Class LinkedQueue

  • All Implemented Interfaces:
    Channel, Puttable, Takable

    public class LinkedQueue
    extends Object
    implements Channel
    A linked list based channel implementation. The algorithm avoids contention between puts and takes when the queue is not empty. Normally a put and a take can proceed simultaneously. (Although it does not allow multiple concurrent puts or takes.) This class tends to perform more efficently than other Channel implementations in producer/consumer applications.

    [ Introduction to this package. ]

    • 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.
      • putLock_

        protected final Object putLock_
        Helper monitor for managing access to last node.
      • last_

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

        protected int waitingForTake_
        The number of threads waiting for a take. Notifications are provided in put only if greater than zero. The bookkeeping is worth it here since in reasonably balanced usages, the notifications will hardly ever be necessary, so the call overhead to notify can be eliminated.
    • Constructor Detail

      • LinkedQueue

        public LinkedQueue()
    • Method Detail

      • insert

        protected void insert​(Object x)
        Main mechanics for put/offer
      • extract

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

        public boolean isEmpty()
      • 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).