Replace toArray(new T[size]) with toArray(new T[0]) to eliminate zero-out and allow the VM to optimize. (#8075)

Motivation:

Using toArray(new T[0]) is usually the faster aproach these days. We should use it.

See also https://shipilev.net/blog/2016/arrays-wisdom-ancients/#_conclusion.

Modifications:

Replace toArray(new T[size]) with toArray(new T[0]).

Result:

Faster code.

buffer/src/main/java/io/netty/buffer/CompositeByteBuf.java

@@ -391,7 +391,7 @@ public class CompositeByteBuf extends AbstractReferenceCountedByteBuf implements
         }
 
         Collection<ByteBuf> col = (Collection<ByteBuf>) buffers;
-        return addComponents0(increaseIndex, cIndex, col.toArray(new ByteBuf[col.size()]), 0 , col.size());
+        return addComponents0(increaseIndex, cIndex, col.toArray(new ByteBuf[0]), 0 , col.size());
     }
 
     /**
@@ -1507,7 +1507,7 @@ public class CompositeByteBuf extends AbstractReferenceCountedByteBuf implements
             i ++;
         }
 
-        return buffers.toArray(new ByteBuffer[buffers.size()]);
+        return buffers.toArray(new ByteBuffer[0]);
     }
 
     /**

buffer/src/main/java/io/netty/buffer/FixedCompositeByteBuf.java

@@ -593,7 +593,7 @@ final class FixedCompositeByteBuf extends AbstractReferenceCountedByteBuf {
                 s = buffer(++i);
             }
 
-            return array.toArray(new ByteBuffer[array.size()]);
+            return array.toArray(new ByteBuffer[0]);
         } finally {
             array.recycle();
         }

buffer/src/test/java/io/netty/buffer/AbstractCompositeByteBufTest.java

@@ -87,7 +87,7 @@ public abstract class AbstractCompositeByteBufTest extends AbstractByteBufTest {
             buffers.add(EMPTY_BUFFER);
         }
 
-        ByteBuf buffer = wrappedBuffer(Integer.MAX_VALUE, buffers.toArray(new ByteBuf[buffers.size()])).order(order);
+        ByteBuf buffer = wrappedBuffer(Integer.MAX_VALUE, buffers.toArray(new ByteBuf[0])).order(order);
 
         // Truncate to the requested capacity.
         buffer.capacity(length);

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

@@ -161,7 +161,7 @@ public final class ClientCookieEncoder extends CookieEncoder {
             if (cookies.size() == 1) {
                 encode(buf, cookies.iterator().next());
             } else {
-                Cookie[] cookiesSorted = cookies.toArray(new Cookie[cookies.size()]);
+                Cookie[] cookiesSorted = cookies.toArray(new Cookie[0]);
                 Arrays.sort(cookiesSorted, COOKIE_COMPARATOR);
                 for (Cookie c : cookiesSorted) {
                     encode(buf, c);
@@ -198,7 +198,7 @@ public final class ClientCookieEncoder extends CookieEncoder {
                 while (cookiesIt.hasNext()) {
                     cookiesList.add(cookiesIt.next());
                 }
-                Cookie[] cookiesSorted = cookiesList.toArray(new Cookie[cookiesList.size()]);
+                Cookie[] cookiesSorted = cookiesList.toArray(new Cookie[0]);
                 Arrays.sort(cookiesSorted, COOKIE_COMPARATOR);
                 for (Cookie c : cookiesSorted) {
                     encode(buf, c);

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

@@ -1515,6 +1515,6 @@ public class HttpPostMultipartRequestDecoder implements InterfaceHttpPostRequest
             }
         }
         values.add(svalue.substring(start));
-        return values.toArray(new String[values.size()]);
+        return values.toArray(new String[0]);
     }
 }

codec-http/src/test/java/io/netty/handler/codec/http/DefaultHttpHeadersTest.java

@@ -232,7 +232,7 @@ public class DefaultHttpHeadersTest {
                 .add(HttpHeaderNames.CONTENT_LENGTH, 10)
                 .names();
 
-        String[] namesArray = nettyHeaders.toArray(new String[nettyHeaders.size()]);
+        String[] namesArray = nettyHeaders.toArray(new String[0]);
         assertArrayEquals(namesArray, new String[] { HttpHeaderNames.CONTENT_LENGTH.toString() });
     }
 

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

@@ -1115,7 +1115,7 @@ public final class AsciiString implements CharSequence, Comparable<CharSequence>
             }
         }
 
-        return res.toArray(new AsciiString[res.size()]);
+        return res.toArray(new AsciiString[0]);
     }
 
     /**

common/src/main/java/io/netty/util/concurrent/AbstractScheduledEventExecutor.java

@@ -78,7 +78,7 @@ public abstract class AbstractScheduledEventExecutor extends AbstractEventExecut
         }
 
         final ScheduledFutureTask<?>[] scheduledTasks =
-                scheduledTaskQueue.toArray(new ScheduledFutureTask<?>[scheduledTaskQueue.size()]);
+                scheduledTaskQueue.toArray(new ScheduledFutureTask<?>[0]);
 
         for (ScheduledFutureTask<?> task: scheduledTasks) {
             task.cancelWithoutRemove(false);

common/src/main/java/io/netty/util/concurrent/FastThreadLocal.java

@@ -62,7 +62,7 @@ public class FastThreadLocal<V> {
                 @SuppressWarnings("unchecked")
                 Set<FastThreadLocal<?>> variablesToRemove = (Set<FastThreadLocal<?>>) v;
                 FastThreadLocal<?>[] variablesToRemoveArray =
-                        variablesToRemove.toArray(new FastThreadLocal[variablesToRemove.size()]);
+                        variablesToRemove.toArray(new FastThreadLocal[0]);
                 for (FastThreadLocal<?> tlv: variablesToRemoveArray) {
                     tlv.remove(threadLocalMap);
                 }

common/src/test/java/io/netty/util/ConstantPoolTest.java

@@ -75,7 +75,7 @@ public class ConstantPoolTest {
         set.add(d);
         set.add(a);
 
-        TestConstant[] array = set.toArray(new TestConstant[5]);
+        TestConstant[] array = set.toArray(new TestConstant[0]);
         assertThat(array.length, is(5));
 
         // Sort by name

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

@@ -71,7 +71,7 @@ abstract class ConscryptAlpnSslEngine extends JdkSslEngine {
         }
 
         // Set the list of supported ALPN protocols on the engine.
-        Conscrypt.setApplicationProtocols(engine, protocols.toArray(new String[protocols.size()]));
+        Conscrypt.setApplicationProtocols(engine, protocols.toArray(new String[0]));
     }
 
     /**

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

@@ -46,8 +46,8 @@ public final class IdentityCipherSuiteFilter implements CipherSuiteFilter {
             Set<String> supportedCiphers) {
         if (ciphers == null) {
             return defaultToDefaultCiphers ?
-                    defaultCiphers.toArray(new String[defaultCiphers.size()]) :
+                    defaultCiphers.toArray(new String[0]) :
-                    supportedCiphers.toArray(new String[supportedCiphers.size()]);
+                    supportedCiphers.toArray(new String[0]);
         } else {
             List<String> newCiphers = new ArrayList<String>(supportedCiphers.size());
             for (String c : ciphers) {
@@ -56,7 +56,7 @@ public final class IdentityCipherSuiteFilter implements CipherSuiteFilter {
                 }
                 newCiphers.add(c);
             }
-            return newCiphers.toArray(new String[newCiphers.size()]);
+            return newCiphers.toArray(new String[0]);
         }
     }
 }

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

@@ -84,7 +84,7 @@ public class JdkSslContext extends SslContext {
                 "TLSv1.2", "TLSv1.1", "TLSv1");
 
         if (!protocols.isEmpty()) {
-            DEFAULT_PROTOCOLS = protocols.toArray(new String[protocols.size()]);
+            DEFAULT_PROTOCOLS = protocols.toArray(new String[0]);
         } else {
             DEFAULT_PROTOCOLS = engine.getEnabledProtocols();
         }

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

@@ -438,7 +438,7 @@ public final class OpenSsl {
         libNames.add(staticLibName);
 
         NativeLibraryLoader.loadFirstAvailable(SSL.class.getClassLoader(),
-            libNames.toArray(new String[libNames.size()]));
+            libNames.toArray(new String[0]));
     }
 
     private static boolean initializeTcNative(String engine) throws Exception {

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

@@ -98,7 +98,7 @@ final class PemReader {
             throw new CertificateException("found no certificates in input stream");
         }
 
-        return certs.toArray(new ByteBuf[certs.size()]);
+        return certs.toArray(new ByteBuf[0]);
     }
 
     static ByteBuf readPrivateKey(File file) throws KeyException {

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

@@ -246,7 +246,7 @@ public final class ReferenceCountedOpenSslClientContext extends ReferenceCounted
             final ReferenceCountedOpenSslEngine engine = engineMap.get(ssl);
             try {
                 final Set<String> keyTypesSet = supportedClientKeyTypes(keyTypeBytes);
-                final String[] keyTypes = keyTypesSet.toArray(new String[keyTypesSet.size()]);
+                final String[] keyTypes = keyTypesSet.toArray(new String[0]);
                 final X500Principal[] issuers;
                 if (asn1DerEncodedPrincipals == null) {
                     issuers = null;

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

@@ -265,7 +265,7 @@ public abstract class ReferenceCountedOpenSslContext extends SslContext implemen
             List<String> nextProtoList = apn.protocols();
                 /* Set next protocols for next protocol negotiation extension, if specified */
             if (!nextProtoList.isEmpty()) {
-                String[] appProtocols = nextProtoList.toArray(new String[nextProtoList.size()]);
+                String[] appProtocols = nextProtoList.toArray(new String[0]);
                 int selectorBehavior = opensslSelectorFailureBehavior(apn.selectorFailureBehavior());
 
                 switch (apn.protocol()) {

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

@@ -1286,7 +1286,7 @@ public class ReferenceCountedOpenSslEngine extends SSLEngine implements Referenc
 
     @Override
     public final String[] getSupportedCipherSuites() {
-        return OpenSsl.AVAILABLE_CIPHER_SUITES.toArray(new String[OpenSsl.AVAILABLE_CIPHER_SUITES.size()]);
+        return OpenSsl.AVAILABLE_CIPHER_SUITES.toArray(new String[0]);
     }
 
     @Override
@@ -1359,7 +1359,7 @@ public class ReferenceCountedOpenSslEngine extends SSLEngine implements Referenc
 
     @Override
     public final String[] getSupportedProtocols() {
-        return OpenSsl.SUPPORTED_PROTOCOLS_SET.toArray(new String[OpenSsl.SUPPORTED_PROTOCOLS_SET.size()]);
+        return OpenSsl.SUPPORTED_PROTOCOLS_SET.toArray(new String[0]);
     }
 
     @Override
@@ -1373,7 +1373,7 @@ public class ReferenceCountedOpenSslEngine extends SSLEngine implements Referenc
             if (!isDestroyed()) {
                 opts = SSL.getOptions(ssl);
             } else {
-                return enabled.toArray(new String[1]);
+                return enabled.toArray(new String[0]);
             }
         }
         if (isProtocolEnabled(opts, SSL.SSL_OP_NO_TLSv1, PROTOCOL_TLS_V1)) {
@@ -1391,7 +1391,7 @@ public class ReferenceCountedOpenSslEngine extends SSLEngine implements Referenc
         if (isProtocolEnabled(opts, SSL.SSL_OP_NO_SSLv3, PROTOCOL_SSL_V3)) {
             enabled.add(PROTOCOL_SSL_V3);
         }
-        return enabled.toArray(new String[enabled.size()]);
+        return enabled.toArray(new String[0]);
     }
 
     private static boolean isProtocolEnabled(int opts, int disableMask, String protocolString) {
@@ -1955,7 +1955,7 @@ public class ReferenceCountedOpenSslEngine extends SSLEngine implements Referenc
             if (values == null || values.isEmpty()) {
                 return EmptyArrays.EMPTY_STRINGS;
             }
-            return values.keySet().toArray(new String[values.size()]);
+            return values.keySet().toArray(new String[0]);
         }
 
         private void notifyUnbound(Object value, String name) {

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

@@ -53,7 +53,7 @@ public final class SupportedCipherSuiteFilter implements CipherSuiteFilter {
                 newCiphers.add(c);
             }
         }
-        return newCiphers.toArray(new String[newCiphers.size()]);
+        return newCiphers.toArray(new String[0]);
     }
 
 }

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

@@ -172,7 +172,7 @@ public final class FingerprintTrustManagerFactory extends SimpleTrustManagerFact
             list.add(f.clone());
         }
 
-        this.fingerprints = list.toArray(new byte[list.size()][]);
+        this.fingerprints = list.toArray(new byte[0][]);
     }
 
     private static byte[][] toFingerprintArray(Iterable<String> fingerprints) {
@@ -197,7 +197,7 @@ public final class FingerprintTrustManagerFactory extends SimpleTrustManagerFact
             list.add(StringUtil.decodeHexDump(f));
         }
 
-        return list.toArray(new byte[list.size()][]);
+        return list.toArray(new byte[0][]);
     }
 
     @Override

handler/src/test/java/io/netty/handler/ssl/OpenSslEngineTest.java

@@ -350,7 +350,7 @@ public class OpenSslEngineTest extends SSLEngineTest {
                 srcsLen += dup.capacity();
             }
 
-            ByteBuffer[] srcs = srcList.toArray(new ByteBuffer[srcList.size()]);
+            ByteBuffer[] srcs = srcList.toArray(new ByteBuffer[0]);
             ByteBuffer dst = allocateBuffer(
                     unwrapEngine(clientEngine).maxEncryptedPacketLength() - 1);
 

microbench/src/main/java/io/netty/microbench/util/AbstractMicrobenchmarkBase.java

@@ -93,8 +93,7 @@ public abstract class AbstractMicrobenchmarkBase {
             }
         }
         if (jvmArgs.length != customArgs.size()) {
-            jvmArgs = new String[customArgs.size()];
+            jvmArgs = customArgs.toArray(new String[0]);
-            customArgs.toArray(jvmArgs);
         }
         return jvmArgs;
     }

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

@@ -142,7 +142,7 @@ public final class DefaultDnsServerAddressStreamProvider implements DnsServerAdd
         }
 
         DEFAULT_NAME_SERVER_LIST = Collections.unmodifiableList(defaultNameServers);
-        DEFAULT_NAME_SERVER_ARRAY = defaultNameServers.toArray(new InetSocketAddress[defaultNameServers.size()]);
+        DEFAULT_NAME_SERVER_ARRAY = defaultNameServers.toArray(new InetSocketAddress[0]);
         DEFAULT_NAME_SERVERS = sequential(DEFAULT_NAME_SERVER_ARRAY);
     }
 

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

@@ -131,7 +131,7 @@ public class DnsNameResolver extends InetNameResolver {
 
             @SuppressWarnings("unchecked")
             List<String> list = (List<String>) nameservers.invoke(instance);
-            searchDomains = list.toArray(new String[list.size()]);
+            searchDomains = list.toArray(new String[0]);
         } catch (Exception ignore) {
             // Failed to get the system name search domain list.
             searchDomains = EmptyArrays.EMPTY_STRINGS;

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

@@ -335,7 +335,7 @@ public final class DnsNameResolverBuilder {
             list.add(f);
         }
 
-        this.searchDomains = list.toArray(new String[list.size()]);
+        this.searchDomains = list.toArray(new String[0]);
         return this;
     }
 

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

@@ -187,7 +187,7 @@ public abstract class DnsServerAddresses {
             throw new IllegalArgumentException("empty addresses");
         }
 
-        return list.toArray(new InetSocketAddress[list.size()]);
+        return list.toArray(new InetSocketAddress[0]);
     }
 
     private static InetSocketAddress[] sanitize(InetSocketAddress[] addresses) {
@@ -210,7 +210,7 @@ public abstract class DnsServerAddresses {
             return defaultAddressArray();
         }
 
-        return list.toArray(new InetSocketAddress[list.size()]);
+        return list.toArray(new InetSocketAddress[0]);
     }
 
     /**

resolver-dns/src/test/java/io/netty/resolver/dns/TestDnsServer.java

@@ -67,7 +67,7 @@ class TestDnsServer extends DnsServer {
         BYTES.put("0:1:1:1:1:1:1:1", new byte[]{0, 0, 0, 1, 0, 1, 0, 1, 0, 1, 0, 1, 0, 1, 0, 1});
         BYTES.put("1:1:1:1:1:1:1:1", new byte[]{0, 1, 0, 1, 0, 1, 0, 1, 0, 1, 0, 1, 0, 1, 0, 1});
 
-        IPV6_ADDRESSES = BYTES.keySet().toArray(new String[BYTES.size()]);
+        IPV6_ADDRESSES = BYTES.keySet().toArray(new String[0]);
     }
 
     private final RecordStore store;

resolver/src/main/java/io/netty/resolver/AddressResolverGroup.java

@@ -102,7 +102,7 @@ public abstract class AddressResolverGroup<T extends SocketAddress> implements C
     public void close() {
         final AddressResolver<T>[] rArray;
         synchronized (resolvers) {
-            rArray = (AddressResolver<T>[]) resolvers.values().toArray(new AddressResolver[resolvers.size()]);
+            rArray = (AddressResolver<T>[]) resolvers.values().toArray(new AddressResolver[0]);
             resolvers.clear();
         }
 

transport-udt/src/test/java/io/netty/test/udt/util/CaliperMeasure.java

@@ -172,7 +172,7 @@ public class CaliperMeasure {
     }
 
     private static MeasurementSet measurementSet(final Map<Long, Measurement> map) {
-        final Measurement[] array = map.values().toArray(new Measurement[map.size()]);
+        final Measurement[] array = map.values().toArray(new Measurement[0]);
         return new MeasurementSet(array);
     }
 

transport/src/main/java/io/netty/bootstrap/ServerBootstrap.java

@@ -160,10 +160,10 @@ public class ServerBootstrap extends AbstractBootstrap<ServerBootstrap, ServerCh
         final Entry<ChannelOption<?>, Object>[] currentChildOptions;
         final Entry<AttributeKey<?>, Object>[] currentChildAttrs;
         synchronized (childOptions) {
-            currentChildOptions = childOptions.entrySet().toArray(newOptionArray(childOptions.size()));
+            currentChildOptions = childOptions.entrySet().toArray(newOptionArray(0));
         }
         synchronized (childAttrs) {
-            currentChildAttrs = childAttrs.entrySet().toArray(newAttrArray(childAttrs.size()));
+            currentChildAttrs = childAttrs.entrySet().toArray(newAttrArray(0));
         }
 
         p.addLast(new ChannelInitializer<Channel>() {