Scala example source code file (FIFOWaitQueue.java)

This example Scala source code file (FIFOWaitQueue.java) is included in my "Source Code Warehouse" project. The intent of this project is to help you more easily find Scala source code examples by using tags.

All credit for the original source code belongs to scala-lang.org; I'm just trying to make examples easier to find. (For my Scala work, see my Scala examples and tutorials.)

Scala tags/keywords

actor, arraylist, collection, fifowaitqueue, list, nullpointerexception, thread, threadpool, waitnode, waitqueue

The FIFOWaitQueue.java Scala example source code

package scala.actors.threadpool.helpers;

import java.util.Collection;
import java.util.ArrayList;
import java.util.List;

/**
 * Simple linked list queue used in FIFOSemaphore.
 * Methods are not synchronized; they depend on synch of callers.
 * Must be public, since it is used by Semaphore (outside this package).
 * NOTE: this class is NOT present in java.util.concurrent.
 **/

public class FIFOWaitQueue extends WaitQueue implements java.io.Serializable {

    private final static long serialVersionUID = 2416444691925378811L;

    protected transient WaitNode head_ = null;
    protected transient WaitNode tail_ = null;

    public FIFOWaitQueue() {}

    public void insert(WaitNode w) {
        if (tail_ == null)
            head_ = tail_ = w;
        else {
            tail_.next = w;
            tail_ = w;
        }
    }

    public WaitNode extract() {
        if (head_ == null)
            return null;
        else {
            WaitNode w = head_;
            head_ = w.next;
            if (head_ == null)
                tail_ = null;
            w.next = null;
            return w;
        }
    }

    public void putBack(WaitNode w) {
        w.next = head_;
        head_ = w;
        if (tail_ == null)
            tail_ = w;
    }

    public boolean hasNodes() {
        return head_ != null;
    }

    public int getLength() {
        int count = 0;
        WaitNode node = head_;
        while (node != null) {
            if (node.waiting) count++;
            node = node.next;
        }
        return count;
    }

    public Collection getWaitingThreads() {
        List<Thread> list = new ArrayList<Thread>();
        int count = 0;
        WaitNode node = head_;
        while (node != null) {
            if (node.waiting) list.add(node.owner);
            node = node.next;
        }
        return list;
    }

    public boolean isWaiting(Thread thread) {
        if (thread == null) throw new NullPointerException();
        for (WaitNode node = head_; node != null; node = node.next) {
            if (node.waiting && node.owner == thread) return true;
        }
        return false;
    }

}