WriteFence.java

/*
 * Copyright © 2015 Cask Data, Inc.
 *
 * 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 co.cask.tephra.visibility;

import co.cask.tephra.Transaction;
import co.cask.tephra.TransactionAware;
import com.google.common.primitives.Bytes;
import com.google.common.primitives.Longs;
import com.google.common.primitives.UnsignedBytes;

import java.util.Collection;
import java.util.TreeSet;

/**
 * Implementation used by {@link FenceWait} to wait for a {@link VisibilityFence}.
 */
class WriteFence implements TransactionAware {
  private final byte[] fenceId;
  private Transaction tx;
  private Collection<byte[]> inProgressChanges;

  public WriteFence(byte[] fenceId) {
    this.fenceId = fenceId;
  }

  @Override
  public void startTx(Transaction tx) {
    this.tx = tx;
    if (inProgressChanges == null) {
      inProgressChanges = new TreeSet<>(UnsignedBytes.lexicographicalComparator());
      for (long inProgressTx : tx.getInProgress()) {
        inProgressChanges.add(Bytes.concat(fenceId, Longs.toByteArray(inProgressTx)));
      }
    }
  }

  @Override
  public void updateTx(Transaction tx) {
    // Fences only need original transaction
  }

  @Override
  public Collection<byte[]> getTxChanges() {
    if (inProgressChanges == null || tx == null) {
      throw new IllegalStateException("Transaction has not started yet");
    }
    return inProgressChanges;
  }

  @Override
  public boolean commitTx() throws Exception {
    // Nothing to persist
    return true;
  }

  @Override
  public void postTxCommit() {
    tx = null;
  }

  @Override
  public boolean rollbackTx() throws Exception {
    // Nothing to rollback
    return true;
  }

  @Override
  public String getTransactionAwareName() {
    return getClass().getSimpleName();
  }
}