edu.emory.mathcs.util.concurrent
Class ArrayBlockingQueue

java.lang.Object
  |
  +--java.util.AbstractCollection
        |
        +--edu.emory.mathcs.util.AbstractQueue
              |
              +--edu.emory.mathcs.util.concurrent.ArrayBlockingQueue
All Implemented Interfaces:
BlockingQueue, java.util.Collection, Queue, java.io.Serializable

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

A bounded blocking queue backed by an array. 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.

This is a classic "bounded buffer", in which a fixed-sized array holds elements inserted by producers and extracted by consumers. Once created, the capacity cannot be increased. Attempts to put an element to a full queue will result in the put operation blocking; attempts to retrieve an element from an empty queue will similarly block.

This class supports an optional fairness policy for ordering waiting producer and consumer threads. By default, this ordering is not guaranteed. However, a queue constructed with fairness set to true grants threads access in FIFO order. Fairness generally decreases throughput but reduces variability and avoids starvation.

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
See Also:
Serialized Form

Constructor Summary
ArrayBlockingQueue(int capacity)
          Creates an ArrayBlockingQueue with the given (fixed) capacity and default access policy.
ArrayBlockingQueue(int capacity, boolean fair)
          Creates an ArrayBlockingQueue with the given (fixed) capacity and the specified access policy.
ArrayBlockingQueue(int capacity, boolean fair, java.util.Collection c)
          Creates an ArrayBlockingQueue with the given (fixed) capacity, the specified access policy and initially containing the elements of the given collection, added in traversal order of the collection's iterator.
 
Method Summary
 void clear()
          Atomically removes all of the elements from this queue.
 boolean contains(java.lang.Object o)
           
 int drainTo(java.util.Collection c)
          Removes all available elements from this queue and adds them into 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 into the given collection.
 java.util.Iterator iterator()
          Returns an iterator over the elements in this queue in proper sequence.
 boolean offer(java.lang.Object o)
          Inserts the specified element at the tail of this queue if possible, returning immediately if this queue is full.
 boolean offer(java.lang.Object o, 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, returning null if this queue is empty.
 java.lang.Object poll()
          Retrieves and removes the head of this queue, or null if this queue is empty.
 java.lang.Object poll(long timeout, TimeUnit unit)
          Retrieves and removes the head of this queue, waiting if necessary up to the specified wait time if no elements are present on this queue.
 void put(java.lang.Object o)
          Adds the specified element to the tail of this queue, waiting if necessary for space to become available.
 int remainingCapacity()
          Returns the number of 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 no elements are present on this queue.
 java.lang.Object[] toArray()
           
 java.lang.Object[] toArray(java.lang.Object[] a)
           
 java.lang.String toString()
           
 
Methods inherited from class edu.emory.mathcs.util.AbstractQueue
add, addAll, element, remove
 
Methods inherited from class java.util.AbstractCollection
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.util.concurrent.BlockingQueue
add
 
Methods inherited from interface edu.emory.mathcs.util.Queue
element, remove
 
Methods inherited from interface java.util.Collection
addAll, containsAll, equals, hashCode, isEmpty, removeAll, retainAll
 

Constructor Detail

ArrayBlockingQueue

public ArrayBlockingQueue(int capacity)
Creates an ArrayBlockingQueue with the given (fixed) capacity and default access policy.

Parameters:
capacity - the capacity of this queue
Throws:
java.lang.IllegalArgumentException - if capacity is less than 1

ArrayBlockingQueue

public ArrayBlockingQueue(int capacity,
                          boolean fair)
Creates an ArrayBlockingQueue with the given (fixed) capacity and the specified access policy.

Parameters:
capacity - the capacity of this queue
fair - if true then queue accesses for threads blocked on insertion or removal, are processed in FIFO order; if false the access order is unspecified.
Throws:
java.lang.IllegalArgumentException - if capacity is less than 1

ArrayBlockingQueue

public ArrayBlockingQueue(int capacity,
                          boolean fair,
                          java.util.Collection c)
Creates an ArrayBlockingQueue with the given (fixed) capacity, the specified access policy and initially containing the elements of the given collection, added in traversal order of the collection's iterator.

Parameters:
capacity - the capacity of this queue
fair - if true then queue accesses for threads blocked on insertion or removal, are processed in FIFO order; if false the access order is unspecified.
c - the collection of elements to initially contain
Throws:
java.lang.IllegalArgumentException - if capacity is less than c.size(), or less than 1.
java.lang.NullPointerException - if c or any element within it is null
Method Detail

offer

public boolean offer(java.lang.Object o)
Inserts the specified element at the tail of this queue if possible, returning immediately if this queue is full.

Specified by:
offer in interface BlockingQueue
Parameters:
o - the element to add.
Returns:
true if it was possible to add the element to this queue, else false
Throws:
java.lang.NullPointerException - if the specified element is null

offer

public boolean offer(java.lang.Object o,
                     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:
o - 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.

poll

public java.lang.Object poll()
Description copied from interface: Queue
Retrieves and removes the head of this queue, or 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 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 if necessary up to the specified wait time if no elements are present on this queue.

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 present.
Throws:
java.lang.InterruptedException - if interrupted while waiting.

remove

public boolean remove(java.lang.Object o)
Removes a single instance of the specified element from this queue, if it is present.

Specified by:
remove in interface java.util.Collection
Overrides:
remove in class java.util.AbstractCollection

peek

public java.lang.Object peek()
Description copied from interface: Queue
Retrieves, but does not remove, the head of this queue, returning 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.

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 no elements are present on this queue.

Specified by:
take in interface BlockingQueue
Returns:
the head of this queue
Throws:
java.lang.InterruptedException - if interrupted while waiting.

put

public void put(java.lang.Object o)
         throws java.lang.InterruptedException
Adds the specified element to the tail of this queue, waiting if necessary for space to become available.

Specified by:
put in interface BlockingQueue
Parameters:
o - the element to add
Throws:
java.lang.InterruptedException - if interrupted while waiting.
java.lang.NullPointerException - if the specified element is null.

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 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 add an element will succeed by inspecting remainingCapacity because it may be the case that a waiting consumer is ready to take an element out of an otherwise full queue.

Specified by:
remainingCapacity in interface BlockingQueue
Returns:
the remaining capacity

contains

public boolean contains(java.lang.Object o)
Specified by:
contains in interface java.util.Collection
Overrides:
contains in class java.util.AbstractCollection

toArray

public java.lang.Object[] toArray()
Specified by:
toArray in interface java.util.Collection
Overrides:
toArray in class java.util.AbstractCollection

toArray

public java.lang.Object[] toArray(java.lang.Object[] a)
Specified by:
toArray in interface java.util.Collection
Overrides:
toArray in class java.util.AbstractCollection

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 into 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.

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 into 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.

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.util.Collection
Specified by:
iterator in class java.util.AbstractCollection
Returns:
an iterator over the elements in this queue in proper sequence.