src/main/java/com/google/devtools/build/lib/skyframe/serialization/UnsafeJdk9StringCodec.java

// Copyright 2018 The Bazel Authors. All rights reserved.
//
// Licensed 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 com.google.devtools.build.lib.skyframe.serialization;

import com.google.common.annotations.VisibleForTesting;
import com.google.devtools.build.lib.unsafe.StringUnsafe;
import com.google.protobuf.CodedInputStream;
import com.google.protobuf.CodedOutputStream;
import java.io.IOException;
import java.util.Arrays;

/**
 * A high-performance {@link ObjectCodec} for {@link String} objects specialized for Strings in
 * JDK9, where a String can be represented as a byte array together with a single byte (0 or 1) for
 * Latin-1 or UTF16 encoding.
 */
public class UnsafeJdk9StringCodec implements ObjectCodec<String> {
  @VisibleForTesting
  public static boolean canUseUnsafeCodec() {
    return StringUnsafe.canUse();
  }

  private final StringUnsafe stringUnsafe;

  public UnsafeJdk9StringCodec() {
    stringUnsafe = StringUnsafe.getInstance();
  }

  @Override
  public Class<? extends String> getEncodedClass() {
    return String.class;
  }

  @Override
  public MemoizationStrategy getStrategy() {
    // Don't memoize strings inside memoizing serialization, to preserve current behavior.
    // TODO(janakr,brandjon,michajlo): Is it actually a problem to memoize strings? Doubt there
    // would be much performance impact from increasing the size of the identity map, and we
    // could potentially drop our string tables in the future.
    return MemoizationStrategy.DO_NOT_MEMOIZE;
  }

  @Override
  public void serialize(SerializationContext context, String obj, CodedOutputStream codedOut)
      throws SerializationException, IOException {
    byte coder = stringUnsafe.getCoder(obj);
    byte[] value = stringUnsafe.getByteArray(obj);
    // Optimize for the case that coder == 0, in which case we can just write the length here,
    // potentially using just one byte. If coder != 0, we'll use 4 bytes, but that's vanishingly
    // rare.
    if (coder == 0) {
      codedOut.writeInt32NoTag(value.length);
    } else if (coder == 1) {
      codedOut.writeInt32NoTag(-value.length);
    } else {
      throw new SerializationException("Unexpected coder value: " + coder + " for " + obj);
    }
    codedOut.writeRawBytes(value);
  }

  @Override
  public String deserialize(DeserializationContext context, CodedInputStream codedIn)
      throws SerializationException, IOException {
    int length = codedIn.readInt32();
    byte coder;
    if (length >= 0) {
      coder = 0;
    } else {
      coder = 1;
      length = -length;
    }
    byte[] value = codedIn.readRawBytes(length);
    try {
      return stringUnsafe.newInstance(value, coder);
    } catch (ReflectiveOperationException e) {
      throw new SerializationException(
          "Could not instantiate string: " + Arrays.toString(value) + ", " + coder, e);
    }
  }
}