Class BoundedLinkedQueue

java.lang.Object
EDU.oswego.cs.dl.util.concurrent.BoundedLinkedQueue
All Implemented Interfaces:
BoundedChannel, Channel, Puttable, Takable

public class BoundedLinkedQueue extends Object implements BoundedChannel
A bounded variant of LinkedQueue class. This class may be preferable to BoundedBuffer because it allows a bit more concurency among puts and takes, because it does not pre-allocate fixed storage for elements, and allows capacity to be dynamically reset. On the other hand, since it allocates a node object on each put, it can be slow on systems with slow allocation and GC. Also, it may be preferable to LinkedQueue when you need to limit the capacity to prevent resource exhaustion. This protection normally does not hurt much performance-wise: When the queue is not empty or full, most puts and takes are still usually able to execute concurrently.
See Also:
  • Field Summary

    Fields
    Modifier and Type
    Field
    Description
    protected int
    Number of elements allowed
    protected LinkedNode
    Dummy header node of list.
    protected LinkedNode
    The last node of list.
    protected final Object
    Helper monitor.
    protected int
    One side of a split permit count.
    protected final Object
    Helper monitor.
    protected int
    Number of takes since last reconcile
  • Constructor Summary

    Constructors
    Constructor
    Description
    Create a queue with the current default capacity
    BoundedLinkedQueue(int capacity)
    Create a queue with the given capacity
  • Method Summary

    Modifier and Type
    Method
    Description
    protected final void
    Notify a waiting take if needed
    int
    Return the current capacity of this queue
    protected Object
    Main mechanics for take/poll
    protected void
    Create and insert a node.
    boolean
     
    boolean
    offer(Object x, long msecs)
    Place item in channel only if it can be accepted within msecs milliseconds.
    Return, but do not remove object at head of Channel, or null if it is empty.
    poll(long msecs)
    Return and remove an item from channel only if one is available within msecs milliseconds.
    void
    Place item in the channel, possibly waiting indefinitely until it can be accepted.
    protected final int
    Move put permits from take side to put side; return the number of put side permits that are available.
    void
    setCapacity(int newCapacity)
    Reset the capacity of this queue.
    int
    Return the number of elements in the queue.
    Return and remove an item from channel, possibly waiting indefinitely until such an item exists.

    Methods inherited from class java.lang.Object

    clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait
  • Field Details

    • head_

      protected 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 LinkedNode last_
      The last node of list. Put() appends to list, so modifies last_
    • putGuard_

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

      protected final Object takeGuard_
      Helper monitor. Protects and provides wait queue for takes
    • capacity_

      protected int capacity_
      Number of elements allowed
    • putSidePutPermits_

      protected 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 int takeSidePutPermits_
      Number of takes since last reconcile
  • Constructor Details

    • BoundedLinkedQueue

      public BoundedLinkedQueue(int capacity)
      Create a queue with the given capacity
      Throws:
      IllegalArgumentException - if capacity less or equal to zero
    • BoundedLinkedQueue

      public BoundedLinkedQueue()
      Create a queue with the current default capacity
  • Method Details

    • 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.
    • capacity

      public int capacity()
      Return the current capacity of this queue
      Specified by:
      capacity in interface BoundedChannel
      Returns:
      the capacity of this channel.
    • size

      public int size()
      Return the number of elements in the queue. This is only a snapshot value, that may be in the midst of changing. The returned value will be unreliable in the presence of active puts and takes, and should only be used as a heuristic estimate, for example for resource monitoring purposes.
    • setCapacity

      public void setCapacity(int newCapacity)
      Reset the capacity of this queue. If the new capacity is less than the old capacity, existing elements are NOT removed, but incoming puts will not proceed until the number of elements is less than the new capacity.
      Throws:
      IllegalArgumentException - if capacity less or equal to zero
    • extract

      protected Object extract()
      Main mechanics for take/poll
    • peek

      public Object peek()
      Description copied from interface: Channel
      Return, but do not remove object at head of Channel, or null if it is empty.
      Specified by:
      peek in interface Channel
    • take

      public Object take() throws InterruptedException
      Description copied from interface: Channel
      Return and remove an item from channel, possibly waiting indefinitely until such an item exists.
      Specified by:
      take in interface Channel
      Specified by:
      take in interface Takable
      Returns:
      some item from the channel. Different implementations may guarantee various properties (such as FIFO) about that item
      Throws:
      InterruptedException - if the current thread has been interrupted at a point at which interruption is detected, in which case state of the channel is unchanged.
    • poll

      public Object poll(long msecs) throws InterruptedException
      Description copied from interface: Channel
      Return and remove an item from channel only if one is available within msecs milliseconds. The time bound is interpreted in a coarse grained, best-effort fashion.
      Specified by:
      poll in interface Channel
      Specified by:
      poll in interface Takable
      Parameters:
      msecs - the number of milliseconds to wait. If less than or equal to zero, the operation does not perform any timed waits, but might still require access to a synchronization lock, which can impose unbounded delay if there is a lot of contention for the channel.
      Returns:
      some item, or null if the channel is empty.
      Throws:
      InterruptedException - if the current thread has been interrupted at a point at which interruption is detected, in which case state of the channel is unchanged (i.e., equivalent to a null return).
    • allowTake

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

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

      public void put(Object x) throws InterruptedException
      Description copied from interface: Channel
      Place item in the channel, possibly waiting indefinitely until it can be accepted. Channels implementing the BoundedChannel subinterface are generally guaranteed to block on puts upon reaching capacity, but other implementations may or may not block.
      Specified by:
      put in interface Channel
      Specified by:
      put in interface Puttable
      Parameters:
      x - the element to be inserted. Should be non-null.
      Throws:
      InterruptedException - if the current thread has been interrupted at a point at which interruption is detected, in which case the element is guaranteed not to be inserted. Otherwise, on normal return, the element is guaranteed to have been inserted.
    • offer

      public boolean offer(Object x, long msecs) throws InterruptedException
      Description copied from interface: Channel
      Place item in channel only if it can be accepted within msecs milliseconds. The time bound is interpreted in a coarse-grained, best-effort fashion.
      Specified by:
      offer in interface Channel
      Specified by:
      offer in interface Puttable
      Parameters:
      x - the element to be inserted. Should be non-null.
      msecs - the number of milliseconds to wait. If less than or equal to zero, the method does not perform any timed waits, but might still require access to a synchronization lock, which can impose unbounded delay if there is a lot of contention for the channel.
      Returns:
      true if accepted, else false
      Throws:
      InterruptedException - if the current thread has been interrupted at a point at which interruption is detected, in which case the element is guaranteed not to be inserted (i.e., is equivalent to a false return).
    • isEmpty

      public boolean isEmpty()