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

Class LinkedBlockingQueue

java.lang.Object

java.util.AbstractCollection

edu.emory.mathcs.backport.java.util.AbstractCollection

edu.emory.mathcs.backport.java.util.AbstractQueue

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

All Implemented Interfaces:

BlockingQueue, Queue, java.io.Serializable, java.lang.Iterable, java.util.Collection

public class LinkedBlockingQueue
extends AbstractQueue
implements BlockingQueue, java.io.Serializable

An optionally-bounded blocking queue based on linked nodes. This queue orders elements FIFO (first-in-first-out). The head of the queue is that element that has been on the queue the longest time. The tail 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.

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

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

This class is a member of the Java Collections Framework.

Since:

1.5

Author:

Doug Lea

See Also:

Serialized Form

Constructor Summary

Constructors

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

Method Summary

Methods

Modifier and Type	Method and Description
void	clear() Atomically removes all of the elements from this queue.
int	drainTo(java.util.Collection c) Removes all available elements from this queue and adds them to the given collection.
int	drainTo(java.util.Collection c, int maxElements) Removes at most the given number of available elements from this queue and adds them to the given collection.
java.util.Iterator	iterator() Returns an iterator over the elements in this queue in proper sequence.
boolean	offer(java.lang.Object 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 true upon success and false if this queue is full.
boolean	offer(java.lang.Object e, long timeout, TimeUnit unit) Inserts the specified element at the tail of this queue, waiting if necessary up to the specified wait time for space to become available.
java.lang.Object	peek() Retrieves, but does not remove, the head of this queue, or returns null if this queue is empty.
java.lang.Object	poll() Retrieves and removes the head of this queue, or returns null if this queue is empty.
java.lang.Object	poll(long timeout, TimeUnit unit) Retrieves and removes the head of this queue, waiting up to the specified wait time if necessary for an element to become available.
void	put(java.lang.Object e) Inserts the specified element at the tail of this queue, waiting if necessary for space to become available.
int	remainingCapacity() Returns the number of additional elements that this queue can ideally (in the absence of memory or resource constraints) accept without blocking.
boolean	remove(java.lang.Object o) Removes a single instance of the specified element from this queue, if it is present.
int	size() Returns the number of elements in this queue.
java.lang.Object	take() Retrieves and removes the head of this queue, waiting if necessary until an element becomes available.
java.lang.Object[]	toArray() Returns an array containing all of the elements in this queue, in proper sequence.
java.lang.Object[]	toArray(java.lang.Object[] a) 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.
java.lang.String	toString()

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

add, addAll, element, remove

Methods inherited from class java.util.AbstractCollection

contains, containsAll, isEmpty, removeAll, retainAll

Methods inherited from class java.lang.Object

clone, equals, finalize, getClass, hashCode, notify, notifyAll, wait, wait, wait

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

add, contains

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

element, remove

Methods inherited from interface java.util.Collection

addAll, containsAll, equals, hashCode, isEmpty, removeAll, retainAll

Constructor Detail

LinkedBlockingQueue

public LinkedBlockingQueue()

Creates a LinkedBlockingQueue with a capacity of Integer.MAX_VALUE.

LinkedBlockingQueue

public LinkedBlockingQueue(int capacity)

Creates a LinkedBlockingQueue with the given (fixed) capacity.

Parameters:

capacity - the capacity of this queue

Throws:

java.lang.IllegalArgumentException - if capacity is not greater than zero

LinkedBlockingQueue

public LinkedBlockingQueue(java.util.Collection c)

Creates a LinkedBlockingQueue 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

Throws:

java.lang.NullPointerException - if the specified collection or any of its elements are null

Method Detail

size

public int size()

Returns the number of elements in this queue.

Specified by:

size in interface java.util.Collection

Specified by:

size in class java.util.AbstractCollection

Returns:

the number of elements in this queue

remainingCapacity

public int remainingCapacity()

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 size of this queue.

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

Returns:

the remaining capacity

put

public void put(java.lang.Object e)
         throws java.lang.InterruptedException

Inserts the specified element at the tail of this queue, waiting if necessary for space to become available.

Specified by:

put in interface BlockingQueue

Parameters:

e - the element to add

Throws:

java.lang.InterruptedException - if interrupted while waiting

java.lang.NullPointerException - if the specified element is null

offer

public boolean offer(java.lang.Object e,
            long timeout,
            TimeUnit unit)
              throws java.lang.InterruptedException

Inserts the specified element at the tail of this queue, waiting if necessary up to the specified wait time for space to become available.

Specified by:

offer in interface BlockingQueue

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.

Throws:

java.lang.InterruptedException - if interrupted while waiting

java.lang.NullPointerException - if the specified element is null

offer

public boolean offer(java.lang.Object 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 true upon success and false if this queue is full. When using a capacity-restricted queue, this method is generally preferable to method add, which can fail to insert an element only by throwing an exception.

Specified by:

offer in interface BlockingQueue

Specified by:

offer in interface Queue

Parameters:

e - the element to add

Returns:

true if the element was added to this queue, else false

Throws:

java.lang.NullPointerException - if the specified element is null

take

public java.lang.Object take()
                      throws java.lang.InterruptedException

Description copied from interface: BlockingQueue

Retrieves and removes the head of this queue, waiting if necessary until an element becomes available.

Specified by:

take in interface BlockingQueue

Returns:

the head of this queue

Throws:

java.lang.InterruptedException - if interrupted while waiting

poll

public java.lang.Object poll(long timeout,
                    TimeUnit unit)
                      throws java.lang.InterruptedException

Description copied from interface: BlockingQueue

Retrieves and removes the head of this queue, waiting up to the specified wait time if necessary for an element to become available.

Specified by:

poll in interface BlockingQueue

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 queue, or null if the specified waiting time elapses before an element is available

Throws:

java.lang.InterruptedException - if interrupted while waiting

poll

public java.lang.Object poll()

Description copied from interface: Queue

Retrieves and removes the head of this queue, or returns null if this queue is empty.

Specified by:

poll in interface Queue

Returns:

the head of this queue, or null if this queue is empty

peek

public java.lang.Object peek()

Description copied from interface: Queue

Retrieves, but does not remove, the head of this queue, or returns null if this queue is empty.

Specified by:

peek in interface Queue

Returns:

the head of this queue, or null if this queue is empty

remove

public boolean remove(java.lang.Object o)

Removes a single instance of the specified element from this queue, if it is present. More formally, removes an element e such that o.equals(e), if this queue contains one or more such elements. Returns true if this queue contained the specified element (or equivalently, if this queue changed as a result of the call).

Specified by:

remove in interface BlockingQueue

Specified by:

remove in interface java.util.Collection

Overrides:

remove in class java.util.AbstractCollection

Parameters:

o - element to be removed from this queue, if present

Returns:

true if this queue changed as a result of the call

toArray

public java.lang.Object[] toArray()

Returns an array containing all of the elements in this queue, in proper sequence.

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.

This method acts as bridge between array-based and collection-based APIs.

Specified by:

toArray in interface java.util.Collection

Overrides:

toArray in class AbstractCollection

Returns:

an array containing all of the elements in this queue

toArray

public java.lang.Object[] toArray(java.lang.Object[] a)

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.

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 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 queue known to contain only strings. The following code can be used to dump the queue 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().

Specified by:

toArray in interface java.util.Collection

Overrides:

toArray in class AbstractCollection

Parameters:

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

Returns:

an array containing all of the elements in this queue

Throws:

java.lang.ArrayStoreException - if the runtime type of the specified array is not a supertype of the runtime type of every element in this queue

java.lang.NullPointerException - if the specified array is null

toString

public java.lang.String toString()

Overrides:

toString in class java.util.AbstractCollection

clear

public void clear()

Atomically removes all of the elements from this queue. The queue will be empty after this call returns.

Specified by:

clear in interface java.util.Collection

Overrides:

clear in class AbstractQueue

drainTo

public int drainTo(java.util.Collection c)

Description copied from interface: BlockingQueue

Removes all available elements from this queue and adds them to the given collection. This operation may be more efficient than repeatedly polling this queue. A failure encountered while attempting to add elements to collection c may result in elements being in neither, either or both collections when the associated exception is thrown. Attempts to drain a queue to itself result in IllegalArgumentException. Further, the behavior of this operation is undefined if the specified collection is modified while the operation is in progress.

Specified by:

drainTo in interface BlockingQueue

Parameters:

c - the collection to transfer elements into

Returns:

the number of elements transferred

Throws:

java.lang.UnsupportedOperationException - if addition of elements is not supported by the specified collection

java.lang.ClassCastException - if the class of an element of this queue prevents it from being added to the specified collection

java.lang.NullPointerException - if the specified collection is null

java.lang.IllegalArgumentException - if the specified collection is this queue, or some property of an element of this queue prevents it from being added to the specified collection

drainTo

public int drainTo(java.util.Collection c,
          int maxElements)

Description copied from interface: BlockingQueue

Removes at most the given number of available elements from this queue and adds them to the given collection. A failure encountered while attempting to add elements to collection c may result in elements being in neither, either or both collections when the associated exception is thrown. Attempts to drain a queue to itself result in IllegalArgumentException. Further, the behavior of this operation is undefined if the specified collection is modified while the operation is in progress.

Specified by:

drainTo in interface BlockingQueue

Parameters:

c - the collection to transfer elements into

maxElements - the maximum number of elements to transfer

Returns:

the number of elements transferred

Throws:

java.lang.UnsupportedOperationException - if addition of elements is not supported by the specified collection

java.lang.ClassCastException - if the class of an element of this queue prevents it from being added to the specified collection

java.lang.NullPointerException - if the specified collection is null

java.lang.IllegalArgumentException - if the specified collection is this queue, or some property of an element of this queue prevents it from being added to the specified collection

iterator

public java.util.Iterator iterator()

Returns an iterator over the elements in this queue in proper sequence. The returned Iterator is a "weakly consistent" iterator that will never throw 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 java.lang.Iterable

Specified by:

iterator in interface java.util.Collection

Specified by:

iterator in class java.util.AbstractCollection

Returns:

an iterator over the elements in this queue in proper sequence