EDU.oswego.cs.dl.util.concurrent
Class LinkedQueue

java.lang.Object
  extended by EDU.oswego.cs.dl.util.concurrent.LinkedQueue
All Implemented Interfaces:
Channel, Puttable, Takable

public class LinkedQueue
extends java.lang.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 Summary
protected  LinkedNode head_
          Dummy header node of list.
protected  LinkedNode last_
          The last node of list.
protected  java.lang.Object putLock_
          Helper monitor for managing access to last node.
protected  int waitingForTake_
          The number of threads waiting for a take.
 
Constructor Summary
LinkedQueue()
           
 
Method Summary
protected  java.lang.Object extract()
          Main mechanics for take/poll
protected  void insert(java.lang.Object x)
          Main mechanics for put/offer
 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.
 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.


putLock_

protected final java.lang.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(java.lang.Object x)
Main mechanics for put/offer


extract

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


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).

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.

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

isEmpty

public boolean isEmpty()

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).