From ce79e16f7a1811e55b140980ebf6f8f68c0370fd Mon Sep 17 00:00:00 2001 From: Jesse Wilson Date: Thu, 28 Apr 2011 22:08:06 +0000 Subject: [PATCH] StringPooling. This makes things up to 20% faster on dalvikvm for some data sets. --- .../com/google/gson/stream/JsonReader.java | 8 ++- .../com/google/gson/stream/StringPool.java | 60 +++++++++++++++++++ 2 files changed, 65 insertions(+), 3 deletions(-) create mode 100644 gson/src/main/java/com/google/gson/stream/StringPool.java diff --git a/gson/src/main/java/com/google/gson/stream/JsonReader.java b/gson/src/main/java/com/google/gson/stream/JsonReader.java index 8cf34dbd..5e90c013 100644 --- a/gson/src/main/java/com/google/gson/stream/JsonReader.java +++ b/gson/src/main/java/com/google/gson/stream/JsonReader.java @@ -188,6 +188,8 @@ public final class JsonReader implements Closeable { /** The only non-execute prefix this parser permits */ private static final char[] NON_EXECUTE_PREFIX = ")]}'\n".toCharArray(); + private final StringPool stringPool = new StringPool(); + /** The input JSON. */ private final Reader in; @@ -942,7 +944,7 @@ public final class JsonReader implements Closeable { if (skipping) { return "skipped!"; } else if (builder == null) { - return new String(buffer, start, pos - start - 1); + return stringPool.get(buffer, start, pos - start - 1); } else { builder.append(buffer, start, pos - start - 1); return builder.toString(); @@ -1002,7 +1004,7 @@ public final class JsonReader implements Closeable { if (skipping) { return "skipped!"; } else if (builder == null) { - return new String(buffer, start, pos - start); + return stringPool.get(buffer, start, pos - start); } else { builder.append(buffer, start, pos - start); return builder.toString(); @@ -1043,7 +1045,7 @@ public final class JsonReader implements Closeable { if (pos + 4 > limit && !fillBuffer(4)) { throw syntaxError("Unterminated escape sequence"); } - String hex = new String(buffer, pos, 4); + String hex = stringPool.get(buffer, pos, 4); pos += 4; return (char) Integer.parseInt(hex, 16); diff --git a/gson/src/main/java/com/google/gson/stream/StringPool.java b/gson/src/main/java/com/google/gson/stream/StringPool.java new file mode 100644 index 00000000..5fa8dab6 --- /dev/null +++ b/gson/src/main/java/com/google/gson/stream/StringPool.java @@ -0,0 +1,60 @@ +/* + * Copyright (C) 2011 Google Inc. + * + * Licensed under the Apache License, Version 2.0 (the "License"); + * you may not use this file except in compliance with the License. + * You may obtain a copy of the License at + * + * http://www.apache.org/licenses/LICENSE-2.0 + * + * Unless required by applicable law or agreed to in writing, software + * distributed under the License is distributed on an "AS IS" BASIS, + * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. + * See the License for the specific language governing permissions and + * limitations under the License. + */ + +package com.google.gson.stream; + +/** + * A pool of string instances. Unlike the {@link String#intern() VM's + * interned strings}, this pool provides no guarantee of reference equality. + * It is intended only to save allocations. This class is not thread safe. + */ +final class StringPool { + + private final String[] pool = new String[512]; + + /** + * Returns a string equal to {@code new String(array, start, length)}. + */ + public String get(char[] array, int start, int length) { + // Compute an arbitrary hash of the content + int hashCode = 0; + for (int i = start; i < start + length; i++) { + hashCode = (hashCode * 31) + array[i]; + } + + // Pick a bucket using Doug Lea's supplemental secondaryHash function (from HashMap) + hashCode ^= (hashCode >>> 20) ^ (hashCode >>> 12); + hashCode ^= (hashCode >>> 7) ^ (hashCode >>> 4); + int index = hashCode & (pool.length - 1); + + String pooled = pool[index]; + if (pooled == null || pooled.length() != length) { + String result = new String(array, start, length); + pool[index] = result; + return result; + } + + for (int i = 0; i < length; i++) { + if (pooled.charAt(i) != array[start + i]) { + String result = new String(array, start, length); + pool[index] = result; + return result; + } + } + + return pooled; + } +} \ No newline at end of file