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/*
 * 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.flink.runtime.state;

import org.apache.flink.util.Preconditions;
import org.apache.flink.util.ResourceGuard;
import org.apache.flink.util.ResourceGuard.Lease;

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

/**
 * Abstract class to implement custom checkpoint output streams which should not be closable for user code.
 * 
 * @param  type of the returned state handle.
 */
public abstract class NonClosingCheckpointOutputStream extends OutputStream {

	protected final CheckpointStreamFactory.CheckpointStateOutputStream delegate;
	private final ResourceGuard resourceGuard = new ResourceGuard();
	

	public NonClosingCheckpointOutputStream(
			CheckpointStreamFactory.CheckpointStateOutputStream delegate) {
		this.delegate = Preconditions.checkNotNull(delegate);
	}

	@Override
	public void flush() throws IOException {
		delegate.flush();
	}

	@Override
	public void write(int b) throws IOException {
		delegate.write(b);
	}

	@Override
	public void write(byte[] b) throws IOException {
		delegate.write(b);
	}

	@Override
	public void write(byte[] b, int off, int len) throws IOException {
		delegate.write(b, off, len);
	}

	@Override
	public void close() throws IOException {
		// users should not be able to actually close the stream, it is closed by the system.
		// TODO if we want to support async writes, this call could trigger a callback to the snapshot context that a handle is available.
	}

	/**
	 * Returns a {@link org.apache.flink.util.ResourceGuard.Lease} that prevents closing this stream. To allow the system
	 * to close this stream, each of the acquired leases need to call {@link Lease#close()}, on their acquired leases.
	 */
	public final ResourceGuard.Lease acquireLease() throws IOException {
		return resourceGuard.acquireResource();
	}

	/**
	 * This method should not be public so as to not expose internals to user code.
	 */
	CheckpointStreamFactory.CheckpointStateOutputStream getDelegate() {
		return delegate;
	}

	/**
	 * This method should not be public so as to not expose internals to user code. Closes the underlying stream and
	 * returns a state handle.
	 */
	abstract T closeAndGetHandle() throws IOException;

	StreamStateHandle closeAndGetHandleAfterLeasesReleased() throws IOException {
		try {
			resourceGuard.closeInterruptibly();
			return delegate.closeAndGetHandle();
		}
		catch (InterruptedException e) {
			Thread.currentThread().interrupt();
			delegate.closeAndGetHandle();
			throw new IOException("Interrupted while awaiting handle.", e);
		}
	}
}