[JOHNZON-403] improved long string perfomance (#121)

* prototype improved large string parsing

* fix regression, fix build

* properly close JsonReader in test

johnzon-core/src/main/java/org/apache/johnzon/core/JsonStreamParserImpl.java

@@ -28,6 +28,8 @@
 import java.io.Reader;
 import java.math.BigDecimal;
 import java.nio.charset.Charset;
+import java.util.LinkedList;
+import java.util.List;
 import java.util.NoSuchElementException;
 
 //This class represents either the Json tokenizer and the Json parser.
@@ -74,6 +76,8 @@ public class JsonStreamParserImpl extends JohnzonJsonParserImpl implements JsonC
     private char[] fallBackCopyBuffer;
     private boolean releaseFallBackCopyBufferLength = true;
     private int fallBackCopyBufferLength;
+    // when boundaries of fallBackCopyBuffer have been reached
+    private List<Buffer> previousFallBackCopyBuffers;
 
     // location (line, column, offset)
     // We try to calculate this efficiently so we do not just increment the values per char read
@@ -115,6 +119,16 @@ private static final class StructureElement {
         }
     }
 
+    private static final class Buffer {
+        private char[] buffer;
+        private int length;
+
+        public Buffer(char[] buffer, int length) {
+            this.buffer = buffer;
+            this.length = length;
+        }
+    }
+
     //detect charset according to RFC 4627
     public JsonStreamParserImpl(final InputStream inputStream, final int maxStringLength,
                                 final BufferStrategy.BufferProvider<char[]> bufferProvider, final BufferStrategy.BufferProvider<char[]> valueBuffer,
@@ -165,7 +179,7 @@ private JsonStreamParserImpl(final InputStream inputStream, final Reader reader,
     //append a single char to the value buffer
     private void appendToCopyBuffer(final char c) {
         if (fallBackCopyBufferLength >= fallBackCopyBuffer.length - 1) {
-            doAutoAdjust(1);
+            createNewFallBackCopyBuffer();
         }
         fallBackCopyBuffer[fallBackCopyBufferLength++] = c;
     }
@@ -180,40 +194,39 @@ private void copyCurrentValue() {
             }
 
             if (fallBackCopyBufferLength >= fallBackCopyBuffer.length - length) { // not good at runtime but handled
-                doAutoAdjust(length);
-            } else {
-                System.arraycopy(buffer, startOfValueInBuffer, fallBackCopyBuffer, fallBackCopyBufferLength, length);
+                createNewFallBackCopyBuffer();
             }
+
+            System.arraycopy(buffer, startOfValueInBuffer, fallBackCopyBuffer, fallBackCopyBufferLength, length);
             fallBackCopyBufferLength += length;
         }
 
         startOfValueInBuffer = endOfValueInBuffer = -1;
     }
 
-    private void doAutoAdjust(final int length) {
+    // Creates new fallBackCopyBuffer and stores the old instance in previousFallBackCopyBuffers,
+    // this is much faster than resizing (recreating + copying) fallBackCopyBuffer
+    private void createNewFallBackCopyBuffer() {
         if (!autoAdjust) {
             throw new ArrayIndexOutOfBoundsException("Buffer too small for such a long string");
         }
 
-        final char[] newArray = new char[fallBackCopyBuffer.length + Math.max(getBufferExtends(fallBackCopyBuffer.length), length)];
-        // TODO: log to adjust size once?
-        System.arraycopy(fallBackCopyBuffer, 0, newArray, 0, fallBackCopyBufferLength);
-        if (startOfValueInBuffer != -1) {
-            System.arraycopy(buffer, startOfValueInBuffer, newArray, fallBackCopyBufferLength, length);
+        if (previousFallBackCopyBuffers == null) {
+            previousFallBackCopyBuffers = new LinkedList<>();
         }
-        if (releaseFallBackCopyBufferLength) {
-            bufferProvider.release(fallBackCopyBuffer);
-            releaseFallBackCopyBufferLength = false;
-        }
-        fallBackCopyBuffer = newArray;
+
+        previousFallBackCopyBuffers.add(new Buffer(fallBackCopyBuffer, fallBackCopyBufferLength));
+        fallBackCopyBuffer = valueProvider.newBuffer();
+        fallBackCopyBufferLength = 0;
     }
 
-    /**
-     * @param currentLength length of the buffer
-     * @return the amount of bytes the current buffer should get extended with
-     */
-    protected int getBufferExtends(int currentLength) {
-        return currentLength / 4;
+    private void releasePreviousFallBackCopyBuffers() {
+        if (previousFallBackCopyBuffers == null) {
+            return;
+        }
+
+        previousFallBackCopyBuffers.forEach(it -> valueProvider.release(it.buffer));
+        previousFallBackCopyBuffers = null;
     }
 
 
@@ -443,6 +456,7 @@ protected final Event internalNext() {
             currentIntegralNumber = Integer.MIN_VALUE;
         }
 
+        releasePreviousFallBackCopyBuffers();
         if (fallBackCopyBufferLength != 0) {
             fallBackCopyBufferLength = 0;
         }
@@ -898,6 +912,7 @@ private Event handleLiteral() {
     @Override
     public String getString() {
         if (previousEvent == KEY_NAME || previousEvent == VALUE_STRING || previousEvent == VALUE_NUMBER) {
+            combinePreviousFallbackBuffersToCurrent();
 
             //if there a content in the value buffer read from them, if not use main buffer
             return fallBackCopyBufferLength > 0 ? new String(fallBackCopyBuffer, 0, fallBackCopyBufferLength) : new String(buffer,
@@ -907,6 +922,30 @@ public String getString() {
         }
     }
 
+    // Combines all old stored fallback buffers into the current fallback buffer again so we have a char[] to easily access
+    // Releases all previous fallback buffers while doing so
+    private void combinePreviousFallbackBuffersToCurrent() {
+        if (previousFallBackCopyBuffers == null) {
+            return;
+        }
+
+        int newSize = previousFallBackCopyBuffers.stream().mapToInt(it -> it.length).sum() + fallBackCopyBufferLength;
+        char[] newBuffer = new char[newSize];
+
+        int index = 0;
+        for (Buffer buffer : previousFallBackCopyBuffers) {
+            System.arraycopy(buffer.buffer, 0, newBuffer, index, buffer.length);
+            index += buffer.length;
+        }
+
+        System.arraycopy(fallBackCopyBuffer, 0, newBuffer, index, fallBackCopyBufferLength);
+        index += fallBackCopyBufferLength;
+
+        releasePreviousFallBackCopyBuffers();
+        fallBackCopyBuffer = newBuffer;
+        fallBackCopyBufferLength = index;
+    }
+
     @Override
     public boolean isIntegralNumber() {
 
@@ -929,6 +968,7 @@ public int getInt() {
         } else if (isCurrentNumberIntegral && currentIntegralNumber != Integer.MIN_VALUE) {
             return currentIntegralNumber;
         } else if (isCurrentNumberIntegral) {
+            combinePreviousFallbackBuffersToCurrent();
             //if there a content in the value buffer read from them, if not use main buffer
             final Integer retVal = fallBackCopyBufferLength > 0 ? parseIntegerFromChars(fallBackCopyBuffer, 0, fallBackCopyBufferLength)
                     : parseIntegerFromChars(buffer, startOfValueInBuffer, endOfValueInBuffer);
@@ -949,6 +989,7 @@ public long getLong() {
         } else if (isCurrentNumberIntegral && currentIntegralNumber != Integer.MIN_VALUE) {
             return currentIntegralNumber;
         } else if (isCurrentNumberIntegral) {
+            combinePreviousFallbackBuffersToCurrent();
             //if there a content in the value buffer read from them, if not use main buffer
             final Long retVal = fallBackCopyBufferLength > 0 ? parseLongFromChars(fallBackCopyBuffer, 0, fallBackCopyBufferLength)
                     : parseLongFromChars(buffer, startOfValueInBuffer, endOfValueInBuffer);
@@ -984,6 +1025,8 @@ public BigDecimal getBigDecimal() {
         } else if (isCurrentNumberIntegral && currentIntegralNumber != Integer.MIN_VALUE) {
             return new BigDecimal(currentIntegralNumber);
         }
+
+        combinePreviousFallbackBuffersToCurrent();
         //if there a content in the value buffer read from them, if not use main buffer
         return (/*currentBigDecimalNumber = */fallBackCopyBufferLength > 0 ? new BigDecimal(fallBackCopyBuffer, 0,
                 fallBackCopyBufferLength) : new BigDecimal(buffer, startOfValueInBuffer, (endOfValueInBuffer - startOfValueInBuffer)));
@@ -1004,6 +1047,7 @@ public void close() {
         if (releaseFallBackCopyBufferLength) {
             valueProvider.release(fallBackCopyBuffer);
         }
+        releasePreviousFallBackCopyBuffers();
 
         try {
             in.close();

johnzon-core/src/test/java/org/apache/johnzon/core/HugeStringTest.java

@@ -0,0 +1,47 @@
+/*
+ * Licensed to the Apache Software Foundation (ASF) under one
+ * or more contributor license agreements. See the NOTICE file
+ * distributed with this work for additional information
+ * regarding copyright ownership. The ASF licenses this file
+ * to you 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 org.apache.johnzon.core;
+
+import jakarta.json.Json;
+import jakarta.json.JsonReader;
+import org.junit.Ignore;
+import org.junit.Test;
+
+import java.io.StringReader;
+
+@Ignore
+public class HugeStringTest {
+    @Test
+    public void test() {
+        String json = "{\"data\":\"" + "a".repeat(50 * 1024 * 1024 + 1) + "\"}";
+
+        // Warmup
+        for (int i = 0; i < 10; i++) {
+            try (JsonReader reader = Json.createReader(new StringReader(json))) {
+                reader.readObject();
+            }
+        }
+
+        long start = System.currentTimeMillis();
+        try (JsonReader reader = Json.createReader(new StringReader(json))) {
+            reader.readObject();
+        }
+        System.err.println("Took " + (System.currentTimeMillis() - start) + "ms");
+    }
+}