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

Class LinkedBlockingQueue

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

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 ../../../../../../../../guide/collections/index.html"> Java Collections Framework.

Author:
Doug Lea
Since:
1.5
See Also:
Serialized Form

Constructor Summary

LinkedBlockingQueue()
Creates a LinkedBlockingQueue with a capacity of Integer.MAX_VALUE.
LinkedBlockingQueue(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

void
clear()
Atomically removes all of the elements from this queue.
int
drainTo(Collection c)
int
drainTo(Collection c, int maxElements)
Iterator
iterator()
Returns an iterator over the elements in this queue in proper sequence.
boolean
offer(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(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.
Object
peek()
Retrieves, but does not remove, the head of this queue, or returns null if this queue is empty.
Object
poll()
Retrieves and removes the head of this queue, or returns null if this queue is empty.
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(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(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.
Object
take()
Retrieves and removes the head of this queue, waiting if necessary until an element becomes available.
Object[]
toArray()
Returns an array containing all of the elements in this queue, in proper sequence.
Object[]
toArray(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.
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

LinkedBlockingQueue

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

LinkedBlockingQueue

public LinkedBlockingQueue(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

LinkedBlockingQueue

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

Method Details

clear

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

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

iterator

public 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 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.
Returns:
an iterator over the elements in this queue in proper sequence

offer

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

offer

public boolean offer(Object e,
                     long timeout,
                     TimeUnit unit)
            throws 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
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 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

poll

public Object poll()
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

poll

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

put

public void put(Object e)
            throws 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

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

remove

public boolean remove(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
Parameters:
o - element to be removed from this queue, if present
Returns:
true if this queue changed as a result of the call

size

public int size()
Returns the number of elements in this queue.
Returns:
the number of elements in this queue

take

public Object take()
            throws InterruptedException
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

toArray

public 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.

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

toArray

public Object[] toArray(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().
Overrides:
toArray in interface 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

toString

public String toString()