org.logicalcobwebs.concurrent
Class LinkedQueue

java.lang.Object
  org.logicalcobwebs.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).