implemented RWI WordReference to return the word position value (was always left empty)

This is needed and enables existing word position ranking for RWI.
The upcoming concurrency issue in word position min/max calculation were eliminated
by iterator.hasHext check before next() access.

source/net/yacy/kelondro/data/word/WordReferenceRow.java

@@ -252,9 +252,16 @@ public final class WordReferenceRow extends AbstractReference implements WordRef
         return (0xff & this.entry.getColByte(col_hitcount));
     }
 
+    /**
+     * First position of word in text
+     * @return Collection with one element
+     */
     @Override
     public Collection<Integer> positions() {
-        return new ArrayList<Integer>(0);
+        int pos = (int) this.entry.getColLong(col_posintext);
+        ArrayList arr = new ArrayList<Integer>(1);
+        arr.add(pos);
+        return arr;
     }
 
     @Override

source/net/yacy/kelondro/data/word/WordReferenceVars.java

@@ -60,7 +60,8 @@ public class WordReferenceVars extends AbstractReference implements WordReferenc
     public final byte[] urlHash;
     private String hostHash = null;
     private final char type;
-    private int hitcount, llocal, lother, phrasesintext,
+    private int hitcount, // how often appears this word in the text
+            llocal, lother, phrasesintext,
             posinphrase, posofphrase,
             urlcomps, urllength,
             wordsintext, wordsintitle;
@@ -210,6 +211,10 @@ public class WordReferenceVars extends AbstractReference implements WordReferenc
         return this.type;
     }
 
+    /**
+     * How often appears this word in the text
+     * @return
+     */
     @Override
     public int hitcount() {
         return this.hitcount;
@@ -259,7 +264,9 @@ public class WordReferenceVars extends AbstractReference implements WordReferenc
                 this.hitcount,      // how often appears this word in the text
                 this.wordsintext,   // total number of words
                 this.phrasesintext, // total number of phrases
-                this.positions.isEmpty() ? 1 : this.positions.iterator().next(), // position of word in all words
+
+                // TODO: positon 1 on empty positions may give high ranking scores for unknown pos (needs to be checked if 0 would be appropriate)
+                this.positions.isEmpty() ? -1 : this.positions.iterator().next(), // position of word in all words
                 this.posinphrase,   // position of word in its phrase
                 this.posofphrase,   // number of the phrase where word appears
                 this.lastModified,  // last-modified time of the document where word appears

source/net/yacy/kelondro/rwi/AbstractReference.java

@@ -63,9 +63,17 @@ public abstract class AbstractReference implements Reference {
     private static int max(Collection<Integer> a) {
         if (a == null || a.isEmpty()) return Integer.MIN_VALUE;
         Iterator<Integer> i = a.iterator();
+        /*
+        expirienced concurrency issue with this short cut 2016-09-06
+        on i.next w/o test of hasNext before
+        java.util.NoSuchElementException at java.util.concurrent.LinkedBlockingQueue$Itr.next(LinkedBlockingQueue.java:828)
+
         if (a.size() == 1) return i.next();
         if (a.size() == 2) return Math.max(i.next(), i.next());
         int r = i.next();
+        */
+        int r = Integer.MIN_VALUE;
+
         int s;
         while (i.hasNext()) {
             s = i.next();
@@ -77,9 +85,12 @@ public abstract class AbstractReference implements Reference {
     private static int min(Collection<Integer> a) {
         if (a == null || a.isEmpty()) return Integer.MAX_VALUE;
         Iterator<Integer> i = a.iterator();
+        /* concurrency issue (see max())
         if (a.size() == 1) return i.next();
         if (a.size() == 2) return Math.min(i.next(), i.next());
         int r = i.next();
+        */
+        int r = Integer.MAX_VALUE;
         int s;
         while (i.hasNext()) {
             s = i.next();
@@ -103,10 +114,11 @@ public abstract class AbstractReference implements Reference {
         if (positions().size() < 2) return 0;
         int d = 0;
         Iterator<Integer> i = positions().iterator();
-        int s0 = i.next(), s1;
+        // int s0 = i.next(), s1; // concurrency issue see max()
+        int s0 = -1, s1;
         while (i.hasNext()) {
             s1 = i.next();
-            d += Math.abs(s0 - s1);
+            if (s0 > 0) d += Math.abs(s0 - s1);
             s0 = s1;
         }
         return d / (positions().size() - 1);