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// public synchronized void critial() {
// some thread critical stuff here
// }
import java.util.ArrayList;
import java.util.List;
/**
* Data structure for a web crawler. Keeps track of the visited sites and keeps
* a list of sites which needs still to be crawled.
*
* @author Akash Das
*
*/
public class CrawledSites {
private List<String> crawledSites = new ArrayList<>();
private List<String> linkedSites = new ArrayList<>();
public void add(String site) {
synchronized (this) {
if (!crawledSites.contains(site)) {
linkedSites.add(site);
}
}
}
/**
* Get next site to crawl. Can return null (if nothing to crawl)
*/
public String next() {
if (linkedSites.size() == 0) {
return null;
}
synchronized (this) {
// Need to check again if size has changed
if (linkedSites.size() > 0) {
String s = linkedSites.get(0);
linkedSites.remove(0);
crawledSites.add(s);
return s;
}
return null;
}
}
} |