src/main/java/com/google/devtools/build/lib/rules/extra/ExtraActionInfoFileWriteAction.java

// Copyright 2015 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.rules.extra;

import com.google.common.collect.ImmutableList;
import com.google.devtools.build.lib.actions.Action;
import com.google.devtools.build.lib.actions.ActionExecutionContext;
import com.google.devtools.build.lib.actions.ActionOwner;
import com.google.devtools.build.lib.actions.Artifact;
import com.google.devtools.build.lib.actions.ExecException;
import com.google.devtools.build.lib.actions.extra.ExtraActionInfo;
import com.google.devtools.build.lib.analysis.actions.AbstractFileWriteAction;
import com.google.devtools.build.lib.util.Fingerprint;
import com.google.devtools.build.lib.util.Preconditions;

import java.io.IOException;
import java.io.OutputStream;

/**
 * Requests extra action info from shadowed action and writes it, in protocol buffer format, to an
 * .xa file for use by an extra action. This can only be done at execution time because actions may
 * store information only known at execution time into the protocol buffer.
 */
public class ExtraActionInfoFileWriteAction extends AbstractFileWriteAction {
  private final Action shadowedAction;

  private static final String UUID = "1759f81d-e72e-477d-b182-c4532bdbaeeb";

  ExtraActionInfoFileWriteAction(ActionOwner owner, Artifact extraActionInfoFile,
      Action shadowedAction) {
    super(owner, ImmutableList.<Artifact>of(), extraActionInfoFile, false);

    this.shadowedAction = Preconditions.checkNotNull(shadowedAction, extraActionInfoFile);
  }

  @Override
  public DeterministicWriter newDeterministicWriter(ActionExecutionContext ctx)
      throws IOException, InterruptedException, ExecException {
    return new DeterministicWriter() {
      // Instantiate the extra action info only on execution, so it is computed freshly each
      // execution, but is constant for the lifetime of this action's execution. These are not
      // large objects, so keeping them in memory for the duration of a single action's execution
      // is acceptable.
      private final ExtraActionInfo extraActionInfo = shadowedAction.getExtraActionInfo().build();

      @Override
      public void writeOutputFile(OutputStream out) throws IOException {
        extraActionInfo.writeTo(out);
      }
    };
  }

  @Override
  protected String computeKey() {
    Fingerprint f = new Fingerprint();
    f.addString(UUID);
    f.addString(shadowedAction.getKey());
    return f.hexDigestAndReset();
  }
}