Add a reusable ArrayList to InternalThreadLocalMap

Motivation:

See netty#3411. A reusable ArrayList in InternalThreadLocalMap can avoid allocations in the following pattern:

```
List<...> list = new ArrayList<...>();

add something to list but never use InternalThreadLocalMap

return list.toArray(new ...[list.size()]);

```

Modifications:

Add a reusable ArrayList to InternalThreadLocalMap and update codes to use it.

Result:

Reuse a thread local ArrayList to avoid allocations.

codec-http/src/main/java/io/netty/handler/codec/http/cookie/ClientCookieEncoder.java

@@ -22,8 +22,8 @@
 import static io.netty.handler.codec.http.cookie.CookieUtil.stripTrailingSeparatorOrNull;
 import static io.netty.util.internal.ObjectUtil.checkNotNull;
 import io.netty.handler.codec.http.HttpRequest;
+import io.netty.util.internal.InternalThreadLocalMap;
 
-import java.util.ArrayList;
 import java.util.Arrays;
 import java.util.Collection;
 import java.util.Comparator;
@@ -196,7 +196,7 @@ public String encode(Iterable<? extends Cookie> cookies) {
             if (!cookiesIt.hasNext()) {
                 encode(buf, firstCookie);
             } else {
-                List<Cookie> cookiesList = new ArrayList<Cookie>();
+                List<Cookie> cookiesList = InternalThreadLocalMap.get().arrayList();
                 cookiesList.add(firstCookie);
                 while (cookiesIt.hasNext()) {
                     cookiesList.add(cookiesIt.next());

codec-http/src/main/java/io/netty/handler/codec/http/multipart/HttpPostMultipartRequestDecoder.java

@@ -30,6 +30,7 @@
 import io.netty.handler.codec.http.multipart.HttpPostRequestDecoder.MultiPartStatus;
 import io.netty.handler.codec.http.multipart.HttpPostRequestDecoder.NotEnoughDataDecoderException;
 import io.netty.util.CharsetUtil;
+import io.netty.util.internal.InternalThreadLocalMap;
 import io.netty.util.internal.StringUtil;
 
 import java.io.IOException;
@@ -1836,7 +1837,7 @@ private static String[] splitMultipartHeader(String sb) {
      * @return an array of String where values that were separated by ';' or ','
      */
     private static String[] splitMultipartHeaderValues(String svalue) {
-        List<String> values = new ArrayList<String>(1);
+        List<String> values = InternalThreadLocalMap.get().arrayList(1);
         boolean inQuote = false;
         boolean escapeNext = false;
         int start = 0;

common/src/main/java/io/netty/util/AsciiString.java

@@ -17,13 +17,13 @@
 
 import io.netty.util.ByteProcessor.IndexOfProcessor;
 import io.netty.util.internal.EmptyArrays;
+import io.netty.util.internal.InternalThreadLocalMap;
 import io.netty.util.internal.PlatformDependent;
 
 import java.nio.ByteBuffer;
 import java.nio.CharBuffer;
 import java.nio.charset.Charset;
 import java.nio.charset.CharsetEncoder;
-import java.util.ArrayList;
 import java.util.Arrays;
 import java.util.Collection;
 import java.util.List;
@@ -1050,7 +1050,7 @@ public AsciiString[] split(String expr, int max) {
      * Splits the specified {@link String} with the specified delimiter..
      */
     public AsciiString[] split(char delim) {
-        final List<AsciiString> res = new ArrayList<AsciiString>();
+        final List<AsciiString> res = InternalThreadLocalMap.get().arrayList();
 
         int start = 0;
         final int length = length();

common/src/main/java/io/netty/util/internal/InternalThreadLocalMap.java

@@ -22,6 +22,7 @@
 import java.nio.charset.Charset;
 import java.nio.charset.CharsetDecoder;
 import java.nio.charset.CharsetEncoder;
+import java.util.ArrayList;
 import java.util.Arrays;
 import java.util.IdentityHashMap;
 import java.util.Map;
@@ -34,6 +35,8 @@
  */
 public final class InternalThreadLocalMap extends UnpaddedInternalThreadLocalMap {
 
+    private static final int DEFAULT_ARRAY_LIST_INITIAL_CAPACITY = 8;
+
     public static final Object UNSET = new Object();
 
     public static InternalThreadLocalMap getIfSet() {
@@ -160,6 +163,9 @@ public int size() {
         if (charsetDecoderCache != null) {
             count ++;
         }
+        if (arrayList != null) {
+            count ++;
+        }
 
         for (Object o: indexedVariables) {
             if (o != UNSET) {
@@ -198,6 +204,21 @@ public Map<Charset, CharsetDecoder> charsetDecoderCache() {
         return cache;
     }
 
+    public <E> ArrayList<E> arrayList() {
+        return arrayList(DEFAULT_ARRAY_LIST_INITIAL_CAPACITY);
+    }
+
+    public <E> ArrayList<E> arrayList(int minCapacity) {
+        ArrayList<E> list = (ArrayList<E>) arrayList;
+        if (list == null) {
+            list = (ArrayList<E>) new ArrayList<Object>(minCapacity);
+        } else {
+            list.clear();
+            list.ensureCapacity(minCapacity);
+        }
+        return list;
+    }
+
     public int futureListenerStackDepth() {
         return futureListenerStackDepth;
     }

common/src/main/java/io/netty/util/internal/StringUtil.java

@@ -16,7 +16,6 @@
 package io.netty.util.internal;
 
 import java.io.IOException;
-import java.util.ArrayList;
 import java.util.Formatter;
 import java.util.List;
 
@@ -94,7 +93,7 @@ public final class StringUtil {
      */
     public static String[] split(String value, char delim) {
         final int end = value.length();
-        final List<String> res = new ArrayList<String>();
+        final List<String> res = InternalThreadLocalMap.get().arrayList();
 
         int start = 0;
         for (int i = 0; i < end; i ++) {
@@ -136,7 +135,7 @@ public static String[] split(String value, char delim) {
      */
     public static String[] split(String value, char delim, int maxParts) {
         final int end = value.length();
-        final List<String> res = new ArrayList<String>();
+        final List<String> res = InternalThreadLocalMap.get().arrayList();
 
         int start = 0;
         int cpt = 1;

common/src/main/java/io/netty/util/internal/UnpaddedInternalThreadLocalMap.java

@@ -21,6 +21,7 @@
 import java.nio.charset.Charset;
 import java.nio.charset.CharsetDecoder;
 import java.nio.charset.CharsetEncoder;
+import java.util.ArrayList;
 import java.util.Map;
 import java.util.concurrent.atomic.AtomicInteger;
 
@@ -51,6 +52,9 @@ class UnpaddedInternalThreadLocalMap {
     Map<Charset, CharsetEncoder> charsetEncoderCache;
     Map<Charset, CharsetDecoder> charsetDecoderCache;
 
+    // ArrayList-related thread-locals
+    ArrayList<Object> arrayList;
+
     UnpaddedInternalThreadLocalMap(Object[] indexedVariables) {
         this.indexedVariables = indexedVariables;
     }

handler/src/main/java/io/netty/handler/ssl/IdentityCipherSuiteFilter.java

@@ -15,7 +15,8 @@
  */
 package io.netty.handler.ssl;
 
-import java.util.ArrayList;
+import io.netty.util.internal.InternalThreadLocalMap;
+
 import java.util.List;
 import java.util.Set;
 
@@ -33,7 +34,7 @@ public String[] filterCipherSuites(Iterable<String> ciphers, List<String> defaul
         if (ciphers == null) {
             return defaultCiphers.toArray(new String[defaultCiphers.size()]);
         } else {
-            List<String> newCiphers = new ArrayList<String>(supportedCiphers.size());
+            List<String> newCiphers = InternalThreadLocalMap.get().arrayList(supportedCiphers.size());
             for (String c : ciphers) {
                 if (c == null) {
                     break;

handler/src/main/java/io/netty/handler/ssl/OpenSslEngine.java

@@ -19,6 +19,7 @@
 import io.netty.buffer.ByteBufAllocator;
 import io.netty.buffer.Unpooled;
 import io.netty.util.internal.EmptyArrays;
+import io.netty.util.internal.InternalThreadLocalMap;
 import io.netty.util.internal.PlatformDependent;
 import io.netty.util.internal.StringUtil;
 import io.netty.util.internal.logging.InternalLogger;
@@ -42,7 +43,6 @@
 import java.nio.ReadOnlyBufferException;
 import java.security.Principal;
 import java.security.cert.Certificate;
-import java.util.ArrayList;
 import java.util.Arrays;
 import java.util.HashMap;
 import java.util.HashSet;
@@ -1018,7 +1018,7 @@ public String[] getSupportedProtocols() {
 
     @Override
     public String[] getEnabledProtocols() {
-        List<String> enabled = new ArrayList<String>();
+        List<String> enabled = InternalThreadLocalMap.get().arrayList();
         // Seems like there is no way to explict disable SSLv2Hello in openssl so it is always enabled
         enabled.add(PROTOCOL_SSL_V2_HELLO);
 

handler/src/main/java/io/netty/handler/ssl/SupportedCipherSuiteFilter.java

@@ -15,8 +15,9 @@
  */
 package io.netty.handler.ssl;
 
+import io.netty.util.internal.InternalThreadLocalMap;
+
 import javax.net.ssl.SSLEngine;
-import java.util.ArrayList;
 import java.util.List;
 import java.util.Set;
 
@@ -40,10 +41,10 @@ public String[] filterCipherSuites(Iterable<String> ciphers, List<String> defaul
 
         final List<String> newCiphers;
         if (ciphers == null) {
-            newCiphers = new ArrayList<String>(defaultCiphers.size());
+            newCiphers = InternalThreadLocalMap.get().arrayList(defaultCiphers.size());
             ciphers = defaultCiphers;
         } else {
-            newCiphers = new ArrayList<String>(supportedCiphers.size());
+            newCiphers = InternalThreadLocalMap.get().arrayList(supportedCiphers.size());
         }
         for (String c : ciphers) {
             if (c == null) {

handler/src/main/java/io/netty/handler/ssl/util/FingerprintTrustManagerFactory.java

@@ -20,6 +20,7 @@
 import io.netty.buffer.Unpooled;
 import io.netty.util.internal.EmptyArrays;
 import io.netty.util.concurrent.FastThreadLocal;
+import io.netty.util.internal.InternalThreadLocalMap;
 
 import javax.net.ssl.ManagerFactoryParameters;
 import javax.net.ssl.TrustManager;
@@ -31,7 +32,6 @@
 import java.security.cert.CertificateEncodingException;
 import java.security.cert.CertificateException;
 import java.security.cert.X509Certificate;
-import java.util.ArrayList;
 import java.util.Arrays;
 import java.util.List;
 import java.util.regex.Pattern;
@@ -151,7 +151,7 @@ public FingerprintTrustManagerFactory(byte[]... fingerprints) {
             throw new NullPointerException("fingerprints");
         }
 
-        List<byte[]> list = new ArrayList<byte[]>();
+        List<byte[]> list = InternalThreadLocalMap.get().arrayList();
         for (byte[] f: fingerprints) {
             if (f == null) {
                 break;
@@ -171,7 +171,7 @@ private static byte[][] toFingerprintArray(Iterable<String> fingerprints) {
             throw new NullPointerException("fingerprints");
         }
 
-        List<byte[]> list = new ArrayList<byte[]>();
+        List<byte[]> list = InternalThreadLocalMap.get().arrayList();
         for (String f: fingerprints) {
             if (f == null) {
                 break;

resolver-dns/src/main/java/io/netty/resolver/dns/DnsNameResolverBuilder.java

@@ -23,9 +23,9 @@
 import io.netty.channel.socket.DatagramChannel;
 import io.netty.channel.socket.InternetProtocolFamily;
 import io.netty.resolver.HostsFileEntriesResolver;
+import io.netty.util.internal.InternalThreadLocalMap;
 
 import java.net.InetSocketAddress;
-import java.util.ArrayList;
 import java.util.List;
 
 import static io.netty.util.internal.ObjectUtil.checkNotNull;
@@ -170,7 +170,7 @@ public DnsNameResolverBuilder resolvedAddressTypes(InternetProtocolFamily... res
         checkNotNull(resolvedAddressTypes, "resolvedAddressTypes");
 
         final List<InternetProtocolFamily> list =
-                new ArrayList<InternetProtocolFamily>(InternetProtocolFamily.values().length);
+                InternalThreadLocalMap.get().arrayList(InternetProtocolFamily.values().length);
 
         for (InternetProtocolFamily f : resolvedAddressTypes) {
             if (f == null) {
@@ -207,7 +207,7 @@ public DnsNameResolverBuilder resolvedAddressTypes(Iterable<InternetProtocolFami
         checkNotNull(resolvedAddressTypes, "resolveAddressTypes");
 
         final List<InternetProtocolFamily> list =
-                new ArrayList<InternetProtocolFamily>(InternetProtocolFamily.values().length);
+                InternalThreadLocalMap.get().arrayList(InternetProtocolFamily.values().length);
 
         for (InternetProtocolFamily f : resolvedAddressTypes) {
             if (f == null) {

resolver-dns/src/main/java/io/netty/resolver/dns/DnsServerAddresses.java

@@ -16,6 +16,7 @@
 
 package io.netty.resolver.dns;
 
+import io.netty.util.internal.InternalThreadLocalMap;
 import io.netty.util.internal.logging.InternalLogger;
 import io.netty.util.internal.logging.InternalLoggerFactory;
 
@@ -241,7 +242,7 @@ private static InetSocketAddress[] sanitize(InetSocketAddress[] addresses) {
             throw new NullPointerException("addresses");
         }
 
-        List<InetSocketAddress> list = new ArrayList<InetSocketAddress>(addresses.length);
+        List<InetSocketAddress> list = InternalThreadLocalMap.get().arrayList(addresses.length);
         for (InetSocketAddress a: addresses) {
             if (a == null) {
                 break;