edu.emory.mathcs.util.concurrent
Class LinkedBlockingQueue

java.lang.Object
  |
  +--java.util.AbstractCollection
        |
        +--edu.emory.mathcs.util.AbstractQueue
              |
              +--edu.emory.mathcs.util.concurrent.LinkedBlockingQueue
All Implemented Interfaces:
BlockingQueue, java.util.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 Java Collections Framework.

Since:
1.5
See Also:
Serialized Form

Field Summary
protected  int capacity_
          Number of elements allowed
protected  edu.emory.mathcs.util.concurrent.LinkedBlockingQueue.LinkedNode head_
          Dummy header node of list.
protected  edu.emory.mathcs.util.concurrent.LinkedBlockingQueue.LinkedNode last_
          The last node of list.
protected  java.lang.Object putGuard_
          Helper monitor.
protected  int putSidePutPermits_
          One side of a split permit count.
protected  java.lang.Object takeGuard_
          Helper monitor.
protected  int takeSidePutPermits_
          Number of takes since last reconcile
 
Constructor Summary
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
protected  void allowTake()
          Notify a waiting take if needed
 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 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.
protected  java.lang.Object extract()
          Main mechanics for take/poll
protected  void insert(java.lang.Object x)
          Create and insert a node.
 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.
protected  int reconcilePutPermits()
          Move put permits from take side to put side; return the number of put side permits that are 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
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.util.concurrent.BlockingQueue
add
 
Methods inherited from interface edu.emory.mathcs.util.Queue
element, remove
 
Methods inherited from interface java.util.Collection
addAll, contains, containsAll, equals, hashCode, isEmpty, removeAll, retainAll
 

Field Detail

head_

protected transient edu.emory.mathcs.util.concurrent.LinkedBlockingQueue.LinkedNode head_
Dummy header node of list. The first actual node, if it exists, is always at head_.next. After each take, the old first node becomes the head.


last_

protected transient edu.emory.mathcs.util.concurrent.LinkedBlockingQueue.LinkedNode last_
The last node of list. Put() appends to list, so modifies last_


putGuard_

protected final java.lang.Object putGuard_
Helper monitor. Ensures that only one put at a time executes.


takeGuard_

protected final java.lang.Object takeGuard_
Helper monitor. Protects and provides wait queue for takes


capacity_

protected int capacity_
Number of elements allowed


putSidePutPermits_

protected transient int putSidePutPermits_
One side of a split permit count. The counts represent permits to do a put. (The queue is full when zero). Invariant: putSidePutPermits_ + takeSidePutPermits_ = capacity_ - length. (The length is never separately recorded, so this cannot be checked explicitly.) To minimize contention between puts and takes, the put side uses up all of its permits before transfering them from the take side. The take side just increments the count upon each take. Thus, most puts and take can run independently of each other unless the queue is empty or full. Initial value is queue capacity.


takeSidePutPermits_

protected transient int takeSidePutPermits_
Number of takes since last reconcile

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 c or any element within it is null
Method Detail

reconcilePutPermits

protected final int reconcilePutPermits()
Move put permits from take side to put side; return the number of put side permits that are available. Call only under synch on puGuard_ AND this.


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

allowTake

protected final void allowTake()
Notify a waiting take if needed


insert

protected void insert(java.lang.Object x)
Create and insert a node. Call only under synch on putGuard_


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.

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.

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

extract

protected java.lang.Object extract()
Main mechanics for take/poll


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.

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.

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.

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.

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

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.