Change all instances of encoded.subSequence() to use a simple start i…

…ndex offset, which reduces the Java memory footprint for TrieParser by at at least 130 MBs. This is because the original call to subSequence() would generate a new String on the heap for each call, where as just using an offset avoids the need to generate a new String all together.

This memory enhancement was found while investigating flakiness issues for some tests which had the same root cause of: java.lang.OutOfMemoryError: GC overhead limit exceeded, mostly in the TrieParser class.

100-test runs at original code:
Memory usage
- maximum: 503MiB (527,769,600 bytes)
- average: 388MiB (407,225,077 bytes)

100-test runs with my changes:
Memory usage
- maximum: 316MiB (325,271,552 bytes)
- average: 221MiB (239,355,320 bytes)

At maximum: 187 MB saved
At average: 167 MB saved

RELNOTES=Reduced heap memory usage when parsing domain names

-------------
Created by MOE: https://github.com/google/moe
MOE_MIGRATED_REVID=188111053

android/guava/src/com/google/thirdparty/publicsuffix/TrieParser.java

@@ -23,7 +23,6 @@
 /** Parser for a map of reversed domain names stored as a serialized radix tree. */
 @GwtCompatible
 final class TrieParser {
-
   private static final Joiner PREFIX_JOINER = Joiner.on("");
 
   /**
@@ -35,9 +34,7 @@ static ImmutableMap<String, PublicSuffixType> parseTrie(CharSequence encoded) {
     int encodedLen = encoded.length();
     int idx = 0;
     while (idx < encodedLen) {
-      idx +=
-          doParseTrieToBuilder(
-              Lists.<CharSequence>newLinkedList(), encoded.subSequence(idx, encodedLen), builder);
+      idx += doParseTrieToBuilder(Lists.<CharSequence>newLinkedList(), encoded, idx, builder);
     }
     return builder.build();
   }
@@ -48,16 +45,18 @@ static ImmutableMap<String, PublicSuffixType> parseTrie(CharSequence encoded) {
    * @param stack The prefixes that precede the characters represented by this node. Each entry of
    *     the stack is in reverse order.
    * @param encoded The serialized trie.
+   * @param start An index in the encoded serialized trie to begin reading characters from.
    * @param builder A map builder to which all entries will be added.
    * @return The number of characters consumed from {@code encoded}.
    */
   private static int doParseTrieToBuilder(
       List<CharSequence> stack,
       CharSequence encoded,
+      int start,
       ImmutableMap.Builder<String, PublicSuffixType> builder) {
 
     int encodedLen = encoded.length();
-    int idx = 0;
+    int idx = start;
     char c = '\0';
 
     // Read all of the characters for this node.
@@ -68,7 +67,7 @@ private static int doParseTrieToBuilder(
       }
     }
 
-    stack.add(0, reverse(encoded.subSequence(0, idx)));
+    stack.add(0, reverse(encoded.subSequence(start, idx)));
 
     if (c == '!' || c == '?' || c == ':' || c == ',') {
       // '!' represents an interior node that represents a REGISTRY entry in the map.
@@ -85,7 +84,7 @@ private static int doParseTrieToBuilder(
     if (c != '?' && c != ',') {
       while (idx < encodedLen) {
         // Read all the children
-        idx += doParseTrieToBuilder(stack, encoded.subSequence(idx, encodedLen), builder);
+        idx += doParseTrieToBuilder(stack, encoded, idx, builder);
         if (encoded.charAt(idx) == '?' || encoded.charAt(idx) == ',') {
           // An extra '?' or ',' after a child node indicates the end of all children of this node.
           idx++;
@@ -94,7 +93,7 @@ private static int doParseTrieToBuilder(
       }
     }
     stack.remove(0);
-    return idx;
+    return idx - start;
   }
 
   private static CharSequence reverse(CharSequence s) {

guava/src/com/google/thirdparty/publicsuffix/TrieParser.java

@@ -23,7 +23,6 @@
 /** Parser for a map of reversed domain names stored as a serialized radix tree. */
 @GwtCompatible
 final class TrieParser {
-
   private static final Joiner PREFIX_JOINER = Joiner.on("");
 
   /**
@@ -35,9 +34,7 @@ static ImmutableMap<String, PublicSuffixType> parseTrie(CharSequence encoded) {
     int encodedLen = encoded.length();
     int idx = 0;
     while (idx < encodedLen) {
-      idx +=
-          doParseTrieToBuilder(
-              Lists.<CharSequence>newLinkedList(), encoded.subSequence(idx, encodedLen), builder);
+      idx += doParseTrieToBuilder(Lists.<CharSequence>newLinkedList(), encoded, idx, builder);
     }
     return builder.build();
   }
@@ -48,16 +45,18 @@ static ImmutableMap<String, PublicSuffixType> parseTrie(CharSequence encoded) {
    * @param stack The prefixes that precede the characters represented by this node. Each entry of
    *     the stack is in reverse order.
    * @param encoded The serialized trie.
+   * @param start An index in the encoded serialized trie to begin reading characters from.
    * @param builder A map builder to which all entries will be added.
    * @return The number of characters consumed from {@code encoded}.
    */
   private static int doParseTrieToBuilder(
       List<CharSequence> stack,
       CharSequence encoded,
+      int start,
       ImmutableMap.Builder<String, PublicSuffixType> builder) {
 
     int encodedLen = encoded.length();
-    int idx = 0;
+    int idx = start;
     char c = '\0';
 
     // Read all of the characters for this node.
@@ -68,7 +67,7 @@ private static int doParseTrieToBuilder(
       }
     }
 
-    stack.add(0, reverse(encoded.subSequence(0, idx)));
+    stack.add(0, reverse(encoded.subSequence(start, idx)));
 
     if (c == '!' || c == '?' || c == ':' || c == ',') {
       // '!' represents an interior node that represents a REGISTRY entry in the map.
@@ -85,7 +84,7 @@ private static int doParseTrieToBuilder(
     if (c != '?' && c != ',') {
       while (idx < encodedLen) {
         // Read all the children
-        idx += doParseTrieToBuilder(stack, encoded.subSequence(idx, encodedLen), builder);
+        idx += doParseTrieToBuilder(stack, encoded, idx, builder);
         if (encoded.charAt(idx) == '?' || encoded.charAt(idx) == ',') {
           // An extra '?' or ',' after a child node indicates the end of all children of this node.
           idx++;
@@ -94,7 +93,7 @@ private static int doParseTrieToBuilder(
       }
     }
     stack.remove(0);
-    return idx;
+    return idx - start;
   }
 
   private static CharSequence reverse(CharSequence s) {