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From "Mingfai Ma (JIRA)" <>
Subject [jira] Commented: (DROIDS-48) Support prioritizing in the TaskQueue
Date Mon, 22 Jun 2009 04:50:07 GMT


Mingfai Ma commented on DROIDS-48:

just come up with a event better design for weight.

Weighted interface
public interface Weighted {
    public int getWeight();

The Link/LinkTask, assume extends HashMap
public class WeightedLink extends Link implements Weighted { //or LinkTask
    public int getWeight() {
        return Integer.parseInt(String.valueOf(this.get("weight")));

WeightComparator :
public class WeightComparator implements Comparator {
    public int compare(Object link1, Object link2) {
        int weight1 = link1 instanceof Weighted ? ((Weighted) link1).getWeight() : 0;
        int weight2 = link2 instanceof Weighted ? ((Weighted) link2).getWeight() : 0;
        return weight2 - weight1;

Task Queue
 Queue queue = new PriorityBlockingQueue(10, new WeightComparator())

so, weighted becomes optional. if user want to support weight, then, they implement Weighted
and let the user decide how to weight. 

> Support prioritizing in the TaskQueue
> -------------------------------------
>                 Key: DROIDS-48
>                 URL:
>             Project: Droids
>          Issue Type: New Feature
>          Components: core
>    Affects Versions: 0.01
>            Reporter: Mingfai Ma
>         Attachments: DROIDS-48d.patch, DROIDS-48d2.patch
> Use case:
>  - when looping a directory, (imagine someone is too stupid and dunno the dmoz database
can be downloaded and try to crawl it with Droids) we got collect a lot of links that will
be handled later. assume the requirement is to fetch dmoz directory +1 link outside,
In the original mechanism, it will keep adding new links to the TaskQueue. Ideally, there
should be a mechanism to give a higher priority to the links, so when non-dmoz
links are added, they are processed first, and be removed from the TaskQueue asap.
> with the patch in DROIDS-47, a constructor is added to the SimpleTaskQueue to support
a custom Queue. This issue suggests to change the SimpleTaskQueue to use a PriorityBlockingQueue
by default, and add a getWeight to the Task interface
> I'm also thinking about a more complex TaskQueue. to be discussed in the mail list later.

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