EDU.oswego.cs.dl.util.concurrent: public class: LinkedQueue

EDU.oswego.cs.dl.util.concurrent
public class: LinkedQueue [javadoc | source]

java.lang.Object
   EDU.oswego.cs.dl.util.concurrent.LinkedQueue

All Implemented Interfaces:
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. The first actual node, if it exists, is always at head_.next. After each take, the old first node becomes the head.
protected final Object putLock_ Helper monitor for managing access to last node.
protected LinkedNode last_ The last node of list. Put() appends to list, so modifies last_
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:

public LinkedQueue()
{ head_ = new LinkedNode(null); last_ = head_; }

Method from EDU.oswego.cs.dl.util.concurrent.LinkedQueue Summary:
extract, insert, isEmpty, offer, peek, poll, put, take
Methods from java.lang.Object:
clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait
Method from EDU.oswego.cs.dl.util.concurrent.LinkedQueue Detail:

protected synchronized Object extract()
{ synchronized(head_) { Object x = null; LinkedNode first = head_.next; if (first != null) { x = first.value; first.value = null; head_ = first; } return x; } }
Main mechanics for take/poll *
protected void insert(Object x)
{ synchronized(putLock_) { LinkedNode p = new LinkedNode(x); synchronized(last_) { last_.next = p; last_ = p; } if (waitingForTake_ > 0) putLock_.notify(); } }
Main mechanics for put/offer *
public boolean isEmpty()
{ synchronized(head_) { return head_.next == null; } }
public boolean offer(Object x, long msecs) throws InterruptedException
{ if (x == null) throw new IllegalArgumentException(); if (Thread.interrupted()) throw new InterruptedException(); insert(x); return true; }
public Object peek()
{ synchronized(head_) { LinkedNode first = head_.next; if (first != null) return first.value; else return null; } }
public Object poll(long msecs) throws InterruptedException
{ if (Thread.interrupted()) throw new InterruptedException(); Object x = extract(); if (x != null) return x; else { synchronized(putLock_) { try { long waitTime = msecs; long start = (msecs < = 0)? 0 : System.currentTimeMillis(); ++waitingForTake_; for (;;) { x = extract(); if (x != null || waitTime < = 0) { --waitingForTake_; return x; } else { putLock_.wait(waitTime); waitTime = msecs - (System.currentTimeMillis() - start); } } } catch(InterruptedException ex) { --waitingForTake_; putLock_.notify(); throw ex; } } } }
public void put(Object x) throws InterruptedException
{ if (x == null) throw new IllegalArgumentException(); if (Thread.interrupted()) throw new InterruptedException(); insert(x); }
public Object take() throws InterruptedException
{ if (Thread.interrupted()) throw new InterruptedException(); // try to extract. If fail, then enter wait-based retry loop Object x = extract(); if (x != null) return x; else { synchronized(putLock_) { try { ++waitingForTake_; for (;;) { x = extract(); if (x != null) { --waitingForTake_; return x; } else { putLock_.wait(); } } } catch(InterruptedException ex) { --waitingForTake_; putLock_.notify(); throw ex; } } } }

Field Summary
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.
protected final Object	putLock_	Helper monitor for managing access to last node.
protected LinkedNode	last_	The last node of list. Put() appends to list, so modifies last_
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.