Remove SoftReferences from StreamInput/StreamOutput

We try to reuse character arrays and UTF8 writers with softreferences.
SoftReferences have negative impact on GC and should be avoided in
general. Yet in this case it can simply replaced with a per-stream
Bytes/CharsRef that is thread local and has the same lifetime as the
stream.

Author: s1monw

src/main/java/org/elasticsearch/common/io/stream/StreamInput.java

@@ -19,9 +19,8 @@
 
 package org.elasticsearch.common.io.stream;
 
-import org.apache.lucene.util.ArrayUtil;
 import org.apache.lucene.util.BytesRef;
-import org.apache.lucene.util.RamUsageEstimator;
+import org.apache.lucene.util.CharsRef;
 import org.elasticsearch.Version;
 import org.elasticsearch.common.Nullable;
 import org.elasticsearch.common.Strings;
@@ -34,26 +33,13 @@
 
 import java.io.IOException;
 import java.io.InputStream;
-import java.lang.ref.SoftReference;
 import java.util.*;
 
 /**
  *
  */
 public abstract class StreamInput extends InputStream {
 
-    private static final ThreadLocal<SoftReference<char[]>> charCache = new ThreadLocal<>();
-
-    private static char[] charCache(int size) {
-        SoftReference<char[]> ref = charCache.get();
-        char[] arr = (ref == null) ? null : ref.get();
-        if (arr == null || arr.length < size) {
-            arr = new char[ArrayUtil.oversize(size, RamUsageEstimator.NUM_BYTES_CHAR)];
-            charCache.set(new SoftReference<>(arr));
-        }
-        return arr;
-    }
-
     private Version version = Version.CURRENT;
 
     public Version getVersion() {
@@ -268,11 +254,15 @@ public String readOptionalSharedString() throws IOException {
         return null;
     }
 
+    private final CharsRef spare = new CharsRef();
+
     public String readString() throws IOException {
-        int charCount = readVInt();
-        char[] chars = charCache(charCount);
-        int c, charIndex = 0;
-        while (charIndex < charCount) {
+        final int charCount = readVInt();
+        spare.offset = 0;
+        spare.length = 0;
+        spare.grow(charCount);
+        int c = 0;
+        while (spare.length < charCount) {
             c = readByte() & 0xff;
             switch (c >> 4) {
                 case 0:
@@ -283,18 +273,18 @@ public String readString() throws IOException {
                 case 5:
                 case 6:
                 case 7:
-                    chars[charIndex++] = (char) c;
+                    spare.chars[spare.length++] = (char) c;
                     break;
                 case 12:
                 case 13:
-                    chars[charIndex++] = (char) ((c & 0x1F) << 6 | readByte() & 0x3F);
+                    spare.chars[spare.length++] = (char) ((c & 0x1F) << 6 | readByte() & 0x3F);
                     break;
                 case 14:
-                    chars[charIndex++] = (char) ((c & 0x0F) << 12 | (readByte() & 0x3F) << 6 | (readByte() & 0x3F) << 0);
+                    spare.chars[spare.length++] = (char) ((c & 0x0F) << 12 | (readByte() & 0x3F) << 6 | (readByte() & 0x3F) << 0);
                     break;
             }
         }
-        return new String(chars, 0, charCount);
+        return spare.toString();
     }
 
     public String readSharedString() throws IOException {

src/main/java/org/elasticsearch/common/io/stream/StreamOutput.java

@@ -20,6 +20,7 @@
 package org.elasticsearch.common.io.stream;
 
 import org.apache.lucene.util.BytesRef;
+import org.apache.lucene.util.UnicodeUtil;
 import org.elasticsearch.Version;
 import org.elasticsearch.common.Nullable;
 import org.elasticsearch.common.bytes.BytesReference;
@@ -40,19 +41,6 @@
  */
 public abstract class StreamOutput extends OutputStream {
 
-    private static ThreadLocal<SoftReference<UTF8StreamWriter>> utf8StreamWriter = new ThreadLocal<>();
-
-    public static UTF8StreamWriter utf8StreamWriter() {
-        SoftReference<UTF8StreamWriter> ref = utf8StreamWriter.get();
-        UTF8StreamWriter writer = (ref == null) ? null : ref.get();
-        if (writer == null) {
-            writer = new UTF8StreamWriter(1024 * 4);
-            utf8StreamWriter.set(new SoftReference<>(writer));
-        }
-        writer.reset();
-        return writer;
-    }
-
     private Version version = Version.CURRENT;
 
     public Version getVersion() {
@@ -207,19 +195,14 @@ public void writeOptionalText(@Nullable Text text) throws IOException {
         }
     }
 
+    private final BytesRef spare = new BytesRef();
+
     public void writeText(Text text) throws IOException {
-        if (!text.hasBytes() && seekPositionSupported()) {
-            long pos1 = position();
-            // make room for the size
-            seek(pos1 + 4);
-            UTF8StreamWriter utf8StreamWriter = utf8StreamWriter();
-            utf8StreamWriter.setOutput(this);
-            utf8StreamWriter.write(text.string());
-            utf8StreamWriter.close();
-            long pos2 = position();
-            seek(pos1);
-            writeInt((int) (pos2 - pos1 - 4));
-            seek(pos2);
+        if (!text.hasBytes()) {
+            final String string = text.string();
+            UnicodeUtil.UTF16toUTF8(string, 0, string.length(), spare);
+            writeInt(spare.length);
+            write(spare.bytes, spare.offset, spare.length);
         } else {
             BytesReference bytes = text.bytes();
             writeInt(bytes.length());