Fix #2118 : limit CtagsReader lookahead for pathologically-long lines

Background: Universal ctags extracts tags from
pathologically-long lines but only shows the
pattern from the initial part of the line.

OpenGrok will now only try to find heuristically
the position of tags beyond the initial pattern
up to a limit of 2,000 characters.

Also, a tiny cache is used to speed sequential
tags from the same line.

Author: idodeclare

src/org/opensolaris/opengrok/analysis/CtagsReader.java

@@ -76,6 +76,8 @@ public class CtagsReader {
      */
     private static final int MAX_METHOD_LINE_LENGTH = 1030;
 
+    private static final int MAX_CUT_LENGTH = 2000;
+
     /**
      * E.g. krb5 src/kdc/kdc_authdata.c has a signature for handle_authdata()
      * split across twelve lines, so use double that number.
@@ -90,6 +92,8 @@ public class CtagsReader {
     private Supplier<SourceSplitter> splitterSupplier;
     private boolean triedSplitterSupplier;
     private SourceSplitter splitter;
+    private long cutCacheKey;
+    private String cutCacheValue;
 
     private int tabSize;
 
@@ -760,12 +764,23 @@ private String trySplitterCut(int lineOffset, int maxLines) {
             }
         }
 
+        long newCutCacheKey = ((long)lineOffset << 32) | maxLines;
+        if (cutCacheKey == newCutCacheKey) {
+            return cutCacheValue;
+        }
+
         StringBuilder cutbld = new StringBuilder();
         for (int i = lineOffset; i < lineOffset + maxLines &&
-                i < splitter.count(); ++i) {
+                i < splitter.count() && cutbld.length() < MAX_CUT_LENGTH;
+                ++i) {
             cutbld.append(splitter.getLine(i));
         }
-        return cutbld.toString();
+        if (cutbld.length() > MAX_CUT_LENGTH) {
+            cutbld.setLength(MAX_CUT_LENGTH);
+        }
+        cutCacheValue = cutbld.toString();
+        cutCacheKey = newCutCacheKey;
+        return cutCacheValue;
     }
 
     /**