Avoid allocating new ExtensionWriters when serializing messages with …

…no extensions

This should speed up serializing Extendable Messages (messages with extension ranges declared in their schema) if those message instances have no extensions set inside them at runtime.

PiperOrigin-RevId: 638087120

java/core/src/main/java/com/google/protobuf/GeneratedMessage.java

@@ -1028,21 +1028,38 @@ public boolean isInitialized() {
  * numbers, but we must write them in canonical (sorted by field number) order. ExtensionWriter
  * helps us write individual ranges of extensions at once.
  */
- protected class ExtensionWriter {
+ protected interface ExtensionWriter {
+ public void writeUntil(final int end, final CodedOutputStream output) throws IOException;
+ }
+
+ // Singleton instance so we can avoid allocating a new one for each message serialization.
+ private static final NoOpExtensionWriter NO_OP_EXTENSION_WRITER = new NoOpExtensionWriter();
+
+ /** No-op implementation that writes nothing, for messages with no extensions. */
+ private static final class NoOpExtensionWriter implements ExtensionWriter {
+ @Override
+ public void writeUntil(final int end, final CodedOutputStream output) {
+ // no-op
+ }
+ }
+
+ /** Implementation that writes extensions from the FieldSet, for messages with extensions. */
+ private final class FieldSetExtensionWriter implements ExtensionWriter {
  // Imagine how much simpler this code would be if Java iterators had
  // a way to get the next element without advancing the iterator.
 
  private final Iterator<Map.Entry<FieldDescriptor, Object>> iter = extensions.iterator();
  private Map.Entry<FieldDescriptor, Object> next;
  private final boolean messageSetWireFormat;
 
- private ExtensionWriter(final boolean messageSetWireFormat) {
+ private FieldSetExtensionWriter(final boolean messageSetWireFormat) {
  if (iter.hasNext()) {
  next = iter.next();
  }
  this.messageSetWireFormat = messageSetWireFormat;
  }
 
+ @Override
  public void writeUntil(final int end, final CodedOutputStream output) throws IOException {
  while (next != null && next.getKey().getNumber() < end) {
  FieldDescriptor descriptor = next.getKey();
@@ -1076,11 +1093,19 @@ public void writeUntil(final int end, final CodedOutputStream output) throws IOE
  }
 
  protected ExtensionWriter newExtensionWriter() {
- return new ExtensionWriter(false);
+ // Avoid allocation in the common case of no extensions.
+ if (extensions.isEmpty()) {
+ return NO_OP_EXTENSION_WRITER;
+ }
+ return new FieldSetExtensionWriter(false);
  }
 
  protected ExtensionWriter newMessageSetExtensionWriter() {
- return new ExtensionWriter(true);
+ // Avoid allocation in the common case of no extensions.
+ if (extensions.isEmpty()) {
+ return NO_OP_EXTENSION_WRITER;
+ }
+ return new FieldSetExtensionWriter(true);
  }
 
  /** Called by subclasses to compute the size of extensions. */

src/google/protobuf/compiler/java/full/message.cc

@@ -587,15 +587,13 @@ void ImmutableMessageGenerator::GenerateMessageSerializationMethods(
  if (descriptor_->options().message_set_wire_format()) {
  printer->Print(
  "com.google.protobuf.GeneratedMessage\n"
- " .ExtendableMessage<$classname$>.ExtensionWriter\n"
- " extensionWriter = newMessageSetExtensionWriter();\n",
- "classname", name_resolver_->GetImmutableClassName(descriptor_));
+ " .ExtendableMessage.ExtensionWriter\n"
+ " extensionWriter = newMessageSetExtensionWriter();\n");
  } else {
  printer->Print(
  "com.google.protobuf.GeneratedMessage\n"
- " .ExtendableMessage<$classname$>.ExtensionWriter\n"
- " extensionWriter = newExtensionWriter();\n",
- "classname", name_resolver_->GetImmutableClassName(descriptor_));
+ " .ExtendableMessage.ExtensionWriter\n"
+ " extensionWriter = newExtensionWriter();\n");
  }
  }