Package EDU.oswego.cs.dl.util.concurrent

Class BoundedLinkedQueue

  • All Implemented Interfaces:
    BoundedChannel, Channel, Puttable, Takable
    public class BoundedLinkedQueue
extends java.lang.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:
    LinkedQueue, [ Introduction to this package. ]

    • Constructor Summary

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

    • Method Summary

      All Methods Instance Methods Concrete Methods 
      Modifier and Type Method Description
      protected void allowTake()
      Notify a waiting take if needed
      int capacity()
      Return the current capacity of this queue
      protected java.lang.Object extract()
      Main mechanics for take/poll
      protected void insert​(java.lang.Object x)
      Create and insert a node.
      boolean isEmpty()  
      boolean offer​(java.lang.Object x, long msecs)
      Place item in channel only if it can be accepted within msecs milliseconds.
      java.lang.Object peek()
      Return, but do not remove object at head of Channel, or null if it is empty.
      java.lang.Object poll​(long msecs)
      Return and remove an item from channel only if one is available within msecs milliseconds.
      void put​(java.lang.Object x)
      Place item in the channel, possibly waiting indefinitely until it can be accepted.
      protected int reconcilePutPermits()
      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 size()
      Return the number of elements in the queue.
      java.lang.Object take()
      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 Detail

      • 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 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 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 Detail

      • BoundedLinkedQueue

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

      • BoundedLinkedQueue

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

    • 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.

      • 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:
        java.lang.IllegalArgumentException - if capacity less or equal to zero

      • extract

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

      • peek

        public java.lang.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 java.lang.Object take()
                      throws java.lang.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:
        java.lang.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 java.lang.Object poll​(long msecs)
                      throws java.lang.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:
        java.lang.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​(java.lang.Object x)
        Create and insert a node. Call only under synch on putGuard_

      • put

        public void put​(java.lang.Object x)
         throws java.lang.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:
        java.lang.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​(java.lang.Object x,
                     long msecs)
              throws java.lang.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:
        java.lang.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()