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This module contains code to support integration with Amazon Web Services.
It also declares the dependencies needed to work with AWS services.
/*
* 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.thirdparty.com.google.common.base.Preconditions;
/**
* A subclass of {@link AbstractStoreOperation} which
* provides a method {@link #execute()} that may be invoked
* exactly once.
* @param return type of executed operation.
*/
public abstract class ExecutingStoreOperation
extends AbstractStoreOperation {
/**
* Used to stop any re-entrancy of the rename.
* This is an execute-once operation.
*/
private final AtomicBoolean executed = new AtomicBoolean(false);
/**
* constructor.
* @param storeContext store context.
*/
protected ExecutingStoreOperation(final StoreContext storeContext) {
super(storeContext);
}
/**
* 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.
* @throws IllegalStateException on a second invocation.
*/
protected void executeOnlyOnce() {
Preconditions.checkState(
!executed.getAndSet(true),
"Operation attempted twice");
}
}