hadoop ExecutingStoreOperation 源码

haddop ExecutingStoreOperation 代码

文件路径：/hadoop-tools/hadoop-aws/src/main/java/org/apache/hadoop/fs/s3a/impl/ExecutingStoreOperation.java

/*
 * Licensed to the Apache Software Foundation (ASF) under one
 * or more contributor license agreements.  See the NOTICE file
 * distributed with this work for additional information
 * regarding copyright ownership.  The ASF licenses this file
 * to you 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 org.apache.hadoop.fs.s3a.impl;

import java.io.IOException;
import java.util.concurrent.atomic.AtomicBoolean;

import org.apache.hadoop.util.Preconditions;

import org.apache.hadoop.fs.store.audit.AuditSpan;
import org.apache.hadoop.util.functional.CallableRaisingIOE;

/**
 * A subclass of {@link AbstractStoreOperation} which
 * provides a method {@link #execute()} that may be invoked
 * exactly once.
 * It declares itself a {@code CallableRaisingIOE} and
 * can be handed straight to methods which take those
 * as parameters.
 * @param <T> return type of executed operation.
 */
public abstract class ExecutingStoreOperation<T>
    extends AbstractStoreOperation
    implements CallableRaisingIOE<T> {

  /**
   * Used to stop any re-entrancy of the rename.
   * This is an execute-once operation.
   */
  private final AtomicBoolean executed = new AtomicBoolean(false);

  /**
   * Constructor.
   * Picks up the active audit span from the store context and
   * stores it for later.
   * @param storeContext store context.
   */
  protected ExecutingStoreOperation(final StoreContext storeContext) {
    this(storeContext, storeContext.getActiveAuditSpan());
  }

  /**
   * Constructor.
   * @param storeContext store context.
   * @param auditSpan active span
   */
  protected ExecutingStoreOperation(
      final StoreContext storeContext,
      final AuditSpan auditSpan) {
    super(storeContext, auditSpan);
  }

  /**
   * Apply calls {@link #execute()}.
   * @return the result.
   * @throws IOException IO problem
   */
  @Override
  public final T apply() throws IOException {
    return execute();
  }

  /**
   * Execute the operation.
   * Subclasses MUST call {@link #executeOnlyOnce()} so as to force
   * the (atomic) re-entrancy check.
   * @return the result.
   * @throws IOException IO problem
   */
  public abstract T execute() throws IOException;

  /**
   * Check that the operation has not been invoked twice.
   * This is an atomic check.
   * After the check: activates the span.
   * @throws IllegalStateException on a second invocation.
   */
  protected void executeOnlyOnce() {
    Preconditions.checkState(
        !executed.getAndSet(true),
        "Operation attempted twice");
    activateAuditSpan();
  }

}

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