)
Inserts the specified element at the end of this deque if it is possible to do so immediately without violating capacity restrictions, returning true upon success and false if no space is currently available.
boolean
offerLast(Object e, long timeout, TimeUnit unit)
Inserts the specified element at the end of this deque, waiting up to the specified wait time if necessary for space to become available.
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
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)
Retrieves and removes the head of the queue represented by this deque (in other words, the first element of this deque), waiting up to the specified wait time if necessary for an element to become available.
Object
pollFirst(long timeout, TimeUnit unit)
Retrieves and removes the first element of this deque, waiting up to the specified wait time if necessary for an element to become available.
Object
pollLast(long timeout, TimeUnit unit)
Retrieves and removes the last element of this deque, waiting up to the specified wait time if necessary for an element to become available.
void
push(Object e)
Pushes an element onto the stack represented by this deque.
void
put(Object e)
Inserts the specified element into the queue represented by this deque (in other words, at the tail of this deque), waiting if necessary for space to become available.
void
putFirst(Object e)
Inserts the specified element at the front of this deque, waiting if necessary for space to become available.
void
putLast(Object e)
Inserts the specified element at the end of this deque, waiting if necessary for space to become available.
Object
remove()
Retrieves and removes the head of the queue represented by this deque (in other words, the first element of this deque).
boolean
remove(Object o)
Removes the first occurrence of the specified element from this deque.
boolean
removeFirstOccurrence(Object o)
Removes the first occurrence of the specified element from this deque.
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()
Retrieves and removes the head of the queue represented by this deque (in other words, the first element of this deque), waiting if necessary until an element becomes available.
Object
takeFirst()
Retrieves and removes the first element of this deque, waiting if necessary until an element becomes available.
Object
takeLast()
Retrieves and removes the last element of this deque, waiting if necessary until an element becomes available.

Methods inherited from interface edu.emory.mathcs.backport.java.util.concurrent.BlockingQueue

add, contains, drainTo, drainTo, offer, offer, poll, put, remainingCapacity, remove, take

Methods inherited from interface edu.emory.mathcs.backport.java.util.Deque

add, addFirst, addLast, contains, descendingIterator, element, getFirst, getLast, iterator, offer, offerFirst, offerLast, peek, peekFirst, peekLast, poll, pollFirst, pollLast, pop, push, remove, remove, removeFirst, removeFirstOccurrence, removeLast, removeLastOccurrence, size

Methods inherited from interface edu.emory.mathcs.backport.java.util.Queue

add, element, offer, peek, poll, remove

Method Details

add

public boolean add(Object e)
Specified by:
add in interface BlockingQueue
add in interface Queue
add in interface Deque
Parameters:
e - the element to add

addFirst

public void addFirst(Object e)
Specified by:
addFirst in interface Deque
Parameters:
e - the element to add

addLast

public void addLast(Object e)
Specified by:
addLast in interface Deque
Parameters:
e - the element to add

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 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

element

public Object element()
Specified by:
element in interface Queue
element in interface Deque
Returns:
the head of this 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).
Specified by:
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 BlockingQueue
offer in interface Queue
offer in interface Deque
Parameters:
e - the element to add

offer

public boolean offer(Object e,
                     long timeout,
                     TimeUnit unit)
            throws InterruptedException
Inserts the specified element into the queue represented by this deque (in other words, at the tail of this deque), waiting up to the specified wait time if necessary for space to become available.

This method is equivalent to offerLast.

Specified by:
offer in interface BlockingQueue
Parameters:
e - the element to add
Returns:
true if the element was added to this deque, else false

offerFirst

public boolean offerFirst(Object e)
Specified by:
offerFirst in interface Deque
Parameters:
e - the element to add

offerFirst

public boolean offerFirst(Object e,
                          long timeout,
                          TimeUnit unit)
            throws InterruptedException
Inserts the specified element at the front of this deque, waiting up to the specified wait time if necessary for space to become available.
Parameters:
e - the element to add
timeout - how long to wait before giving up, in units of unit
unit - a TimeUnit determining how to interpret the timeout parameter
Returns:
true if successful, or false if the specified waiting time elapses before space is available

offerLast

public boolean offerLast(Object e)
Specified by:
offerLast in interface Deque
Parameters:
e - the element to add

offerLast

public boolean offerLast(Object e,
                         long timeout,
                         TimeUnit unit)
            throws InterruptedException
Inserts the specified element at the end of this deque, waiting up to the specified wait time if necessary for space to become available.
Parameters:
e - the element to add
timeout - how long to wait before giving up, in units of unit
unit - a TimeUnit determining how to interpret the timeout parameter
Returns:
true if successful, or false if the specified waiting time elapses before space is available

peek

public 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.

This method is equivalent to peekFirst.

Specified by:
peek in interface Queue
peek in interface Deque
Returns:
the head of this deque, or null if this deque is empty

poll

public 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.

This method is equivalent to pollFirst().

Specified by:
poll in interface Queue
poll in interface Deque
Returns:
the head of this deque, or null if this deque is empty

poll

public Object poll(long timeout,
                   TimeUnit unit)
            throws InterruptedException
Retrieves and removes the head of the queue represented by this deque (in other words, the first element of this deque), waiting up to the specified wait time if necessary for an element to become available.

This method is equivalent to pollFirst.

Specified by:
poll in interface BlockingQueue
Returns:
the head of this deque, or null if the specified waiting time elapses before an element is available

pollFirst

public Object pollFirst(long timeout,
                        TimeUnit unit)
            throws InterruptedException
Retrieves and removes the first element of this deque, waiting up to the specified wait time if necessary for an element to become available.
Parameters:
timeout - how long to wait before giving up, in units of unit
unit - a TimeUnit determining how to interpret the timeout parameter
Returns:
the head of this deque, or null if the specified waiting time elapses before an element is available

pollLast

public Object pollLast(long timeout,
                       TimeUnit unit)
            throws InterruptedException
Retrieves and removes the last element of this deque, waiting up to the specified wait time if necessary for an element to become available.
Parameters:
timeout - how long to wait before giving up, in units of unit
unit - a TimeUnit determining how to interpret the timeout parameter
Returns:
the tail of this deque, or null if the specified waiting time elapses before an element is available

push

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

put

public void put(Object e)
            throws InterruptedException
Specified by:
put in interface BlockingQueue
Parameters:
e - the element to add

putFirst

public void putFirst(Object e)
            throws InterruptedException
Inserts the specified element at the front of this deque, waiting if necessary for space to become available.
Parameters:
e - the element to add

putLast

public void putLast(Object e)
            throws InterruptedException
Inserts the specified element at the end of this deque, waiting if necessary for space to become available.
Parameters:
e - the element to add

remove

public Object remove()
Retrieves and removes the head of the queue represented by this deque (in other words, the first element of this deque). This method differs from poll only in that it throws an exception if this deque is empty.

This method is equivalent to removeFirst.

Specified by:
remove in interface Queue
remove in interface Deque
Returns:
the head of the queue represented by this deque

remove

public boolean remove(Object o)
Specified by:
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

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.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 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

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.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 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 Deque
Returns:
the number of elements in this deque

take

public Object take()
            throws InterruptedException
Specified by:
take in interface BlockingQueue
Returns:
the head of this deque

takeFirst

public Object takeFirst()
            throws InterruptedException
Retrieves and removes the first element of this deque, waiting if necessary until an element becomes available.
Returns:
the head of this deque

takeLast

public Object takeLast()
            throws InterruptedException
Retrieves and removes the last element of this deque, waiting if necessary until an element becomes available.
Returns:
the tail of this deque